Co-reporter:Ting-Zheng Xie, Xiaolei Wu, Kevin J. Endres, Zaihong Guo, Xiaocun Lu, Jingyi Li, Erendra Manandhar, James M. Ludlow III, Charles N. Moorefield, Mary Jane Saunders, Chrys Wesdemiotis, and George R. Newkome
Journal of the American Chemical Society November 8, 2017 Volume 139(Issue 44) pp:15652-15652
Publication Date(Web):October 27, 2017
DOI:10.1021/jacs.7b10328
Synthesis of giant unimolecular dendrimers is challenging due, in part, to difficulties encountered at higher generations, in both convergent and divergent protocols because of the multistep construction/purification process. Herein, we report a hybrid synthetic procedure in which the core is constructed last. This quantitative assembly generated a metallodendrimer that is supercharged (120+), large (11.3 nm diameter), and its core was previously established. The series of complexes has been unequivocally characterized by NMR, ESI-IM-MS, and TEM techniques.
Co-reporter:Sourav Chakraborty, Wei Hong, Kevin J. Endres, Ting-Zheng Xie, Lukasz Wojtas, Charles N. Moorefield, Chrys Wesdemiotis, and George R. Newkome
Journal of the American Chemical Society March 1, 2017 Volume 139(Issue 8) pp:3012-3012
Publication Date(Web):February 6, 2017
DOI:10.1021/jacs.6b11784
A three-dimensional, highly symmetric sphere-like nanocage was synthesized using a terpyridine (tpy)-based, flexible tris-dentate ligand and characterized by single crystal X-ray analysis. To introduce more rigidity, one of the tpy units of the tris-dentate ligand was preblocked by stable connectivity to form the corresponding Ru2+-dimer. The complexation between Ru2+-dimer and Fe2+ demonstrates an unexpected temperature-dependent assembly between two irreversible isomeric 3D nanocages. Investigation of the coordination process and structural configurations of the metal–ligand framework, affected by the introduction of rigidity and in the presence of external stimuli (temperature), is reported.
Co-reporter:Qiming He, Jialin Mao, Chrys Wesdemiotis, Roderic P. Quirk, and Mark D. Foster
Macromolecules August 8, 2017 Volume 50(Issue 15) pp:5779-5779
Publication Date(Web):July 28, 2017
DOI:10.1021/acs.macromol.7b01121
A methodology to efficiently synthesize well-defined, 8-shaped polystyrene using anionic polymerization, silicon chloride linking chemistry, and metathesis ring closure has been developed, and the 8-shaped architecture was ascertained using the fragmentation pattern of the corresponding Ag+ adduct, acquired with tandem mass spectrometry. The 4-arm star precursor, 4-star-α-4-pentenylpolystyrene, was formed by linking α-4-pentenylpoly(styryl)lithium (PSLi) with 1,2-bis(methyldichlorosilyl)ethane and reacting the excess PSLi with 1,2-epoxybutane to facilitate purification. Ring closure of 4-star-α-4-pentenylpolystyrene was carried out in dichloromethane under mild conditions using a Grubbs metathesis catalyst, bis(tricyclohexylphosphine)benzylidine ruthenium(IV) chloride. Both the 4-arm star precursor and resulting 8-shaped polystyrene were characterized using SEC, NMR, and MALDI-ToF mass spectrometry (MS). Tandem mass spectrometry (MS2) was used for the first time to study the fragmentation pattern of 8-shaped polystyrene. The results confirmed the formation of the intra-silicon-linked, 8-shaped polystyrene isomer, but the observed spectra left open the possibility that the inter-silicon-linked, 8-shaped polystyrene isomer was also produced.
Co-reporter:Yuchen Yao;Sourav Chakraborty;Shiying Zhu;Kevin J. Endres;Ting-Zheng Xie;Wei Hong;Erendra Manandhar;Charles N. Moorefield;George R. Newkome
Chemical Communications 2017 vol. 53(Issue 57) pp:8038-8041
Publication Date(Web):2017/07/13
DOI:10.1039/C7CC04080F
A novel terpyridine-based, trapezoidal architecture was synthesized by a coordination-driven multicomponent assembly and features three different tpy–M2+–tpy bonds (M2+ = Ru2+, Fe2+, and Zn2+) in the macrocyclic ring. This trimetallic macrocycle introduces the construction of polymetallosupramolecular assemblies possessing multiple, differing metal centers in an ordered, predetermined pattern. Characterization was accomplished by NMR spectroscopy, mass spectrometry, and UV-Vis spectroscopy.
Co-reporter:Selim Gerislioglu, Chrys Wesdemiotis
International Journal of Mass Spectrometry 2017 Volume 413(Volume 413) pp:
Publication Date(Web):1 February 2017
DOI:10.1016/j.ijms.2016.08.001
•In-depth structural characterization of end-group functionalized pNIPAMs by MSn.•Inefficient random backbone cleavages with single-stage CAD or ETD.•New structural features in initial ETD fragments open new sequential CAD pathways.•CAD on select ETD fragments allows characterization of the backbone structure.Electrospray ionization multistage mass spectrometry (ESI–MSn) was employed for the structural characterization of poly(N-isopropylacrylamide) (pNIPAM) compounds, a widely used class of thermoresponsive materials. Experiments were performed on singly and doubly sodiated pNIPAMs terminated with thiopropionic acid or thiopropyl triethoxysilane substituents, using collisionally activated dissociation (CAD) and electron transfer dissociation (ETD) techniques. Single stages of CAD or ETD only caused small neutral losses diagnostic of the side chains and end groups. A more thorough structural characterization of the pNIPAMs was possible by applying a sequential stage of CAD on fragments generated by ETD, as no surviving charge-reduced precursor was present in the ETD spectra. The ETD fragments were selected such that they preserved differentiation of the two chain ends and contained features that led to random backbone cleavages. ETD fragments with an unpaired electron or with a particularly stable charge site fulfilled this requirement, giving rise to backbone fragments that made it possible to characterize the chain connectivity in addition to the end group and side chain structures. Whether a radical ion or an ion with a well stabilized charge site is used to obtain structurally diagnostic fragments by ETD-CAD depends on the end groups, the functional group being reduced in the ETD step and the structure of the ETD fragment chosen for consecutive CAD.Download high-res image (149KB)Download full-size image
Co-reporter:Ahlam Alalwiat, Wen Tang, Selim Gerişlioğlu, Matthew L. BeckerChrys Wesdemiotis
Analytical Chemistry 2017 Volume 89(Issue 2) pp:
Publication Date(Web):December 12, 2016
DOI:10.1021/acs.analchem.6b03553
The bioconjugate BMP2-(PEO-HA)2, composed of a dendron with two monodisperse poly(ethylene oxide) (PEO) branches terminated by a hydroxyapatite binding peptide (HA), and a focal point substituted with a bone growth stimulating peptide (BMP2), has been comprehensively characterized by mass spectrometry (MS) methods, encompassing matrix-assisted laser desorption ionization (MALDI), electrospray ionization (ESI), tandem mass spectrometry (MS2), and ion mobility mass spectrometry (IM-MS). MS2 experiments using different ion activation techniques validated the sequences of the synthetic, bioactive peptides HA and BMP2, which contained highly basic amino acid residues either at the N-terminus (BMP2) or C-terminus (HA). Application of MALDI-MS, ESI-MS, and IM-MS to the polymer–peptide biomaterial confirmed its composition. Collision cross-section measurements and molecular modeling indicated that BMP2-(PEO-HA)2 exists in several folded and extended conformations, depending on the degree of protonation. Protonation of all basic sites of the hybrid material nearly doubles its conformational space and accessible surface area.
Co-reporter:Ting-Zheng Xie, Kevin J. Endres, Zaihong Guo, James M. Ludlow III, Charles N. Moorefield, Mary Jane Saunders, Chrys Wesdemiotis, and George R. Newkome
Journal of the American Chemical Society 2016 Volume 138(Issue 38) pp:12344-12347
Publication Date(Web):September 9, 2016
DOI:10.1021/jacs.6b07969
Metallomacromolecular architectural conversion is expanded by the characterization of three different structures. A quantitative, single-step, self-assembly of a shape-persistent monomer, containing a flexible crown ether moiety, gives an initial Archimedean-based cuboctahedron that has been unequivocally characterized by 1D and 2D NMR spectroscopy, mass spectrometry, and collision cross section analysis. Both dilution and exchange of counterions, transforms this cuboctahedron into two identical octahedrons, which upon further dilution convert into four, superposed, bistrianglar complexes; increasing the concentration reverses the process. Ion binding studies using the cuboctahedral cage were undertaken.
Co-reporter:Bryan C. Katzenmeyer, Shayna F. Hague, and Chrys Wesdemiotis
Analytical Chemistry 2016 Volume 88(Issue 1) pp:851
Publication Date(Web):December 7, 2015
DOI:10.1021/acs.analchem.5b03400
Mass spectrometry (MS) and tandem mass spectrometry (MS/MS) were interfaced with ultra-performance liquid chromatography (UPLC) and ion mobility (IM) separation to characterize a complex nonionic surfactant, consisting of a methylated glucose core (glucam) conjugated with poly(ethylene oxide) (PEOn) branches that were partially esterified with stearic acid to form ethoxylated glucam (PEOn-glucam) stearates. Reverse-phase LC-MS afforded fast separation according to polarity into five major fractions. Accurate mass measurements of the ions in the mass spectra extracted from these fractions enabled conclusive identification of six components in the surfactant, including PEOn-glucam mono-, di-, and tristearates as well as free and esterified PEOn as byproducts. MS/MS experiments provided corroborating evidence for the fatty acid content in each fraction based on the number of stearic acid losses observed. With IM-MS, the total surfactant ions were separated according to charge and shape into four distinct bands. Extracted mass spectra confirmed the presence of two disaccharide stearates in the surfactant, which were undetectable by LC-MS. PEOn-glucam tristearates were, however, not observed upon IM-MS. Hence, LC-MS and IM-MS unveiled complementary compositional insight. With each method, certain components were particularly well separated from other ingredients (by either polarity or shape), to be detected with confidence. Consequently, combined LC-MS and IM-MS offer a superior approach for the characterization of surfactants and other amphiphilic polymers and for the differentiation of similarly composed amphiphilic blends. It is finally noteworthy that NH4+ charges minimized chemical noise in MS mode and Li+ charges maximized the fragmentation efficiency in MS/MS mode.
Co-reporter:Sarah Crotty, Selim Gerişlioğlu, Kevin J. Endres, Chrys Wesdemiotis, Ulrich S. Schubert
Analytica Chimica Acta 2016 Volume 932() pp:1-21
Publication Date(Web):17 August 2016
DOI:10.1016/j.aca.2016.05.024
•Novel approaches in MS characterization of polymers are discussed.•Publications on MS and hyphenated strategies toward analysis of polymers architectures are reviewed.•Computational methods for the interpretation of polymer MS data are encouraged.•Upcoming expectances using MS-based methods on polymer analysis are suggested.This review covers the application of mass spectrometry (MS) and its hyphenated techniques to synthetic polymers of varying architectural complexities. The synthetic polymers are discussed as according to their architectural complexity from linear homopolymers and copolymers to stars, dendrimers, cyclic copolymers and other polymers. MS and tandem MS (MS/MS) has been extensively used for the analysis of synthetic polymers. However, the increase in structural or architectural complexity can result in analytical challenges that MS or MS/MS cannot overcome alone. Hyphenation to MS with different chromatographic techniques (2D × LC, SEC, HPLC etc.), utilization of other ionization methods (APCI, DESI etc.) and various mass analyzers (FT-ICR, quadrupole, time-of-flight, ion trap etc.) are applied to overcome these challenges and achieve more detailed structural characterizations of complex polymeric systems. In addition, computational methods (software: MassChrom2D, COCONUT, 2D maps etc.) have also reached polymer science to facilitate and accelerate data interpretation. Developments in technology and the comprehension of different polymer classes with diverse architectures have significantly improved, which allow for smart polymer designs to be examined and advanced. We present specific examples covering diverse analytical aspects as well as forthcoming prospects in polymer science.
Co-reporter:Ting-Zheng Xie;Jing-Yi Li;Zaihong Guo;James M. Ludlow III;Xiaocun Lu;Charles N. Moorefield;George R. Newkome
European Journal of Inorganic Chemistry 2016 Volume 2016( Issue 11) pp:1671-1677
Publication Date(Web):
DOI:10.1002/ejic.201600048
Abstract
A series of coordination-driven, heteroleptic self-assembled, bowtie-shaped bis-macrocycles were designed and constructed by combining tetrakis(terpyridinyl)thianthrene and bis-terpyridine, 60°-directed, Ru2+ dimers. The resulting complexes were characterized by NMR spectroscopy and ESI-MS coupled with travelling wave ion mobility spectrometry (ESI-TWIM-MS) experiments. The desired bis-macrocycles were obtained in quantitative yields through the use of long alkyl-chain substituents, in contrast to the lower yields obtained for smaller alkyl moieties.
Co-reporter:Rajarshi Sarkar, Zaihong Guo, Jingyi Li, Tarak N. Burai, Charles Moorefield, Chrys Wesdemiotis and George R. Newkome
Chemical Communications 2015 vol. 51(Issue 64) pp:12851-12854
Publication Date(Web):03 Jul 2015
DOI:10.1039/C5CC05048K
Mixing of metallocyclic trimers and tetramers in an exact 1:1.5 stoichiometry provided new supramolecular triangles in quantitative yields. Characterization of the new hetero-nuclear metallomacrocycles was achieved by 1H, 2D-COSY, 2D-NOESY, and 13C NMR spectroscopy, along with ESI and TWIM mass spectrometry. Gradient tandem MS (gMS2) provided insight into the stabilities of the binuclear structures.
Co-reporter:Kai Guo;Zaihong Guo;James M. Ludlow III;Tingzheng Xie;Shengyun Liao;George R. Newkome
Macromolecular Rapid Communications 2015 Volume 36( Issue 17) pp:1539-1552
Publication Date(Web):
DOI:10.1002/marc.201500084
Co-reporter:Xiumin Liu, Lydia R. Cool, Kenneth Lin, Andrea M. Kasko and Chrys Wesdemiotis
Analyst 2015 vol. 140(Issue 4) pp:1182-1191
Publication Date(Web):10 Dec 2014
DOI:10.1039/C4AN01599A
Multidimensional mass spectrometry techniques, combining matrix-assisted laser desorption/ionization (MALDI) or electrospray ionization (ESI) with tandem mass spectrometry (MS2), multistage mass spectrometry (MSn) or ion mobility mass spectrometry (IM-MS), have been employed to gain precise structural insight on the compositions, sequences and architectures of small oligomers of a hyperbranched glycopolymer, prepared by atom transfer radical copolymerization of an acrylate monomer (A) and an acrylate inimer (B), both carrying mannose ester pendants. The MS data confirmed the incorporation of multiple inimer repeat units, which ultimately lead to the hyperbranched material. The various possible structures of n-mers with the same composition were subsequently elucidated based on MS2 and MSn studies. The characteristic elimination of bromomethane molecule provided definitive information about the comonomer connectivity in the copolymeric AB2 trimer and A2B2 tetramer, identifying as present only one of the three possible trimeric isomers (viz. sequence BBA) and only two of the six possible tetrameric isomers (viz. sequences BBA2 and BABA). Complementary IM-MS studies confirmed that only one of the tetrameric structures is formed. Comparison of the experimentally determined collision cross-section of the detected isomer with those predicted by molecular simulations for the two possible sequences ascertained BBA2 as the predominant tetrameric architecture. The multidimensional MS approaches presented provide connectivity information at the atomic level without requiring high product purity (due to the dispersive nature of MS) and, hence, should be particularly useful for the microstructure characterization of novel glycopolymers and other types of complex copolymers.
Co-reporter:Ahlam Alalwiat, Sarah E. Grieshaber, Bradford A. Paik, Kristi L. Kiick, Xinqiao Jia and Chrys Wesdemiotis
Analyst 2015 vol. 140(Issue 22) pp:7550-7564
Publication Date(Web):05 Oct 2015
DOI:10.1039/C5AN01600B
A multidimensional mass spectrometry (MS) methodology is introduced for the molecular level characterization of polymer–peptide (or polymer–protein) copolymers that cannot be crystallized or chromatographically purified. It encompasses electrospray ionization (ESI) or matrix-assisted laser desorption ionization (MALDI) coupled with mass analysis, tandem mass spectrometry (MS2) and gas-phase separation by ion mobility mass spectrometry (IM-MS). The entire analysis is performed in the mass spectrometer (“top-down” approach) within milliseconds and with high sensitivity, as demonstrated for hybrid materials composed of hydrophobic poly(tert-butyl acrylate) (PtBA) or hydrophilic poly(acrylic acid) (PAA) blocks tethered to the hydrophobic decapeptide VPGVGVPGVG (VG2) via triazole linkages. The composition of the major products can be rapidly surveyed by MALDI-MS and MS2. For a more comprehensive characterization, the ESI-IM-MS (and MS2) combination is more suitable, as it separates the hybrid materials based on their unique charges and shapes from unconjugated polymer and partially hydrolyzed products. Such separation is essential for reducing spectral congestion, deconvoluting overlapping compositions and enabling straightforward structural assignments, both for the hybrid copolymers as well as the polymer and peptide reactants. The IM dimension also permits the measurement of collision cross-sections (CCSs), which reveal molecular architecture. The MS and MS2 spectra of the mobility separated ions conclusively showed that [PtBA-VG2]m and [PAA-VG2]m chains with the expected compositions and sequences were formed. Single and double copolymer blocks (m = 1–2) could be detected. Further, the CCSs of the hybrids, which were prepared via azide/alkyne cycloadditions, confirmed the formation of macrocyclic structures. The top-down methodology described would be particularly useful for the detection and identification of peptide/protein–polymer conjugates which are increasingly used in biomedical and pharmaceutical applications.
Co-reporter:James M. Ludlow III;Zaihong Guo;Anthony Schultz;Rajarshi Sarkar;Charles N. Moorefield;George R. Newkome
European Journal of Inorganic Chemistry 2015 Volume 2015( Issue 34) pp:5662-5668
Publication Date(Web):
DOI:10.1002/ejic.201500971
Abstract
The one-step synthesis of the first homoleptic <tpy–OsII–tpy> metallomacrocycle is reported. Characterization of the OsII complex, along with its FeII and RuII analogues, was accomplished by NMR spectroscopy, ESI-MS, TWIM-MS, gradient tandem-MS, CV, luminescence and UV/Vis spectroscopy. Center-of-mass collision energies, derived from gradient tandem-MS, reveal that the <tpy–RuII–tpy>-based structures are more stable than those of <tpy–OsII–tpy>.
Co-reporter:Bryan C. Katzenmeyer, Lydia R. Cool, Jonathan P. Williams, Kirsten Craven, Jeffery M. Brown, Chrys Wesdemiotis
International Journal of Mass Spectrometry 2015 Volume 378() pp:303-311
Publication Date(Web):15 February 2015
DOI:10.1016/j.ijms.2014.09.021
•ETD of sodiated polyesters is optimized at short ion–ion reaction times.•Long ion–ion reaction times cause H/Na or Na/H exchange and spectral crowding.•Coupling ETD with CAD promotes fragmentation of the reduced precursor ion.•ETD coupled with IM–MS unveils insight on the architecture of ETD fragments.•ETD mass spectra acquired with QIT and Q/ToF instrumentation are similar.The electron transfer dissociation (ETD) characteristics of doubly sodiated polylactide were investigated at varying ion–ion reaction times, ranging from 20 to 220 ms. ETD product ion yields and signal-to-noise ratio maximized at the shortest reaction time. At longer times, the extent of Na/H or H/Na exchange reactions rose, causing spectral crowding; in addition, the sensitivity decreased significantly due to ion losses from neutralization and scattering. ETD in quadrupole ion trap (QIT) and quadrupole/time-of-flight (Q/ToF) mass spectrometers using fluoranthene and p-nitrotoluene reagent anions, respectively, led to similar product ions. The Q/ToF configuration allowed for collisionally activated dissociation (CAD) of the ETD total ion current under mild activation conditions, which gave rise to new and more abundant fragment distributions by mainly depleting residual reduced precursor ions. The ETD and ETD/CAD fragmentation patterns were markedly different from the fragments generated by simple CAD, thereby providing complementary structural information about the analyzed polyester. The collision cross-sections of the major ETD fragment series, determined by ion mobility mass spectrometry (IM–MS) experiments on the Q/ToF instrument, agreed well with the linear architectures expected from radical-induced cleavages at the (CO)-O-alkyl bonds promoted by the electron added in the ETD event.
Co-reporter:Ting-Zheng Xie ; Sheng-Yun Liao ; Kai Guo ; Xiaocun Lu ; Xuehui Dong ; Mingjun Huang ; Charles N. Moorefield ; Stephen Z. D. Cheng ; Xin Liu ; Chrys Wesdemiotis ;George R. Newkome
Journal of the American Chemical Society 2014 Volume 136(Issue 23) pp:8165-8168
Publication Date(Web):May 19, 2014
DOI:10.1021/ja502962j
A three-dimensional, highly symmetric, terpyridine-based, spherical complex was synthesized via the coordination of four novel, trisdentate ligands and six Ru2+ ions, and it exhibits excellent stability over a wide range of pH values (1–14). Structural confirmation was obtained by NMR and ESI-TWIM-MS.
Co-reporter:Xiaocun Lu ; Xiaopeng Li ; Kai Guo ; Ting-Zheng Xie ; Charles N. Moorefield ; Chrys Wesdemiotis ;George R. Newkome
Journal of the American Chemical Society 2014 Volume 136(Issue 52) pp:18149-18155
Publication Date(Web):December 3, 2014
DOI:10.1021/ja511341z
A terpyridine-based, concentration-dependent, facile self-assembly process is reported, resulting in two three-dimensional metallosupramolecular architectures, a bis-rhombus and a tetrahedron, which are formed using a two-dimensional, planar, tris-terpyridine ligand. The interconversion between these two structures is concentration-dependent: at a concentration higher than 12 mg mL–1, only a bis-rhombus, composed of eight ligands and 12 Cd2+ ions, is formed; whereas a self-assembled tetrahedron, composed of four ligands and six Cd2+ ions, appears upon sufficient dilution of the tris-terpyridine-metal solution. At concentrations less than 0.5 mg mL–1, only the tetrahedron possessing an S4 symmetry axis is detected; upon attempted isolation, it quantitatively reverts to the bis-rhombus. This observation opens an unexpected door to unusual chemical pathways under high dilution conditions.
Co-reporter:Yiwen Li, Kai Guo, Hao Su, Xiaopeng Li, Xueyan Feng, Zhao Wang, Wei Zhang, Sunsheng Zhu, Chrys Wesdemiotis, Stephen Z. D. Cheng and Wen-Bin Zhang
Chemical Science 2014 vol. 5(Issue 3) pp:1046-1053
Publication Date(Web):18 Nov 2013
DOI:10.1039/C3SC52718B
The convenient synthesis of nano-building blocks with strategically placed functional groups constitutes a fundamental challenge in nano-science. Here, we describe the facile preparation of a library of mono- and di-functional (containing three isomers) polyhedral oligomeric silsesquioxane (POSS) building blocks with different symmetries (C3v, C2v, and D3d) using thiol-ene chemistry. The method is straightforward and general, possessing many advantages including minimum set-up, simple work-up, and a short reaction time (about 0.5 h). It facilitates the precise introduction of a large variety of functional groups to desired sites of the POSS cage. The yields of the monoadducts increase significantly using stoichiometric amounts of bulky ligands. Regio-selective di-functionalization of the POSS cage was also attempted using bulky thiol ligands, such as a thiol-functionalized POSS. Electrospray ionization (ESI) mass spectrometry coupled with travelling wave ion mobility (TWIM) separation revealed that the majority of diadducts are para-compounds (∼59%), although meta-compounds (∼20%) and ortho-compounds (∼21%) are also present. Therefore, the thiol-ene reaction provides a robust approach for the convenient synthesis of mono-functional POSS derivatives and, potentially, of regio-selective multi-functionalized POSS derivatives as versatile nano-building blocks.
Co-reporter:Aleer M. Yol, Jonathan Janoski, Roderic P. Quirk, and Chrys Wesdemiotis
Analytical Chemistry 2014 Volume 86(Issue 19) pp:9576
Publication Date(Web):September 2, 2014
DOI:10.1021/ac5019815
Styrene and smaller molar amounts of either m-dimethylsilylstyrene (m-DMSS) or p-dimethylsilylstyrene (p-DMSS) were copolymerized under living anionic polymerization conditions, and the compositions, architectures, and sequences of the resulting copolymers were characterized by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and tandem mass spectrometry (MS2). MS analysis revealed that linear copolymer chains containing phenyl–Si(CH3)2H pendants were the major product for both DMSS comonomers. In addition, two-armed architectures with phenyl–Si(CH3)2–benzyl branches were detected as minor products. The comonomer sequence in the linear chains was established by MS2 experiments on lithiated oligomers, based on the DMSS content of fragments generated by backbone C–C bond scissions and with the help of reference MS2 spectra obtained from a polystyrene homopolymer and polystyrene end-capped with a p-DMSS block. The MS2 data provided conclusive evidence that copolymerization of styrene/DMSS mixtures leads to chains with a rather random distribution of the silylated comonomer when m-DMSS is used, but to chains with tapered block structures, with the silylated units near the initiator, when p-DMSS is used. Hence, MS2 fragmentation patterns permit not only differentiation of the sequences generated in the synthesis, but also the determination of specific comonomer locations along the polymer chain.
Co-reporter:Nilüfer Solak Erdem, Nadrah Alawani, Chrys Wesdemiotis
Analytica Chimica Acta 2014 Volume 808() pp:83-93
Publication Date(Web):15 January 2014
DOI:10.1016/j.aca.2013.07.026
•Liquid chromatography (LC) separates amphiphilic blends according to hydrophobicity.•Ion mobility (IM) spectrometry separates these blends based on molecular size/shape.•LC–MS provides the separation resolution needed for quantifying fatty acid content.•IM–MS enables rapid, solvent-free separation and the detection of trace components.•With either method, tandem MS allows to count the hydrophobic substituents.Liquid chromatography (LC) and ion mobility (IM) separation have been coupled with mass spectrometry (MS) and tandem mass spectrometry (MS2) to characterize a commercially important nonionic surfactant, polysorbate 85. The constituents of this amphiphilic blend contained a sorbitan or isosorbide core that was chain extended with poly(ethylene oxide) (PEO) and partially esterified at the PEO termini with oleic acid or, to a lesser extent, other fatty acids. Using interactive LC in reverse-phase mode, the oligomers of the surfactant were separated according to their hydrophobicity/hydrophilicity balance. On the other hand, IM spectrometry dispersed the surfactant oligomers by their charge and collision cross section (i.e. size/shape). With either separation method, an increased number of fatty ester groups and/or lack of the polar sorbitan (or isosorbide) core led to higher retention/drift times, enabling the separation of isobaric species or species with superimposed isotope patterns, so that their ester content could be conclusively identified by MS2. LC–MS and IM–MS permitted the detection of several byproducts besides the major PEO-sorbitan oleate oligomers. LC–MS provides the separation resolution needed for quantitative determination of the degree of esterification. IM–MS, which minimizes analysis time and solvent use, is ideally suitable for a fast, qualitative survey of samples differing in their minor constituents or impurities.
Co-reporter:James M. Ludlow III, Masato Tominaga, Yoshiki Chujo, Anthony Schultz, Xiaocun Lu, Tingzheng Xie, Kai Guo, Charles N. Moorefield, Chrys Wesdemiotis and George R. Newkome
Dalton Transactions 2014 vol. 43(Issue 25) pp:9604-9611
Publication Date(Web):06 May 2014
DOI:10.1039/C4DT00989D
The self-assembly of the o-carborane-based, bisterpyridyl monomer, 1,2-bis[4′-(4-ethynylphenyl)-2,2′:6′,2′′-terpyridine]-o-carborane, utilizing either ZnII or FeII in a precise metal:ligand ratio (1:1), generated a family of metallomacrocycles that were studied via ESI-TWIM-MS, 1H NMR, and 2D NMR (COSY, NOESY). Under kinetic control, via formation of FeII complexes, the main cyclic product was triangular, as is typical of 60°-based bisligands. Under thermodynamic control using more labile transition metal complexes, e.g. ZnII, the ratio of cyclic species was found to be concentration and temperature dependent, and under an adequate entropic driving force, the cyclic dimer was formed. This system was probed via variable temperature NMR to reveal dynamic equilibrium between the entropically favored dimer and enthalpically favored trimer.
Co-reporter:Dr. Xiaocun Lu ; Xiaopeng Li ;Kai Guo;Jing Wang;Mingjun Huang; Jin-Liang Wang;Dr. Ting-Zheng Xie;Dr. Charles N. Moorefield; Stephen Z. D. Cheng; Chrys Wesdemiotis; George R. Newkome
Chemistry - A European Journal 2014 Volume 20( Issue 41) pp:13094-13098
Publication Date(Web):
DOI:10.1002/chem.201404358
Abstract
A facile high yield, self-assembly process that leads to a terpyridine-based, three-dimensional, bis-rhomboidal-shaped, molecular wheel is reported. The desired coordination-driven supramolecular wheel involves eight structurally distorted tristerpyridine (tpy) ligands possessing a 60° angle between the adjacent tpy units and twelve Zn2+ ions. The tpy ligand plays dual roles in the self-assembly process: two are staggered at 180° to create the internal hub, while six produce the external rim. The wheel can be readily generated by mixing the tpy ligand and Zn2+ in a stoichiometric ratio of 2:3; full characterization is provided by ESI-MS, NMR spectroscopy, and TEM imaging.
Co-reporter:Rajarshi Sarkar;Kai Guo;Dr. Charles N. Moorefield; Mary Jane Saunders; Chrys Wesdemiotis; George R. Newkome
Angewandte Chemie International Edition 2014 Volume 53( Issue 45) pp:12182-12185
Publication Date(Web):
DOI:10.1002/anie.201407285
Abstract
A novel terpyridine-based architecture that mimics a first-generation Sierpiński triangle has been synthesized by multicomponent assembly and features tpyCdIItpy connectivity (tpy=terpyridine). The key terpyridine ligands were synthesized by the Suzuki cross-coupling reaction. Mixing two different terpyridine-based ligands and CdII in a precise stoichiometric ratio (1:1:3) produced the desired fractal architecture in near-quantitative yield. Characterization was accomplished by NMR spectroscopy, mass spectrometry, and transmission electron microscopy.
Co-reporter:Dr. Ting-Zheng Xie;Kai Guo;Mingjun Huang;Dr. Xiaocun Lu;Sheng-Yun Liao;Rajarshi Sarkar;Dr. Charles N. Moorefield; Stephen Z. D. Cheng; Chrys Wesdemiotis; George R. Newkome
Chemistry - A European Journal 2014 Volume 20( Issue 36) pp:11291-11294
Publication Date(Web):
DOI:10.1002/chem.201403840
Abstract
The design and construction of the first multicomponent stepwise assembly of a <tpy-RuII-tpy>-based (tpy=terpyridine), three-dimensional, propeller-shaped trismacrocycle, 8, are reported. Key steps in the synthesis involve the preparation of a hexaterpyridinyl triptycene and its reaction with dimeric, 60°-directional, bisterpyridine-RuII building blocks. Characterization includes ESI- and ESI-TWIM-MS and TEM, along with 1D and 2D 1H NMR spectroscopy.
Co-reporter:Aleer M. Yol, Chrys Wesdemiotis
Reactive and Functional Polymers 2014 80() pp: 95-108
Publication Date(Web):July 2014
DOI:10.1016/j.reactfunctpolym.2014.03.010
Co-reporter:Rajarshi Sarkar;Kai Guo;Dr. Charles N. Moorefield; Mary Jane Saunders; Chrys Wesdemiotis; George R. Newkome
Angewandte Chemie 2014 Volume 126( Issue 45) pp:12378-12381
Publication Date(Web):
DOI:10.1002/ange.201407285
Abstract
A novel terpyridine-based architecture that mimics a first-generation Sierpiński triangle has been synthesized by multicomponent assembly and features tpyCdIItpy connectivity (tpy=terpyridine). The key terpyridine ligands were synthesized by the Suzuki cross-coupling reaction. Mixing two different terpyridine-based ligands and CdII in a precise stoichiometric ratio (1:1:3) produced the desired fractal architecture in near-quantitative yield. Characterization was accomplished by NMR spectroscopy, mass spectrometry, and transmission electron microscopy.
Co-reporter:Longhe Zhang, Bryan C. Katzenmeyer, Kevin A. Cavicchi, R. A. Weiss, and Chrys Wesdemiotis
ACS Macro Letters 2013 Volume 2(Issue 3) pp:217
Publication Date(Web):February 22, 2013
DOI:10.1021/mz3006632
Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF MS) was used to quantify the sulfonation level and sulfonation distribution of sulfonated polystyrene ionomers prepared by homogeneous solution sulfonation. The sulfonation levels obtained by MALDI-ToF MS and acid–base titration were compared, and the sulfonate distributions determined by MALDI-ToF MS were compared with theoretical random distributions. The results indicate that the sulfonation reaction used produces a sample with a random sulfonate distribution.
Co-reporter:Hany El-Batal;Kai Guo;Xiaopeng Li;Charles N. Moorefield;George R. Newkome
European Journal of Organic Chemistry 2013 Volume 2013( Issue 18) pp:3640-3644
Publication Date(Web):
DOI:10.1002/ejoc.201300329
Abstract
A series of metallodendrimers 9–11, as well as their corresponding ligands, were designed and synthesized. These materials integrate perylene as a functional core with <tpyRuIItpy> termini; both chromophores are known for their photovoltaic properties. The products were fully characterized by a combination of 1H NMR and 13C NMR spectroscopy, COSY, and MS. Their photophysical properties revealed a broad absorption spectrum with enhanced molar absorption coefficients corresponding to the increase in the number of <tpyRuIItpy> units, which is indicative of their potential as candidates for light harvesting.
Co-reporter:Anthony Schultz;Xiaopeng Li;Charles N. Moorefield;George R. Newkome
European Journal of Inorganic Chemistry 2013 Volume 2013( Issue 14) pp:2492-2497
Publication Date(Web):
DOI:10.1002/ejic.201300286
Abstract
We report the self-assembly and isolation of two metallamacromolecular constitutional isomeric pairs based on <tpy-MII-tpy> connectivity. Utilizing a robust <tpy-RuII-tpy> dimer with varying substitution to the core benzene ring resulted not only in the isolation of the expected 60°-oriented tetramer and 120°-oriented hexamer but also in the unexpected isolation of a 60°-oriented hexamer and a 120°-oriented tetramer. These isomers were characterized by 1H NMR spectroscopy and mass spectrometry (ESI-travelling wave ion mobility), which revealed significant structural differences. Molecular modeling was utilized to aid in characterization.
Co-reporter:Madalis Casiano-Maldonado, Goy Teck Lim, Xiaopeng Li, Darrell H. Reneker, Judit E. Puskas, Chrys Wesdemiotis
International Journal of Mass Spectrometry 2013 Volumes 354–355() pp:391-397
Publication Date(Web):15 November 2013
DOI:10.1016/j.ijms.2013.08.007
•Protein adsorption on tissue engineering surfaces quantified by mass spectrometry.•Quantities in the range of 0.1–400 pmol/cm2 were detected by MALDI-ToF MS.•Adsorption on nonpolar surfaces increases with protein and surface hydrophobicity.•Amount adsorbed maximizes at the isoelectric point and decreases with protein size.•Electrospun surface morphologies adsorb more protein than molded surfaces.Protein interaction with an implant material is the key event for subsequent cell and tissue growth and ultimately determines the biocompatibility of the material. In this study, a dendritic poly(isobutylene-b-styrene) (D_IBS) block copolymer developed for soft tissue engineering was processed with electrospinning and compression molding to create a fibrous mat and a flat surface, respectively. Proteins (insulin, ubiquitin and lysozyme) were incubated with these surfaces at various pH levels, and the protein adsorption capability of the surfaces was quantified using matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF MS). A reference material, polystyrene (PS), was processed like the D_IBS polymer to elucidate the influence of surface morphology and polymer chemistry on protein adsorption. Water contact angle (WCA) measurements demonstrated the efficacy of electrospinning to produce fibers with superior surface hydrophobicity and surface area-to-volume ratio, as compared to the flat surfaces obtained by compression molding, which in turn led to a significantly higher protein adsorption performance across all pH levels; the three-dimensionality of the fiber surface also played a role in the increased protein adsorption. Compared to the PS fiber mat, the D_IBS fiber mat surface adsorbed far more proteins, in spite of a lower hydrophobicity (based on WCA data), due to the segregation of a thin polyisobutylene (PIB) layer to the fiber surface. Protein adsorption was also found to depend on the protein's isoelectric point (pI). Binding affinity peaked at a pH close to the pI, at which the protein carries no net charge and, thus, can maximize hydrophobic interactions with the surface; at a lower or higher pH, proteins become charged, shielding off their hydrophobic sites and limiting hydrophobic interactions with a surface. The size and hydrophobicity of a protein also affected the binding to a surface; insulin, the smallest molecule with the highest proportion of hydrophobic amino acids, was adsorbed in larger quantities than the bigger and more hydrophilic lysozyme.
Co-reporter:Xiaocun Lu; Xiaopeng Li;Dr. Yan Cao;Dr. Anthony Schultz;Dr. Jin-Liang Wang;Dr. Charles N. Moorefield; Chrys Wesdemiotis; Stephen Z. D. Cheng; George R. Newkome
Angewandte Chemie International Edition 2013 Volume 52( Issue 30) pp:7728-7731
Publication Date(Web):
DOI:10.1002/anie.201302362
Co-reporter:Xiaocun Lu; Xiaopeng Li;Dr. Yan Cao;Dr. Anthony Schultz;Dr. Jin-Liang Wang;Dr. Charles N. Moorefield; Chrys Wesdemiotis; Stephen Z. D. Cheng; George R. Newkome
Angewandte Chemie 2013 Volume 125( Issue 30) pp:7882-7885
Publication Date(Web):
DOI:10.1002/ange.201302362
Co-reporter:Aleer M. Yol;David E. Dabney;Shih-Fan Wang
Journal of The American Society for Mass Spectrometry 2013 Volume 24( Issue 1) pp:74-82
Publication Date(Web):2013 January
DOI:10.1007/s13361-012-0497-5
[M + Ag]+ ions from cyclic and linear polystyrenes and polybutadienes, formed by matrix-assisted laser desorption ionization (MALDI), give rise to significantly different fragmentation patterns in tandem mass spectrometry (MS2) experiments. In both cases, fragmentation starts with homolytic cleavage at the weakest bond, usually a C–C bond, to generate two radicals. From linear structures, the separated radicals depolymerize extensively by monomer losses and backbiting rearrangements, leading to low-mass radical ions and much less abundant medium- and high-mass closed-shell fragments that contain one of the original end groups, along with internal fragments. With cyclic structures, depolymerization is less efficient, as it can readily be terminated by intramolecular H-atom transfer between the still interconnected radical sites (disproportionation). These differences in fragmentation reactivity result in substantially different fragment ion distributions in the MS2 spectra. Simple inspection of the relative intensities of low- versus high-mass fragments permits conclusive determination of the macromolecular architecture, while full spectral interpretation reveals the individual end groups of linear polymers or the identity of the linker used to form the cyclic polymer.
Co-reporter:Anthony Schultz ; Xiaopeng Li ; Balaka Barkakaty ; Charles N. Moorefield ; Chrys Wesdemiotis ;George R. Newkome
Journal of the American Chemical Society 2012 Volume 134(Issue 18) pp:7672-7675
Publication Date(Web):April 24, 2012
DOI:10.1021/ja303177v
Two novel macromolecular constitutional isomers have been self-assembled from previously unreported terpyridine ligands in a three-component system. The terpyridine ligands were synthesized in high yields via a key Suzuki coupling. Restrictions of the possible outcomes for self-assembly ultimately provided optimum conditions for isolation of either a molecular bowtie or its isomeric butterfly motif. These isomers have been characterized by ESI-MS, TWIM-MS, 1H NMR, and 13C NMR. Notably, these structural isomers have remarkably different drift times in ion mobility separation, corresponding to different sizes and shapes at high charge states.
Co-reporter:Xiaocun Lu, Xiaopeng Li, Jin-Liang Wang, Charles N. Moorefield, Chrys Wesdemiotis and George R. Newkome
Chemical Communications 2012 vol. 48(Issue 79) pp:9873-9875
Publication Date(Web):21 Aug 2012
DOI:10.1039/C2CC35510H
Multicomponent, self-assembled rhomboidal constructs are reported, in which bis-terpyridines possessing 120° or 60° directionality and ZnII or CdII in a stoichiometric ratio (1:1:2) initially form rhomboid and triangle mixtures; whereas, a tris-terpyridine reacts with the 60°-based bis-ligand and metal to quantitatively form a heteroleptic, centrally fused, rhomboidal structure.
Co-reporter:Shih-Fan Wang, Xiaopeng Li, Rebecca L. Agapov, Chrys Wesdemiotis, and Mark D. Foster
ACS Macro Letters 2012 Volume 1(Issue 8) pp:1024
Publication Date(Web):July 26, 2012
DOI:10.1021/mz300271w
Surface layer matrix-assisted laser desorption ionization time-of-flight mass spectrometry (SL-MALDI-TOF MS) is a powerful new surface sensitive technique to quantify the surface concentration of multicomponent polymer films with enrichment of one component at the surface. Its capabilities are demonstrated for the novel case of a blend of cyclic polystyrene with linear polystyrene, in which we find the composition of linear chains enriched at the surface after annealing, contrary to the expectation of a self-consistent field theory. The probing depth was confirmed to be monomolecular, which for these short chains is less than 2 nm, even though material at a much greater depth is removed by the analysis.
Co-reporter:Anthony Schultz, Yan Cao, Mingjun Huang, Stephen Z. D. Cheng, Xiaopeng Li, Charles N. Moorefield, Chrys Wesdemiotis and George R. Newkome
Dalton Transactions 2012 vol. 41(Issue 38) pp:11573-11575
Publication Date(Web):20 Aug 2012
DOI:10.1039/C2DT31813J
A series of trimeric, Zn(II)- and Cd(II)-metallocycles is reported. Structural characterization of the highly stable triangles was supported by traveling-wave ion mobility-mass spectrometry (TWIM-MS) and gradient tandem mass spectrometry (gMS2). Their unique photophysical properties and self-assembly to form nanofibers are also described.
Co-reporter:Jin-Liang Wang, Xiaopeng Li, Carol D. Shreiner, Xiaocun Lu, Charles N. Moorefield, Sreedhar R. Tummalapalli, Douglas A. Medvetz, Matthew J. Panzner, Frank R. Fronczek, Chrys Wesdemiotis and George R. Newkome
New Journal of Chemistry 2012 vol. 36(Issue 2) pp:484-491
Publication Date(Web):12 Jan 2012
DOI:10.1039/C2NJ20799K
A class of shape-persistent metallodendrimer has been developed through a self-assembly strategy, in which 〈tpy-RuII-tpy〉 or 〈tpy-FeII-tpy〉 connectivity is utilized, as branching moieties or nodes. These metallomacromolecules were fully characterized by 1H and 13C NMR, traveling wave ion mobility mass spectrometry (TWIM MS), single crystal X-ray, UV-vis absorption, photoluminescence, and cyclic voltammetry. Significant increase in the drift times of the same charge states was observed with increasing generation of these complexes, which is in line with the change of molecular size. Moreover, the photophysical properties (molar extinction coefficients) and electrochemical stability of the complexes were noticeably different depending on size and metal ion center.
Co-reporter:Danijela Smiljanic, Chrys Wesdemiotis
International Journal of Mass Spectrometry 2012 Volumes 316–318() pp:235-243
Publication Date(Web):15 April 2012
DOI:10.1016/j.ijms.2012.02.016
Ternary non-covalent complexes composed of poly(ethylene imine) (P), a pentadeoxynucleotide (N) and glutamic acid monomer or dipeptide (E or EE) were prepared by mixing aqueous P, N and E (or EE) solutions in various molar ratios. Five nucleotides were examined, viz., d(TTTTT), d(CCCCC), d(AAAAA), d(GGGGG) and d(GCGAT). The compositions, solution stabilities and intrinsic stabilities of the ternary complexes (“terplexes”) were probed by electrospray ionization mass spectrometry (ESI-MS), tandem mass spectrometry (MS2) and ion mobility mass spectrometry (IM-MS). ESI-MS experiments confirmed the formation of terplexes with four of the five N molecules tested, the favored stoichiometry being 1:1:1 P-to-N-to-E (or EE) in all cases; d(GGGGG) did not form any detectable ternary complexes. Other compositions, involving higher order terplexes with multiple units or P, N and/or E (or EE), as well as several binary combinations, could be identified by IM-MS. The solution stabilities of the ternary complexes, assessed from their relative intensities in ESI mass spectra, depend on the sequence of N for PNE terplexes, maximizing with thymine-rich oligonucleotides. This selectivity is lost in the more weakly bound PN(EE) terplexes, whose binding interactions are barely influenced by the oligonucleotide sequence. Gas-phase (intrinsic) stabilities, assessed by dissociation extents in MS2 experiments, follow the same order as the corresponding solution stabilities, suggesting similar terplex structures in both media.Graphical abstractHighlights► Molecular self-assembly to non-covalent ternary complexes (terplexes). ► The major self-assembly products have a stoichiometry of 1:1:1. ► Longer glutamic acid n-mers decrease the terplex stabilities. ► Solution and intrinsic stabilities of the terplexes follow the same order. ► Terplex stability is sensitive to nucleotide sequence if the Glu n-mer is short.
Co-reporter:Jin-Liang Wang ; Xiaopeng Li ; Xiaocun Lu ; I-Fan Hsieh ; Yan Cao ; Charles N. Moorefield ; Chrys Wesdemiotis ; Stephen Z. D. Cheng ;George R. Newkome
Journal of the American Chemical Society 2011 Volume 133(Issue 30) pp:11450-11453
Publication Date(Web):June 9, 2011
DOI:10.1021/ja203645m
An approach to multicomponent coordination-driven self-assembly of the first terpyridine-based, shape-persistent, giant two-dimensional D6h supramacromolecular spoked wheel is reported. Mixing core T6, rim T3, and ZnII or CdII ions in a stoichiometric ratio (1:6:12) permitted the selective generation of a highly symmetric spoked wheel in 94% isolated yield via geometric and thermodynamic control. The products were characterized by a combination of traveling-wave ion mobility mass spectrometry and NMR techniques together with TEM imaging, which agreed with computational simulations.
Co-reporter:Yi-Tsu Chan ; Xiaopeng Li ; Jing Yu ; Gustavo A. Carri ; Charles N. Moorefield ; George R. Newkome
Journal of the American Chemical Society 2011 Volume 133(Issue 31) pp:11967-11976
Publication Date(Web):June 30, 2011
DOI:10.1021/ja107307u
New metallomacrocycles composed of 2,2′:6′,2″-terpyridine (tpy) ligands and RuII or FeII transition metal ions were prepared by stepwise directed assembly and characterized by 2D diffusion NMR spectroscopy (DOSY), electrospray ionization traveling wave ion mobility mass spectrometry (ESI TWIM MS), and molecular modeling. The supramolecular polymers synthesized include a homonuclear all-Ru hexamer as well as heteronuclear hexamer and nonamer with alternating Ru/Ru/Fe metal centers. ESI MS yields several charge states from each supramacromolecule. If ESI is interfaced with TWIM MS, overlapping charge states and the isomeric components of an individual charge state are separated based on their unique drift times through the TWIM region. From experimentally measured drift times, collision cross-sections can be deduced. The collision cross-sections obtained for the synthesized supramacromolecules are in good agreement with those predicted by molecular modeling for macrocyclic structures. Similarly, the hydrodynamic radii of the synthesized complexes derived from 2D DOSY NMR experiments agree excellently with the radii calculated for macrocyclic architectures, confirming the ESI TWIM MS finding. ESI TWIM MS and 2D DOSY NMR spectroscopy provide an alternative approach for the structural analysis of supramolecules that are difficult or impossible to crystallize, such as the large macrocyclic assemblies investigated. ESI TWIM MS will be particularly valuable for the characterization of supramolecular assemblies not available in the quantity or purity required for NMR studies.
Co-reporter:Sujith Perera, Xiaopeng Li, Mingming Guo, Chrys Wesdemiotis, Charles N. Moorefield and George R. Newkome
Chemical Communications 2011 vol. 47(Issue 16) pp:4658-4660
Publication Date(Web):17 Mar 2011
DOI:10.1039/C1CC10649J
Hexagonal PdII- or CdII-tetrakispyridinyl-based macrocycles are quantitatively self-assembled from 4′-(3-pyridinyl)-4,4′′-di(tert-butyl)-2,2′:6′,2′′-terpyridine and structurally confirmed by NMR and TWIM-MS.
Co-reporter:Xiaopeng Li, Yi-Tsu Chan, Madalis Casiano-Maldonado, Jing Yu, Gustavo A. Carri, George R. Newkome, and Chrys Wesdemiotis
Analytical Chemistry 2011 Volume 83(Issue 17) pp:6667
Publication Date(Web):July 11, 2011
DOI:10.1021/ac201161u
The self-assembly of ZnII ions and bis(terpyridine) (tpy) ligands carrying 120° or 180° angles between their metal binding sites was utilized to prepare metallosupramolecular libraries with the connectivity. These combinatorial libraries were separated and characterized by ion mobility mass spectrometry (IM MS) and tandem mass spectrometry (MS2). The 180°-angle building blocks generate exclusively linear complexes, which were used as standards to determine the architectures of the assemblies resulting from the 120°-angle ligands. The latter ligand geometry promotes the formation of macrocyclic hexamers, but other n-mers with smaller (n = 5) or larger ring sizes (n = 7–9) were identified as minor products, indicating that the angles in the bis(terpyridine) ligand and within the coordinative tpy–ZnII–tpy bonds are not as rigid, as previously believed. Macrocyclic and linear isomers were detected in penta- and heptameric assemblies; in the larger octa- and nonameric assemblies, ring-opened conformers with compact and folded geometries were observed in addition to linear extended and cyclic architectures. IM MS2 experiments provided strong evidence that the macrocycles present in the libraries were already formed in solution, during the self-assembly process, not by dissociation of larger complexes in the gas phase. The IM MS/MS2 methods provide a means to analyze, based on size and shape (architecture), supramolecular libraries that are not amenable to liquid chromatography, LC-MS, NMR, and/or X-ray techniques.
Co-reporter:Xiaopeng Li, Yi-Tsu Chan, George R. Newkome, and Chrys Wesdemiotis
Analytical Chemistry 2011 Volume 83(Issue 4) pp:1284
Publication Date(Web):January 24, 2011
DOI:10.1021/ac1022875
Traveling wave ion mobility mass spectrometry (TWIM MS) was combined with gradient tandem mass spectrometry (gMS2) to deconvolute and characterize superimposed ions with different charges and shapes formed by electrospray ionization (ESI) of self-assembled, hexameric metallomacrocycles composed of terpyridine-based ligands and CdII ions. ESI conditions were optimized to obtain intact hexameric cation assemblies in a low charge state (2+), in order to minimize overlapping fragments of the same mass-to-charge ratio. With TWIM MS, intact hexameric ions could be separated from remaining fragments and aggregates. Collisional activation of these hexameric ions at varying collision energies (gMS2), followed by TWIM separation, was then performed to resolve macrocyclic from linear hexameric species. Because of the different stabilities of these architectures, gMS2 changes their relative amounts, which can be monitored individually after subsequent ion mobility separation. On the basis of this unique strategy, hexameric cyclic and linear isomers have been successfully resolved and identified. Complementary structural information was gained by the gMS2 fragmentation pattern of the metallosupramolecules, acquired by collisionally activated dissociation after TWIM dispersion. TWIM MS interfaced with gMS2 should be particularly valuable for the characterization of a variety of supramolecular polymers, which often contain isomeric architectures that yield overlapping fragments and aggregates upon ESI MS analysis.
Co-reporter:Danijela Smiljanic, Chrys Wesdemiotis
International Journal of Mass Spectrometry 2011 Volume 304(2–3) pp:148-153
Publication Date(Web):1 July 2011
DOI:10.1016/j.ijms.2010.06.035
Non-covalent complexes between low molecular weight poly(ethylene imine) (PEI 400 and 800) and single-stranded oligodeoxynucleotides (ODNs) were prepared in aqueous solution by combining polymer and ODN in molar ratios ranging from 1:10 to 10:1. Five ODNs were investigated, including d(TTTTT), d(CCCCC), d(AAAAA), d(GGGGG) and d(GCGAT). The compositions, solution stabilities and gas-phase stabilities of the complexes (termed polyplexes) were examined by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS2). Independent of the mixing ratio of the reactants, the polyplex with 1:1 polymer-to-nucleotide stoichiometry, PN, is the dominant product, while the polyplexes PN2 and P2N are observed as byproducts with all ODNs. The relative polyplex ion abundances in the ESI mass spectra reveal the following order of solution stabilities for the major product PN: PEI-d(TTTTT) > PEI-d(GGGGG) ≈ PEI-d(GCGAT) ≈ PEI-d(CCCCC) > PEI-d(AAAAA). The gas-phase stabilities, assessed by MS2 and collisionally activated dissociation, follow the same order, providing evidence that the polyplex structures in aqueous solution and the more hydrophobic environment of the gas-phase are very similar. PEI 800 leads to more stable polyplexes than PEI 400. PEI–ODN polyplexes have been used in gene delivery. The particularly high binding affinity of d(TTTTT) vs. the other ODNs suggests that sequence-specific delivery systems could be developed by appropriate design of the size and composition of the polymeric delivery vehicle.The dominant polyplexes formed by pentadeoxynucleotides with poly(ethylene imine) 400 or 800 have 1:1 stoichiometry. Solution and intrinsic stabilities of these non-covalent complexes follow the same order, with thymine-rich nucleotides showing the highest binding affinities.
Co-reporter:Bethany L. Subel, Chrys Wesdemiotis
International Journal of Mass Spectrometry 2011 Volume 301(1–3) pp:195-201
Publication Date(Web):30 March 2011
DOI:10.1016/j.ijms.2010.08.031
Electrospray ionization (ESI) of poly(styrene sulfonate sodium salt) (PSS) with a molar mass of 1100 Da (weight average) efficiently produces distributions of [M + Na]+ cations in positive mode and [M–Na]−as well as [M–2Na]2−anions in negative mode. From these distributions, repeat unit, end groups, and defects in the poly(electrolyte) can readily be determined by quadrupole ion trap mass spectrometry (QiT MS). During MS analysis, sodium/proton exchanges in the SO3Na substituents of the [M–Na]−ions take place, with the number of exchanges observed being equal to the number of sulfonate groups present in the analyzed oligomer. Such exchanges are less pronounced for the oligomers with 2− charges and absent in the sodium-cationized oligomers (1+ charge). Collisionally activated dissociation (CAD) of the sodiated cations proceeds via charge-remote homolytic C–C bond cleavages in the polymer backbone, ultimately leading to fragments that contain both or neither of the end groups. The same chemistry is observed for the anions if they have not exchanged sodium ions for protons. In sharp contrast, precursor ions that contain SO3H (sulfonic acid) groups due to Na/H exchange dissociate mainly by charge-catalyzed SO3 losses. The number of SO3 units lost is identical to the number of sulfonic acid pendants in the oligomer. The CAD results suggest that PSS may degrade to polystyrene under acidic conditions.Graphical abstractResearch highlights▶ ESI ionizes efficiently sulfonated styrene poly(electrolytes). ▶ Such compounds readily undergo sodium/proton exchanges in anionic charge states. ▶ Polymers with sulfonate salt pendants decompose by charge-remote homolytic chain cleavages via ion/radical complexes. ▶Polymers with sulfonic acid pendants degrade by proton-catalyzed sulfur trioxide losses.
Co-reporter:Dr. Yi-Tsu Chan;Dr. Xiaopeng Li;Dr. Charles N. Moorefield;Dr. Chrys Wesdemiotis;Dr. George R. Newkome
Chemistry - A European Journal 2011 Volume 17( Issue 28) pp:7750-7754
Publication Date(Web):
DOI:10.1002/chem.201100559
Co-reporter:Dr. Jin-Liang Wang;Dr. Xiaopeng Li;Xiaocun Lu;Dr. Yi-Tsu Chan;Dr. Charles N. Moorefield;Dr. Chrys Wesdemiotis;Dr. George R. Newkome
Chemistry - A European Journal 2011 Volume 17( Issue 17) pp:4830-4838
Publication Date(Web):
DOI:10.1002/chem.201003681
Abstract
The synthesis, purification, structural analysis, and photophysical properties of a series of five-, six-, and seven-sided FeII macrocycles and the corresponding hexameric CdII macrocycle, all prepared by self-assembly of a 120° bis(terpyridine) ligand modified with first- and second-generation 13 C-branched dendrons, are reported. All metallomacrocycles were fully characterized by 1H and 13C NMR spectroscopy, traveling-wave ion-mobility mass spectrometry (TWIM MS), molecular modeling, UV/Vis absorption spectroscopy, photoluminescence, and cyclic voltammetry. A gradual increase of the collision cross sections of the FeII metallomacrocycles was observed with a successive increase of the number and molecular size of the ligands. The combination of ion-mobility mass spectrometry and NMR techniques unveils structural features that agree well with calculations. Extinction coefficients and emission are significantly modulated by increasing the ring size and changing the metal ion center from FeII to CdII.
Co-reporter:Xiaopeng Li, Li Guo, Madalis Casiano-Maldonado, Donghui Zhang, and Chrys Wesdemiotis
Macromolecules 2011 Volume 44(Issue 12) pp:4555-4564
Publication Date(Web):June 7, 2011
DOI:10.1021/ma200542p
The ability of multidimensional mass spectrometry (MS) approaches, interfacing different ionization methods with tandem mass spectrometry (MS2) fragmentation and ion mobility (IM) separation, to characterize synthetic polymers is demonstrated for poly(α-peptoid)s synthesized by N-heterocyclic carbene (NHC)-mediated zwitterionic ring-opening polymerization. Matrix-assisted laser desorption ionization (MALDI) causes elimination of the NHC initiator, if performed in the presence of cationizing salts. Electrospray ionization (ESI) is softer, allowing for the detection of the intact sample. It also shows that in proper solvents self-assembly of the poly(α-peptoid) occurs to form supramacromolecules; since these noncovalent self-assemblies overlap with the main product, separation by IM MS is essential for their conclusive identification. MS2 confirms the connectivity of the poly(α-peptoid)s, whereas MS2 combined with IM separation renders valuable insight into the binding interactions in the supramolecular assemblies and on the structures and conformations of the poly(α-peptoid) resulting after NHC elimination. Performing all analyses inside the mass spectrometer (“top-down”) enables fast, sensitive, and cost-effective analysis of polymer composition, structure, and architecture without prior derivatization, separation, or degradation.
Co-reporter:Sujith Perera Dr.;Xiaopeng Li Dr.;Monica Soler Dr.;Anthony Schultz, Dr.;CharlesN. Moorefield Dr. ;GeorgeR. Newkome Dr.
Angewandte Chemie 2010 Volume 122( Issue 37) pp:6689-6694
Publication Date(Web):
DOI:10.1002/ange.200906198
Co-reporter:Sujith Perera Dr.;Xiaopeng Li Dr.;Monica Soler Dr.;Anthony Schultz, Dr.;CharlesN. Moorefield Dr. ;GeorgeR. Newkome Dr.
Angewandte Chemie International Edition 2010 Volume 49( Issue 37) pp:6539-6544
Publication Date(Web):
DOI:10.1002/anie.200906198
Co-reporter:Yi-Tsu Chan ; Xiaopeng Li ; Monica Soler ; Jin-Liang Wang ; Chrys Wesdemiotis ;George R. Newkome
Journal of the American Chemical Society 2009 Volume 131(Issue 45) pp:16395-16397
Publication Date(Web):October 15, 2009
DOI:10.1021/ja907262c
Self-assembly of 1,3-di(4′-terpyridinyl)arenes by using the labile tpy-Cd(II)-tpy (where tpy = 2,2′:6′,2′′-terpyridine) connectivity afforded access to hexacadmium macrocycles in high yield. These supramolecular assemblies were characterized by traveling wave ion mobility mass spectrometry (TWIM-MS).
Co-reporter:Sara E. Whitson, Gabor Erdodi, Joseph P. Kennedy, Robert P. Lattimer and Chrys Wesdemiotis
Analytical Chemistry 2008 Volume 80(Issue 20) pp:7778
Publication Date(Web):September 12, 2008
DOI:10.1021/ac801198g
Complex copolymers are heated to slowly increasing temperatures on a direct probe (DP) inside the plasma of the atmospheric pressure chemical ionization (APCI) source of a quadrupole ion trap. Slow heating allows for temporal separation of the thermal degradation products according to the stabilities of the bonds being cleaved. The products released from the DP are identified in situ by APCI mass spectrometry and tandem mass spectrometry. DP-APCI experiments on amphiphilic copolymers provide conclusive information about the nature of the hydrophobic and hydrophilic components present and can readily distinguish between copolymers with different comonomer compositions as well as between cross-linked copolymers and copolymer blends with similar physical properties. The dependence of DP-APCI mass spectra on temperature additionally reveals information about the thermal stability of the different domains within a copolymer.
Co-reporter:Ping Wang, Gilles Ohanessian, Chrys Wesdemiotis
International Journal of Mass Spectrometry 2008 Volume 269(1–2) pp:34-45
Publication Date(Web):1 January 2008
DOI:10.1016/j.ijms.2007.09.008
The sodium ion affinities of the amino acids Asn, Gln, His and Arg have been determined by experimental and computational approaches (for Asn, His and Arg). Na+-bound heterodimers with amino acid and peptide ligands (Pep1, Pep2) were produced by electrospray ionization. From the dissociation kinetics of these Pep1–Na+–Pep2 ions to Pep1–Na+ and Pep2–Na+, determined by collisionally activated dissociation, a ladder of relative affinities was constructed and subsequently converted to absolute affinities by anchoring the relative values to known Na+ affinities. The Na+ affinities of Asn, His and Arg, were calculated at the MP2(full)/6-311+G(2d,2p)//MP2/6-31G(d) level of ab initio theory. The resulting experimental and computed Na+ affinities are in excellent agreement with one another. These results, combined with those of our previous studies, yield the sodium ion affinities of 18 out of the 20 α-amino acids naturally occurring in peptides and proteins of living systems.
Co-reporter:Kittisak Chaicharoen;Michael J. Polce
Analytical and Bioanalytical Chemistry 2008 Volume 392( Issue 4) pp:595-607
Publication Date(Web):2008 October
DOI:10.1007/s00216-008-1969-0
The unimolecular degradation of alkali-metal cationized polyacrylates with the repeat unit CH2CH(COOR) and a variety of ester pendants has been examined by tandem mass spectrometry. The fragmentation patterns resulting from collisionally activated dissociation depend sensitively on the size of the ester alkyl substituent (R). With small alkyl groups, as in poly(methyl acrylate), lithiated or sodiated oligomers (M) decompose via free-radical chemistry, initiated by random homolytic C-C bond cleavages along the polymer chain. The radical ions formed this way dissociate further by backbiting rearrangements and β scissions to yield a distribution of terminal fragments with one of the original end groups and internal fragments with 2–3 repeat units. If the ester alkyl group bears three or more carbon atoms, cleavages within the ester moieties become the predominant decomposition channel. This distinct reactivity is observed if R = t-butyl, n-butyl, or the mesogenic group (CH2)11-O-C6H4-C6H4-CN. The [M+alkali metal]+ ions of the latter polyacrylates dissociate largely by charge-remote 1,5-H rearrangements that convert COOR to COOH groups by expulsion of 1-alkenes. The acid groups may displace an alcohol unit from a neighboring ester pendant to form a cyclic anhydride, unless hindered by steric effects. Using atom transfer radical polymerization, hyperbranched polyacrylates were prepared carrying ester groups both within and between the branches. Unique alkenes and alcohols are cleaved from ester groups at the branching points, enabling determination of the branching architecture.
Co-reporter:Francesco Pingitore, Christian Bleiholder, Béla Paizs, Chrys Wesdemiotis
International Journal of Mass Spectrometry 2007 Volume 265(2–3) pp:251-260
Publication Date(Web):1 September 2007
DOI:10.1016/j.ijms.2007.02.029
The Li+ complexes of the isomeric α-dipeptide radicals H2NCHC(O)NHCH2COOH (GlyGly) and H2NCH2C(O)NHCHCOOH (GlyGly) are formed in the gas phase from the isomeric complexes [PheGly + Li]+ and [GlyPhe + Li]+, respectively, via homolytic cleavage of the corresponding benzyl side chains. The isomers undergo distinctively different reactions upon collisionally activated dissociation (CAD) and, hence, represent unique, non-interconverting species. The investigation of deuterated isotopomers and of dipeptide radicals with Ala residues permits complete elucidation of the dissociation pathways of the radical complexes. The majority of reactions observed are promoted by the radical site, with the location of the unpaired electron playing an important role in the types of reactions taking place. Analogous differences are found for dilithiated complexes of GlyGly and GlyGly, in which the COOH termini are derivatized to COO−Li+ salt bridges. Density functional theory calculations confirm that the lithiated and dilithiated α-dipeptide radicals have distonic character; the radical is largely localized on the N- or C-terminal α-C atom and the charge is largely localized on the metal ions. In the most stable conformers, the Li+ ion(s) are bound between the amide carbonyl and C-terminal carbonyl (or carboxylate) groups. Theory predicts a higher thermodynamic stability for the complexes of the N-terminal radical GlyGly, as reflected by the significantly higher yield, with which these complexes are formed (from their PheGly precursors), compared to the GlyGly complexes.
Co-reporter:Benjamin J. Bythell;Douglas F. Barofsky
Journal of The American Society for Mass Spectrometry 2007 Volume 18( Issue 7) pp:1291-1303
Publication Date(Web):2007 July
DOI:10.1016/j.jasms.2007.03.029
The fragmentation characteristics of protonated alanylglycylglycine, [AGG+H]+, were investigated by tandem mass spectrometry in MALDI-TOF/TOF, ion trap, and hybrid sector instruments. b2 is the most abundant fragment ion in MALDI-TOF/TOF, ion trap, and hybrid sector metastable ion (MI) experiments, while y2 is slightly more abundant than b2 in collision activated dissociation (CAD) performed in the sector instrument. The A-G amide bond is cleaved on the a1-y2 pathway resulting in a proton-bound dimer of GG and MeCH=NH. Depending on the fragmentation conditions employed, this dimer can then (1) be detected as [AGG+H−CO]+, (2) dissociate to produce y2 ions, [GG+H]+, (3) dissociate to produce a1 ions, [MeCH=NH+H]+, or (4) rearrange to expel NH3 forming a [AGG+H−CO−NH3]+ ion. The activation method and the experimental timescale employed largely dictate which of, and to what extent, these processes occur. These effects are qualitatively rationalized with the help of quantum chemical and RRKM calculations. Two mechanisms for formation of the [AGG+H−CO−NH3]+ ion were evaluated through nitrogen-15 labeling experiments and quantum chemical calculations. A mechanism involving intermolecular nucleophilic attack and association of the GG and imine fragments followed by ammonia loss was found to be more energetically favorable than expulsion of ammonia in an SN2-type reaction.
Co-reporter:Ping Wang
Journal of The American Society for Mass Spectrometry 2007 Volume 18( Issue 3) pp:541-552
Publication Date(Web):2007 March
DOI:10.1016/j.jasms.2006.10.024
The sodium ion affinities (binding energies) of nineteen peptides containing 2–4 residues have been determined by experimental and computational approaches. Na+-bound heterodimers with amino acid and peptide ligands (Pep1, Pep2) were produced by electrospray ionization. The dissociations of these Pep1-Na+-Pep2 ions to Pep1-Na+ and Pep2-Na+ were examined by collisionally activated dissociation to construct a ladder of relative affinities via the kinetic method. The accuracy of this ladder was subsequently ascertained by experiments using several excitation energies for four peptide pairs. The relative scale was converted to absolute affinities by anchoring the relative values to the known Na+ affinity of GlyGly. The Na+ affinities of AlaAla, HisGly, GlyHis, GlyGlyGly, AlaAlaAla, GlyGlyGlyGly, and AlaAlaAlaAla were also calculated at the MP2(full)/6-311+G(2d,2p) level of ab initio theory using geometries that were optimized at the MP2(full)/6-31G(d) level for AlaAla or HF/6-31G(d) level for the other peptides; the resulting values agree well with experimental Na+ affinities. Increasing the peptide size is found to dramatically augment the Na+ binding energy. The calculations show that in nearly all cases, all available carbonyl oxygens are sodium binding sites in the most stable structures. Whenever side chains are available, as in HisGly and GlyHis, specific additional binding sites are provided to the cation. Oligoglycines and oligoalanines have similar binding modes for the di- and tripeptides, but differ significantly for the tetrapeptides: while the lowest energy structure of GlyGlyGlyGly-Na+ has the peptide folded around the ion with all four carbonyl oxygens in close contact with Na+, that of AlaAlaAlaAla_Na+ involves a pseudo-cyclic peptide in which the C and N termini interact via hydrogen bonding, while Na+ sits on top of the oxygens of three nearly parallel C=O bonds.
Co-reporter:Andras Nagy, Joseph P. Kennedy, Ping Wang, Chrys Wesdemiotis, Scott D. Hanton
Applied Surface Science 2006 Volume 252(Issue 10) pp:3751-3759
Publication Date(Web):15 March 2006
DOI:10.1016/j.apsusc.2005.05.063
Abstract
Glass surfaces were treated with various hydrophobizing microemulsions (HME) containing mineral seal oil or polyisobutylene as hydrophobes emulsified by dimethyl dicoco ammonium chloride (i.e. mimicking commercial car wash practices) and characterized by mass spectrometry (MS) and contact angle measurements. The cationic emulsifier mediates the anchoring of hydrophobes to the polar glass surface. It is demonstrated that by the use of even very low (0.3–3.0 w%) HME concentrations the surfaces become hydrophobic and repel water even after numerous (∼20) rinsing cycles. According to MS evidence, however, the surfaces are not fully saturated with hydrophobes and the unprotected areas remain vulnerable to environmental damage.
Co-reporter:Ping Wang, George R. Newkome, Chrys Wesdemiotis
International Journal of Mass Spectrometry 2006 Volumes 255–256() pp:86-92
Publication Date(Web):1 September 2006
DOI:10.1016/j.ijms.2006.03.006
Organometallic assemblies, containing the bis-terpyridinyl-Ru(II) connectivity (symbolized as [–〈Ru〉–]) in a range of small bismetal complexes to macrocycles possessing up to 12 metal ions, have been studied by electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS). ESI MS is found to be a more suitable characterization method than MALDI MS, because (1) it can directly detect multiply charged ions, (2) does not alter the connectivity of the complexes through disassembly/reassembly sequences and (3) causes essentially no or very little fragmentation. Requirements for the optimum signal-to-noise ratio in ESI mass spectra include: (1) a low ionization source temperature (30 °C), (2) low skimmer voltage (10–15 V), (3) moderate flow rates of both the nebulizing and drying gases and (4) a pre-cooled sample. Tandem mass spectrometry experiments on intact complex ions indicate that the noncovalent interactions between the Ru(II) center and the two terpyridine ligands, which hold the supramolecular assembly together, are very strong.
Co-reporter:Kathleen M. Wollyung;Joseph P. Kennedy;Andras Nagy
Journal of Polymer Science Part A: Polymer Chemistry 2005 Volume 43(Issue 5) pp:946-958
Publication Date(Web):21 JAN 2005
DOI:10.1002/pola.20566
This article reports the facile synthesis of novel terminally and centrally functionalized polyisobutylenes (PIBs) and the detailed characterization of the products by various mass spectrometry techniques. Specifically, HPIBCH2C(OH)CH3CH2NHCH3 and [HPIBCH2CH(OH)CH3CH2]2NCH3 were synthesized by the quantitative epoxidation of HPIBCH2C(CH3)CH2 and the subsequent conversion of the resulting epoxide with excess CH3NH2. Quaternization with CH3Cl of these mixtures of secondary and tertiary amines yielded exclusively HPIBCH2C(OCH3)CH3CH2N(CH3)2 from the secondary amine, whereas the tertiary (centrally functionalized) amine remained unchanged. Tandem mass spectrometry experiments provided unique insight into the precise connectivity of the functional end groups added to the PIB frame. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 946–958, 2005
Co-reporter:Mark A. Arnould, Michael J. Polce, Roderic P. Quirk, Chrys Wesdemiotis
International Journal of Mass Spectrometry 2004 Volume 238(Issue 3) pp:245-255
Publication Date(Web):15 November 2004
DOI:10.1016/j.ijms.2004.05.014
Matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) is applied to examine the products arising upon the preparation of chain-end functional polymers via living anionic polymerization techniques. Both post-polymerization functionalizations as well as the use of functionalized initiators are investigated. MALDI-TOF MS is shown to be a sensitive probe for the qualitative analysis of the major and minor oligomers from novel functionalization reactions whose mechanisms are not yet well established. The method is particularly valuable for the identification of the end groups of the minor, and often unexpected, distributions that may be undetectable by other analytical means. Complete characterization of all oligomers generated during functionalization reactions provides an essential tool to the synthetic chemist for understanding the corresponding mechanisms. This insight is necessary for selecting alternative routes or making modifications to the reaction conditions. It is demonstrated that MALDI-TOF MS can convey quantitative information about the yields of the chain-end groups introduced during functionalization. From the cases presented it is evident that post-polymerization reactions allow for better control of chain-end functionality and molecular weight than functionalization with the limited number of currently available protected functionalized initiators.
Co-reporter:Michelle M. Kish, Gilles Ohanessian, Chrys Wesdemiotis
International Journal of Mass Spectrometry 2003 Volume 227(Issue 3) pp:509-524
Publication Date(Web):July 2003
DOI:10.1016/S1387-3806(03)00082-4
Na+-bound heterodimers of amino acids (AA) are produced in the gas phase by electrospray ionization (ESI). The dissociation kinetics of these AA1Na+AA2 ions are determined by collisionally activated dissociation (CAD) and converted to a ladder of relative Na+ affinities via the Cooks kinetic method. The affinities derived follow the order (kJ mol−1, relative to Gly): Gly (0), Ala (6), Val (12), Leu (13), Cys (14), Ile (15), Ser (31), Pro (35), Thr (36), Phe (37), Tyr (40), Asp (42), Glu (43), Asn (45), Trp (49), Gln (51), His (57). Absolute Na+ binding energies are estimated by anchoring the relative values to the Na+ affinity of Ala (167 kJ mol−1), measured by the same approach using Na+-bound dimers of Ala and a series of acetamide derivatives. The Na+ binding energies of the acetamide reference bases and of representative aliphatic and side-chain functionalized amino acids (Gly, Ala, Pro, Cys and Ser) are determined by ab initio theory. Experimental and ab initio affinities agree very well. The combined data show that functional side chains increase the AANa+ bond strength by providing an extra ligand to the metal ion. Aromatic and carbonyl substituents in the side chain bring about substantial increases in the Na+ binding energy, with particularly large increments observed for amide and electron-rich (N-containing) aromatic groups. A poor correlation is found between sodium ion and proton affinities, strongly suggesting that the Na+ complexes do not have salt-bridge structures involving zwitterionic amino acids (in which the most basic site is protonated).
Co-reporter:Mark A Arnould, Chrys Wesdemiotis, Robert J Geiger, Michael E Park, Rita W Buehner, Daniel Vanderorst
Progress in Organic Coatings 2002 Volume 45(2–3) pp:305-312
Publication Date(Web):October 2002
DOI:10.1016/S0300-9440(02)00114-5
A polyester copolymer is produced by step-growth polymerization of neopentyl glycol (50 mol%), trimethylol propane (1%), terephthalic acid (45%) and adipic acid (5%) and its microstructure is characterized by gel permeation chromatography and matrix-assisted laser desorption ionization mass and tandem mass spectrometry. The combination of these analytical methods is shown to yield detailed insight about the composition, end groups, molecular weight, and sequence of the product.
Co-reporter:Jody M. Talley;Blas A. Cerda Dr.;Gilles Ohanessian Dr. Dr.
Chemistry - A European Journal 2002 Volume 8(Issue 6) pp:
Publication Date(Web):15 MAR 2002
DOI:10.1002/1521-3765(20020315)8:6<1377::AID-CHEM1377>3.0.CO;2-D
The relative alkali metal ion (M+) affinities (binding energies) between seventeen different amino acids (AA) and the corresponding methyl esters (AAOMe) were determined in the gas phase by the kinetic method based on the dissociation of AA–M+–AAOMe heterodimers (M=Li, Na, K, Cs). With the exception of proline, the Li+, Na+, and K+ affinities of the other aliphatic amino acids increase in the order AA<AAOMe, while their Cs+ affinities generally decrease in this direction. For aliphatic β-amino acids, which are particularly basic molecules, the order AA>AAOMe is already observed for K+. Proline binds more strongly than its methyl ester to all M+ except Li+. Ab initio calculations on the M+ complexes of alanine, β-aminoisobutyric acid, proline, glycine methyl ester, alanine methyl ester, and proline methyl ester show that their energetically most favorable complexes result from charge solvation, except for proline which forms salt bridges. The most stable mode of charge solvation depends on the ligand (AA or AAOMe) and, for AA, it gradually changes with metal ion size. Esters chelate all M+ ions through the amine and carbonyl groups. Amino acids coordinate Li+ and Na+ ions through the amine and carbonyl groups as well, but K+ and Cs+ ions are coordinated by the O atoms of the carboxyl group. Upon consideration of these differences in favored binding geometries, the theoretically derived relative M+ affinities between aliphatic AA and AAOMe are in good overall agreement with the above given experimental trends. The majority of side chain functionalized amino acids studied show experimentally the affinity order AA<AAOMe for all M+ ions, which is consistent with charge solvation. Deviations are only observed with the most basic amino acids lysine and arginine, whose K+ (for arginine) and Cs+ complexes (for both) follow the affinity order AA>AAOMe. The latter ranking is attributed to salt bridge formation.
Co-reporter:Jianglin Wu, Michael J Polce, Chrys Wesdemiotis
International Journal of Mass Spectrometry 2001 Volume 204(1–3) pp:125-131
Publication Date(Web):6 February 2001
DOI:10.1016/S1387-3806(00)00333-X
The hypervalent complexes of Li atom with water and ammonia, viz. Li–OH2 and Li–NH3, are generated in the gas phase by neutralization of Li+–OH2 and Li+–NH3, respectively. The mass spectra obtained by subsequent reionization ∼0.3 μs later clearly indicate that the neutral complexes Li–OH2 and Li–NH3 are stable species in the gas phase, as had been predicted by theory. Li–OH2/Li–NH3 dissociate partly to Li+H2O/NH3 within the timescale of the experiments, the dissociating fraction of the water complex being larger. Parallel ab initio calculations reveal that the more extensive dissociation of Li–OH2 versus Li–NH3 is the result of a lower binding energy (51 versus 62 kJ mol−1 for Li–OH2 and Li–NH3, respectively) and a less favorable Franck-Condon factor for transitions between Li–OH2 and Li+–OH2, as compared to transitions between Li–NH3 and Li+–NH3.
Co-reporter:Michael J. Nold, Blas A. Cerda, Chrys Wesdemiotis
Journal of the American Society for Mass Spectrometry 1999 Volume 10(Issue 1) pp:1-8
Publication Date(Web):January 1999
DOI:10.1016/S1044-0305(98)00120-2
Dissociation of the amide bonds in a protonated peptide leads to N-terminal sequence fragments with cyclic structures and C-terminal sequence fragments with linear structures. The ionic fragments containing the N-terminus (bn) have been shown to be protonated oxazolones, whereas those containing the C-terminus (yn) are protonated linear peptides. The coproduced neutral fragments are cyclic peptides from the N-terminus and linear peptides from the C-terminus. A likely determinant of these structural choices is the proton affinity (PA) of the described peptide segments. This study determines the PA values of such segments (Pep), i.e., cyclic and linear dipeptides and a relevant oxazolone, based on the dissociations of proton-bound dimers [Pep + Bi]H+ in which Bi is a reference base of known PA value (Cooks kinetic method). The dissociations are assessed at different internal energies to thereby obtain both proton affinities as well as entropies of protonation. For species with comparable amino acid composition, the proton affinity (and gas phase basicity) follows the order cyclic peptide ≪ oxazolone ≈ linear peptide. This ranking is consistent with dissociation of the protonated peptide via interconverting proton-bound complexes involving N-terminal oxazolone (O) or cyclopeptide (C) segments and C-terminal linear peptide segments (L), viz. O ⋯ H+ ⋯ L ⇄ C ⋯ H+ ⋯ L. N-terminal sequence ions (bn) are formed with oxazolone structures which can efficiently compete for the proton with the linear segments. On the other hand, N-terminal neutral fragments detach as cyclic peptides, with H+ now being retained by the more basic linear segment from the C-terminus to yield yn.
Co-reporter:Blas A. Cerda, Chrys Wesdemiotis
International Journal of Mass Spectrometry 1999 Volume 189(2–3) pp:189-204
Publication Date(Web):11 August 1999
DOI:10.1016/S1387-3806(99)00085-8
The Na+ affinities of several mono- and disaccharide stereoisomers are determined in the gas phase based on the dissociations of Na+-bound heterodimers [saccharide + Bi]Na+, where Bi represents a reference base of known Na+ affinity (kinetic method). The compounds investigated include the pentoses arabinose, xylose, and ribose; the hexoses glucose, galactose, and mannose; and the disaccharides melibiose, gentiobiose, and lactose. The decompositions of [saccharide + Bi]Na+ are assessed as a function of internal energy, to thereby obtain both absolute Na+ affinities as well as relative entropies of Na+ attachment. The Na+ affinities measured are consistent with multidentate coordination of sodium ion by the oxygen sites of the saccharides. In general, hexoses bind Na+ stronger than pentoses, suggesting that the hydroxymethyl substituent equips them with more conformational flexibility and larger inductive effects for complexing Na+. The latter properties are further enhanced in the disaccharides, which also carry more basic substituents; as a result, disaccharides form even stronger bonds to Na+. The entropies of Na+ attachment are found to rise in the order pentose < hexose < disaccharide, pointing to an increase in this direction of the rotational flexibility lost after attachment of Na+. The favored [monosaccharide + Na]+ structures predicted computationally contain pyranose rings in chair or boat conformations that permit tri- or tetradentate Na+ coordination and hydrogen bonds between the hydroxyl ligands; the most stable disaccharide complexes are tetradentate and involve chair forms. In the calculated structures, the pyranose O atom and the hydroxymethyl group(s) generally participate in the Na+ binding, in agreement with the experimental trends. Small changes in the saccharide stereochemistry alter the optimum Na+ coordination possible and, therefore, the Na+ affinity; as a result, the latter thermochemical property is ideally suitable for the distinction of stereoisomeric saccharides.
Co-reporter:Blas A Cerda, Leticia Cornett, Chrys Wesdemiotis
International Journal of Mass Spectrometry 1999 Volume 193(2–3) pp:205-226
Publication Date(Web):20 December 1999
DOI:10.1016/S1387-3806(99)00164-5
The complexes of the peptides (Pep) bradykinin (RPPGFSPFR), des-Arg1-bradykinin, and des-Arg9-bradykinin with the metal (M) ions Na+, K+, Cs+, Cu+, Ag+, Co2+, Ni2+, and Zn2+ are generated in the gas phase by matrix-assisted laser desorption/ionization and the structures of the corresponding [Pep + M+]+ or [Pep − H+ + M2+]+ cations are probed by postsource decay (PSD) mass spectrometry. The PSD spectra depend significantly on the metal ion attached; moreover, the various metal ions respond differently to the presence or absence of a basic arginine residue. The Na+ and K+ adducts of all three peptides mainly produce N-terminal sequence ions upon PSD; the fragments observed point out that these metal ions are anchored by the PPGF segment and not the arginine residue(s). In contrast, the adducts of Cu+ and Ag+ show a strong dependence on the position of Arg; complexes of des-Arg1-Pep (which contains a C-terminal Arg) produce primarily yn ions whereas those of des-Arg9-Pep generate exclusively an and bn ions. These trends are consistent with Cu+ ligation by Arg’s guanidine group. The [Pep + Cs+]+ ions mainly yield Cs+; a second significant fragmentation occurs only if a C-terminal arginine is present and involves elimination of this arginine’s side chain plus water. This reaction is rationalized through a salt bridge mechanism. The most prominent PSD products from [Pep − H+ + Co2+]+ and [Pep − H+ + Ni2+]+ contain at least one phenylalanine residue, revealing a marked preference for these divalent metal ions to bind to aromatic rings; the fragmentation patterns of the complexes further suggest that Co2+ and Ni2+ bind to deprotonated amide nitrogens. The coordination chemistry of Zn2+ combines features found with the divalent Co2+/Ni2+ as well as the monovalent Cu+/Ag+ transition metal ions. Generally, the structure and fragmentation behavior of each complex reflects the intrinsic coordination preferences of the corresponding metal ion.
Co-reporter:Benjamin J. Bythell, Douglas F. Barofsky, Francesco Pingitore, Michael J. Polce, Ping Wang, Chrys Wesdemiotis, Béla Paizs
Journal of the American Society for Mass Spectrometry (July 2007) Volume 18(Issue 7) pp:1291-1303
Publication Date(Web):1 July 2007
DOI:10.1016/j.jasms.2007.03.029
The fragmentation characteristics of protonated alanylglycylglycine, [AGG + H]+, were investigated by tandem mass spectrometry in MALDI-TOF/TOF, ion trap, and hybrid sector instruments. b2 is the most abundant fragment ion in MALDI-TOF/TOF, ion trap, and hybrid sector metastable ion (MI) experiments, while y2 is slightly more abundant than b2 in collision activated dissociation (CAD) performed in the sector instrument. The A–G amide bond is cleaved on the a1-y2 pathway resulting in a proton-bound dimer of GG and MeCH=NH. Depending on the fragmentation conditions employed, this dimer can then (1) be detected as [AGG + H − CO]+, (2) dissociate to produce y2 ions, [GG + H]+, (3) dissociate to produce a1 ions, [MeCH=NH + H]+, or (4) rearrange to expel NH3 forming a [AGG + H − CO − NH3]+ ion. The activation method and the experimental timescale employed largely dictate which of, and to what extent, these processes occur. These effects are qualitatively rationalized with the help of quantum chemical and RRKM calculations. Two mechanisms for formation of the [AGG + H − CO − NH3]+ ion were evaluated through nitrogen-15 labeling experiments and quantum chemical calculations. A mechanism involving intermolecular nucleophilic attack and association of the GG and imine fragments followed by ammonia loss was found to be more energetically favorable than expulsion of ammonia in an SN2-type reaction.
Co-reporter:Anthony Schultz, Yan Cao, Mingjun Huang, Stephen Z. D. Cheng, Xiaopeng Li, Charles N. Moorefield, Chrys Wesdemiotis and George R. Newkome
Dalton Transactions 2012 - vol. 41(Issue 38) pp:NaN11575-11575
Publication Date(Web):2012/08/20
DOI:10.1039/C2DT31813J
A series of trimeric, Zn(II)- and Cd(II)-metallocycles is reported. Structural characterization of the highly stable triangles was supported by traveling-wave ion mobility-mass spectrometry (TWIM-MS) and gradient tandem mass spectrometry (gMS2). Their unique photophysical properties and self-assembly to form nanofibers are also described.
Co-reporter:Xiaocun Lu, Xiaopeng Li, Jin-Liang Wang, Charles N. Moorefield, Chrys Wesdemiotis and George R. Newkome
Chemical Communications 2012 - vol. 48(Issue 79) pp:NaN9875-9875
Publication Date(Web):2012/08/21
DOI:10.1039/C2CC35510H
Multicomponent, self-assembled rhomboidal constructs are reported, in which bis-terpyridines possessing 120° or 60° directionality and ZnII or CdII in a stoichiometric ratio (1:1:2) initially form rhomboid and triangle mixtures; whereas, a tris-terpyridine reacts with the 60°-based bis-ligand and metal to quantitatively form a heteroleptic, centrally fused, rhomboidal structure.
Co-reporter:Yiwen Li, Kai Guo, Hao Su, Xiaopeng Li, Xueyan Feng, Zhao Wang, Wei Zhang, Sunsheng Zhu, Chrys Wesdemiotis, Stephen Z. D. Cheng and Wen-Bin Zhang
Chemical Science (2010-Present) 2014 - vol. 5(Issue 3) pp:NaN1053-1053
Publication Date(Web):2013/11/18
DOI:10.1039/C3SC52718B
The convenient synthesis of nano-building blocks with strategically placed functional groups constitutes a fundamental challenge in nano-science. Here, we describe the facile preparation of a library of mono- and di-functional (containing three isomers) polyhedral oligomeric silsesquioxane (POSS) building blocks with different symmetries (C3v, C2v, and D3d) using thiol-ene chemistry. The method is straightforward and general, possessing many advantages including minimum set-up, simple work-up, and a short reaction time (about 0.5 h). It facilitates the precise introduction of a large variety of functional groups to desired sites of the POSS cage. The yields of the monoadducts increase significantly using stoichiometric amounts of bulky ligands. Regio-selective di-functionalization of the POSS cage was also attempted using bulky thiol ligands, such as a thiol-functionalized POSS. Electrospray ionization (ESI) mass spectrometry coupled with travelling wave ion mobility (TWIM) separation revealed that the majority of diadducts are para-compounds (∼59%), although meta-compounds (∼20%) and ortho-compounds (∼21%) are also present. Therefore, the thiol-ene reaction provides a robust approach for the convenient synthesis of mono-functional POSS derivatives and, potentially, of regio-selective multi-functionalized POSS derivatives as versatile nano-building blocks.
Co-reporter:Yuchen Yao, Sourav Chakraborty, Shiying Zhu, Kevin J. Endres, Ting-Zheng Xie, Wei Hong, Erendra Manandhar, Charles N. Moorefield, Chrys Wesdemiotis and George R. Newkome
Chemical Communications 2017 - vol. 53(Issue 57) pp:NaN8041-8041
Publication Date(Web):2017/06/26
DOI:10.1039/C7CC04080F
A novel terpyridine-based, trapezoidal architecture was synthesized by a coordination-driven multicomponent assembly and features three different tpy–M2+–tpy bonds (M2+ = Ru2+, Fe2+, and Zn2+) in the macrocyclic ring. This trimetallic macrocycle introduces the construction of polymetallosupramolecular assemblies possessing multiple, differing metal centers in an ordered, predetermined pattern. Characterization was accomplished by NMR spectroscopy, mass spectrometry, and UV-Vis spectroscopy.
Co-reporter:James M. Ludlow III, Masato Tominaga, Yoshiki Chujo, Anthony Schultz, Xiaocun Lu, Tingzheng Xie, Kai Guo, Charles N. Moorefield, Chrys Wesdemiotis and George R. Newkome
Dalton Transactions 2014 - vol. 43(Issue 25) pp:NaN9611-9611
Publication Date(Web):2014/05/06
DOI:10.1039/C4DT00989D
The self-assembly of the o-carborane-based, bisterpyridyl monomer, 1,2-bis[4′-(4-ethynylphenyl)-2,2′:6′,2′′-terpyridine]-o-carborane, utilizing either ZnII or FeII in a precise metal:ligand ratio (1:1), generated a family of metallomacrocycles that were studied via ESI-TWIM-MS, 1H NMR, and 2D NMR (COSY, NOESY). Under kinetic control, via formation of FeII complexes, the main cyclic product was triangular, as is typical of 60°-based bisligands. Under thermodynamic control using more labile transition metal complexes, e.g. ZnII, the ratio of cyclic species was found to be concentration and temperature dependent, and under an adequate entropic driving force, the cyclic dimer was formed. This system was probed via variable temperature NMR to reveal dynamic equilibrium between the entropically favored dimer and enthalpically favored trimer.
Co-reporter:Sujith Perera, Xiaopeng Li, Mingming Guo, Chrys Wesdemiotis, Charles N. Moorefield and George R. Newkome
Chemical Communications 2011 - vol. 47(Issue 16) pp:NaN4660-4660
Publication Date(Web):2011/03/17
DOI:10.1039/C1CC10649J
Hexagonal PdII- or CdII-tetrakispyridinyl-based macrocycles are quantitatively self-assembled from 4′-(3-pyridinyl)-4,4′′-di(tert-butyl)-2,2′:6′,2′′-terpyridine and structurally confirmed by NMR and TWIM-MS.
Co-reporter:Rajarshi Sarkar, Zaihong Guo, Jingyi Li, Tarak N. Burai, Charles Moorefield, Chrys Wesdemiotis and George R. Newkome
Chemical Communications 2015 - vol. 51(Issue 64) pp:NaN12854-12854
Publication Date(Web):2015/07/03
DOI:10.1039/C5CC05048K
Mixing of metallocyclic trimers and tetramers in an exact 1:1.5 stoichiometry provided new supramolecular triangles in quantitative yields. Characterization of the new hetero-nuclear metallomacrocycles was achieved by 1H, 2D-COSY, 2D-NOESY, and 13C NMR spectroscopy, along with ESI and TWIM mass spectrometry. Gradient tandem MS (gMS2) provided insight into the stabilities of the binuclear structures.
![Pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane, 1-ethenyl-3,5,7,9,11,13,15-heptakis(2-methylpropyl)-](/data/chemimg/65400/444315-18-8.png)
![Pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane, 1-ethenyl-3,5,7,9,11,13,15-heptakis(2-methylpropyl)-](/data/chemimg/65400/444315-18-8_b.png)
![Acetic acid, 2-[[2-(3,5,7,9,11,13,15-heptaethenylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-yl)ethyl]thio]-](/data/chemimg/3783000/1588948-21-3.png)
![Acetic acid, 2-[[2-(3,5,7,9,11,13,15-heptaethenylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-yl)ethyl]thio]-](/data/chemimg/3783000/1588948-21-3_b.png)
![Butanedioic acid, 1-(11,12-didehydro-5,6-dihydrodibenzo[a,e]cycloocten-5-yl) 4-[2-[(4-formylbenzoyl)oxy]-1-[[[2-(3,5,7,9,11,13,15-heptaethenylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-yl)ethyl]thio]methyl]ethyl] ester](/data/chemimg/3783000/1478782-00-1.png)
![Butanedioic acid, 1-(11,12-didehydro-5,6-dihydrodibenzo[a,e]cycloocten-5-yl) 4-[2-[(4-formylbenzoyl)oxy]-1-[[[2-(3,5,7,9,11,13,15-heptaethenylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-yl)ethyl]thio]methyl]ethyl] ester](/data/chemimg/3783000/1478782-00-1_b.png)
![Anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetrone, 2,9-bis[4-[3,5,7,9,11,13,15-heptakis(2-methylpropyl)pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-yl]phenyl]-](/data/chemimg/3783500/1222472-02-7.png)
![Anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetrone, 2,9-bis[4-[3,5,7,9,11,13,15-heptakis(2-methylpropyl)pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-yl]phenyl]-](/data/chemimg/3783500/1222472-02-7_b.png)
![2-Propenoic acid, 1,1',1'',1''',1'''',1''''',1'''''',1'''''''-(pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane-1,3,5,7,9,11,13,15-octaylocta-3,1-propanediyl) ester](/data/chemimg/3783300/1204591-17-2.png)
![2-Propenoic acid, 1,1',1'',1''',1'''',1''''',1'''''',1'''''''-(pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane-1,3,5,7,9,11,13,15-octaylocta-3,1-propanediyl) ester](/data/chemimg/3783300/1204591-17-2_b.png)
![Benzenamine, 4-[3,5,7,9,11,13,15-heptakis(2-methylpropyl)pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-yl]-](/data/chemimg/3783700/875588-35-5.png)
![Benzenamine, 4-[3,5,7,9,11,13,15-heptakis(2-methylpropyl)pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-yl]-](/data/chemimg/3783700/875588-35-5_b.png)
![Tricyclo[7.3.3.15,11]heptasiloxane-3,7,14-triol, 1,3,5,7,9,11,14-heptaphenyl-, stereoisomer](/data/chemimg/3783000/723302-16-7.png)
![Tricyclo[7.3.3.15,11]heptasiloxane-3,7,14-triol, 1,3,5,7,9,11,14-heptaphenyl-, stereoisomer](/data/chemimg/3783000/723302-16-7_b.png)
![Pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane-1-propanethiol, 3,5,7,9,11,13,15-heptakis(2-methylpropyl)-](/data/chemimg/68400/480438-85-5.png)
![Pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane-1-propanethiol, 3,5,7,9,11,13,15-heptakis(2-methylpropyl)-](/data/chemimg/68400/480438-85-5_b.png)
![Poly[(ethylimino)(1-oxo-1,3-propanediyl)]](http://img.cochemist.com/ccimg/442600/442557-95-1.png)
![Poly[(ethylimino)(1-oxo-1,3-propanediyl)]](http://img.cochemist.com/ccimg/442600/442557-95-1_b.png)
![Tetracyclo[9.5.1.13,9.15,15]octasiloxane-7,13-diol, 1,3,5,7,9,11,13,15-octakis(2-methylpropyl)-](/data/chemimg/3783600/307531-90-4.png)
![Tetracyclo[9.5.1.13,9.15,15]octasiloxane-7,13-diol, 1,3,5,7,9,11,13,15-octakis(2-methylpropyl)-](/data/chemimg/3783600/307531-90-4_b.png)
![4-Pentynoic acid, 4'-cyano[1,1'-biphenyl]-4-yl ester](http://img.cochemist.com/ccimg/204500/204451-02-5.png)
![4-Pentynoic acid, 4'-cyano[1,1'-biphenyl]-4-yl ester](http://img.cochemist.com/ccimg/204500/204451-02-5_b.png)
![Propanedioic acid, bis[2-(1,1-dimethylethoxy)-2-oxoethyl] ester](http://img.cochemist.com/ccimg/188500/188409-24-7.png)
![Propanedioic acid, bis[2-(1,1-dimethylethoxy)-2-oxoethyl] ester](http://img.cochemist.com/ccimg/188500/188409-24-7_b.png)
![Tricyclo[7.3.3.15,11]heptasiloxane-3,7,14-triol, 1,3,5,7,9,11,14-heptacyclopentyl-](/data/chemimg/3783000/183387-28-2.png)
![Tricyclo[7.3.3.15,11]heptasiloxane-3,7,14-triol, 1,3,5,7,9,11,14-heptacyclopentyl-](/data/chemimg/3783000/183387-28-2_b.png)
![Perylo[3,4-cd:9,10-c'd']dipyran-1,3,8,10-tetrone, 5,6,12,13-tetrakis[4-(1,1-dimethylethyl)phenoxy]-](/data/chemimg/102800/156028-30-7.png)
![Perylo[3,4-cd:9,10-c'd']dipyran-1,3,8,10-tetrone, 5,6,12,13-tetrakis[4-(1,1-dimethylethyl)phenoxy]-](/data/chemimg/102800/156028-30-7_b.png)
![4-[3,5-BIS(2,6-DIPYRIDIN-2-YLPYRIDIN-4-YL)PHENYL]-2,6-DIPYRIDIN-2-YLPYRIDINE](/data/chemimg/512300/142030-40-8.png)
![4-[3,5-BIS(2,6-DIPYRIDIN-2-YLPYRIDIN-4-YL)PHENYL]-2,6-DIPYRIDIN-2-YLPYRIDINE](/data/chemimg/512300/142030-40-8_b.png)
![1,3,5,7,9,11,14-HEPTACYCLOPENTYLTRICYCLO[7.3.3.1(5,11)]HEPTASILOXANE-ENDO-3,7,14-TRIOL](http://img.cochemist.com/ccimg/135300/135225-24-0.png)
![1,3,5,7,9,11,14-HEPTACYCLOPENTYLTRICYCLO[7.3.3.1(5,11)]HEPTASILOXANE-ENDO-3,7,14-TRIOL](http://img.cochemist.com/ccimg/135300/135225-24-0_b.png)
![5,11-Epoxydibenzo[a,e]cyclooctene, 5,6,11,12-tetrahydro-](http://img.cochemist.com/ccimg/66400/66365-45-5.png)
![5,11-Epoxydibenzo[a,e]cyclooctene, 5,6,11,12-tetrahydro-](http://img.cochemist.com/ccimg/66400/66365-45-5_b.png)
](http://img.cochemist.com/ccimg/27000/26913-06-4.png)
](http://img.cochemist.com/ccimg/27000/26913-06-4_b.png)
![Poly[imino(1-oxo-1,2-ethanediyl)]](http://img.cochemist.com/ccimg/25800/25734-27-4.png)
![Poly[imino(1-oxo-1,2-ethanediyl)]](http://img.cochemist.com/ccimg/25800/25734-27-4_b.png)
![Poly[oxy-1,4-butanediyloxy(1,6-dioxo-1,6-hexanediyl)]](http://img.cochemist.com/ccimg/25000/24936-97-8.png)
![Poly[oxy-1,4-butanediyloxy(1,6-dioxo-1,6-hexanediyl)]](http://img.cochemist.com/ccimg/25000/24936-97-8_b.png)
![N-phenyl-1-[4-(phenyliminomethyl)phenyl]methanimine](http://img.cochemist.com/ccimg/14400/14326-69-3.png)
![N-phenyl-1-[4-(phenyliminomethyl)phenyl]methanimine](http://img.cochemist.com/ccimg/14400/14326-69-3_b.png)
![L-Proline,1-[[5-(dimethylamino)-1-naphthalenyl]sulfonyl]-](http://img.cochemist.com/ccimg/1300/1239-94-7.png)
![L-Proline,1-[[5-(dimethylamino)-1-naphthalenyl]sulfonyl]-](http://img.cochemist.com/ccimg/1300/1239-94-7_b.png)
![1-Propanamine, 3-[(3,5-bis[2,2':6',2''-terpyridin]-4'-yl)phenoxy]-](http://img.cochemist.com/ccimg/686800/686781-04-4.png)
![1-Propanamine, 3-[(3,5-bis[2,2':6',2''-terpyridin]-4'-yl)phenoxy]-](http://img.cochemist.com/ccimg/686800/686781-04-4_b.png)
![Poly[imino[(1S)-1-methyl-2-oxo-1,2-ethanediyl]]](http://img.cochemist.com/ccimg/25300/25213-34-7.png)
![Poly[imino[(1S)-1-methyl-2-oxo-1,2-ethanediyl]]](http://img.cochemist.com/ccimg/25300/25213-34-7_b.png)
![2-Anthracenesulfonicacid, 1-amino-4-[[4-[[4-chloro-6-[[3(or4)-sulfophenyl]amino]-1,3,5-triazin-2-yl]amino]-3-sulfophenyl]amino]-9,10-dihydro-9,10-dioxo-](http://img.cochemist.com/ccimg/12300/12236-82-7.png)
![2-Anthracenesulfonicacid, 1-amino-4-[[4-[[4-chloro-6-[[3(or4)-sulfophenyl]amino]-1,3,5-triazin-2-yl]amino]-3-sulfophenyl]amino]-9,10-dihydro-9,10-dioxo-](http://img.cochemist.com/ccimg/12300/12236-82-7_b.png)
![4-Pentynoic acid, 2-(3,5,7,9,11,13,15-heptaethenylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-yl)ethyl ester](/data/chemimg/3783000/1402130-70-4.png)
![4-Pentynoic acid, 2-(3,5,7,9,11,13,15-heptaethenylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-yl)ethyl ester](/data/chemimg/3783000/1402130-70-4_b.png)
![1,2-Propanediol, 3-[[2-(3,5,7,9,11,13,15-heptaethenylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-yl)ethyl]thio]-](/data/chemimg/3783000/1383079-34-2.png)
![1,2-Propanediol, 3-[[2-(3,5,7,9,11,13,15-heptaethenylpentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-yl)ethyl]thio]-](/data/chemimg/3783000/1383079-34-2_b.png)
