Co-reporter:Mehdi Rashvand Avei and Angel E. Kaifer
The Journal of Organic Chemistry August 18, 2017 Volume 82(Issue 16) pp:8590-8590
Publication Date(Web):July 19, 2017
DOI:10.1021/acs.joc.7b01366
The electrochemical reduction of five partially oxidized pillar[5]arenes containing variable numbers (1–5) of quinone units was investigated in acetonitrile and dichloromethane solutions. The cathodic voltammetric behavior of all the macrocyclic compounds containing two or more quinone units indicates the existence of detectable levels of electronic communication between them. We have also investigated these compounds and their reduced forms using DFT computations. Our computational results indicate the presence of through-space communication between quinone units.
Co-reporter:Angel E. Kaifer
Inorganica Chimica Acta 2017 Volume 468(Volume 468) pp:
Publication Date(Web):1 November 2017
DOI:10.1016/j.ica.2017.04.055
•Cucurbit[7]uril (CB7) forms highly stable inclusion complexes with ferrocenyl derivatives in aqueous solution.•With most cationic ferrocenyl derivatives, the half-wave potential for one-electron oxidation exhibits a pronounced CB7-induced shift to more positive values.•With neutral ferrocenyl derivatives, the half-wave potential for the complex is typically within 25 mV of the value for the unbound compound.In aqueous media the host cucurbit[7]uril (CB7) forms inclusion complexes of high thermodynamic stability with ferrocenyl-containing guests. These complexes are characterized by the inclusion of the ferrocenyl group inside the CB7 cavity, primarily driven by hydrophobic forces. This mini-review provides a summary of the properties of these inclusion complexes, with emphasis on their electrochemical properties and, particularly, on the CB7-induced shift in the half-wave potential for one-electron oxidation of the ferrocenyl residues.Download high-res image (82KB)Download full-size image
Co-reporter:Vivian Iglesias, Mehdi Rashvand Avei, Sonia Bruña, Isabel Cuadrado, and Angel E. Kaifer
The Journal of Organic Chemistry 2017 Volume 82(Issue 1) pp:415-419
Publication Date(Web):December 16, 2016
DOI:10.1021/acs.joc.6b02508
The binding interactions between a novel ferrocenylguanidinium derivative (FcG+) and the macrocyclic hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated in aqueous solution. 1H NMR spectroscopic experiments indicated that both hosts form stable 1:1 inclusion complexes with FcG+, in which the ferrocenyl group is engulfed by the host cavity. The stoichiometry of the CB7·FcG+ complex was also confirmed by electrospray mass spectrometric (ESI MS) experiments. The association equilibrium constants (K) were determined from NMR competition experiments. The measured K values were 3.5 × 109 and 2.5 × 108 M–1 for CB7 and CB8, respectively, in 50 mM sodium acetate-d3 D2O solution (pD 4.7). DFT computational studies confirmed the 1:1 stoichiometry and the inclusion character of both complexes. Voltammetric experiments were carried out to measure the complexation-induced shifts on the half-wave potentials for the one-electron oxidation of the ferrocenyl moiety. Complexation by CB7 led to a 12 mV anodic shift, while CB8 caused a larger 32 mV shift also in the positive direction. These potential shifts suggest that the delocalization of the positive charge on the side arm over the three nitrogens in the guanidinium unit results in electrochemical behavior similar to that observed with neutral ferrocene derivatives.
Co-reporter:Beijun Cheng
Journal of the American Chemical Society 2015 Volume 137(Issue 31) pp:9788-9791
Publication Date(Web):July 28, 2015
DOI:10.1021/jacs.5b05546
The cathodic voltammetric behavior of pillar[5]quinone was investigated in dichloromethane solution. Our data show that the symmetry of the macrocycle has a pronounced effect on the electron uptake sequence. The uptake of the first five electrons follows a 2-1-2 pattern, and only a total of eight electrons could be injected into the macrocycle under our experimental conditions.
Co-reporter:Beijun Cheng and Angel E. Kaifer
Langmuir 2015 Volume 31(Issue 10) pp:2997-3002
Publication Date(Web):February 17, 2015
DOI:10.1021/la505005r
The cathodic voltammetric behavior of N,N′-dimethyl-4,4′-bipyridinium (methylviologen, MV2+), N,N′-dipropyl-4,4′-bipyridinium (propylviologen, PV2+), N,N′-dibutyl-4,4′-bipyridinium (butylviologen, BV2+), and N-heptyl-N′-ethyl-4,4′-bipyridinium (heptyl-ethylviologen, HEV2+) was investigated in aqueous solution containing variable concentrations of sodium cholate. In general, the presence of cholate was found to solubilize the more hydrophobic forms of the viologen probes. Among the three accessible viologen oxidation states (V2+, V+•, and V), the intermediate cation radical (V+•) was preferentially stabilized by the cholate aggregates regardless of the nature of the N-alkyl substituents. This stabilization leads to anodic shifts in the first half-wave potential (V2+/V+•) and cathodic shifts in the second half-wave potential (V+•/V) for viologen reduction. Both potential shifts were considerably more pronounced as the hydrophobic character of the viologen probe increased. The presence of the cucurbit[7]uril host in the solution leads to the formation of very stable inclusion complexes with the viologen probes, which tend to eliminate or substantially decrease the interactions between the viologens and the cholate micellar aggregates.
Co-reporter:Rui-Lian Lin, Jia-Qing Li, Jing-Xin Liu, and Angel E. Kaifer
The Journal of Organic Chemistry 2015 Volume 80(Issue 21) pp:10505-10511
Publication Date(Web):October 9, 2015
DOI:10.1021/acs.joc.5b01557
The binding interactions between the cyclohexanocucurbit[6]uril (Cy6CB6) host and a series of dialkyl-4,4′-bipyridinium (viologen) dicationic guests were investigated in the solution phase, using 1H NMR spectroscopy, and in the solid phase, using X-ray diffraction methods. In D2O solution, methyl viologen (MV2+) and ethyl viologen (EV2+) form 1:1 complexes in which the bipyridinium aromatic nucleus is partially included inside the Cy6CB6 cavity. Propyl viologen (PV2+), butyl viologen (BV2+), pentyl viologen (FV2+), and heptyl viologen (HV2+) form 2:1 complexes with Cy6CB6, in which each of the viologen aliphatic chains is included by a host molecule. In the solid state, EV2+ forms a polypseudorotaxane via pseudorotaxane interdigitation of Cy6CB6 hosts. The PV2+ guest forms a dumbbell-shaped structure with a Cy6CB6 host residing over each of the terminal propyl groups of the guest. In contrast to this, the BV2+ guest and Cy6CB6 form a different polypseudorotaxane structure in which dumbbell-shaped structures, formed by two host molecules interacting with a single guest, are interconnected through metal–host coordination.
Co-reporter:Angel E. Kaifer
Accounts of Chemical Research 2014 Volume 47(Issue 7) pp:2160-2167
Publication Date(Web):June 2, 2014
DOI:10.1021/ar5001204
A series of guest compounds containing paramagnetic 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) residues also exhibit interesting binding properties with CB7 and CB8. The latter host forms a very stable host–guest pair with TEMPO subunits, in which the nitroxide group resides inside the host cavity. Finally, with suitable ditopic guests, we have detected distinct microscopic complexes using experimental techniques with relatively slow time scales, such as NMR spectroscopy. These unusual findings are the result of the considerable thermodynamic and kinetic stability of CBn inclusion complexes.
Co-reporter:Sanem Senler, Beijun Cheng, and Angel E. Kaifer
Organic Letters 2014 Volume 16(Issue 22) pp:5834-5837
Publication Date(Web):November 10, 2014
DOI:10.1021/ol502479k
The cucurbit[7]uril (CB7) host forms rotaxane-type complexes with dumbbell-shaped, cationic guests bis(3,5-dimethoxybenzyl)-4,4′-bipyridinium (12+) and bis(3,5-diethoxybenzyl)-4,4′-bipyridinium (22+). The kinetics of complex formation is slower with the latter guest because of its bulkier end groups. Rotaxane formation was found to be thermodynamically more favorable and kinetically faster in D2O than in DMSO-d6 solution, which highlights the importance of hydrophobic interactions in the assembly of cucurbituril complexes.
Co-reporter:Mohammad Hossein Tootoonchi ; Song Yi
Journal of the American Chemical Society 2013 Volume 135(Issue 29) pp:10804-10809
Publication Date(Web):June 24, 2013
DOI:10.1021/ja404797y
The formation of inclusion complexes between the cucurbit[7]uril host and a cationic guest containing ferrocenylmethyl and adamantyl residues connected to an ammonium nitrogen initially leads to an ∼1:1 mixture of two isomeric microscopic complexes, which evolves as a function of time toward the thermodynamically stable mixture, dominated by the adamantyl-included complex.
Co-reporter:Song Yi, Wei Li, Daniel Nieto, Isabel Cuadrado and Angel E. Kaifer
Organic & Biomolecular Chemistry 2013 vol. 11(Issue 2) pp:287-293
Publication Date(Web):12 Nov 2012
DOI:10.1039/C2OB26834E
The binding properties of the cucurbit[7]uril host with three structurally related ferrocene-containing guests, ferrocenyltrimethylammonium, ferrocenylmethyltrimethylammonium and ferrocenylethyltrimethylammonium, have been investigated using 1H NMR spectroscopy, mass spectrometry, voltammetry and computational methods. The experimental and computational data indicate that the stability of the cucurbit[7]uril inclusion complexes is relatively insensitive to the number of methylenes connecting the trimethylammonium and the ferrocenyl groups, although some of their properties are affected in significant ways.
Co-reporter: Angel E. Kaifer
ChemPhysChem 2013 Volume 14( Issue 6) pp:1107-1108
Publication Date(Web):
DOI:10.1002/cphc.201300147
Co-reporter:Wei Li and Angel E. Kaifer
Organometallics 2013 Volume 32(Issue 20) pp:6091-6097
Publication Date(Web):September 23, 2013
DOI:10.1021/om400717z
The binding interactions between two cucurbit[n]uril hosts (n = 7, 8, CB7 and CB8) and the three new guests 1,1′-bis(cyclohexylammoniomethyl)ferrocene (1H22+), 1,1′-bis(cyclohexylmethylammoniomethyl)ferrocene (2H22+), and 1,1′-bis(cyclohexyldimethylammoniomethyl)ferrocene (32+) were investigated in aqueous solution using 1H NMR spectroscopy, voltammetry, and electrospray (ESI) mass spectrometry. The experimental data reveal that guests 1H22+ and 2H22+ behave similarly with both hosts, leading to the formation of pseudorotaxane complexes in which the host is located centrally around the ferrocenyl residue. A similar complex forms also between 32+ and CB7, but its formation is slower (k = 2.5 × 10–4 s–1) and can be monitored by NMR spectroscopy. Finally, 32+ and CB8 give rise to a ternary 2:1 complex, in which CB8 receptors are bound to the terminal cyclohexyl groups, when the concentration of the host exceeds that of the guest.
Co-reporter:Wei Wang;Dongmei Xu;Daniel Gesua
Journal of Solid State Electrochemistry 2013 Volume 17( Issue 12) pp:3063-3066
Publication Date(Web):2013 December
DOI:10.1007/s10008-013-2162-8
We prepared a new series of bisaminoferrocenyl triazine derivatives and investigated their anodic voltammetric behavior. The electronic nature of the third substituent on the triazine nucleus, that is, its electronic donor/acceptor character determines the level of interactions between the two ferrocenyl centers as measured by the separation between their two oxidation half-wave potentials.
Co-reporter:Song Yi, Valentina Brega, Burjor Captain and Angel E. Kaifer
Chemical Communications 2012 vol. 48(Issue 83) pp:10295-10297
Publication Date(Web):03 Sep 2012
DOI:10.1039/C2CC35095E
Six equivalents of N,N′-bis(4-aminobenzyl)urea, 12 equivalents of 2-formylpyridine and four equivalents of FeSO4 or NiSO4 undergo subcomponent self-assembly in aqueous solution to form tetrahedral cages around a single, encapsulated sulfate anion.
Co-reporter:Angel E. Kaifer, Wei Li, Serena Silvi and Vladimir Sindelar
Chemical Communications 2012 vol. 48(Issue 53) pp:6693-6695
Publication Date(Web):15 May 2012
DOI:10.1039/C2CC32871B
Deprotonation of the two terminal COOH groups on a 4,4′-bipyridinium linear derivative leads to a pronounced slow down on the kinetics of threading and unthreading by the cucurbit[7]uril host.
Co-reporter:Jan Svec, Vladimir Sindelar and Angel E. Kaifer
New Journal of Chemistry 2012 vol. 36(Issue 9) pp:1721-1724
Publication Date(Web):19 Jul 2012
DOI:10.1039/C2NJ40381A
Six- and seven-membered cucurbiturils form inclusion complexes with a lutidine derivative. These inclusion complexes differ in the binding mode, stability, kinetics of complexation, and sensitivity toward basic media.
Co-reporter:Sanem Senler;Lu Cui;Ana Michelle Broomes;Erika L. Smith;James N. Wilson
Journal of Physical Organic Chemistry 2012 Volume 25( Issue 7) pp:592-596
Publication Date(Web):
DOI:10.1002/poc.2928
On the basis of the highly stable G2H (2 : 1) ternary complex formed by two methyl viologen cation radicals inside the cavity of cucurbit[8]uril, we prepared three monocationic 4-phenylpyridinium derivatives: 1-(hydroxyethyl)-4-phenyl-pyridinium (1+) bromide, 1-(octaethyleneglycol)-4-phenyl-pyridinium (2+) chloride, and 4-[4-(methoxymethoxy)phenyl]pyridinium (3+) iodide, as possible guests for 2 : 1 complexation inside cucurbit[8]uril. We also investigated a fourth monocationic guest (4+), in which a central vinylidene group is inserted to elongate the 4-phenyl-pyridinium residue. Using 1H NMR and UV–Vis spectroscopic data and mass spectrometric data, we obtained unequivocal evidence for the formation of G2H (2 : 1) ternary complexes in all cases. The stoichiometry of the complexes was further verified by continuous variation (Job) plots, and in some cases, high resolution ESI-MS spectrometric data. Diffusion coefficient measurements, using 1H NMR pulse gradient spin echo techniques, yielded values consistent with the formation and expected structures of the ternary complexes. Copyright © 2012 John Wiley & Sons, Ltd.
Co-reporter:Yanhua Qiu, Song Yi, and Angel E. Kaifer
The Journal of Organic Chemistry 2012 Volume 77(Issue 10) pp:4622-4627
Publication Date(Web):April 23, 2012
DOI:10.1021/jo3003387
The inclusion of three bulky guests, adamantyl(ferrocenylmethyl)amine (2), adamantylferrocenecarboxylamide (3), and 1,1′-bis(adamantylaminomethyl)ferrocene (4), inside dimeric molecular capsules formed by an octaacid deep-cavity cavitand (1) was investigated using 1H NMR spectroscopy and voltammetric techniques. Guests 2 and 3 were encapsulated inside 12 assemblies, as evidenced by 1H NMR spectroscopic data. Although both guests are electroactive, the supramolecular complexes 2@12 and 3@12 showed no voltammetric current responses in the potential window corresponding to the electrochemical oxidation of their ferrocenyl groups. In contrast, each of the adamantyl ends of compound 4 is bound by the cavitand 1, but the central ferrocene residue was not fully encapsulated in this supramolecular assembly and the voltammetric behavior of 4·12 was clearly detected. In marked contrast with the experimental results obtained with guests 2 and 3, we could not obtain any evidence for the simultaneous encapsulation of free ferrocene and adamantane inside the 12 capsular assembly.
Co-reporter:Wei Li and Angel E. Kaifer
Langmuir 2012 Volume 28(Issue 42) pp:15075-15079
Publication Date(Web):September 25, 2012
DOI:10.1021/la303258g
(Ferrocenylmethyl)methylammonium (1H+) is an excellent cationic guest for inclusion complexation by the cucurbit[7]uril host. However, deprotonation of the guest leads to a decrease of 14.8 kJ mol–1 in the overall stability of its inclusion complex, and one-electron oxidation of the guest’s ferrocene residue further diminishes the complex stability by another 12.3 kJ mol–1. Overall, guest deprotonation followed by its oxidation constitutes an accessible method to lower the equilibrium association constant for the CB7·1H+ complex by more than 4 orders of magnitude.
Co-reporter:Daniel Nieto, Ana M
a
González-Vadillo, Sonia Bruña, César J. Pastor, Angel E. Kaifer and Isabel Cuadrado
Chemical Communications 2011 vol. 47(Issue 37) pp:10398-10400
Publication Date(Web):15 Aug 2011
DOI:10.1039/C1CC13704B
A new heterometallic electroactive compound having the ferrocenyl moiety attached to the platinum atom through an amidine functionality has been prepared viaPt(II)-mediated nucleophilic addition of β-aminoethylferrocene to a benzonitrile ligand. This neutral receptor shows remarkable electrochemical anion-sensing redox response to H2PO4−.
Co-reporter:Song Yi, Burjor Captain and Angel E. Kaifer
Chemical Communications 2011 vol. 47(Issue 19) pp:5500-5502
Publication Date(Web):08 Apr 2011
DOI:10.1039/C1CC11212K
The extent of methylation of the central nitrogen in (ferrocenylmethyl)tempammonium guests determines the main binding site for complexation by the cucurbit[8]uril host.
Co-reporter:Angel E. Kaifer;Wei Li ;Song Yi
Israel Journal of Chemistry 2011 Volume 51( Issue 5-6) pp:496-505
Publication Date(Web):
DOI:10.1002/ijch.201100042
Abstract
Research on the chemistry of cucurbit[n]uril (CBn) hosts has picked up and maintained an impressive pace in the last decade, primarily due to the isolation of hosts with relatively larger cavity sizes, such as CB7 and CB8. This review article summarizes our involvement in this research effort, with particular emphasis on the binding of redox active guests by the CB7 and CB8 hosts. The binding of 4,4′-bipyridinium (viologen) derivatives was the starting point of our CB research. While methylviologen is encapsulated by CB7, forming a highly symmetric inclusion complex, more hydrophobic viologens are bound by inclusion of one of the terminal N-substituents inside the host cavity. Cationic ferrocene derivatives reach extremely high binding affinities with CB7. Binding by CB8 offers additional possibilities, since this host may accommodate two aromatic units inside its cavity, which can be utilized to exert redox control on the assembly of suitably dendronized guests. From a purely electrochemical standpoint, CB7-included viologens maintain their voltammetric reversibility, but CB7-included ferrocene residues experience a pronounced attenuation of their electron transfer kinetics. We have also applied these binding and electrochemical properties to the design and preparation of switchable, CB-based pseudorotaxanes.
Co-reporter:Song Yi and Angel E. Kaifer
The Journal of Organic Chemistry 2011 Volume 76(Issue 24) pp:10275-10278
Publication Date(Web):November 3, 2011
DOI:10.1021/jo2018312
The formation of highly stable inclusion complexes in aqueous solution between the organometallic cobaltocenium cation (Cob+) and the hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) was used to develop a simple method, based on UV–vis titrations, to assay the purity of samples of these two hosts. The equilibrium association constant (K) of the Cob+@CB7 complex had been previously reported by our group as 5.7 × 109 M–1 at 25 °C in 50 mM sodium acetate medium. In this work, we determine a K value of 1.9 × 108 M–1 at 25 °C in the same medium for the Cob+@CB8 complex. The high stability of these complexes and their decreased molar absorptivity coefficients (at 261 nm), compared to that for free Cob+, lead to straightforward titration plots when graphing absorbance versus concentration of added CB7 (or CB8) host, at constant Cob+ concentration.
Co-reporter:Song Yi, Burjor Captain, M. Francesca Ottaviani, and Angel E. Kaifer
Langmuir 2011 Volume 27(Issue 9) pp:5624-5632
Publication Date(Web):April 4, 2011
DOI:10.1021/la2005198
The binding interactions between two paramagnetic cobaltocenium guests and the hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated using a combination of electronic absorption, NMR, and electron paramagnetic resonance (EPR) spectroscopies, mass spectrometry, and X-ray crystallography. Guest 1, (4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl)cobaltocenium, forms very stable inclusion complexes with CB7 and CB8. However, CB7 interacts with 1 by including the organometallic cobaltocenium unit, while CB8 engulfs the TEMPO residue. The corresponding equilibrium association constant (K) values are 2.8 ± 0.3 × 106 M−1 for CB7•1 and 2.1 ± 1.0 × 108 M−1 for CB8•1. Biradical guest 2, 1,1′-bis(4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl)cobaltocenium, forms a very stable ternary complex with two CB8 hosts, in which each 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) residue is encircled by a host molecule. The structure of this ternary complex was confirmed in the solid state using single-crystal X-ray diffraction. Binding of the TEMPO side arms by the CB8 hosts gradually decreases the observed level of spin exchange coupling between the two nitroxide groups. In the final 2:1 complex, no spin exchange coupling was observed, but the initial levels of spin exchange coupling could be regenerated in a reversible fashion by adding a competing guest, adamantyltrimethylammonium (AdTMA), to the solution. The binding interactions between 2 and CB7 are similar but the stabilities of the 1:1 and 2:1 complexes are much lower than those of the corresponding CB8 complexes.
Co-reporter:Dagmara Podkoscielny ; Suresh Gadde
Journal of the American Chemical Society 2009 Volume 131(Issue 36) pp:12876-12877
Publication Date(Web):August 19, 2009
DOI:10.1021/ja9045108
While the direct electrochemical oxidation of ferrocene encapsulated inside a dimeric molecular capsule is essentially suppressed, a cationic ferrocene derivative binds to the capsule’s external surface and acts as an effective electrochemical mediator.
Co-reporter:Song Yi, Elisabetta Mileo and Angel E. Kaifer
Organic Letters 2009 Volume 11(Issue 24) pp:5690-5693
Publication Date(Web):November 17, 2009
DOI:10.1021/ol902391u
EPR experiments in water-saturated CH2Cl2 solution clearly indicate that oxotempo is not included inside hexameric molecular capsules of resorcin[4]arene. In fact, the tumbling rate of oxotempo only experiences minor changes when resorcinarene is present in the solution. However, NMR spectroscopic data suggest that oxotempo engages in labile hydrogen-bonding interactions with water molecules interacting with the resorcinarene molecular capsules.
Co-reporter:Suresh Gadde Dr.;ElizabethK. Batchelor ;AngelE. Kaifer
Chemistry - A European Journal 2009 Volume 15( Issue 24) pp:6025-6031
Publication Date(Web):
DOI:10.1002/chem.200802546
Co-reporter:Elisabetta Mileo;Song Yi;Papri Bhattacharya;AngelE. Kaifer Dr.
Angewandte Chemie International Edition 2009 Volume 48( Issue 29) pp:5337-5340
Publication Date(Web):
DOI:10.1002/anie.200901272
Co-reporter:Elisabetta Mileo;Song Yi;Papri Bhattacharya;AngelE. Kaifer Dr.
Angewandte Chemie 2009 Volume 121( Issue 29) pp:5441-5444
Publication Date(Web):
DOI:10.1002/ange.200901272
Co-reporter:Lu Cui, Suresh Gadde, Wei Li and Angel E. Kaifer
Langmuir 2009 Volume 25(Issue 24) pp:13763-13769
Publication Date(Web):June 22, 2009
DOI:10.1021/la9015096
We have investigated the formation of inclusion complexes between the host cucurbit[7]uril (CB7) and three cationic and four neutral ferrocene-containing guests: (ferrocenylmethyl)trimethylammonium (2+), butyl(ferrocenylmethyl)-dimethylammonium (3+), (ferrocenylmethyl)heptyldimethylammonium (4+), hydroxymethylferrocene (5), (((methoxy)-ethoxy)ethoxy)methylferrocene (6), 1,1′-di(hydroxymethyl)ferrocene (7), and 1,1’-di((((methoxy)ethoxy)ethoxy)methyl)ferrocene (8). The formation of highly stable inclusion complexes (K > 107 M−1) was verified in all cases using NMR spectroscopic techniques. From cyclic voltammetric experiments, we observed that CB7 complexation of the cationic guests (2+−4+) leads to significant anodic shifts on the ferrocene oxidation half-wave potentials, while the measured potential shifts were smaller in the case of the neutral guests (5−8). Encapsulation of all guests resulted in a substantial decrease of the standard rate constant for heterogeneous electron transfer. However, inclusion complexation of the neutral guests led to quasi-reversible voltammetric behavior, in which the anodic peak potential is more sensitive to scan rate than the corresponding cathodic peak potential, suggesting a minor degree of strutural rearrangement in the neutral inclusion complex after oxidation.
Co-reporter:Lu Cui, Suresh Gadde, Atindra D. Shukla, Hao Sun, Joel T. Mague and Angel E. Kaifer
Chemical Communications 2008 (Issue 12) pp:1446-1448
Publication Date(Web):25 Jan 2008
DOI:10.1039/B717285K
Ureido pyrimidinedione derivatives with phenyl, 1-naphthyl and 2-naphthyl substituents form stable dimers via quadruple hydrogen bonding, but the 1-naphthyl derivative presents an unexpected tautomer in the solid state.
Co-reporter:Dagmara Podkoscielny;Ivy Philip Dr.;CorinneL.D. Gibb Dr.;BruceC. Gibb ;AngelE. Kaifer
Chemistry - A European Journal 2008 Volume 14( Issue 15) pp:4704-4710
Publication Date(Web):
DOI:10.1002/chem.200701961
Abstract
In aqueous media the deep-cavity cavitand octaacid 1 forms stable dimeric molecular capsules 12, which are stabilized by hydrophobic effects. In this work we investigate the binding interactions in aqueous solution between these capsules and the redox active guests, ferrocene (Fc) and three 4,4′-bipyridinium (viologen) dications: methyl viologen (MV2+), ethyl viologen (EV2+), and butyl viologen (BV2+). Using NMR spectroscopic and electrochemical techniques we clearly show that the hydrophobic Fc guest is encapsulated inside 12. An interesting effect of this encapsulation is that the reversible voltammetric response of Fc is completely eliminated when it resides inside the 12 capsular assembly, a finding that is attributed to very slow electrochemical kinetics for the oxidation of Fc@12. Diffusion coefficient measurements (PGSE NMR spectroscopy) reveal that all three viologen guests are strongly bound to the dimeric capsules. However, the 1H NMR spectroscopic data are not consistent with encapsulation and the measured diffusion coefficients indicate that two viologen guests can strongly associate with a single dimeric capsule. Furthermore, the (V2+)2⋅ 12 complex is capable of encapsulating ferrocene, clearly suggesting that the viologen guests are bound externally, via coulombic interactions, to the anionic polar ends of the capsule. The electrochemical kinetic rate constants for the reduction of the viologen residue in the V2+⋅12 complexes were measured and found to be substantially lower than those for the free viologen guests.
Co-reporter:S. Silvi;S. E. Parker;V. Sindelar;D. Sobransingh;A. E. Kaifer
Advanced Functional Materials 2007 Volume 17(Issue 5) pp:694-701
Publication Date(Web):19 FEB 2007
DOI:10.1002/adfm.200600969
This paper presents an overview of recent work on the binding interactions between a series of 4,4'-bipyridinium (viologen) derivatives and the hosts cucurbit[6]uril (CB6) and cucurbit[7]uril (CB7), which give rise to stable ‘wheel-on-an-axle' inclusion complexes (pseudorotaxanes) in aqueous solution. The carboxylic acid termini on the pseudorotaxane axle can be used as handles to control—via proton transfer reactions—the relative position of the CB wheel along the axle. We also report on a different type of pseudorotaxane in which the reversible oxidation of the axle's ferrocenyl end groups leads to controlled displacement of the CB7 wheel.
Co-reporter:Yonghua Ling, Wei Wang and Angel E. Kaifer
Chemical Communications 2007 (Issue 6) pp:610-612
Publication Date(Web):07 Nov 2006
DOI:10.1039/B611559D
The dicationic guest 2,7-dimethyldiazaphenanthrenium forms a fluorescent inclusion complex with the cucurbit[8]uril host, which can be used to effectively bind and detect indole derivatives, such as serotonin and tryptophan.
Co-reporter:Angel E. Kaifer
European Journal of Inorganic Chemistry 2007 Volume 2007(Issue 32) pp:
Publication Date(Web):9 OCT 2007
DOI:10.1002/ejic.200700817
This manuscript provides a summary of the relatively large body of research on the preparation and characterization of dendrimers containing (1) multiple copies of metallocene residues on their surfaces or (2) a single metallocene residue at their core. Special emphasis is placed on dendrimers functionalized with either ferrocene or cobaltocenium groups, because their reversible electrochemistry makes them particularly attractive to the author's group. Dendrimers containing multiple, peripheral metallocene residues are of interest to develop multivalent interactions with suitable receptors or receptor assemblies. With dendrimers containing a single metallocene at their cores, the key questions relate to the effects of the dendritic mass on their properties and degree of encapsulation or site isolation. We focused our work on the electrochemical properties of these dendrimers as well as on their use as guests in molecular recognition processes with freely diffusing hosts.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Co-reporter:Vladimir Sindelar, Samantha E. Parker and Angel E. Kaifer
New Journal of Chemistry 2007 vol. 31(Issue 5) pp:725-728
Publication Date(Web):15 Feb 2007
DOI:10.1039/B615803J
Two simple cationic anthraquinone derivatives were found to form stable complexes with the cucurbit[7]uril host, in which the anthraquinone residue is included by the host cavity. The corresponding equilibrium association constants were relatively low (K
∼103 M−1)—compared to those of other complexes formed by the same host—suggesting that anthraquinone is not an ideal guest. However, the electrochemical behavior of the guests is strongly affected by inclusion inside the host cavity.
Co-reporter:Kwangyul Moon;Ivy Philip;Hao Sun
Journal of Solid State Electrochemistry 2007 Volume 11( Issue 12) pp:1635-1641
Publication Date(Web):2007 December
DOI:10.1007/s10008-007-0323-3
Hydrogen bonding is one of the most important intermolecular forces in molecular self-assembly or non-covalent synthesis. It is now possible to prepare rather large supramolecular assemblies (>1,000 Da) held together by hydrogen bonds between their molecular building blocks. From the standpoint of electrochemistry, this opens up interesting research avenues. This manuscript reviews recent results-mostly from the authors’ own group—on the electrochemistry of systems in which hydrogen bonding plays a crucial role. First, we explore the encapsulation of redox-active centers inside large hydrogen-bonded assemblies and its effects on the kinetics and thermodynamics of the electron transfer reactions of the encapsulated center. Second, we survey the use of electrochemistry to modulate the strength of hydrogen bonding between complementary partners. In this regard, the association and dissociation of dimeric calixarene molecular capsules can be fully controlled by the oxidation state of ferrocenyl centers located nearby the hydrogen-bonding sites. Finally, we also present very recent and intriguing results on the strong electronic coupling between two equivalent ferrocenyl centers held together by four hydrogen bonds in a non-covalent dimer.
Co-reporter:Yonghua Ling;Joel T. Mague Dr.;Angel E. Kaifer Dr.
Chemistry - A European Journal 2007 Volume 13(Issue 28) pp:
Publication Date(Web):8 AUG 2007
DOI:10.1002/chem.200700402
The binding interactions in aqueous solution between the dicationic guest diquat (DQ2+) and the cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) hosts were investigated by 1H NMR, UV/Vis, and fluorescence spectroscopy; mass spectrometry; single-crystal X-ray diffraction; and electrochemical techniques. The binding data were compared with previously reported results for the related paraquat guest (PQ2+). DQ2+ was found to bind poorly (K=350 m−1) inside CB7 and more effectively (K=4.8×104 m−1) inside CB8. One-electron reduction led to increased binding affinity with both hosts (Kr=1×104 m−1 with CB7 and Kr=6×105 m−1 for CB8). While 1H NMR spectroscopic data revealed that DQ2+ is not fully included by CB7, the crystal structure of the CB8⋅DQ2+ complex—obtained from single-crystal X-ray diffraction—clearly establishes its inclusion nature. Overall, both diquat and its one-electron reduced radical cation are bound more effectively by CB8 than by CB7. In contrast to this, paraquat exhibits selectivity for CB7, but its radical cation forms a highly stable dimer inside CB8. These differences highlight the pronounced sensitivity of cucurbit[n]uril hosts to guest features such as charge, charge distribution and shape.
Co-reporter:Hyunuk Kim;Mikhail V. Rekharsky;Tadashi Mori;Simin Liu;David Sobransingh;Cheng Yang;Kimoon Kim;Wei Chen;N. Selvapalam;Michael K. Gilson;Lyle Isaacs;Sarvin Moghaddam;Young Ho Ko;Yoshihisa Inoue
PNAS 2007 Volume 104 (Issue 52 ) pp:20737-20742
Publication Date(Web):2007-12-26
DOI:10.1073/pnas.0706407105
The molecular host cucurbit[7]uril forms an extremely stable inclusion complex with the dicationic ferrocene derivative bis(trimethylammoniomethyl)ferrocene
in aqueous solution. The equilibrium association constant for this host-guest pair is 3 × 1015 M−1 (K
d = 3 × 10−16 M), equivalent to that exhibited by the avidin–biotin pair. Although purely synthetic systems with larger association constants
have been reported, the present one is unique because it does not rely on polyvalency. Instead, it achieves its extreme affinity
by overcoming the compensatory enthalpy–entropy relationship usually observed in supramolecular complexes. Its disproportionately
low entropic cost is traced to extensive host desolvation and to the rigidity of both the host and the guest.
Co-reporter:Vladimir Sindelar, Serena Silvi and Angel E. Kaifer
Chemical Communications 2006 (Issue 20) pp:2185-2187
Publication Date(Web):31 Mar 2006
DOI:10.1039/B601959E
Cucurbit[7[uril, the wheel component in two new and structurally simple pseudorotaxanes, shuttles between the two axle termini at low pH, whereas the shuttling motion stops at higher pH, as the wheel is bound to the center of the axle.
Co-reporter:Wei Wang Dr.
Angewandte Chemie 2006 Volume 118(Issue 42) pp:
Publication Date(Web):2 OCT 2006
DOI:10.1002/ange.200602220
Ein vielseitiger Wirt: Cucurbit[8]uril als Wirt vermittelt hoch effizient die Bildung von Charge-Transfer-Komplexen zwischen Dendrimeren mit zugänglichen π-Donor- und π-Acceptor-Einheiten (siehe Schema). Durch Redoxschaltung der Selbstorganisation lässt sich die Größe der vorherrschenden Dendrimerassoziate einstellen.
Co-reporter:Wei Wang Dr.
Angewandte Chemie International Edition 2006 Volume 45(Issue 42) pp:
Publication Date(Web):2 OCT 2006
DOI:10.1002/anie.200602220
A host of possibilities: Cucurbit[8]uril acts as a host to mediate in a highly effective way the formation of charge-transfer complexes between dendrimers containing accessible π-donor and π-acceptor units (see scheme). Redox switching of the self-assembly affords control over the size of the predominant dendrimer assemblies.
Co-reporter:David Sobransingh and Angel E. Kaifer
Chemical Communications 2005 (Issue 40) pp:5071-5073
Publication Date(Web):13 Sep 2005
DOI:10.1039/B510780F
The stability of the inclusion complexes formed between the host cucurbit[7]uril and dendrimers containing a single ferrocene residue is strongly affected by the solution pH and the growth of the dendrimer, reaching its highest values on the second and third generation dendrimers, whereas no complex is formed with the first generation compound.
Co-reporter:Jie-Wen Ying, David R. Sobransingh, Guo-Lin Xu, Angel E. Kaifer and Tong Ren
Chemical Communications 2005 (Issue 3) pp:357-359
Publication Date(Web):30 Nov 2004
DOI:10.1039/B412336K
A new series of Ru2(DMBA)4(oligo(phenyleneethyne))2 compounds bearing sulfide termini was synthesized; structural characterization revealed both the rigid rod nature and extended π-conjugation in these metallaynes; in the presence of these metallaynes, Au nanoparticles readily assembled into dimers and chains with well-defined inter-dimer distances.
Co-reporter:Vladimir Sindelar, Mabel A. Cejas, Françisco M. Raymo and Angel E. Kaifer
New Journal of Chemistry 2005 vol. 29(Issue 2) pp:280-282
Publication Date(Web):17 Jan 2005
DOI:10.1039/B418017H
The dicationic guest 2,7-dimethyldiazapyrenium is bound inside the host cucurbit[7]uril, forming a very stable inclusion complex in which the host undergoes structural distortions to accommodate the guest.
Co-reporter:Vladimir Sindelar Dr.;Mabel A. Cejas Dr.;Françisco M. Raymo ;Weizhong Chen;Samantha E. Parker
Chemistry - A European Journal 2005 Volume 11(Issue 23) pp:
Publication Date(Web):21 SEP 2005
DOI:10.1002/chem.200500917
The formation of a highly stable inclusion complex between 2,7-dimethyldiazapyrenium (Me2DAP2+) and the cucurbit[8]uril host (CB8) was demonstrated by X-ray crystallography; MALDI-TOF mass spectrometry; and 1H NMR, electronic absorption, and emission spectroscopy. The equilibrium association constant was determined to be 8.9(±0.2)×105 L mol−1 from UV-visible data and 8.4(±1.5)×105 L mol−1 from fluorescence data. The Me2DAP2+⋅CB8 inclusion complex acted as a host to bind compounds containing aromatic π-donor moieties (D), such as catechol and dopamine. This point was demonstrated by 1H NMR spectroscopy, and electrochemical and emission measurements. Fluorescence detection of the Me2DAP2+⋅D⋅CB8 ternary complexes was evident in aqueous solution and on the surface of silica particles, to which fluorescent diazapyrenium units had been covalently immobilized.
Co-reporter:Winston Ong, Marielle Gómez-Kaifer and Angel E. Kaifer
Chemical Communications 2004 (Issue 15) pp:1677-1683
Publication Date(Web):14 Apr 2004
DOI:10.1039/B401186D
Dendrimers are highly branched macromolecules which may engage in host–guest interactions, acting as either hosts or guests; this review is specifically concerned with the binding behavior of dendrimers containing single or multiple guest residues interacting with individual, freely diffusing hosts.
Co-reporter:Kwangyul Moon;Jodi Grindstaff;David Sobransingh
Angewandte Chemie 2004 Volume 116(Issue 41) pp:
Publication Date(Web):13 OCT 2004
DOI:10.1002/ange.200460179
Erheblich vereinfacht wird die Dimerisierung von Dendrimeren mit einer einzigen 4,4′-Bipyridinium(Viologen)-Einheit nach Einelektronenreduktion durch den Wirt Cucurbit[8]uril. Als Grund dafür wird die Bildung eines stabilen Einschlusskomplexes zwischen dem Wirt und zwei π-gestapelten Viologen-Radikalkationen – der einelektronenreduzierten Form von Viologen – angenommen (siehe Bild).
Co-reporter:Kwangyul Moon;Jodi Grindstaff;David Sobransingh
Angewandte Chemie International Edition 2004 Volume 43(Issue 41) pp:
Publication Date(Web):13 OCT 2004
DOI:10.1002/anie.200460179
The dimerization of dendrimers that contain a single 4,4′-bipyridinium (viologen) unit, upon one-electron reduction, is strongly enhanced by the presence of the host cucurbit[8]uril. This behavior is attributed to the formation of a stable inclusion complex between the host and two π-stacked viologen radical-cation guests—the one-electron-reduced form of viologen (see scheme).
Co-reporter:Kwangyul Moon, Wei-Zhong Chen, Tong Ren and Angel E. Kaifer
CrystEngComm 2003 vol. 5(Issue 79) pp:451-453
Publication Date(Web):06 Nov 2003
DOI:10.1039/B313267F
Diphenylglycoluril assembles into a unique, two-dimensional hydrogen bonding network in the solid state, while exhibiting a twisted molecular structure.
Co-reporter:Winston Ong
Angewandte Chemie 2003 Volume 115(Issue 19) pp:
Publication Date(Web):14 MAY 2003
DOI:10.1002/ange.200250214
Auch Dendrimere können Gäste sein: Dendrimere, die mit einer einzelnen 4,4′-Bipyridinium-Einheit funktionalisiert sind, werden in wässriger Lösung fest durch Cucurbit[7]uril gebunden (siehe schematische Darstellung). Die Komplexbildung wurde durch NMR- und UV/Vis-Spektroskopie sowie Massenspektometrie verfolgt und quantifiziert.
Co-reporter:Winston Ong
Angewandte Chemie International Edition 2003 Volume 42(Issue 19) pp:
Publication Date(Web):14 MAY 2003
DOI:10.1002/anie.200250214
Dendrimers as guests: Dendrimers containing a single 4,4′-bipyridinium residue covalently attached to the focal points of carboxylate-terminated dendrons are strongly complexed by cucurbit[7]uril in aqueous solution (see schematic representation). The complexation has been monitored and quantified by NMR spectroscopic, UV/Vis spectroscopic, and mass spectometric techniques.
Co-reporter:Beatriz Alonso, Carmen M. Casado, Isabel Cuadrado, Moisés Morán and Angel E. Kaifer
Chemical Communications 2002 (Issue 16) pp:1778-1779
Publication Date(Web):15 Jul 2002
DOI:10.1039/B205619D
A new series of dendrimers with poly(propylene imine) backbones and 4, 8, 16, or 32 peripheral ferrocenyl-urea groups were prepared and characterized; their voltammetric behavior in DMSO solution was very sensitive to the presence of hydrogenphosphate anions at submillimolar concentration levels.
Co-reporter:Rosa Toba, José María Quintela, Carlos Peinador, Esteban Román and Angel E. Kaifer
Chemical Communications 2002 (Issue 16) pp:1768-1769
Publication Date(Web):17 Jul 2002
DOI:10.1039/B204572A
A new series of dendrimers containing a central cavitand core with four appended Fréchet-type dendrons, linked to the core through 4,4′-bipyridinium (viologen) subunits, have been synthesized, characterized and their electrochemical properties investigated using cyclic voltammetric measurements.
Co-reporter:Rosa Toba, José María Quintela, Carlos Peinador, Esteban Román and Angel E. Kaifer
Chemical Communications 2001 (Issue 9) pp:857-858
Publication Date(Web):17 Apr 2001
DOI:10.1039/B102134F
A new series of dendrimers containing a single
4,4′-bipyridinium (viologen) core has been synthesised and
characterized that exhibit fast heterogeneous electron transfer reactions
from the first to the third generation of dendritic growth.
Co-reporter:Christoph Naumann;Esteban Román;Carlos Peinador Dr.;Tong Ren;Brian O. Patrick Dr. Dr.;John C. Sherman Dr.
Chemistry - A European Journal 2001 Volume 7(Issue 8) pp:
Publication Date(Web):23 MAR 2001
DOI:10.1002/1521-3765(20010417)7:8<1637::AID-CHEM16370>3.0.CO;2-X
The preparation of cavitands composed of 4, 5, 6, and 7 aromatic subunits ([n]cavitands, n=4–7) is described. The simple, two-step synthetic procedure utilized readily available starting materials (2-methylresorcinol and diethoxymethane). The two cavitand products having 4 and 5 aromatic subunits exhibited highly symmetric cone conformations, while the larger cavitands (n=6 and 7) adopt conformations of lower symmetry. 1H NMR spectroscopic studies of [6]cavitand and [7]cavitand revealed that these hosts undergo exchange between equivalent conformations at room temperature. The departure of these two cavitands from cone conformations is related to steric crowding on their Ar-O-CH2-O-Ar bridges and is predicted by simple molecular mechanics calculations (MM2 force field). X-ray diffraction studies on single crystals of the [4]cavitand, [5]cavitand, and [6]cavitand hosts afforded additional experimental support for these conclusions.
Co-reporter:Julio Alvarez, Yuhua Ni, Tong Ren, Angel E. Kaifer
Journal of Supramolecular Chemistry 2001 Volume 1(Issue 1) pp:7-16
Publication Date(Web):January–February 2001
DOI:10.1016/S1472-7862(01)00007-7
A series of six new dinuclear ferrocene compounds with the bridging fragment CH2–N(R)–CH2 were prepared and characterized. Bis(ferrocenylmethyl)-t-butylamine (1), bis(ferrocenylmethyl)-isopropylamine (2), bis(ferrocenylmethyl)-hexylamine (3), bis(ferrocenylmethyl)-p-methoxyaniline (4), bis(ferrocenylmethyl)aniline (5) and bis(ferrocenylmethyl)-p-nitroaniline (6), as well as the quaternized amine bis(ferrocenylmethyl)hexylmethylammonium hexaflurophosphate (3+·PF6−), were investigated using electrochemical techniques, 1H NMR spectroscopy and single crystal X-ray diffraction analysis. The voltammetric data indicate that the extent of electronic communication between the equivalent ferrocene centers increases in low polarity solvents and when bulky aliphatic groups are covalently attached to the central tertiary nitrogen. The observed experimental data are consistent with through-space communication effects, essentially electrostatic in nature. The extent of electronic communication can be modulated by reversible and irreversible reactions in the solution phase. Protonation or methylation of the tertiary nitrogen in the middle of the bridge disrupts the electronic communication between the ferrocene residues.
Co-reporter:J. Liu;J. Alvarez;A. E. Kaifer
Advanced Materials 2000 Volume 12(Issue 18) pp:
Publication Date(Web):14 SEP 2000
DOI:10.1002/1521-4095(200009)12:18<1381::AID-ADMA1381>3.0.CO;2-U
Cyclodextrin-modified metal nanoparticles illustrate the role that protective organic shells can play in the modulation of the properties of nanoparticles, endowing them with molecular recognition abilities, as highlighted here. These nanocomposite materials are of fundamental interest for the organized self-assembly of metal nanoparticles.
Co-reporter:Julio Alvarez, Jian Liu, Esteban Román and Angel E. Kaifer
Chemical Communications 2000 (Issue 13) pp:1151-1152
Publication Date(Web):12 Jun 2000
DOI:10.1039/B002423F
Pt and Pd nanoparticles can be modified with surface-attached
cyclodextrin receptors leading to water-soluble materials that exhibit
catalytic activity for the hydrogenation of allylamine.
Co-reporter:Angel E. Kaifer, Wei Li, Serena Silvi and Vladimir Sindelar
Chemical Communications 2012 - vol. 48(Issue 53) pp:NaN6695-6695
Publication Date(Web):2012/05/15
DOI:10.1039/C2CC32871B
Deprotonation of the two terminal COOH groups on a 4,4′-bipyridinium linear derivative leads to a pronounced slow down on the kinetics of threading and unthreading by the cucurbit[7]uril host.
Co-reporter:Song Yi, Burjor Captain and Angel E. Kaifer
Chemical Communications 2011 - vol. 47(Issue 19) pp:NaN5502-5502
Publication Date(Web):2011/04/08
DOI:10.1039/C1CC11212K
The extent of methylation of the central nitrogen in (ferrocenylmethyl)tempammonium guests determines the main binding site for complexation by the cucurbit[8]uril host.
Co-reporter:Daniel Nieto, Ana M
a
González-Vadillo, Sonia Bruña, César J. Pastor, Angel E. Kaifer and Isabel Cuadrado
Chemical Communications 2011 - vol. 47(Issue 37) pp:NaN10400-10400
Publication Date(Web):2011/08/15
DOI:10.1039/C1CC13704B
A new heterometallic electroactive compound having the ferrocenyl moiety attached to the platinum atom through an amidine functionality has been prepared viaPt(II)-mediated nucleophilic addition of β-aminoethylferrocene to a benzonitrile ligand. This neutral receptor shows remarkable electrochemical anion-sensing redox response to H2PO4−.
Co-reporter:Song Yi, Wei Li, Daniel Nieto, Isabel Cuadrado and Angel E. Kaifer
Organic & Biomolecular Chemistry 2013 - vol. 11(Issue 2) pp:NaN293-293
Publication Date(Web):2012/11/12
DOI:10.1039/C2OB26834E
The binding properties of the cucurbit[7]uril host with three structurally related ferrocene-containing guests, ferrocenyltrimethylammonium, ferrocenylmethyltrimethylammonium and ferrocenylethyltrimethylammonium, have been investigated using 1H NMR spectroscopy, mass spectrometry, voltammetry and computational methods. The experimental and computational data indicate that the stability of the cucurbit[7]uril inclusion complexes is relatively insensitive to the number of methylenes connecting the trimethylammonium and the ferrocenyl groups, although some of their properties are affected in significant ways.
Co-reporter:Yonghua Ling, Wei Wang and Angel E. Kaifer
Chemical Communications 2007(Issue 6) pp:NaN612-612
Publication Date(Web):2006/11/07
DOI:10.1039/B611559D
The dicationic guest 2,7-dimethyldiazaphenanthrenium forms a fluorescent inclusion complex with the cucurbit[8]uril host, which can be used to effectively bind and detect indole derivatives, such as serotonin and tryptophan.
Co-reporter:Lu Cui, Suresh Gadde, Atindra D. Shukla, Hao Sun, Joel T. Mague and Angel E. Kaifer
Chemical Communications 2008(Issue 12) pp:NaN1448-1448
Publication Date(Web):2008/01/25
DOI:10.1039/B717285K
Ureido pyrimidinedione derivatives with phenyl, 1-naphthyl and 2-naphthyl substituents form stable dimers via quadruple hydrogen bonding, but the 1-naphthyl derivative presents an unexpected tautomer in the solid state.
Co-reporter:Song Yi, Valentina Brega, Burjor Captain and Angel E. Kaifer
Chemical Communications 2012 - vol. 48(Issue 83) pp:NaN10297-10297
Publication Date(Web):2012/09/03
DOI:10.1039/C2CC35095E
Six equivalents of N,N′-bis(4-aminobenzyl)urea, 12 equivalents of 2-formylpyridine and four equivalents of FeSO4 or NiSO4 undergo subcomponent self-assembly in aqueous solution to form tetrahedral cages around a single, encapsulated sulfate anion.
