Co-reporter:Omkar V. Zore, Patrick J. Lenehan, Challa V. Kumar, and Rajeswari M. Kasi
Langmuir May 13, 2014 Volume 30(Issue 18) pp:5176-5184
Publication Date(Web):May 13, 2014
DOI:10.1021/la501034b
We previously reported that the stability and aqueous catalytic activity of met-hemoglobin (Hb) was improved when covalently conjugated with poly(acrylic acid) (PAA). In the current study, the Hb–PAA–water interface was modified to improve Hb catalytic efficiency in organic solvents (0–80% v/v organic solvent; remainder is the conjugate, the substrate, and water). The protein–polymer–solvent interface modification was achieved by esterifying the carboxylic acid groups of Hb–PAA with ethanol (EtOH) or 1-propanol (1-prop) after activation with carbodiimide. The resulting esters (Hb–PAA–Eth and Hb–PAA–1-prop, respectively) showed high peroxidase-like catalytic activities in acetonitrile (ACN), dimethylformamide (DMF), EtOH, and methanol (MeOH). Catalytic activities depended on the log(P) values of the solvents, which is a measure of solvent lipophilicity. The highest weighted-average activities were noted in MeOH for all three conjugates, and the lowest average activities were noted in DMF for two of the conjugates. Interestingly, the average activities of the conjugates were higher than that of Hb in all solvents except in ACN. The ratio of the catalytic rate constant (kcat) to the Michaelis constant (KM), the catalytic efficiency, for Hb–PAA–Eth in MeOH was the highest noted, and it is ∼3-fold higher than that of Hb in buffer; conjugates offered higher efficiencies than Hb at most solvent compositions. This is the very first general, versatile, modular strategy of coupling the enhanced stability of Hb with improved activity in organic solvents via the chemical manipulation of the polymer shell around Hb and provides a robust approach to efficient biocatalysis in organic solvents.
Co-reporter:Omkar V. Zore;Paritosh Pande;Oghenenyerovwo Okifo;Ashis K. Basu;Challa V. Kumar
RSC Advances (2011-Present) 2017 vol. 7(Issue 47) pp:29563-29574
Publication Date(Web):2017/06/05
DOI:10.1039/C7RA05666D
We report a general and modular approach for the synthesis of multi enzyme–polymer conjugates (MECs) consisting of five different enzymes of diverse isoelectric points and distinct catalytic properties conjugated within a single universal polymer scaffold. The five model enzymes chosen include glucose oxidase (GOx), acid phosphatase (AP), lactate dehydrogenase (LDH), horseradish peroxidase (HRP) and lipase (Lip). Poly(acrylic acid) (PAA) is used as the model synthetic polymer scaffold that will covalently conjugate and stabilize multiple enzymes concurrently. Parallel and sequential synthetic protocols are used to synthesise MECs, 5-P and 5-S, respectively. Also, five different single enzyme–PAA conjugates (SECs) including GOx–PAA, AP–PAA, LDH–PAA, HRP–PAA and Lip–PAA are synthesized. The composition, structure and morphology of MECs and SECs are confirmed by agarose gel electrophoresis, dynamic light scattering, circular dichroism spectroscopy and transmission electron microscopy. The bioreactor comprising MEC functions as a single biocatalyst can carry out at least five different or orthogonal catalytic reactions by virtue of the five stabilized enzymes, which has never been achieved to-date. Using activity assays relevant for each of the enzymes, for example AP, the specific activity of AP at room temperature and 7.4 pH in PB is determined and set at 100%. Interestingly, MECs 5-P and 5-S show specific activities of 1800% and 600%, respectively, compared to 100% specific activity of AP at room temperature (RT). The catalytic efficiencies of 5-P and 5-S are 1.55 × 10−3 and 1.68 × 10−3, respectively, compared to 9.11 × 10−5 for AP under similar RT conditions. Similarly, AP relevant catalytic activities of 5-P and 5-S at 65 °C show 100 and 300%, respectively, relative to native AP activity at RT as the native AP is catalytically inactive at 65 °C. The catalytic activity trends suggest: (1) MECs show enhanced catalytic activities compared to native enzymes under similar assay conditions and (2) 5-S is better suited for high temperature biocatalysis, while both 5-S and 5-P are suitable for room temperature biocatalysis. Initial cytotoxicity results show that these MECs are non-lethal to human cells including human embryonic kidney [HEK] cells when treated with doses of 0.01 mg mL−1 for 72 h. This cytotoxicity data is relevant for future biological applications.
Co-reporter:Omkar V. Zore, Ajith Pattammattel, Shailaja Gnanaguru, Challa V. Kumar, and Rajeswari M. Kasi
ACS Catalysis 2015 Volume 5(Issue 9) pp:4979
Publication Date(Web):July 8, 2015
DOI:10.1021/acscatal.5b00958
An example of a highly stable and functional bienzyme–polymer conjugate triad assembled on a topologically orthogonal support, layered graphene oxide (GO), is reported here. Glucose oxidase (GOx) and horseradish peroxidase (HRP) catalytic dyad were used as the model system for cascade biocatalysis. Poly(acrylic acid) (PAA) was used to covalently conjugate these enzymes, and then the conjugate has been subsequently adsorbed onto GO. The resultant nanobiocatalysts are represented as GOx-HRP-PAA/GO. Their morphology and structural characteristics were examined by transmission electron microscopy (TEM), agarose gel electrophoresis, circular dichroism (CD), and zeta potential. These robust conjugates remarkably functioned as active catalysts under biologically challenging conditions such as extreme pHs, high temperature (65 °C), and in the presence of a chemical denaturant. In one example, GOx-HRP-PAA/GO presented doubling of the Kcat (TON) (68 × 10–2 s–1) at pH 7.0 and room temperature, when compared to the corresponding physical mixture of GOx/HRP (32 × 10–2 s–1) under similar conditions. In another case, at 65 °C, GOx-HRP-PAA/GO displayed ∼120% specific activity, whereas GOx/HRP showed only 16% of its original activity. At pH 2.0 and in the presence of 4.0 mM SDS as the denaturant, GOx-HRP-PAA/GO presented greater than 100% specific activity, whereas GOx/HRP was completely deactivated under these conditions. Thus, we combined two concepts, enzyme–polymer conjugation followed by adsorption onto a 2D nanolayered material to obtain enhanced substrate channeling and excellent enzyme stability under challenging conditions. These features have never been attained by either traditional enzyme–polymer conjugates or enzyme–GO hybrids. This general, modular, and powerful approach may also be used to produce environmentally benign, biologically compatible (edible), and efficient cascade biocatalysts.Keywords: enzyme−polymer conjugate; graphene oxide; high temperature activity; multienzyme; substrate channeling
Co-reporter:Chi Thanh Nguyen, Yumin Zhu, Xiaorui Chen, Gregory A. Sotzing, Sergio Granados-Focil and Rajeswari M. Kasi
Journal of Materials Chemistry A 2015 vol. 3(Issue 2) pp:399-408
Publication Date(Web):29 Sep 2014
DOI:10.1039/C4TC01702A
We examine the influence of confining gold nanoparticles on the overall nanoscale morphology, mechanical and electrochemical properties of nanocomposite ion gels. Stimuli-responsive ion gels are generated via the synthesis of gold nanoparticles (AuNPs) within a thiol-functionalized liquid crystalline brush-like block copolymer (LCBBC) and subsequent gelation in ionic liquids. AuNPs are prepared by in situ reduction of the gold ions and stabilized by direct anchoring through coordination bonds with the thiol-functionalized LCBBC. The resulting LCBBC/AuNP nanocomposite comprises a hierarchical structure in which polymer-coated AuNPs are dispersed in a microsegregated LCBBC matrix that further contains both liquid crystalline (LC) and block copolymer ordering. More importantly, this LCBBC/AuNP nanocomposite is solubilized in an ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate, to form a nanocomposite ion gel. At 5 wt% concentration, LCBBC/AuNP nanocomposite ion-gel exhibits interesting characteristics including excellent mechanical strength (∼103 Pa), good optical properties with higher ionic conductivity (∼10−2 S cm−1) and long-term electrochemical stability over a larger potential range compared to the plain LCBBC ion gel. Thus, nanocomposite ion gels present tunable optical, thermal and mechanical properties by virtue of their polymer architecture, morphology and functionality. These are versatile and modular hybrid materials to design nanocomposite ion gels with multiple functionalities for applications in electrochemical devices, photonics, and opto-electronics.
Co-reporter:Chi Thanh Nguyen and Rajeswari M. Kasi
Chemical Communications 2015 vol. 51(Issue 61) pp:12174-12177
Publication Date(Web):28 May 2015
DOI:10.1039/C5CC02559A
New nanocomposite hydrogels from liquid crystalline brush-like block copolymers (LCBBCs) and gold nanorods (AuNRs) were synthesized and characterized. The hydrogels protected and stabilized AuNRs, which presented peroxidase-like activity and catalysed the oxidation of a substrate in the presence of H2O2 and elicited a sensitive chromogenic response. This reusable, table-top stable, free-standing nanocomposite hydrogel platform can be used to develop a simple and reproducible method to detect H2O2.
Co-reporter:Chi Thanh Nguyen, Thanh Huyen Tran, Mansoor Amiji, Xiuling Lu, Rajeswari M. Kasi
Nanomedicine: Nanotechnology, Biology and Medicine 2015 Volume 11(Issue 8) pp:2071-2082
Publication Date(Web):November 2015
DOI:10.1016/j.nano.2015.06.011
Co-reporter:Chi Thanh Nguyen, Thanh Huyen Tran, Xiuling Lu and Rajeswari M. Kasi
Polymer Chemistry 2014 vol. 5(Issue 8) pp:2774-2783
Publication Date(Web):06 Jan 2014
DOI:10.1039/C3PY01636F
We synthesized new amphiphilic brush liquid crystalline block copolymers (brush-chol-BCP) comprised of polymethacrylates bearing polyethylene oxide (PEO) in one block and polymethacrylates bearing a cholesterol mesogen with a hemitelechelic thiol end group. Polymethacrylate bearing PEO (PMA-g-PEO) was first synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT) and used as a macro-chain transfer agent to prepare block copolymer (PMA-g-PEO)-b-PC5MA-thioester (brush-chol-BCP-thioester). Brush-chol-BCP-thiol was obtained by the reduction of a thioester to thiol in the presence of butylamine. Gold nanoparticles (AuNPs) were prepared in situ with the brush-chol-BCP-thiol template via the reduction of gold ions and were stabilized by directly anchoring to the brush-chol-BCP-thiol chains through the coordination bonds with the thiol groups in the copolymer. The hydrophobic anticancer drug doxorubicin (DOX) was successfully encapsulated into AuNP-templated brush-chol-BCP-thiol via physical entrapment to form dual-encapsulated NPs with a high drug loading of 21.4% (w/w) and a high encapsulation efficiency of 85.6%. The dual-encapsulated NPs had an average size of 157 nm, spherical shape, excellent stability, and a sustained drug release pattern. More importantly, the dual-encapsulated NPs could be effectively internalized by human cervical cancer cells (Hela) and showed dose-dependent cytotoxicity, while the blank nanoparticles were non-cytotoxic at the tested concentrations. The results indicate that the brush-chol-BCP-thiol and their nanoparticles are promising carriers for dual encapsulation and delivery of an anticancer drug and metal nanoparticles.
Co-reporter:Prashant Deshmukh, Manesh Gopinadhan, Youngwoo Choo, Suk-kyun Ahn, Pawel W. Majewski, Sook Young Yoon, Olgica Bakajin, Menachem Elimelech, Chinedum O. Osuji, and Rajeswari M. Kasi
ACS Macro Letters 2014 Volume 3(Issue 5) pp:462
Publication Date(Web):May 1, 2014
DOI:10.1021/mz500161k
We report on the development of a liquid crystalline block copolymer with brush-type architecture as a platform for creating functional materials by magnetic-field-directed self-assembly. Ring-opening metathesis of n-alkyloxy cyanobiphenyl and polylactide (PLA) functionalized norbornene monomers provides efficient polymerization yielding low polydispersity block copolymers. The mesogenic species, spacer length, monomer functionality, brush-chain length, and overall molecular weight were chosen and optimized to produce hexagonally packed cylindrical PLA domains which self-assemble and align parallel to an applied magnetic field. The PLA domains can be selectively removed by hydrolytic degradation resulting in the production of nanoporous films. The polymers described here provide a versatile platform for scalable fabrication of aligned nanoporous materials and other functional materials based on such templates.
Co-reporter:Caterina M. Riccardi, Kyle S. Cole, Kyle R. Benson, Jessamyn R. Ward, Kayla M. Bassett, Yiren Zhang, Omkar V. Zore, Bobbi Stromer, Rajeswari M. Kasi, and Challa V. Kumar
Bioconjugate Chemistry 2014 Volume 25(Issue 8) pp:1501
Publication Date(Web):July 21, 2014
DOI:10.1021/bc500233u
Several key properties of catalase such as thermal stability, resistance to protease degradation, and resistance to ascorbate inhibition were improved, while retaining its structure and activity, by conjugation to poly(acrylic acid) (PAA, Mw 8000) via carbodiimide chemistry where the amine groups on the protein are appended to the carboxyl groups of the polymer. Catalase conjugation was examined at three different pH values (pH 5.0, 6.0, and 7.0) and at three distinct mole ratios (1:100, 1:500, and 1:1000) of catalase to PAA at each reaction pH. The corresponding products are labeled as Cat-PAA(x)-y, where x is the protein to polymer mole ratio and y is the pH used for the synthesis. The coupling reaction consumed about 60–70% of the primary amines on the catalase; all samples were completely water-soluble and formed nanogels, as evidenced by gel electrophoresis and electron microscopy. The UV circular dichroism (CD) spectra indicated substantial retention of protein secondary structure for all samples, which increased to 100% with increasing pH of the synthesis and polymer mole fraction. Soret CD bands of all samples indicated loss of ∼50% of band intensities, independent of the reaction pH. Catalytic activities of the conjugates increased with increasing synthesis pH, where 55–80% and 90–100% activity was retained for all samples synthesized at pH 5.0 and pH 7.0, respectively, and the Km or Vmax values of Cat-PAA(100)-7 did not differ significantly from those of the free enzyme. All conjugates synthesized at pH 7.0 were thermally stable even when heated to ∼85–90 °C, while native catalase denatured between 55 and 65 °C. All conjugates retained 40–90% of their original activities even after storing for 10 weeks at 8 °C, while unmodified catalase lost all of its activity within 2 weeks, under similar storage conditions. Interestingly, PAA surrounding catalase limited access to the enzyme from large molecules like proteases and significantly increased resistance to trypsin digestion compared to unmodified catalase. Similarly, negatively charged PAA surrounding the catalase in these conjugates protected the enzyme against inhibition by negatively charged inhibitors such as ascorbate. While Cat-PAA(100)-7 did not show any inhibition by ascorbate in the presence of 270 μM ascorbate, unmodified catalase lost ∼70% of its activity under similar conditions. This simple, facile, and rational methodology produced thermostable, storable catalase that is also protected from protease digestion and ascorbate inhibition and most likely prevented the dissociation of the multimer. Using synthetic polymers to protect and improve enzyme properties could be an attractive approach for making “Stable-on-the-Table” enzymes, as a viable alternative to protein engineering.
Co-reporter:Ananta Ghimire, Rajeswari M. Kasi, and Challa V. Kumar
The Journal of Physical Chemistry B 2014 Volume 118(Issue 19) pp:5026-5033
Publication Date(Web):April 16, 2014
DOI:10.1021/jp500310w
Rational design of protein–polymer composites and their use, under the influence of the stimulus, for numerous applications requires a clear understanding of protein–polymer interfaces. Here, using poly(acrylic acid) (PAA) and lysozyme as model systems, the binding interactions between these macromolecules were investigated by isothermal titration calorimetry. The binding is proposed to require and be governed by “charge neutralization of the protein/polymer interface” and predicted to depend on solution pH. Calorimetric data show strong exothermic binding of lysozyme to PAA with a molar ΔH and TΔS values of −107 and −95 kcal/mol, respectively, at pH 7 and room temperature. Both ΔH and TΔS decreased linearly with increasing pH from 3 to 8, and these plots had slopes of −17.7 and −17.5 kcal/mol per pH unit, respectively. The net result was that the binding propensity (ΔG) was nearly independent of pH but the binding stoichiometry, surprisingly, increased rapidly with increasing pH from 1 lysozyme binding per PAA molecule at pH 3 to 16 lysozyme molecules binding per PAA molecule at pH 8. A plot of stoichiometry vs pH was linear, and consistent with this result, a plot of ln(average size of the protein/polymer complex) vs pH was also linear. Thus, protonation–deprotonation plays a major role in the binding mechanism. “Charge neutralization” of the lysozyme/PAA interface controls the binding stoichiometry as well as the binding enthalpies/entropies in a predictable fashion, but it did not control the binding affinity (ΔG). The pH dependence of lysozyme binding to PAA, demonstrated here, provides a stimuli-responsive system for protein binding and release from the polymer surface.
Co-reporter:Omkar V. Zore, Patrick J. Lenehan, Challa V. Kumar, and Rajeswari M. Kasi
Langmuir 2014 Volume 30(Issue 18) pp:5176-5184
Publication Date(Web):2017-2-22
DOI:10.1021/la501034b
We previously reported that the stability and aqueous catalytic activity of met-hemoglobin (Hb) was improved when covalently conjugated with poly(acrylic acid) (PAA). In the current study, the Hb–PAA–water interface was modified to improve Hb catalytic efficiency in organic solvents (0–80% v/v organic solvent; remainder is the conjugate, the substrate, and water). The protein–polymer–solvent interface modification was achieved by esterifying the carboxylic acid groups of Hb–PAA with ethanol (EtOH) or 1-propanol (1-prop) after activation with carbodiimide. The resulting esters (Hb–PAA–Eth and Hb–PAA–1-prop, respectively) showed high peroxidase-like catalytic activities in acetonitrile (ACN), dimethylformamide (DMF), EtOH, and methanol (MeOH). Catalytic activities depended on the log(P) values of the solvents, which is a measure of solvent lipophilicity. The highest weighted-average activities were noted in MeOH for all three conjugates, and the lowest average activities were noted in DMF for two of the conjugates. Interestingly, the average activities of the conjugates were higher than that of Hb in all solvents except in ACN. The ratio of the catalytic rate constant (kcat) to the Michaelis constant (KM), the catalytic efficiency, for Hb–PAA–Eth in MeOH was the highest noted, and it is ∼3-fold higher than that of Hb in buffer; conjugates offered higher efficiencies than Hb at most solvent compositions. This is the very first general, versatile, modular strategy of coupling the enhanced stability of Hb with improved activity in organic solvents via the chemical manipulation of the polymer shell around Hb and provides a robust approach to efficient biocatalysis in organic solvents.
Co-reporter:Nitin Sharma;Rubinder Kaur Lakhman;Yuxiang Zhou
Journal of Applied Polymer Science 2013 Volume 128( Issue 6) pp:3982-3992
Publication Date(Web):
DOI:10.1002/app.38629
Abstract
We report a strategy to prepare and characterize mechanically robust, transparent, thermoreversible physical gels of an ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], to harness its good ionic conductivity and electrolytic properties for solid-state electrolyte and lithium ion battery applications. Physical gels are prepared using a triblock copolymer comprising central polyethylene oxide block that is soluble in [BMIM][BF4] and the end blocks, poly(N-tert-butylacrylamide), that are insoluble in [BMIM][BF4]. Transparent, strong, physical ion-gels with significant mechanical strength can be formed at low concentration of the triblock copolymer (∼5 wt %), unlike previous reports in which chemical gels of [BMIM][BF4] are obtained at very high polymer concentration. Our gels are thermoreversible and thermally stable, showing 1–4% weight loss up to 200°C in air. Gelation behavior, mechanical properties, and ionic conductivity of these ion-gels can be easily tuned by varying the concentration or N-tert-butylacrylamide block length in the triblock copolymer. These new non-volatile, reprocessable, mechanically robust, [BMIM][BF4]-based physical ion-gels obtained from a simple and convenient preparation method are promising materials for solid-state electrolyte applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Co-reporter:Prashant Deshmukh, Suk-kyun Ahn, Ludovic Geelhand de Merxem, and Rajeswari M. Kasi
Macromolecules 2013 Volume 46(Issue 20) pp:8245-8252
Publication Date(Web):October 14, 2013
DOI:10.1021/ma401448j
Herein we investigate the influence of competing self-organizing phenomena on the hierarchical self-assembly of liquid crystalline brush block copolymers (LCBBCs). A library of LCBBCs are synthesized using ring-opening metathesis polymerization (ROMP) of norbornene side-chain functionalized monomers comprising (1) cholesteryl mesogen with nine methylene spacer and (2) semicrystalline poly(ethylene glycol) (PEG). The self-assembly of LCBBCs with variations in LC block content (7–80 wt %) are investigated in their melt state. All LCBBCs show two distinct thermal transitions corresponding to PEG semicrystalline phase and LC mesophases. Interestingly, the LCBBCs display a multilevel hierarchical structure evidenced by the results from X-ray scattering and transmission electron microscopy (TEM): (1) smectic A (SmA) mesophases (d = 3–7 nm) by the assembly of cholesteryl side chains and (2) microphase segregation into lamellar or cylinder (d = 40–75 nm) resulting from the incompatibility between LC moieties and PEG side chain. Surprisingly, the presence of microphase-segregated domains in LCBBCs prevents the formation of cholesteric mesophase in sharp contrast to side-chain liquid crystalline homopolymer (SCLCP) bearing the same mesogen and the flexible spacer. This could be attributed to very high surface to volume ratio at intermaterial dividing surface (IMDS) in LCBBCs, by which only LC layers (i.e., SmA mesophase) are favored to form at the IMDS. On the fundamental side, these LCBBCs are an interesting scaffold to explore the impact of interactions between LC order and microphase segregation of side-chain polymeric brushes on the self-assembly of LCBBCs. Moreover, these new LCBBC scaffolds will serve as a tool box for rational design of hierarchically organized functional materials for stimuli responsive applications.
Co-reporter:Prashant Deshmukh, Suk-kyun Ahn, Manesh Gopinadhan, Chinedum O. Osuji, and Rajeswari M. Kasi
Macromolecules 2013 Volume 46(Issue 11) pp:4558-4566
Publication Date(Web):May 30, 2013
DOI:10.1021/ma400846y
Here we report a general methodology to attain novel hierarchical nanostructures using new polymer scaffolds that self-assemble to form cholesteric 1D photonic mesophases existing in conjunction with microphase segregated domains. To achieve this, a series of liquid-crystalline random brush copolymers (LCRBC) consisting of cholesteryl liquid crystalline (LC) mesogen and brushlike PEG as side chain functionality are synthesized. At room temperature, all LCRBCs exhibits microphase segregation of PEG side chains on length scale of 10–15 nm, whereas LC domain forms smectic mesophase (3–7 nm LC layers). Interestingly, upon heating a cholesteric mesophase is exclusively observed for copolymer containing 78 and 85 wt % of LC content (LCRBC78 and LCRBC85, respectively) existing along with microphase segregated PEG domains. Moreover, the phase behavior of these copolymers studied by temperature-controlled small-angle X-ray scattering (SAXS) suggests the order–disorder transition for the microphase segregated structure coincides with the cholesteric–isotropic transition. Remarkably, LCRBC78 and LCRBC85 quenched from cholesteric mesophase exhibits nanoscale hierarchical order consisting of (1) smectic LC ordering with 3–7 nm periodicity, (2) microphase segregation of PEG side chain on 10–12 nm length scale, and (3) periodicities from helical mesophase (cholesteric phase) on optical length scales of 150–200 nm. Thus, by exploiting LCRBC molecular architecture and composition, hierarchical nanostructure can be obtained and preserved which allows for the creation of unique 1D-photonic materials.
Co-reporter:Suk-kyun Ahn, Manesh Gopinadhan, Prashant Deshmukh, Rubinder Kaur Lakhman, Chinedum O. Osuji and Rajeswari M. Kasi
Soft Matter 2012 vol. 8(Issue 11) pp:3185-3191
Publication Date(Web):08 Feb 2012
DOI:10.1039/C2SM07115K
In this paper, the thermal, optical and mesomorphic properties of side-chain liquid crystalline (SCLC) homopolymers (PNBCh-n), in which cholesteryl mesogens are linked to a polynorbornene backbone by different lengths of methylene spacer (n = 4, 5, 9, 10 and 15), are investigated. By doing so, the impact of flexible spacer length on the formation of different types of LC mesophase is explained. Because of comb-shaped SCLC polymer architecture, smectic mesophases are primarily found in PNBCh-n. Interestingly, cholesteric mesophases are identified only in PNBCh-9 and 10, which are proved by (1) the selective light reflection in UV-Vis analysis, (2) the characteristic oily streak texture under polarized optical microscope (POM) and (3) a long range periodicity in the cross-sectioned films from transmission electron microscope (TEM) investigation. Moreover, temperature-controlled X-ray scattering measurements are performed to examine mesomorphic structure evolution. By comparing the mesomorphic structures in this series of SCLC homopolymers, both extent of mesogen interdigitation and motional decoupling between backbone and mesogenic side-chains are found to play a critical role in the development of cholesteric mesophase. This structure–property study of PNBCh-n will help elucidate the importance of molecular structure, particularly the length of spacers, on the formation of cholesteric mesophase and its importance in the design of thermochromic devices.
Co-reporter:Yuxiang Zhou ; Nitin Sharma ; Prashant Deshmukh ; Rubinder Kaur Lakhman ; Menka Jain
Journal of the American Chemical Society 2011 Volume 134(Issue 3) pp:1630-1641
Publication Date(Web):December 26, 2011
DOI:10.1021/ja208349x
Here we report a modular strategy for preparing physically cross-linked and mechanically robust free-standing hydrogels comprising unique thermotropic liquid crystalline (LC) domains and magnetic nanoparticles both of which serve as the physical cross-linkers resulting in hydrogels that can be used as magnetically responsive soft actuators. A series of amphiphilic LC pentablock copolymers of poly(acrylic acid) (PAA), poly(5-cholesteryloxypentyl methacrylate) (PC5MA), and poly(ethylene oxide) (PEO) blocks in the sequence of PAA–PC5MA–PEO–PC5MA–PAA were prepared using reversible addition–fragmentation chain transfer polymerization. These pentablock copolymers served as macromolecular ligands to template Fe3O4 magnetic nanoparticles (MNPs), which were directly anchored to the polymer chains through the coordination bonds with the carboxyl groups of PAA blocks. The resulting polymer/MNP nanocomposites comprised a complicated hierarchical structure in which polymer-coated MNP clusters were dispersed in a microsegregated pentablock copolymer matrix that further contained LC ordering. Upon swelling, the hierarchical structure was disrupted and converted to a network structure, in which MNP clusters were anchored to the polymer chains and LC domains stayed intact to connect solvated PEO and PAA blocks, leading to a free-standing LC magnetic hydrogel (LC ferrogel). By varying the PAA weight fraction (fAA) in the pentablock copolymers, the swelling degrees (Q) of the resulting LC ferrogels were tailored. Rheological experiments showed that these physically cross-linked free-standing LC ferrogels exhibit good mechanical strength with storage moduli G′ of around 104–105 Pa, similar to that of natural tissues. Furthermore, application of a magnetic field induced bending actuation of the LC ferrogels. Therefore, these physically cross-linked and mechanically robust LC ferrogels can be used as soft actuators and artificial muscles. Moreover, this design strategy is a versatile platform for incorporation of different types of nanoparticles (metallic, inorganic, biological, etc.) into multifunctional amphiphilic block copolymers, resulting in unique free-standing hybrid hydrogels of good mechanical strength and integrity with tailored properties and end applications.
Co-reporter:Suk-kyun Ahn
Advanced Functional Materials 2011 Volume 21( Issue 23) pp:4543-4549
Publication Date(Web):
DOI:10.1002/adfm.201101369
Abstract
We report a new strategy to achieve triple shape memory properties by using side-chain liquid crystalline (SCLC) type random terpolymer networks (XL- TP-n), where n is the length of flexible methylene spacer (n = 5, 10, and 15) to link backbone and mesogen. A lower glass transition temperature (Tg = Tlow) and a higher liquid crystalline clearing temperature (Tcl = Thigh) of XL-TP-n serve as molecular switches to trigger a shape memory effect (SME). Two different triple shape creation procedures (TSCPs), thermomechanical treatments to obtain temporary shapes prior to the proceeding recovery step, are used to investigate the triple shape memory behavior of XL-TP-n. The discrete Tg and Tcl as well as unique microphase-separated morphologies (backbone-rich and mesogen-rich domains) within smectic layers of XL-TP-n enables triple shape memory properties. Motional decoupling between backbone-rich and mesogen-rich domains is also critical to determine the resulting macroscopic shape memory properties. Our strategy for obtaining triple shape memory properties will pave the way for exploiting a broad range of SCLC polymers to develop a new class of actively moving polymers.
Co-reporter:Yuxiang Zhou, Suk-kyun Ahn, Rubinder Kaur Lakhman, Manesh Gopinadhan, Chinedum O. Osuji, and Rajeswari M. Kasi
Macromolecules 2011 Volume 44(Issue 10) pp:3924-3934
Publication Date(Web):April 25, 2011
DOI:10.1021/ma102922u
A series of liquid crystalline–semicrystalline–liquid crystalline triblock copolymers, with poly(ethylene oxide) (PEO) as the semicrystalline central block and polymethacrylate bearing side-chain cholesteryl mesogens as the liquid crystalline (LC) end blocks, are prepared using reversible addition–fragmentation chain transfer (RAFT) polymerization. Starting with 20 kg/mol PEO, the weight fractions of the LC blocks in the triblock copolymers are varied from 21 to 86 wt %. The wide-angle and small-angle X-ray scattering (WAXS and SAXS) as well as transmission electron microscopy (TEM) studies show that with the increased LC content in the triblock copolymers different hierarchical structures including “LC lamellae in PEO lamellae” and “PEO cylinders in LC matrix” are observed sequentially. Differential scanning calorimetry (DSC) study shows that the triblock copolymers with “LC lamellae in PEO lamellae” crystallize at normal undercooling conditions (crystallization temperature Tc observed at 31.0–36.4 °C, which is close to that of homopolymer PEO), while those with “PEO cylinders in LC matrix” crystallize at very large undercooling (Tc drops to −23.5 to −27.8 °C). The large variation of the undercooling conditions required for PEO crystallization is attributed to the nanoconfinement effect from different hierarchical structures at varied LC contents. Avrami analysis has been performed to understand the PEO crystallization mechanism. In “LC lamellae in PEO lamellae”, the PEO crystallization is confined within 2D microdomains between LC lamellae and follows heterogeneous nucleation mechanism with subsequent long-range crystal growth. In “PEO cylinders in LC matrix”, the PEO crystallization is confined within 1D cylindrical microdomains and dominated by homogeneous nucleation, and long-range crystal growth is prohibited by the surrounding LC matrix. This study demonstrates that microsegregated LC domains can provide efficient confinement of the PEO crystallization, and by simply increasing the LC content, amorphous PEO can be obtained at room temperature. These LC–semicrystalline–LC triblock copolymers, with room temperature amorphous PEO confined in microsegregated nanodomains, may be used as scaffolds for lithium ion batteries and solid-state electrolytes.
Co-reporter:Vindya Thilakarathne, Victoria A. Briand, Yuxiang Zhou, Rajeswari M. Kasi, and Challa V. Kumar
Langmuir 2011 Volume 27(Issue 12) pp:7663-7671
Publication Date(Web):May 18, 2011
DOI:10.1021/la2015034
The synthesis, characterization, and evaluation of a novel polymer–protein conjugate are reported here. The covalent conjugation of high-molecular weight poly(acrylic acid) (PAA) to the lysine amino groups of met-hemoglobin (Hb) resulted in the covalent conjugation of Hb to PAA (Hb-PAA conjugate), as confirmed by dialysis and electrophoresis studies. The retention of native-like structure of Hb in Hb-PAA was established from Soret absorption, circular dichroism studies, and the redox activity of the iron center in Hb-PAA. The peroxidase-like activities of the Hb-PAA conjugate further confirmed the retention of Hb structure and biological activity. Thermal denaturation of the conjugate was investigated by differential scanning calorimetry and steam sterilization studies. The Hb-PAA conjugate indicated an improved denaturation temperature (Td) when compared to that of the unmodified Hb. One astonishing observation was that polymer conjugation significantly enhanced the Hb-PAA storage stability at room temperature. After 120 h of storage at room temperature in phosphate-buffered saline (PBS) at pH 7.4, for example, Hb-PAA retained 90% of its initial activity and unmodified Hb retained <60% of its original activity under identical conditions of buffer, pH, and temperature. Our conjugate demonstrates the key role of polymers in enhancing Hb stability via a very simple, efficient, general route. Water-swollen, lightly cross-linked, stable Hb-polymer nanogels of 100–200 nm were produced quickly and economically by this approach for a wide variety of applications.
Co-reporter:Suk-kyun Ahn, Prashant Deshmukh, Manesh Gopinadhan, Chinedum O. Osuji, and Rajeswari M. Kasi
ACS Nano 2011 Volume 5(Issue 4) pp:3085
Publication Date(Web):March 14, 2011
DOI:10.1021/nn200211c
Herein, we investigate the influence of nanoscale smectic polymorphism within end-on fixed side-chain liquid crystalline polymer networks (SCLCNs) on macroscopic shape-memory and actuation properties. We have synthesized a series of SCLC-type linear (TP-n) and cross-linked random terpolymers (XL-TP-n) with varying length of flexible methylene spacers (n = 5, 10, and 15) between polynorbornene main-chain and cholesteryl ester side-chains. Thermal and mechanical analyses by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) confirm a glass transition (Tg), a clearing temperature (Tcl), and a network structure in the XL-TP-n. Detailed structural investigation conducted using wide-angle and small-angle X-ray scattering (WAXS and SAXS) at room temperature proves self-assembled smectic A (SmA) polymorphism of the XL-TP-n which evolves from non-interdigitated bilayer (SmA2) for n = 5 to mixed layers of monolayer-like highly interdigitated layer (SmA1) and SmA2 for n = 10 and to SmA1 for n = 15. In addition, TP10 at temperatures above 60 °C interestingly shows transformation of SmA structure from mixed layer (SmA1 + SmA2) to interdigitated structure (SmAd). The SmA polymorphism developed in TP-n during shape-memory cycles (SMCs) significantly impacts the ultimate strain responses. A mechanism for the unique interdigitation-based thermostrictive behavior is proposed. More importantly, this new actuation mechanism observed in these XL-TP-n can be exploited to develop intelligent thermal actuators.Keywords: actuators; liquid crystals; nanostructured smart materials; self-assembly; shape-memory materials; structure−property relationships
Co-reporter:Nitin Sharma and Rajeswari M. Kasi
Langmuir 2010 Volume 26(Issue 10) pp:7418-7424
Publication Date(Web):April 13, 2010
DOI:10.1021/la100666t
We present dynamic viscoelastic studies of styrene and N-tert-butylacrylamide block copolymers (S278NtBAM517 and S93NtBAM252) in 1-octanol as a function of copolymer concentration at 15, 25, and 35 °C. Dilute solutions of these diblock copolymers in 1-octanol, a selective solvent for N-tert-butylacrylamide units, yield spherical micelles as evidenced by transmission electron microscopy (TEM). Dynamic light scattering (DLS) is used to determine hydrodynamic radius of the micelles as a function of temperature (15, 25, and 35 °C). Dilute solutions of these block copolymers behave as viscoelastic fluids in the low frequency range. At higher concentrations, these copolymer solutions form glass-clear gels. Rheological measurements show that these block copolymer solutions exhibit power-law behavior at the gel point (G′(ω) ∼ G′′(ω) ∼ ωn). In this paper, we discuss the formation and properties of critical gel states of SmNtBAMn in 1-octanol based on (1) concentration dependence of micelle-gel transition, (2) determination of critical state by rheology, and (3) temperature dependence of critical gel concentration and material parameters.
Co-reporter:Suk-kyun Ahn, Prashant Deshmukh and Rajeswari M. Kasi
Macromolecules 2010 Volume 43(Issue 17) pp:7330-7340
Publication Date(Web):August 6, 2010
DOI:10.1021/ma101145r
We report synthesis and characterization of a new class of side-chain liquid crystalline random terpolymers (SCLCP), its cross-linked network (SCLCN), and the corresponding shape memory properties. The SCLCP comprising three monomers, 5-{15-(cholesteryloxycarbonyl)-pentadecyloxycarbonyl}-bicyclo[2.2.1]hept-2-ene (NBCh15), 5-(acryloyl butoxycarbonyl)-bicyclo[2.2.1]hept-2-ene (NBBA), and poly(ethylene glycol) functionalized norbornene (NBPEG), is synthesized by ring-opening metathesis polymerization (ROMP) using Grubbs catalyst second generation, resulting in a random terpolymer. Each monomer provides a specific function in the terpolymer: (1) NBCh15 affords liquid crystalline properties, (2) NBBA is a cross-linkable unit, and (3) NBPEG acts as an internal plasticizer. The mesomorphic structure of the terpolymer investigated by X-ray diffraction (XRD) exhibits highly interdigitated smectic A (SmA) mesophase comprising cholesteryl ester mesogens. The acrylate end group in the NBBA undergoes cross-linking by curing at 120 °C, resulting in the SCLCN. Optimal cross-linking conditions are determined by monitoring gel fraction produced from different curing times. Thermal transitions including glass transition temperature (Tg) and clearing temperature (Tcl) before and after cross-linking are analyzed by differential scanning calorimetry (DSC). Linear viscoelastic properties of the SCLCN reveal three different relaxations associated with dynamic soft elasticity as well as Tg and Tcl. One-way shape memory cycles (1W-SMCs) of the SCLCN are programmed using (1) Tg, (2) Tcl, and (3) combined (Tg and Tcl) as a shape memory transition temperature (Ttrans). The Tg-based SMCs exhibits excellent shape fixing (>97%) and shape recovery ratio (>96%) with large strain (>150%). In the Tcl-based SMCs, the cooling induced elongation of strain is observed due to the development of interdigitated SmA mesophase. The shape fixing by interdigitated SmA is achieved during the Tcl-based SMCs unlike conventional shape fixing methods such as vitrification or crystallization. If both Tg and Tcl serve as Ttrans for SMCs, the permanent shape is restored by two stages of shape recovery around Tg and Tcl. The dual Ttrans (Tg and Tcl) inherent in this SCLCN allows for creating different types of SMCs and for the memorization of shape at two different temperature windows, thereby, programmed shapes by different mechanism would be recovered in a more precise manner.
Co-reporter:Suk-Kyun Ahn;Long T. Nguyen Le
Journal of Polymer Science Part A: Polymer Chemistry 2009 Volume 47( Issue 10) pp:2690-2701
Publication Date(Web):
DOI:10.1002/pola.23354
Abstract
A series of new norbornene carboxylic cholesteryl ester monomers with and without alkyl spacers, NBCh, and NBCh-n, respectively, were synthesized. New side-chain liquid crystalline homopolymers, PNBCh and PNBCh-n, were cleanly prepared using NBCh and NBCh-n, respectively, with Grubbs 2nd generation catalyst. Molecular and structural characterization of monomers and polymers were carried out by nuclear magnetic resonance, NMR, Fourier transform infrared, FT-IR, spectroscopy, and gel permeation chromatography, GPC. The thermal and liquid crystalline properties of the homopolymers were investigated by differential scanning calorimetry, DSC, thermogravimetric analysis, TGA, and polarized optical microscopy, POM. Small angle and wide angle X-ray studies of PNBCh-n in powder and fiber states not only confirmed the formation of smectic A mesophases, but also established their morphologies. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2690–2701, 2009
Co-reporter:Yuxiang Zhou
Journal of Polymer Science Part A: Polymer Chemistry 2008 Volume 46( Issue 20) pp:6801-6809
Publication Date(Web):
DOI:10.1002/pola.22988
Abstract
We report the synthesis and characterization of a series of novel diblock copolymers, poly(cholesteryl methacrylate-b-2-hydroxyethyl methacrylate) (PCMA-b-PHEMA). Monomers, cholesteryl methacrylate (CMA) and 2-(trimethylsiloxy)ethyl methacrylate (HEMA-TMS), were prepared from methyacryloyl chloride and 2-hydroxyethyl methacrylate, respectively. Homopolymers of CMA, PCMA, with well-defined molecular weights and polydispersity indices (PDI), were prepared by reversible addition fragmentation and chain transfer (RAFT) method. Precursor diblock copolymers, PCMA-b-P(HEMA-TMS), were synthesized using PCMA as macromolecular chain transfer agent and monomer, HEMA-TMS. Product diblock copolymers, PCMA-b-PHEMA, were prepared by deprotecting trimethylsilyl units in the precursor diblock copolymers using acid catalysts. Detailed molecular characterization of the precursor diblock copolymers, PCMA-b-P(HEMA-TMS), and the product diblock copolymers, PCMA-b-PHEMA, confirmed the composition and structure of these polymers. This versatile synthetic strategy can be used to prepare new amphiphilic block copolymers with cholesterol in one block and hydrogen-bonding moieties in the second block. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6801–6809, 2008
Co-reporter:Chi Thanh Nguyen and Rajeswari M. Kasi
Chemical Communications 2015 - vol. 51(Issue 61) pp:NaN12177-12177
Publication Date(Web):2015/05/28
DOI:10.1039/C5CC02559A
New nanocomposite hydrogels from liquid crystalline brush-like block copolymers (LCBBCs) and gold nanorods (AuNRs) were synthesized and characterized. The hydrogels protected and stabilized AuNRs, which presented peroxidase-like activity and catalysed the oxidation of a substrate in the presence of H2O2 and elicited a sensitive chromogenic response. This reusable, table-top stable, free-standing nanocomposite hydrogel platform can be used to develop a simple and reproducible method to detect H2O2.
Co-reporter:Chi Thanh Nguyen, Yumin Zhu, Xiaorui Chen, Gregory A. Sotzing, Sergio Granados-Focil and Rajeswari M. Kasi
Journal of Materials Chemistry A 2015 - vol. 3(Issue 2) pp:NaN408-408
Publication Date(Web):2014/09/29
DOI:10.1039/C4TC01702A
We examine the influence of confining gold nanoparticles on the overall nanoscale morphology, mechanical and electrochemical properties of nanocomposite ion gels. Stimuli-responsive ion gels are generated via the synthesis of gold nanoparticles (AuNPs) within a thiol-functionalized liquid crystalline brush-like block copolymer (LCBBC) and subsequent gelation in ionic liquids. AuNPs are prepared by in situ reduction of the gold ions and stabilized by direct anchoring through coordination bonds with the thiol-functionalized LCBBC. The resulting LCBBC/AuNP nanocomposite comprises a hierarchical structure in which polymer-coated AuNPs are dispersed in a microsegregated LCBBC matrix that further contains both liquid crystalline (LC) and block copolymer ordering. More importantly, this LCBBC/AuNP nanocomposite is solubilized in an ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate, to form a nanocomposite ion gel. At 5 wt% concentration, LCBBC/AuNP nanocomposite ion-gel exhibits interesting characteristics including excellent mechanical strength (∼103 Pa), good optical properties with higher ionic conductivity (∼10−2 S cm−1) and long-term electrochemical stability over a larger potential range compared to the plain LCBBC ion gel. Thus, nanocomposite ion gels present tunable optical, thermal and mechanical properties by virtue of their polymer architecture, morphology and functionality. These are versatile and modular hybrid materials to design nanocomposite ion gels with multiple functionalities for applications in electrochemical devices, photonics, and opto-electronics.
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