Unprecedented Scissor Effect of Macromolecular Cross-linkers on the Glass Transition Temperature of Poly(N-vinylimidazole), Crystallinity Suppression of Poly(tetrahydrofuran) and Molecular Mobility by Solid State NMR in Poly(N-vinylimidazole)-l-poly(tetrahydrofuran) Conetworks

Unexpected correlations have been found between structural parameters and glass transition temperatures (Tg) of poly(N-vinylimidazole) (PVIm) and crystallinity of poly(tetrahydrofuran) (PTHF) in a series of novel, unique PVIm-l-PTHF amphiphilic conetworks synthesized in broad composition ranges via free radical copolymerisation of VIm and semicrystalline, methacrylate-telechelic PTHF macromolecular cross-linkers with varying Mn from 2170 to 10 000 g mol−1. Differential scanning calorimetry (DSC) investigations revealed microphase separation between the covalently bonded PVIm and PTHF components, that is two distinct Tgs corresponding to the respective polymers (PVIm and PTHF) were obtained in these optically clear, transparent materials. Complete microphase separation, i.e. absence of mixed phases, was also confirmed by solid state NMR measurements. The Tg of the PVIm phase significantly decreases with increasing PTHF content, and Fox–Flory type correlation was surprisingly found between the Tg of PVIm and its Mc (average molecular weight between cross-links). This striking finding indicates a unique, unpredicted scissor effect of the macromolecular PTHF cross-linker in these materials, i.e. with respect to glass transition, PVIm behaves as individual chains between cross-links. The molecular mobility in the PVIm chain segments obtained by solid state NMR investigations shows a similar trend as a function of Mc. In the DSC thermograms, the semicrystalline PTHF has a sharp endothermic melting peak (Tm) indicating partial crystallisation of this polymer. It was found that the Tm and the crystalline fraction (Xc) of the PTHF phase are suppressed by even a minimal content of PVIm phase in the conetworks. Even complete diminishing of Xc occurs in conetworks with lower than 40 wt% PTHF of the lowest Mn (2170 g mol−1). Unexpectedly, Tm linearly decreases with Mc in conetworks with constant Mn of PTHF. These data indicate that the decrease of both Tm and Xc of PTHF is not only composition dependent, but the MW of the macromolecular PTHF cross-linker and the Mc of the PVIm component also have effects on these parameters. These results also indicate that chemical bonding of polymer chains in conetworks yields novel materials with unprecedented property variation. This provides unique opportunities for fine tuning of the investigated fundamental material properties, i.e. Tg, Tm and Xc, within certain ranges in the novel PVIm-l-PTHF amphiphilic conetworks by selecting the proper synthesis parameters, that is, composition and MW of the telechelic PTHF macromonomer cross-linker

Acrylic polyampholyte solutions for protein separations

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1994.Includes bibliographical references.by Costas S. Patrickios.Ph.D

Application of the functional renormalization group method to classical free energy models

A simple functional renormalization group method is presented to correct the behavior of classical free energy models near the critical point. This approach is applied to the Soave-Redlich-Kwong equation of state to illustrate its ability to better reproduce the phase behavior of simple fluids and to understand the influence of its parameters on the shape of the vapor-liquid phase diagram. The method is then extended to account for the correlations induced by intramolecular bonds. It is then applied to a first order thermodynamic perturbation theory for chain fluids to examine fluids composed of linearly bonded Lennard-Jones atoms. Unlike previous approaches for applying renormalization group corrections to chain fluids, this is able to accurately reproduce the critical point without predicting an overly flat liquid-vapor coexistence region

Thermally Responsive Amphiphilic Conetworks and Gels Based on Poly(N‑isopropylacrylamide) and Polyisobutylene

Novel amphiphilic conetworks (APCN) consisting of thermoresponsive poly(N-isoproplyacrylamide) (PNiPAAm) cross-linked by hydrophobic methacrylate-telechelic polyisobutylene (MA-PIB-MA) were successfully synthesized in a broad composition range. The resulting PNiPAAm-l-PIB conetworks (“l” stands for “linked by”) were obtained by radical copolymerization of NiPAAm with MA-PIB-MA in tetrahydrofuran, a cosolvent for all the components. Low amounts of extractables substantiated efficient network formation. The composition dependent two glass transition temperatures (Tg) by DSC analysis indicate microphase separation of the cross-linked components without mixed phases. It was found that the PNiPAAm-l-PIB conetworks are uniformly swellable in both water and n-hexane; i.e., these new materials behave either as hydrogels or as hydrophobic gels in aqueous or nonpolar media, respectively. The uniform swelling in both polar and nonpolar solutes indicates cocontinuous (bicontinuous) phase morphology. The equilibrium swelling degrees (R) depend on composition, that is, the higher the PIB content, the lower the R in water and the higher in n-hexane. The PNiPAAm phase keeps its thermoresponsive behavior in the conetworks as shown by significant decrease of the swelling degree in water between 20 and 35 °C. The lower critical solubility temperature (LCST) values determined by DSC are found to decrease from 34.1 °C (for the pure PNiPAAm homopolymer) to the range of 25–28 °C in the conetworks, and the extent of the LCST decrease is proportional with the PIB content. Deswelling-swelling, i.e., heating–cooling, cycle indicates insignificant hysteresis in these new thermoresponsive materials. This indicates that PNiPAAm-l-PIB conetworks with predetermined and thermoresponsive swelling behavior can be designed and utilized in several advanced applications on the basis of results obtained in the course of this study

The Isoelectric Region of Proteins: A Systematic Analysis

Background: Binding of proteins in ion exchange chromatography is dominated by electrostatic interactions and can be tuned by adjusting pH and ionic strength of the solvent. Therefore, the isoelectric region (IER), the pH region of almost zero charge near the pI, has been used to predict the binding properties of proteins. Principal findings: Usually the IER is small and binding and elution is carried out at pH values near to the pI. However, some proteins with an extended IER have been shown to bind and elute far away from its pI. To analyze factors that mediate the size of the IER and to identify proteins with an extended IER, two protein families consisting of more than 7000 proteins were systematically investigated. Most proteins were found to have a small IER and thus are expected to bind or elute near to their pI, while only a small fraction of less than 2 % had a large IER. Conclusions: Only four factors, the number of histidines, the pI, the number of titratable amino acids and the ratio of acidic to basic residues, are sufficient to reliably classify proteins by their IER based on their sequence only, and thus to predict their binding and elution behaviour in ion exchange chromatography

Calibrative approaches to protein solubility modeling of a mutant series using physicochemical descriptors

A set of physicochemical properties describing a protein of known structure is employed for a calibrative approach to protein solubility. Common hydrodynamic and electrophoretic properties routinely measured in the bio-analytical laboratory such as zeta potential, dipole moment, the second osmotic virial coefficient are first estimated in silico as a function a pH and solution ionic strength starting with the protein crystal structure. The utility of these descriptors in understanding the solubility of a series of ribonuclease Sa mutants is investigated. A simple two parameter model was trained using solubility data of the wild type protein measured at a restricted number of solution pHs. Solubility estimates of the mutants demonstrate that zeta potential and dipole moment may be used to rationalize solubility trends over a wide pH range. Additionally a calibrative model based on the protein’s second osmotic virial coefficient, B22 was developed. A modified DVLO type potential along with a simplified representation of the protein allowed for efficient computation of the second viral coefficient. The standard error of prediction for both models was on the order of 0.3 log S units. These results are very encouraging and demonstrate that these models may be trained with a small number of samples and employed extrapolatively for estimating mutant solubilities

Protein surface functionalisation as a general strategy for facilitating biomimetic mineralisation of ZIF-8

The durability of enzymes in harsh conditions can be enhanced by encapsulation within metal-organic frameworks (MOFs) via a process called biomimetic mineralisation. Herein we show that the surface charge and chemistry of a protein determines its ability to seed MOF growth. We demonstrate that chemical modification of amino acids on the protein surface is an effective method for systematically controlling biomimetic mineralisation by zeolitic imidazolate framework-8 (ZIF-8). Reaction of surface lysine residues with succinic (or acetic) anhydride facilitates biomimetic mineralisation by increasing the surface negative charge, whereas reaction of surface carboxylate moieties with ethylenediamine affords a more positively charged protein and hinders the process. Moreover, computational studies confirm that the surface electrostatic potential of a protein is a good indicator of its ability to induce biomimetic mineralisation. This study highlights the important role played by protein surface chemistry in encapsulation and outlines a general method for facilitating the biomimetic mineralisation of proteins.Natasha K. Maddigan, Andrew Tarzia, David M. Huang, Christopher J. Sumby, Stephen G. Bell, Paolo Falcaro and Christian. J. Doona

Association behavior of thermo-responsive block copolymers based on poly(vinyl ethers)

Thermo-sensitive nanosized structures have been prepared in water from poly(methyl vinyl ether)-block-poly(isobutyl vinyl ether) (PMVE-b-PIBVE) block copolymers. The composition and the architecture (diblock and triblock architectures) of the PMVE-b-PIBVE copolymers have been varied. The investigated copolymers had an asymmetric composition with a major PMVE block, While the PIBVE blocks are hydrophobic, the PMVE blocks are hydrophilic at room temperature and become hydrophobic above their demixing temperature (around 36 degrees C) as a result of the lower critical solution temperature (LCST) behavior. At room temperature, the amphiphilic copolymers aggregate in water above a critical micelle concentration, which has been experimentally measured by hydrophobic dye solubilization. The hydrodynamic diameter of the structures formed above the cmc has been measured by dynamic light scattering (DLS) while their morphology has been studied by transmission electron microscopy (TEM). H-1 NMR measurements in D2O at room temperature reveal that the aggregates contain PIBVE insoluble regions surrounded by solvated PMVE chains. These investigations have shown that polydisperse spherical micelles are formed for asymmetric PMVE-b-PIBVE copolymers containing at least 9 IBVE units. For copolymers containing less IBVE units, loose aggregates are formed. Finally, the thermo-responsive, reversible properties of these structures have been investigated. Above the cloud point of the copolymers, the loose aggregates precipitate while the micelles form large spherical structures