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

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

Equation of state for star polymers in good solvents

We develop a free-energy model for star polymers in good solvents that accurately describes concentrated polymer solutions and displays the correct universal scaling behavior, in the limit of infinite molecular weight, for dilute and semidilute polymer concentrations.The architecture of the polymer molecules enters the model through the value of the second virial coefficient and the rescaled penetration function <(Psi)over bar>, the ratio of the penetration function Psi(f)to its asymptotic, infinite-molecular-weight value Psi*(f), wheref is the number of arms on the star polymer. The direction of approach of the equation of state to the universal, infinite-molecular-weight scaling limit depends on the relative magnitude of <(Psi)over bar>.For <(Psi)over bar>>1, the scaling equation of state is approached from "above," while for <(Psi)over bar><1, the scaling equation of state is approached from "below." We also perform new Monte Carlo simulations for the pressure and mean-square radius of gyration of star polymers composed of tangent-hard-spheres. The theory compares well with the Monte Carlo simulation data for the equation of state.(C) 2000 American Institute of Physics. [S0021-9606(00)50637-0]

Synthesis and characterization of novel networks with nano-engineered structures: cross-linked star homopolymers

Group transfer polymerization was used for the one-pot preparation of a network structure comprising cross-linked star homopolymers. The structure contains many dangling chains (constituting the arms of the primary stars), whose number is approximately equal to the number of the elastic chains. 2-(Dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate were used as the monomer and cross-linker, respectively. The synthesis involved a four-step sequential addition of monomer/cross-linker/monomer/cross-linker, which produced linear polymer, “arm-first” star polymer, “in-out” star polymer, and cross-linked star polymer network, respectively. The products of the first three steps of the synthesis were characterized in terms of their relative molecular weights by gel permeation chromatography, and in terms of their absolute molecular weights by static light scattering, which indicated that the number of arms in the “arm-first” stars is about 50, whereas that in the “in-out” stars is about 100. Seven networks were prepared in total, covering a range of degrees of polymerization of the primary and the secondary arms. The degrees of swelling of all the networks were measured in water and were found to increase by lowering the pH, a result of the ionization of the tertiary amine group of the monomer repeat unit

Synthesis and characterization of novel networks with nano-engineered structures: Cross-linked star homopolymers

Group transfer polymerization was used for the one-pot preparation of a network structure comprising cross-linked star homopolymers. The structure contains many dangling chains (constituting the arms of the primary stars), whose number is approximately equal to the number of the elastic chains. 2-(Dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate were used as the monomer and cross-linker, respectively. The synthesis involved a four-step sequential addition of monomer/cross-linker/monomer/cross-linker, which produced linear polymer, “arm-first” star polymer, “in-out” star polymer, and cross-linked star polymer network, respectively. The products of the first three steps of the synthesis were characterized in terms of their relative molecular weights by gel permeation chromatography, and in terms of their absolute molecular weights by static light scattering, which indicated that the number of arms in the “arm-first” stars is about 50, whereas that in the “in-out” stars is about 100. Seven networks were prepared in total, covering a range of degrees of polymerization of the primary and the secondary arms. The degrees of swelling of all the networks were measured in water and were found to increase by lowering the pH, a result of the ionization of the tertiary amine group of the monomer repeat unit