Thermodynamic analysis of inverted bifurcation

We present a thermodynamic analysis of inverted bifurcation in binary mixtures heated from below. From this analysis it follows that an inverted bifurcation is caused by the competition between a stabilizing effect with a long relaxation time and a destabilizing effect with a short relaxation time. These conditions are precisely the same as those that give rise to overstability. This might explain why overstability and inverted bifurcation occur in the same systems

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

Pair interaction and phase separation in mixtures of colloids and excluded volume polymers

The interactions in polymer-colloid mixtures and their phase stability are calculated using the adsorption method. Starting from appropriate expressions for the correlation length and the osmotic pressure of a polymer solution in the excluded volume interaction limit, this method allows computation of the potential between two plates, two spheres and between a sphere and a plate. The results are in close agreement with computer simulation results. Extended to a many body system of colloids and polymers, the same approach allows one to calculate the thermodynamic properties and phase behavior. Results are presented for the phase behavior of polymer-sphere and polymer-platelet mixtures. The agreement with experimental data is satisfactory and helps to better explain the polymer-colloid phase behavior