Ion-Specific Potential of Mean Force Between twoAqueous Proteins

摘要

There is a considerable effort in the literature trying to calculate the mean force betweenglobular proteins (and colloidal particles). To this purpose, we used here the ion-specificPoisson-Boltzmann (PB) equation that presents good results of ionic concentrationprofiles around a macroion, especially for salt solutions containing monovalent ions.The ion-specific PB equation includes not only electrostatic interactions but alsodispersion potentials, originated from polarizabilities of ions and proteins. This enablesus to predict ion-specific properties of colloidal systems. Results are in agreement withthe experimental observed Hofmeister series. The main contribution of this paper is theuse of a differential approach to calculate the mean force between aqueous proteins andcolloidal particles instead of the classical quadrature approach. The integral expressionsneeded to calculate the mean force, potential of mean force and second virialcoefficients have been avoided using this new numerical procedure. These integralswere transformed in a set of first order partial differential equations solvedsimultaneously with the ion-specific PB equation. Resulted expressions were written inbispherical coordinates, and then numerically solved through finite volume method.This simultaneous approach presents more accuracy in the calculation of the mean forcein comparison with the classical approach, where the potential profile is obtained bysolving the PB equation, and mean force is calculated afterwards. Importantthermodynamic properties are obtained from the mean force (and consequently, fromthe potential of mean force), e.g., osmotic second virial coefficients and phase diagrams.These thermodynamic properties are related to protein aggregation, essential inbiotechnology and pharmaceutical industries.