Ion-specific thermodynamical properties of aqueous proteins

Abstract

Ion-specific interactions between two colloidal particles are calculated using a modified Poisson-Boltzmann (PB) equation and Monte Carlo (MC) simulations. PB equations present good results of ionic concentration profiles around a macroion, especially for salt solutions containing monovalent ions. These equations include not only electrostatic interactions, but also dispersion potentials originated from polarizabilities of ions and proteins. This enables us to predict ion-specific properties of colloidal systems. We compared results obtained from the modified PB equation with those from MC simulations and integral equations. Phase diagrams and osmotic second virial coefficients are also presented for different salt solutions at different pH and ionic strengths, in agreement with the experimental results observed Hofmeister effects. In order to include the water structure and hydration effect, we have used an effective interaction obtained from molecular dynamics of each ion and a hydrophobic surface combined with PB equation. The method has been proved to be efficient and suitable for describing phenomena where the water structure close to the interface plays an essential role. Important thermodynamic properties related to protein aggregation, essential in biotechnology and pharmaceutical industries, can be obtained from the method shown here.

Consequences of shifted ion adsorption equilibria due to nonelectrostatic interaction potentials in electrical double layers

“…In many studies in which nonelectrostatic interaction potentials have been included and typically modelled with ionic dispersion potentials [20][21][22][23][24][25][26][32][33][34][35], P NES,cs was not included in the total pressure. It has previously been noted [22] that indeed the nonelectrostatic addition causes a constant shift in the adsorption isotherms, which can trivially be accommodated for in the CR case by shifting the effective pK value.…”

Effect of Nonelectrostatic Ion Interactions on Surface Forces Involving Ion Adsorption Equilibria

“…This was done either by only applying dispersion to the indifferent salt ions in solution, in which case ionic dispersion interactions only affected the physisorption free energy. That condition gives a consistent treatment for the case of constant charge, − but not for systems modeled under constant potential , or charge regulation. − Even where dispersion was applied to the potential determining ion (H + ), such that the adsorption isotherms were correctly described, the additional chemisorption force component was still neglected. − …”