SCL Seminar by Natasa Adzic

Scientific Computing Laboratory seminar will be held on Thursday, 6 October 2016 at 14:00 in the library reading room “Dr. Dragan Popović" of the Institute of Physics Belgrade.

The talk title:

"Phenomenology of electrostatic interactions in protein physics"

The talk will be given by Dr. Nataša Adžić from Jožef Stefan Institute, Ljubljana, Slovenia.

Abstract of the talk:

In the world of proteins one can find exotic electrostatic phenomena such as long- ranged attraction between two electro-neutral protein particles in an aqueous solution, stemming from thermal charge fluctuations of dissociable charge groups on their surface. It was first observed by Kirkwood and Schumaker, half a century ago, who described it in the framework of statistical mechanical perturbation  theory and showed that this interaction scales different from standard van der Waals interaction [1,2]. Inspired by the work of Kirkwood and Shumaker, we were investigating the interaction that they had proposed in a more general theoretic framework, obtaining the results also valid in the regimes where the original derivation fails. The general idea was to broaden the existing modern field-theoretic approach to the statistical mechanics of Coulomb fluid [3], by including within this framework the concept of charge regulation in the form of an additional field-depended general surface free energy. Charge regulation implies that the effective charge on a macroion, e.g. protein surface, responds to the local solution conditions, such as local pH, local electrostatic potential, salt concentration, dielectric constant variation and most importantly the presence of other vicinal charged groups. Although this is an old concept, modern theories of electrostatic interaction beetween macroions immersed in Coulomb fluids mostly deal with constant surface charge of a macroion, bypassing the complications introduced by charge regulation. We present a theoretical framework that allows to consistently generalize the ideas of Kirkwood and Shumaker, or indeed of any electrostatic interaction that includes charge regulation, in such a way that one can use advanced concepts and methods of the Coulomb fluid statistical mechanics in order to analyze its salient features in various regions of the parameter space [4,5,6].

[1] J. Kirkwood and J.B. Shumaker, Proc. Natl. Acad. Sci. USA 38 855 (1952).
[2] J. Kirkwood and J.B. Shumaker, Proc. Natl. Acad. Sci. USA 38 863 (1952).
[3] A. Naji, M. Kanduc, J. Forsman, and R. Podgornik, J. Chem. Phys. 139, 150901 (2013).
[4] N. Adžic and R. Podgornik, Euro. Phys. J. E 37, 49 (2014).
[5] N. Adžic and R. Podgornik, Phys. Rev. E 91, 022715 (2015).
[6] N. Adžic and R. Podgornik, J. Chem. Phys. 144, 214901 (2016).