Title: Fluid of fused spheres as a model for protein solution
Author(s):

	M. Kastelic (Faculty of Chemistry and Chemical Technology, University of Ljubljana, Vecna pot 113, 1000 Ljubljana, Slovenia) ,
	Yu.V. Kalyuzhnyi (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii St., 79011 Lviv, Ukraine) ,
	V. Vlachy (Faculty of Chemistry and Chemical Technology, University of Ljubljana, Vecna pot 113, 1000 Ljubljana, Slovenia)

In this work we examine thermodynamics of fluid with "molecules" represented by two fused hard spheres, decorated by the attractive square-well sites. Interactions between these sites are of short-range and cause association between the fused-sphere particles. The model can be used to study the non-spherical (or dimerized) proteins in solution. Thermodynamic quantities of the system are calculated using a modification of Wertheim's thermodynamic perturbation theory and the results compared with new Monte Carlo simulations under isobaric-isothermal conditions. In particular, we are interested in the liquid-liquid phase separation in such systems. The model fluid serves to evaluate the effect of the shape of the molecules, changing from spherical to more elongated (two fused spheres) ones. The results indicate that the effect of the non-spherical shape is to reduce the critical density and temperature. This finding is consistent with experimental observations for the antibodies of non-spherical shape.

Key words: non-spherical proteins, liquid-liquid transition, directional forces, aggregation, thermodynamic perturbation theory
PACS: 87.15.A-, 87.15.ad, 87.15.km, 87.15.nr, 82.60.Lf, 64.70.Ja

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