Abstract

We analyse the possibility of the application of the statistical-mechanical approaches developed in the modern theory of associative fluids for the description of self-assembly phenomena of surfactant molecules in aqueous solutions [1]. In developed theoretical formalism, the potentials of intermolecular interactions are split into three parts. One of them is the short-range repulsive part responsible for excluded volume effects by molecules. The second one is the short-range strongly attractive part responsible for different clusterization effects, including self-assembly phenomena. The third part is long-range and responsible for the screening and renormalization phenomena. The specificity of the developed approach are connected with the application of the activity diagram expansions for the description of the short-range attractive part of interactions and the density diagram expansions for the description of the last two parts of interactions. Classification and reduction of the obtained diagrams in such expansions leads to the multidensity formalism, whose specificity strongly depends on types of described clusterization phenomena.

In this report special attention is focused on the application of the developed approach for the description of solubilization of biological molecules in reverse micellar systems and the study of biomolecules’ influence on the properties of considered systems. As an example, we consider solubilization of cytochrome-c in water in oil reverse micellar systems. For the explanation and the treatment of cytochrome-c influence on the properties of considered micellar systems, a pairing sticky hard sphere model was introduced [2]. In this approach, the empty micelles are described by the sticky hard sphere model, and the presence of cytochrome-c is represented by an additional attractive potential characterized by an association parameter that leads to the pair formation of micelles. This association parameter was determined by fitting the experimental structure factors obtained by SAXS measurements. From this parameter the decrease in the percolation threshold has been estimated, and the change in the critical parameters of liquid–liquid phase transition, induced by cytochrome-c, was interpreted. As the second example, we consider the solubilization of mRNA in water in reverse wormlike micellar systems with lipid covering. The structure properties of the considered system are described in the framework of the analytical treatment of the fused hard-sphere chain model [3] with a small modification for direct inclusion of micellar resistance length. It is shown that the influence of mRNA leads to an increase in the rigidity of micelles.

References

[1] I. Yukhnovskii, M. Holovko. Statistical Theory of Classical Equilibrium Systems. Kyiv, Akademperiodyka, 2025.

[2] G. Cassin, Yu. Duda, M. Holovko, J. P. Badiali, M. P. Pileni. J. Chem. Phys., 107 (1997), 2683.

[3] Yu. Duda, E. Vakarin, Yu. Kalyuzhnyi, M. Holovko. Physica, A 245 (1997), 393.