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Adsorption of three-domain antifreeze proteins on ice: a study using LGMMAS theory and Monte Carlo simulations

Abstract

In the present work, the adsorption of three-domain antifreeze proteins on ice is studied by combining a statistical thermodynamics based-theory and Monte Carlo simulations. The three-domain protein is modeled by a trimer, and the ice surface is represented by a lattice of adsorption sites. The statistical theory, obtained from the exact partition function of non-interacting trimers adsorbed in one dimension and its extension to two dimensions, includes the configuration of the molecule in the adsorbed state, and allows the existence of multiple adsorption states for the protein. We called this theory “lattice-gas model of molecules with multiple adsorption states" (LGMMAS). The main thermodynamics functions (partial and total adsorption isotherms, Helmholtz free energy and configurational entropy) are obtained by solving a non-linear system of j equations, where j is the total number of possible adsorption states of the protein. The theoretical results are contrasted with Monte Carlo simulations, and a modified Langmuir model (MLM) where the arrangement of the adsorption sites in space is immaterial. The formalism introduced here provides exact results in one-dimensional lattices, and offers a very accurate description in two dimensions (2D). In addition, the scheme is capable to predict the proportion between coverage degrees corresponding to different conformations in the same energetic state. In contrast, the MLM does not distinguish between different adsorption states, and shows severe discrepancies with the 2D simulation results. This finding indicates that adsorbate structure and lattice geometry play fundamental roles in determining the statistics of multistate adsorbed molecules, and consequently, must be included in the theory.

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Publication details

The article was received on 27 Sep 2017, accepted on 07 Nov 2017 and first published on 10 Nov 2017


Article type: Paper
DOI: 10.1039/C7CP06618J
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    Adsorption of three-domain antifreeze proteins on ice: a study using LGMMAS theory and Monte Carlo simulations

    J. I. Lopez-Ortiz, P. B. Torres, E. Quiroga, C. F. Narambuena and A. Ramirez-Pastor, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP06618J

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