Statistical Mechanical Studies of Aqueous solutions and Biomolecular Systems

University dissertation from Department of Theoretical Chemistry, Lund University

Abstract: This thesis is concerned with theoretical studies of aqueous solutions and biomolecular systems. Part of the present work is to understand equilibrium solvent and solute properties, while the other part is to study processes that occur in these solutions. Three points were focused: (a) the study of structure and dynamics of 1M aqueous NaCl electrolyte solution at a molecular level, which revealed particular features of these solutions such as the formation of large clusters; (b) the development of a new simulation algorithm for the Reverse Monte Carlo technique aimed to study aqueous solutions and disordered systems. Results for spherical molecules and liquid water are presented; (c) the study of binding small ions to macromolecules (proteins and micelles). The Tanford-Kirkwood model is critically analysed for models of biomolecules by means of Monte Carlo calculations. Anomalous behaviour found for the binding of ions to macromolecules in the presence of highly charged macroparticles is also reported. And, a titration study is performed to characterize interfacial properties of a prototropic molecule in self-assembled surfactant aggregates. The core of our discussion is based on electrostatic interactions and statistical mechanics. The studied systems were modeled by effective Hamiltonians within the Born-Oppenheimer and McMillan-Mayer model levels. These Hamiltonians were solved by computer simulations (Monte Carlo and Molecular Dynamics), and, in some cases, also by solving the Poisson-Boltzmann equation. Dielectric continuum models are largely used, and a discussion of uniform and non-uniform cases for studies with biomolecules and micellar systems is also included.

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