Preferential Solvation of Triglycine in Aqueous Urea: An Open Boundary Simulation Approach

Solvation free energies of peptides in water decrease with increasing urea concentration and therefore lead to increased solubility. In this work, we study the solvation thermodynamics of a triglycine in aqueous urea solutions at room temperature T = 300 K. We perform our analysis within the framework of the Kirkwood-Buff theory of liquid mixtures, developed for open systems. For this purpose, we use a recently proposed approach to study liquid mixtures within an "effective" open boundary simulation scheme (AdResS). We couple a small open boundary all-atom (explicit) region to a much larger coarse-grained particle reservoir. This coupling allows the free exchange of particles in thermodynamic equilibrium. Our approach preserves correct particle fluctuations that are important for studying the concentration driven conformational transition of (bio)molecules.