engleski

The structuring in the aqueous trifluoroethanol mixture

Aqueous mixtures of amphiphiles display a rich variety of molecular self-assembly, from defined objects such as micelles in micro-emulsions to micro-heterogeneity in molecular liquids. 2, 2, 2- trifluoroethanol (TFE), a flourinated mono-ol, is an example of a such an amphiphile. Its aqueous mixture is relevant in the biological context, as TFE-water mixtures are known for promoting or inducing the regular secondary structuring in peptides and proteins [1] and are often used in CD and liquid NMR experiments. On the molecular scale, aqueous TFE mixtures are micro- heterogenous, as witnessed by scattering experiments [2]. This particular type of microheterogenous organization may also contribute in promoting the regular structuring in the solvation process of a peptide. For example, at around 40v/v concentration of TFE - where the microheterogeneity shows the strongest signals - the transition from unfolded to folded protein states is also observed [3]. In this work, we aim at characterizing the structuring in TFE-water mixtures using computer simulations. Since recent studies have shown the issues in achieving correct mixing of the TFE and water [4], a lot of consideration was put into the choice of the force field models, the system sizes and simulation times. By calculating static site-site properties, we track the way the mixture evolves with the change in the molar fraction of the co-solvents. The self-association, induced by self H-bonding, and cross-species associations due to the effect of solvent are particularly distinguished. Oftentimes in the literature, the term "clusters" is used for both cases, which hides the fact that these structures are due to different mechanisms of associations. We also present thermodynamic properties, such as enthalpies and entropies of mixing and concentration fluctuations which again highlight the complex nature of the TFE-water mixture. [1] Goodman M, Listowsky I (1962) Conformational Aspects of Synthetic Polypeptides. VI. Hypochromic Spectral Studies of Oligo-γ - Methyl-L-Glutamate Peptides. J. Am. Chem. Soc. 84:3770 [2] Hong DP, Hoshino M, Kuboi R, Goto Y (1999) Clustering of Fluorine-Substituted Alcohols as a Factor Responsible for Their Marked Effects on Proteins and Peptides. J. Am. Chem. Soc. 121:8427 [3] Gast K, Zirwer D, Müller-Frohne M, Damaschun G (1999) Trifluoroethanol-induced conformational transitions of proteins: Insights gained from the differences between ribonuclease A. Protein Science, Cold Spring Harbor Laboratory Press 8:625 [4] Gerig J (2014) Toward a Molecular Dynamics Force Field for Simulation of 40% Trifluoroethanol-Water. J. Phys. Chem. B 118:1471

molecular-dynamics ; binary-mixtures ; water-alcohol ; water-TFE

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