Negligible Effect on the Structure and Vibrational Spectral Dynamics of Water Molecules Near Hydrophobic Solutes

Biswas, Sohag and Mallik, Bhabani S. (2020) Negligible Effect on the Structure and Vibrational Spectral Dynamics of Water Molecules Near Hydrophobic Solutes. ChemistrySelect, 5 (37). pp. 11549-11559. ISSN 2365-6549

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Abstract

The first principles molecular dynamics simulations were performed to study the structural, dynamical, and spectral properties of water molecules in the vicinity of hydrophobic molecules. A layer-wise distance-dependent angular distribution calculation was performed to understand the effects of neopentane (NEO) and tert-butyl alcohol (TBA) on the orientation profile of water molecules. We found no evidence of an increasing tetrahedral structure of water molecules inside the first solvation shell of NEO and TBA; this indicates the presence of less ordered water molecules inside the solvation shell. The water molecules, however, retained their bulk-like property by accruing three to four hydrogen bonds per water molecule in bulk. The long-lived non-hydrogen-bonded or dangling OH bonds were observed in the hydration shells of both the molecules as compared to the bulk water, where such dangling OH bonds were less. The high peak frequency of dangling OH oscillators in the hydration shell was found to be similar to the previously obtained dangling OH chromophores in experimental and theoretical studies. We also report the rotational dynamics of water molecules. Our calculations suggest that the slowing down of water molecules near the hydrophobic solutes is moderate as compared to that of bulk water due to the lack of hydrogen bond exchangeable partners. Therefore, our results are in complete contrast with the idea of the iceberg of Frank and Evan.

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