Nonlinear composition dependence of hydrogen bond lifetime in water-DMSO binary mixtures: The role of hydrophobic interaction

Mondal, S and Bagchi, B (2024) Nonlinear composition dependence of hydrogen bond lifetime in water-DMSO binary mixtures: The role of hydrophobic interaction. In: Journal of Chemical Physics, 161 (2).

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Abstract

The lifetime of a hydrogen bond between water and dimethyl sulfoxide (DMSO) is found to be considerably longer than that between two water molecules in neat water. This is counter-intuitive because the charge on the oxygen in DMSO is considerably less than that in water. Additionally, the strength of the water-dimethyl sulfoxide (w-D) hydrogen bond is found to be strongly composition dependent; the lifetime of the hydrogen bond is ten times larger at 30 than at very low concentrations. Using computer simulations, we perform microscopic structural and dynamic analysis to find that these anomalies arise at least partly from an �action-at-a-distance� effect where the attraction between the hydrophobic methyl groups results in the self-aggregation of DMSO molecules that �cages� both the rotational and linear motions of the molecules involved. This is reflected in the observed strong correlation of the lifetime with the local coordination number of the associated methyl groups. The elongated w-D h-bond lifetime causes a slowdown of collective dynamics and affects the lifetime of the w-w h-bond. This nonlinear feedback mechanism explains the strong composition dependence of viscosity and is anticipated to play a dominant role in many self-assemblies. Furthermore, the w-D hydrogen bond breaking mechanism changes from low to high DMSO concentration, a phenomenon not anticipated a priori. We introduce a new order parameter-based free energy surface of the bond breaking pathway. A two-dimensional transition state rate theory calculation is performed for the lifetime of the w-D h-bond that is found to be semi-quantitatively accurate. © 2024 Author(s).

Item Type:	Journal Article
Publication:	Journal of Chemical Physics
Publisher:	American Institute of Physics
Additional Information:	The copyright for this article belongs to American Institute of Physics.
Keywords:	Binary mixtures; Free energy; Hydrogen bonds; Hydrophobicity; Molecules; Nonlinear feedback; Organic solvents, Bond lifetime; Bond-breaking; Composition dependence; Dynamics analysis; H-bonds; Hydrophobic interactions; Low concentrations; Methyl group; Nonlinear composition; Water molecule, Dimethyl sulfoxide, dimethyl sulfoxide; methyl group, article; computer simulation; controlled study; feedback system; hydrogen bond; lifespan; motion; viscosity; water
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	18 Dec 2024 04:26
Last Modified:	18 Dec 2024 04:26
URI:	http://eprints.iisc.ac.in/id/eprint/85825

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