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Ultrafast dynamics at the lipid-water interface: DMSO modulates H-bond lifetimes.

R. Venkatraman,Carlos R. Baiz

Published 2020 in Langmuir

ABSTRACT

Dimethyl sulfoxide (DMSO) is a common cosolvent and cryopreservation agent used to freeze cells and tissues. DMSO alters the H-bond structure of water, but its interactions with biomolecules, and specifically with biological interfaces, remain poorly understood. Here we investigate the effects of DMSO on the H-bond dynamics at the lipid-water interface using a combination of ultrafast two-dimensional (2D IR) infrared spectroscopy and molecular dynamics simulations. Ester carbonyl absorption spectra show that DMSO dehydrates the interface, and simulations show that area-per-lipid is decreased. Ultrafast 2D IR spectra measure the timescales of frequency fluctuations at the ester carbonyl positions located precisely between the hydrophobic and hydrophilic regions of the membrane. 2D IR measurements show that low DMSO concentrations (<10 mol%) induce ~40% faster H-bond dynamics compared to pure water, whereas increased concentrations (>10-20 mol%) once again slow down the dynamics. This slow-fast-slow trend is described in terms of two different solvation regimes. Below 10 mol% DMSO weakens the interfacial H-bond, leading to faster "bulk-like" dynamics, whereas above 10 mol% water molecules become "trapped" as the H-bond networks becoming disrupted by the H-bond donor/acceptor imbalance at the interface. These studies are an important step towards characterizing the environments around lipid membranes, which are essential to numerous biological processes.

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