Understanding DMSO/Water Interactions
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Dimethyl sulfoxide (DMSO) is a commonly used cosolvent in many laboratories, as it has the ability to disrupt the hydrogen bonding network of water and serve as a useful cryoprotectant for biological systems. In recent years, there has been a growing movement to study organ preservation in an attempt to vitrify organs and extend their ex-vivo lifetimes. This ability would dramatically impact the organ waitlist and potentially save a countless number of patients every year. DMSO has been widely studied as a cryoprotectant since it can depress the freezing point of water to -70 C, but it has been shown to be toxic on living systems at high concentrations. There is evidence that cryoprotectants modify the hydrogen bonding environment of water and de-stabilize proteins and lipid membranes. Insight into the details of the DMSO/water hydrogen bonding process could have far reaching consequences and lead to breakthroughs in organ preservation experiements, but until now the exact DMSO/water hydrogen bonding interactions have not been fully determined. In this research, infrared absorption spectroscopy of the S=O stretch (in the 900:1100 wavenumber region) was performed alongside quantum mechanical calculations to directly quantify hydrogen bonding populations in DMSO/water binary mixtures. Four distinct populations of DMSO species were found in a range of concentrations: self-associated (aggregated), free (monomer), singly hydrogen-bonded, and doubly hydrogen-bonded. The hydrogen bond making and breaking process between DMSO and water can be described with a "step-in" mechanism that describes populations shifts at different concentrations and explains the process in which DMSO interacts with water. These results signify the first thorough quantification of hydrogen bond populations in DMSO/water mixtures and are a vital step towards understanding the dynamics of biomolecules. This study provides a molecular explanation of empirically known phenomena and paves the field for future research in the investigation of biomolecules in complex environments.