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Abstract Dimethyl sulfoxide (DMSO) disrupts the hydrogen‐bond networks in water. The widespread use of DMSO as a cosolvent, along with its unusual attributes, have inspired numerous studies. Herein, infrared absorption spectroscopy of the S=O stretching mode combined with molecular dynamics and quantum chemistry models were used to directly quantify DMSO/water hydrogen‐bond populations in binary mixtures. Singly H‐bonded species are dominant at 10 mol %, due to strong DMSO–water interactions. We found an unexpected increase in non‐hydrogen‐bonded DMSO near the eutectic point (ca. 35 mol %) which also correlates with several abnormalities in the bulk solution properties. We find evidence for three distinct regimes: 1) strong DMSO–water interactions (90 mol %). We propose a “step in” mechanism, which involves hydrogen bonding between water and the DMSO aggregate species.
Oh et al. (Thu,) studied this question.