High-pressure spectroscopic probe of hydrophobic hydration of the methyl groups in dimethyl sulfoxide.

The hydrophobic hydration of dimethylsulfoxide (DMSO)/D[sub 2]O was explored using a combination of the high-pressure method and ab initio calculations. The frequencies of the C-H stretching vibration of DMSO increase as the mole fraction of D[sub 2]O increases, while no appreciable changes in spectral shapes are observed upon dilution. Interestingly, the infrared spectra of DMSO/D[sub 2]O observed under high-pressure exhibits dramatic changes, while the new spectral features locating at ∼2942 and ∼3033 cm[sup -1] appear. The spectral changes were attributed to the combined effect of C-H-O hydrogen bonding between C-H in DMSO and oxygen atom in D[sub 2]O, a phase change, pressure increase, etc. Ab initio calculation results, forecasting the frequency shift of the C-H stretching vibration as C-H-O is interacting via hydrogen bonding, are discussed. The reorganization of the hydrogen-bond network or geometry may be responsible for spectral changes as the pressure was elevated. [ABSTRACT FROM AUTHOR]