Dimethyl
sulfoxide (DMSO), a polar solvent molecule, is used in
a wide range of therapeutic and pharmacological applications. Different
intermolecular interactions, such as dimerization and hydrogen bonding
with water, are crucial to understanding the role of DMSO in applications.
Herein, we study DMSO in various solvation environments to decipher
the environment-dependent dimerization and hydrogen-bonding propensity.
We use a combination of infrared spectroscopy, quantum mechanical
calculations, and molecular dynamics simulations to reach our conclusions.
Although DMSO can exist in a dynamic equilibrium between monomers
and dimers, our results show that the relative intensity of the SO
stretch and the CH3 rocking modes is a spectroscopic indicator
of the extent of DMSO dimerization in solution. The dimerization (self-association)
is seen to be maximum in neat DMSO. When dissolved in different solvents,
the dimerization propensity decreases with increasing solvent polarity.
In the presence of a protic solvent, such as water, DMSO forms a hydrogen
bond with the solvent molecules, thereby reducing the extent of dimerization.
Further, we estimate the hydrogen-bond occupancy of DMSO. Our results
show that DMSO predominantly exists as doubly hydrogen-bonded in water.