Spectroscopic and theoretical evidence for the cooperativity between red-shift hydrogen bond and blue-shift hydrogen bond in DMSO aqueous solutions

The cooperativity between red-shifted hydrogen bond and blue-shifting hydrogen bond in dimethyl sulfoxide aqueous solutions was studied by methods of quantum chemical calculations and infrared spectroscopy. The water molecule plays a different role in two types of hydrogen bonds: proton–donor in red-shifted hydrogen bond and proton–acceptor in blue-shifting hydrogen bond. The cooperativity is not prominent if the ring structure is formed through the OH⋯OS H-bond and CH⋯Ow H-bond. However, if the methyl groups in the above ring structure participate in second CH⋯Ow H-bond, the cooperativity is increased. The second CH⋯Ow H-bond enhances OH⋯OS H-bond and weakens the first CH⋯Ow H-bond.