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 O-H center dot center dot center dot O=S=H-bond and C-H center dot center dot center dot O-w H-bond. However, if the methyl groups in the above ring structure participate in second C-H center dot center dot center dot O-w H-bond, the cooperativity is increased. The second C-H center dot center dot center dot O-w H-bond enhances O-H center dot center dot center dot O--S=H-bond and weakens the first C-H center dot center dot center dot O-w H-bond. (C) 2007 Elsevier B.V. All rights reserved.