Effects of dimethyl sulfoxide on the hydrogen bonding structure and dynamics of aqueous N-methylacetamide solution

Effects of dimethyl-sulfoxide (DMSO) on the hydrogen bonding structure and dynamics in aqueous N-methylacetamide (NMA) solution are investigated by classical molecular dynamics simulations. The modifications of structure and interaction between water and NMA in presence of DMSO molecules are calculated by various site-site radial distribution functions and average interaction energies between these species in the solution. It is observed that the aqueous peptide hydrogen bond interaction is relatively stronger with increasing concentration of DMSO, whereas methyl-methyl interaction between NMA and DMSO decreases significantly. The DMSO molecule prefers to interact with amide-hydrogen of NMA even at lower DMSO concentration. The lifetimes and structural-relaxation times of NMA-water, water-water and DMSO-water hydrogen bonds are found to increase with increasing DMSO concentration in the solution. The slower translational and rotational dynamics of NMA is observed in concentrated DMSO solution due to formation of stronger inter-species hydrogen bonds in the solution.