MOLECULAR-DYNAMICS WITH DIMETHYL-SULFOXIDE AS A SOLVENT - CONFORMATION OF A CYCLIC HEXAPEPTIDE

Molecular dynamics simulations including dimethyl sulfoxide (DMSO) as solvent are reported. Simulations of the pure solvent produce good agreement with the X-ray diffraction data of liquid DMSO. Simulations of the cyclic hexapeptide cyclo[-D-Ala-Phe2-Val-Lys-Trp-Phe6-] in the presence of DMSO have been carried out. The conformation of the peptide in DMSO has been well refined from NMR studies and is used as a model system. The solvent forms hydrogen bonds with backbone amide protons and the Lys side chain. However, besides this small amount of ordering close to the peptide, the solvent is randomly distributed. The radial distribution of the solvent atoms quickly approaches that of pure DMSO. The effects of the solvent on the conformational preferences of the cyclic hexapeptide are discussed.