Fluorescence study of the state of tryptophane in aqueous dimethylsulfoxide

The fluorescence spectra of tryptophane were measured in a wide range of concentrations of aqueous dimethylsulfoxide (DMSO) solutions. In solutions with different compositions, tryptophane is surrounded by water molecules alone. This result is in agreement with the known fact of microseparation of aqueous DMSO solutions. Evidently, in a water-DMSO system, the tryptophane molecules are built into water microregions, in which they have a pure aqueous environment and are thus isolated from the nonelectrolyte present in the solution. Based on the experimental data, we determined induced relaxation time of water molecules forming the nearest environment of excited tryptophane (0.59 ns for aqueous tryptophane).