LASER TEMPERATURE JUMP STUDY OF SOLVENT EFFECTS ON PROFLAVIN STACKING

The Raman laser temperature jump technique has been used to determine rate constants for proflavin dimerization in aqueous solutions of methanol, ethanol, l-propanol, glycerol, and urea. Forward rates for solutions in aqueous ethanol are quantitatively analyzed using a specific solvation model. The reverse rates are characterized by the molecularity of ethanol attack on the dye dimer. Thioninc requires approximately three ethanols to disrupt a dimer, whereas proflavin requires only one. Poor correlations are found between the reverse rates and bulk solvent properties. The results suggest that solvent effects on dye stacking are determined by specific dye-solvent interactions. Comparison with previous results for thionine stacking indicates the detailed electronic structure of the dye determines these interactions, and that solvent-solvent contributions are relatively unimportant. © 1979, American Chemical Society. All rights reserved.