SOLVENT EFFECTS ON THE TAUTOMERIZATION OF 5'-DEOXYPYRIDOXAL - A PHOTOPHYSICAL STUDY

Absorption and fluorescence spectra of 5'-deoxypyridoxal (DPL) in vari ous pure solvents and mixtures were recorded both at room temperature and over the range 10-65-degrees-C. The areas under the absorption ban ds were analyzed to obtain the mole fraction (f(N), f(Z)) of two tauto mers (the zwitterionic, Z, and neutral, N, forms) in the ground state. The following spectral parameters were determined from the fluorescen ce spectra: Stokes shift (DELTAnu), fluorescence quantum yield of the neutral form (Q(N)), fluorescence ratio of the neutral to the zwitteri onic form (phi(N)/phi(Z)) and the rate constant of tautomerization (k( l)) from Z to N in the excited state. Some of these parameters (f(N), DELTAnu, Q(N), k(l)) were found to depend on the proton donor characte r of the solvent, whereas others (phi(N)/phi(Z)) depended on its dipol e moment. Thus, the absorption and fluorescence spectra of DPL allow o ne to obtain information on the polarity and the concentration of -OH groups on its environment.