| Popis: |
Changes in fluorescence intensity of riboflavin and lumiflavin with the nature of the solvent were studied. A series of mixtures of ethanol, acetone and dioxane with water were used as solvents. Changes in absorption and fluorescence spectra expressed as transition energies, apparent absorption coefficients and quantum yields of fluorescence were correlated with each other, with dielectric constants and with the Z-values, expressing solvent polarity of the solvent mixtures used. Rough linearity was observed for all parameters except of dielectric constants for flavin solutions containing no more than 90% of organic solvent. In riboflavin solutions containing higher concentrations of organic solvents deviations from linearity were observed. The possibility is discussed, that in such higher concentrations of organic solvents relative measurements accepted do not adequately reflect changes in flavin molecules. In solvent mixtures of lowest polarity riboflavin and, to a greater extent lumiflavin, were photodecomposed much faster than in aqueous solutions. It is suggested that the decrease of the stability of flavin molecules is caused by lowering of the degree of association with water molecules, and by a secondary solvent polarity effect on the electron system of light-excited flavin molecules. |
