The solvent effect on the fluorescence and light absorption of riboflavin and lumiflavin
Central Research Institute of Food Industry, Prague, and Institute for Pharmacy and Biochemistry, Prague CzechoslovakiaBiochimica et Biophysica Acta (BBA) - Biophysics including Photosynthesis 05/1965; 102(1):289-300. DOI: 10.1016/0926-6585(65)90221-9
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.
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ABSTRACT: The nature of the intramolecular complex of flavin-adenine dinucleotide and the electronic structure of the isoalloxazine chromophore have been investigated using circular dichroism techniques. Seven circular dichroism extrema which are clearly visible in the spectra of flavin mononucleotide and riboflavin at about 450, 370, 340, 307, 265, 235, and 220 mμ are remarkably altered in the interacted state of flavin-adenine dinucleotide. The presence of reciprocal relations in the circular dichroism spectra of flavin-adenine dinucleotide, demonstrated by solvent, pH, and temperature studies, gives strong evidence that the interacted state is substantially populated at low temperature in aqueous solution. The interbase coupling of several sets of electronic transitions gives rise to regions wherein pairs of circular dichroism bands of opposite sign and almost equal rotational strengths are found. These results are found to be in qualitative accord with recent theoretical studies of the electronic structure of the adenine and isoalloxazine chromophores. A stacked conformation consistent with the analysis and based on the calculations of Song is included for the interacted state of flavinadenine dinucleotide.
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ABSTRACT: Abstract— A detailed in vitro study was made of the flavin sensitized photoinactivation of indoleacetic acid, using primarily riboflavin as sensitizer. The dependence of the quantum yield on reactant concentrations, pH, presence of oxygen, viscosity, temperature, KI concentration, and solvent was determined. The involvement of a limiting dark reaction was demonstrated, using an intermittent light technique. The results are consistent with a mechanism involving a metastable state of riboflavin as the photochemically reactive species. The calculated rate constant for intersystem crossing to this state was found to be 2.5 times 108/sec. Riboflavin, in the metastable state, is believed to oxidize indoleacetic acid to indolealdehyde, with subsequent recovery of riboflavin by autoxidation. The maximum quantum yield of the photoinactivation of IAA is 0.71, indicating a highly efficient process, approaching 100% when energy loss due to riboflavin fluorescence is taken into account. Both carotenoids and pure chlorophyll-a were found to be inactive as sensitizers.
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