The solvent effect on the fluorescence and light absorption of riboflavin and lumiflavin
ABSTRACT 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.
- SourceAvailable from: Fumio TanakaJournal of Photochemistry and Photobiology A Chemistry 12/2012; 250:6-17. · 2.42 Impact Factor
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ABSTRACT: Samples of enriched pasta were stored under controlled lighting conditions and the loss of riboflavin was determined. After an initial rapid degradation, the riboflavin level continued to decrease slowly. After 12 wk, more than 80% the riboflavin had degraded. When pasta samples- with varied levels of riboflavin enrichment were exposed to light for 2 days, riboflavin losses ranged from 57.8–64.3%. Riboflavin leaching from pasta during cooking was also shown to be concentration independent with 34.5–37.6% of the riboflavin solubilized in the cooking water. Riboflavin in pasta which had been exposed to light for 2 days prior to cooking had a similar percentage of the undegraded riboflavin leached into the cooking water.Journal of Food Science 08/2006; 49(4):984 - 986. · 1.78 Impact Factor
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ABSTRACT: — The photoreduction of riboflavin, FMN, and lumiflavin in a series of hydroxylic solvents has been examined using flash photolysis. A comparison of the relative quantum yields for the photoxidation of several alcohols and esters by lumiflavin demonstrated that the hydroxyl hydrogen of the alcohol is abstracted approximately twice as readily as is the alpha hydrogen. The use of glycerol as both solvent and reductant provided direct evidence that the initial reaction proceeds by a one-electron reduction to form the flavin semi-quinone. In the case of riboflavin (and FMN) the kinetic results are consistent with an initial intramolecular hydrogen atom transfer, analogous to photobleaching in aqueous solution, followed by a reaction of the semi-quinone with the reductant which prevents degradation of the ribityl side-chain. Quenching by iodide indicates that all the reactions proceed via the flavin triplet state, as is the case in aqueous systems.Photochemistry and Photobiology 01/1968; 7(2):129-143. · 2.29 Impact Factor