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 Tanaka[Show abstract] [Hide abstract]
ABSTRACT: D-Amino acid oxidase (DAAO) from pig kidney binds Flavin adenine dinucleotide (FAD) as a cofactor. The DAAO-benzoate (Bz) complex (DAUB) is remarkably more stable than DAAO. It was previously reported that the fluorescence lifetime of FAD in DAAO is reduced by 66% upon Bz binding. The mechanism of photoinduced electron transfer (ET) in the DAUB monomer from Bz to the excited isoalloxazine (Iso*) was studied by molecular dynamics simulation (MDS) and by Kakitani and Mataga electron transfer theory (KM theory), and compared with that in DAAO. The ET parameters contained in KM theory were determined to obtain the fluorescence lifetime of DAUB (60 ps). The ET mechanism in DAUB is different from other flavoproteins, where neutral tryptophans and tyrosines are the ET donors, since the anionic Bz acts as the anionic ET donor in DAUB. Moreover, ET takes place in the inverted region. Charge transfer interaction (Cl) was studied by semi-empirical molecular orbital (MO) methods. The dipole moment in the Iso*-Bz system was lower than that in the isoalloxazine (Iso)-Bz system, which was ascribed to CT from the negatively charged Bz to Iso*. The mean interaction energies between Iso and Bz over 100 snapshots were -16.8 and -8.1 kcal/mol in the excited and the ground states, respectively, with mean charge densities for the excited and the ground states of -0.354 and -0.013 at Iso and -0.646 and -0.987 at Bz, respectively. The ionization potential of Bz was evaluated as 7.3 eV by ET analysis, which was in excellent agreement with that obtained by MO calculations. The dielectric constant between Is and the donors was 2.2 in DAUB, compared to 5.8 in DAAO. According to the MDS, several water molecules existed around Iso in DAAO that were all removed upon Bz binding resulting in a strongly non-polar environment near Iso in DAUB.Journal of Photochemistry and Photobiology A Chemistry 12/2012; 250:6-17. DOI:10.1016/j.jphotochem.2012.09.004 · 2.29 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 02/1968; 7(2):129-143. DOI:10.1111/j.1751-1097.1968.tb08000.x · 2.68 Impact Factor
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ABSTRACT: The association of aromatic hydrocarbons with riboflavin has been examined by changes in light absorption and fluorescence emission of flavin solutions. Aromatic hydrocarbons cause a decrease in flavin absorbance in the near-ultraviolet region and quench the flavin fluorescence. The quenching phenomenon is related to concentration of an aromatic hydrocarbon, and association constants for flavin-aromatic hydrocarbon complexes can be calculated. Associations involved appear to be of the general electron donor—acceptor complex, but other factors may be operating.Spectrochimica Acta Part A Molecular Spectroscopy 08/1967; 23(8):2353–2358. DOI:10.1016/0584-8539(67)80128-4