New photochemically stable riboflavin analogue - 3-Methyl-riboflavin tetraacetate

Spectroscopic and photophysical properties of a flavin analogue - 3-methyl-riboflavin tetraacetate - were studied in methanol, ethanol, water and acetonitrile. We compared experimental spectroscopic data with the results of theoretical predictions, obtained using the TD-DFT method. Based on these calculations, we assigned (pi,pi*) symmetry to both the lowest excited singlet and triplet states. We found the title compound to be a very efficient photosensitizer of singlet oxygen production (phi(Delta) = 0.61). The triplet state quantum yield of 3-methyl-riboflavin tetraacetate was determined as 0.54 in methanolic solutions. Photodegradation quantum yield measurements demonstrate that the title compound may be used as a much more stable substitute of riboflavin, being two orders of magnitude more photostable (phi(R) = 2 x 10(-5)). We also present exhaustive crystallographic characteristics of 3-methyl-riboflavin tetraacetate, along with time-resolved fluorescence spectra of its polycrystals. (c) 2006 Elsevier B.V. All rights reserved.