Issue 7, 2006

Photolysis of formylmethylflavin in aqueous and organic solvents

Abstract

The photolysis of formylmethylflavin (FMF), a major intermediate in the photodegradation sequence of riboflavin, has been carried out in water (pH 7.0) and in several organic solvents. FMF produces lumichrome (LC) in organic solvents and LC and lumiflavin (LF) in aqueous solution. FMF and its photoproducts have been analysed using a specific multicomponent spectrophotometric method. FMF undergoes a bimolecular redox reaction on photolysis. The second-order rate constants for the reaction range from 0.66 (chloroform) to 2.44 M−1 s−1 (water) and are a linear function of the solvent dielectric constant. A plot of ln k against 1/ε is linear for the reactions in 1-butanol, 1-propanol, ethanol, methanol, acetonitrile and water (ε ∼ 17–79) and non-linear in chloroform and dichloroethane (ε ∼ 5–10) suggesting a change in reaction mechanism in the two regions. This may be explained on the basis of the existence of a dipolar intermediate along the reaction pathway. The rate of photolysis is governed by the solvation of the intermediate and is thus influenced by the dielectric constant of the medium. The solvent effect on the rate of photolysis of FMF has been expressed in terms of the solvent acceptor number. A linear relationship has been found between ln k and the solvent acceptor number.

Graphical abstract: Photolysis of formylmethylflavin in aqueous and organic solvents

Article information

Article type
Paper
Submitted
27 Feb 2006
Accepted
25 Apr 2006
First published
03 May 2006

Photochem. Photobiol. Sci., 2006,5, 680-685

Photolysis of formylmethylflavin in aqueous and organic solvents

I. Ahmad, Q. Fasihullah and F. H. M. Vaid, Photochem. Photobiol. Sci., 2006, 5, 680 DOI: 10.1039/B602917E

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