Solvent Effect on the Photolysis of Riboflavin
Journal Title: AAPS PharmSciTech - Year 2015, Vol 16, Issue 5
Abstract
The kinetics of photolysis of riboflavin (RF) in water (pH 7.0) and in organic solvents (acetonitrile, methanol, ethanol, 1-propanol, 1-butanol, ethyl acetate) has been studied using a multicomponent spectrometric method for the assay of RF and its major photoproducts, formylmethylflavin and lumichrome. The apparent first-order rate constants (kobs) for the reaction range from 3.19 (ethyl acetate) to 4.61 × 10−3 min−1 (water). The values of kobs have been found to be a linear function of solvent dielectric constant implying the participation of a dipolar intermediate along the reaction pathway. The degradation of this intermediate is promoted by the polarity of the medium. This indicates a greater stabilization of the excited-triplet states of RF with an increase in solvent polarity to facilitate its reduction. The rate constants for the reaction show a linear relation with the solvent acceptor number indicating the degree of solute–solvent interaction in different solvents. It would depend on the electron-donating capacity of RF molecule in organic solvents. The values of kobs are inversely proportional to the viscosity of the medium as a result of diffusion-controlled processes.
Authors and Affiliations
Iqbal Ahmad, Zubair Anwar, Sofia Ahmed, Muhammad Ali Sheraz, Raheela Bano, Ambreen Hafeez
Keywords
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- EP ID EP682300
- DOI 10.1208/s12249-015-0304-2
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