Solvent Effect on the Photolysis of Riboflavin

• Published in: AAPS PharmSciTech 2015-10, Vol.16 (5), p.1122-1128
• Main Authors: Ahmad, Iqbal, Anwar, Zubair, Ahmed, Sofia, Sheraz, Muhammad Ali, Bano, Raheela, Hafeez, Ambreen
• Format: Article
• Language: English
• Subjects: Biochemistry; Biomedical and Life Sciences; Biomedicine; Biotechnology; Diffusion; Drug Stability; Flavins - chemistry; Hydrogen-Ion Concentration; Kinetics; Light; Linear Models; Models, Chemical; Pharmacology/Toxicology; Pharmacy; Photolysis; Research Article; Riboflavin - chemistry; Riboflavin - radiation effects; Solvents - chemistry; Spectrophotometry, Ultraviolet; Viscosity; Water - chemistry
• ISSN: 1530-9932; 1530-9932
• DOI: 10.1208/s12249-015-0304-2

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 ( k obs ) for the reaction range from 3.19 (ethyl acetate) to 4.61 × 10 −3  min −1 (water). The values of k obs 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 k obs are inversely proportional to the viscosity of the medium as a result of diffusion-controlled processes.