title: Solvent Effect on the Photolysis of Riboflavin.
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 (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.
authors.affiliation: Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi, 74600, Pakistan.
authors.forename: Iqbal
authors.initials: I
authors.lastname: Ahmad
authors.affiliation: Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi, 74600, Pakistan.
authors.forename: Zubair
authors.initials: Z
authors.lastname: Anwar
authors.affiliation: Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi, 74600, Pakistan.
authors.forename: Sofia
authors.initials: S
authors.lastname: Ahmed
authors.affiliation: Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi, 74600, Pakistan. ali_sheraz80@hotmail.com.
authors.forename: Muhammad Ali
authors.initials: MA
authors.lastname: Sheraz
authors.affiliation: Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi, 74600, Pakistan.
authors.forename: Raheela
authors.initials: R
authors.lastname: Bano
authors.affiliation: Department of Biochemistry, Dow International Medical College, Dow University of Health Sciences, Ojha Campus, Karachi, 74200, Pakistan.
authors.forename: Ambreen
authors.initials: A
authors.lastname: Hafeez
mesh_terms: D004058:Diffusion; D004355:Drug Stability; D005415:Flavins / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008027:Light; D016014:Linear Models; D008956:Models, Chemical; D010782:Photolysis; D012256:Riboflavin / Q000737:chemistry / Q000528:radiation effects*; D012997:Solvents / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: C115829:10-formylmethylflavin; D005415:Flavins; D012997:Solvents; D014867:Water; C001559:7,8-dimethylalloxazine; D012256:Riboflavin
keywords: dielectric constant; kinetics; photolysis; riboflavin; solvent effect; viscosity