Abstract. The photolysis of riboflavin (RF) in the presence of acetate buffer (pH 3.8-5.6) and carbonate buffer (pH 9.2-10.8) has been studied using a multicomponent spectrophotometric method for the simultaneous assay of RF and its photoproducts. Acetate and carbonate buffers have been found to catalyze the photolysis reaction of RF. The apparent first-order rate constants for the acetate-catalyzed reaction range from 0.20 to 2.86 ×10 −4 s −1 and for the carbonate-catalyzed reaction from 3.33 to. The second-order rate constants for the interaction of RF with the acetate and the carbonate ions range from 2.04 to 4.33×10 −4 M −1 s −1 and from 3.71 to 11.80×10, respectively. The k-pH profile for the acetate-catalyzed reaction is bell shaped and for the carbonate-catalyzed reaction a steep curve. Both HCO 3 − and CO 3 2− ions are involved in the catalysis of the photolysis reaction in alkaline solution. The rate constants for the HCO 3 − and CO 3 2− ions catalyzed reactions are 0.72 and 1.38×10, respectively, indicating a major role of CO 3 2− ions in the catalysis reaction. The loss of RF fluorescence in acetate buffer suggests an interaction between RF and acetate ions to promote the photolysis reaction. The optimum stability of RF solutions is observed in the pH range 5-6, which is suitable for pharmaceutical preparations.
A photodegradation study of 5-fluorouracil (5-FU) has been carried out in the water (pH 7.0) and organic solvents (chloroform, ethyl acetate, acetone, 1butanol, 1-propanol, ethanol, methanol, and acetonitrile) using developed and validated high-performance liquid chromatography (HPLC) method. The test method was found to be simple, accurate (% recovery, 100.25%-101.08%), precise (%RSD < 2.00), and sensitive. The apparent first-order rate constants are in the range of 0.85 (chloroform) to 4.25 × 10 −4 min −1 (water). The values obtained for k obs were found to be linear as a function of the dielectric constant indicating the involvement of the dipolar intermediate in the reaction. The increase in the rate of degradation of this intermediate is enhanced by the polarity of the medium. Rates of photolysis for 5-FU show a linear relationship with the solvent acceptor number (AN) which indicates the degree of solute-solvent interaction. The values of k obs were found to be linear to the inverse of the viscosity of the medium due to the diffusion-controlled process.
Carboxymethylflavin (CMF) undergoes photolysis in acid solution to form lumichrome (LC) and in alkaline solution, LC and lumiflavin (LF) by side-chain cleavage and β-keto acid and a dioxoquinoxalaine (DQ) compound by isoalloxazine ring cleavage.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.