Ahmad Iqbal, Anwar Zubair, Ahmed Sofia, Sheraz Muhammad Ali, Bano Raheela, Hafeez Ambreen
Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi, 74600, Pakistan.
Department of Biochemistry, Dow International Medical College, Dow University of Health Sciences, Ojha Campus, Karachi, 74200, Pakistan.
AAPS PharmSciTech. 2015 Oct;16(5):1122-8. doi: 10.1208/s12249-015-0304-2. Epub 2015 Feb 21.
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.
利用多组分光谱法测定核黄素（RF）及其主要光产物甲酰甲基黄素和光色素，研究了核黄素（RF）在水（pH 7.0）和有机溶剂（乙腈、甲醇、乙醇、1-丙醇、1-丁醇、乙酸乙酯）中的光解动力学。该反应的表观一级速率常数（k obs）范围为3.19（乙酸乙酯）至4.61×10⁻³ min⁻¹（水）。已发现k obs值是溶剂介电常数的线性函数，这意味着在反应途径中存在偶极中间体参与。该中间体的降解受到介质极性的促进。这表明随着溶剂极性增加，RF激发三重态的稳定性增强，有利于其还原。反应的速率常数与溶剂受体数呈线性关系，表明在不同溶剂中溶质 - 溶剂相互作用的程度。这将取决于RF分子在有机溶剂中的给电子能力。由于扩散控制过程，k obs值与介质的粘度成反比。
