A kinetic study for the estimation of riboflavin sensitized photooxidation of pyridoxine HCl using green UV-visible spectrometric and HPLC methods

Abstract

Riboflavin (RF) sensitized photooxidation of pyridoxine HCl (PD) in the pH range of 2.0–12.0 has been carried out under UV and visible irradiation in aerobic and anaerobic conditions. PD follows first-order kinetics in the absence and presence of RF for its photodegradation. The first-order rate constants (k_obs) for the photodegradation of PD in the presence of RF (0.05–0.50 × 10⁻⁴ M) in aerobic and anaerobic conditions range from 0.046–0.755 and 0.0089–0.755 × 10⁻² min⁻¹, respectively. RF acts as a promoter for the photodegradation of PD and the second-order rate constants (k₂) are in the range of 0.026–1.285 and 0.004–0.128 × 10⁻² M⁻¹ min⁻¹ in aerobic and anaerobic conditions, respectively. The k₂–pH profile for the photodegradation shows a slanted curve, indicating that with an increase in pH, the rate of photodegradation of PD also increases. Green UV-visible spectrometric and high-performance liquid chromatographic (HPLC) methods have been developed for the simultaneous determination of PD and RF in pure and degraded solutions. These two developed methods are statistically compared and it is found that there is no significant difference between them. We have conducted in silico studies to assess the formation of ground state complexes, molecular interactions, and the binding affinities of RF and PD.