Photochemical, chemical, and thermal studies on bilirubin in CDCl₃ and NaOH solutions

This study examined the depletion and growth of bilirubin and biliverdin, respectively, after exposing dilute solutions of the unconjugated specimen of bilirubin to light and heat. Firstly, the solar photolysis of bilirubin in CHCl₃ resembled a chemical reaction of bilirubin in CDCl₃. Secondly, at temperatures up to about 70°C, appreciable yields of biliverdin were converted from bilirubin in NaOH, before and after irradiation with cool white light produced from a phototherapy facility. This derivation augurs well for purposes of separating suitable quantities of biliverdin for implementation as precursors in biochemical studies. The aspect of the study associated with CDCl₃ demonstrated that the systematic decrease in the characteristic bilirubin peak at 453 nm, via a chemical reaction, emulated the photolysis of bilirubin with sunlight in regular chloroform. The respective rate constants of the photochemical and chemical reactions were approximately 0.15 s^-1 and 0.17 s^-1 The temperature dependence of the conversion of bilirubin in a NaOH solution to biliverdin was examined with high-resolution spectrophotometry. Bilirubin was prepared at low concentrations (typically 10^-2 mM) in NaOH and subjected to progressive increases in temperature from 25-67.5°C. No significant changes were observed from the status at 67.5°C on cooling. The results for both CDCl₃ and NaOH revealed that a considerable drop in the bilirubin concentrations was encountered. This was accompanied by a corresponding enhancement in the yields of biliverdin in both cases. A mathematical fit to the data provided a means of estimating the level of conversion with temperature.