Photostabilization of menadione sodium bisulfite by glutathione.

Photodecomposition of solutions of menadione sodium bisulfite (MSB) in the presence and absence of glutathione (GSH) under artificial sunlight was investigated. In presence of 0.02% (GSH), an appreciable increase in photostability was observed when clear glass vials were used. The pH and the temperature of the solution significantly influenced the stability of MSB. Photodegradation of MSB appeared to follow first-order kinetics. Photostabilization of MSB was attributed in part to complex formation between MSB and GSH and the antioxidant property of the latter. Stability constants for the various solutions were determined at several temperatures. Thermodynamic parameters were calculated and were found to support complex formation.