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RESEARCH ARTICLE
Contents Vol 66(5)

Effect of pH, Buffer, and Viscosity on the Photolysis of Formylmethylflavin: A Kinetic Study

Iqbal Ahmad A , Tania Mirza A , Kefi Iqbal B , Sofia Ahmed A , Muhammad Ali Sheraz A D and Faiyaz H. M. Vaid C
+ Author Affiliations
- Author Affiliations

A Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi-74600, Pakistan.

B Department of Material Science, Baqai Dental College, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi-74600, Pakistan.

C Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Karachi, Karachi-75270, Pakistan.

D Corresponding author. Email: ali_sheraz80@hotmail.com

Australian Journal of Chemistry 66(5) 579-585 https://doi.org/10.1071/CH12457
Submitted: 7 October 2012  Accepted: 29 January 2013   Published: 22 February 2013

Abstract

The kinetics of the photolysis of formylmethylflavin, a major intermediate product in the aerobic and anaerobic photolysis of riboflavin, was studied in the pH range 2.0–11.0. Formylmethylflavin and its photoproducts, lumichrome and lumiflavin, were determined in degraded solutions using a specific multicomponent spectrophotometric method. The photolysis of formylmethylflavin in alkaline medium takes place by first-order kinetics and the rate constants (kobs) at pH 7.5–11.0 range from 0.27 × 10–4 to 3.88 × 10–4 and 0.36 × 10–4 to 5.63 × 10–4 s–1 under aerobic and anaerobic conditions respectively. In acid medium, the photolysis involves a second-order mechanism and the rate constants at pH 2.0–7.0 range from 1.37 to 2.11 and 2.03 to 2.94 M–1 s–1 under aerobic and anaerobic conditions respectively. The rate–pH profiles for the photolysis reactions indicate the highest rate of formylmethylflavin degradation is at ~pH 4 and above pH 10. In the alkaline region, the increase in rate with pH is due to higher reactivity of the flavin triplet state. The photolysis of formylmethylflavin is catalyzed by phosphate ions and is affected by the solvent viscosity.


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