ELECTRONIC-SPECTRA AND STRUCTURE OF ALLOPURINOL - A XANTHINE-OXIDASE INHIBITOR

Electronic absorption, fluorescence and fluorescence excitation spectr a of allopurinol, a well-known inhibitor of the enzyme xanthine oxidas e, have been studied in aqueous solution at different pH. The observed spectra have been interpreted in terms of the neutral, anionic and ca tionic forms of allopurinol with the help of molecular orbital calcula tions which included optimisation of geometries of the neutral keto an d enol forms of the molecule in the lowest singlet excited state. Elec trostatic potential mapping has been performed to identify the most pr obable site of binding of allopurinol with xanthine oxidase.