Fluorescence Titration of Some Purines Determination of Lowest Excited-State Ionization Constants

Abstract

Excited-state ionization equilibria of 6-methyl purine and xanthine were investigated in a wide range of pH.

6-Methyl purine is known to have two ionization equilibria in its ground-state. It was found that it had one more ionization equilibrium in strongly acidic region. In the excited state, four ionization equilibria were observed. The pK? values of three of them were determined by means of fluorescence titration.

In the case of xanthine, there exist three ground-state equilibria. In the excited-state, four equilibria were observed. The pK? values of two of them were determined by means of fluorescence titration.