On the Luminescence Properties of Some Purines and Pyrimidines. A Study by Fluorescence Spectrophotometry of the Sites of Protonation and of the Types of Lowest Excited Singlet States.

Abstract

The fluorescence of some purines and pyrimidines including adenine and guanine nucleotides has been observed in aqueous solutions at room temperature. The effects of pH are reported in detail. The protolytic reactions are usually found to activate or deactivate the fluorescence, while in some cases only a displacement of the emission maximum is observed. The authenticity of the fluorescence is discussed, on the basis of fluorescence activation spectra and of the values of pKa deduced from the dependence of the fluorescence intensity on pH. An attempt is made to formulate the mechanism of the fluorescence activating effect of some substituents and protolytic reactions in terms of interchange of the energetic levels of the lowest excited singlet states of n [forward arrow] [pi] * and [pi][forward arrow] [pi] * promotion type. In the light of this interpretation we consider the sites of protonation of purine nucleotides in acid media, as well as the electronic structure of the excited purine nucleotides at physiological pH.