New Insights about Equilibrium Constants, pKa, of Purine Nitrogenous Bases: The Case of Adenine and Guanine. A UV-Vis Spectrophotometric Study at I = 0.4 M

Abstract

In the present work, novel experimental evidence about acidity constants has been found for adenine and guanine in aqueous medium. Despite being molecules widely studied there is some inconsistences about their chemical speciation in the literature. The study that we presented by UV-Vis spectrophotometry and subsequent data processing using the SQUAD software allowed the determination of three acidity constants for both adenine (pKa1 = 3.361± 0.102, pKa2 = 9.056 ± 0.091 y pKa3 = 10.132 ± 0.057) and guanine (pKa1 = 3.402± 0.028, pKa2 = 9.708 ± 0.022 y pKa3 = 12.721 ± 0.015) at ionic strength 0.4 M and T = (25.0 ± 0.1) °C. Being theses bases fundamental components of DNA and RNA, it is relevant to know in depth their physicochemical properties to improve the understanding of the biological processes involved in the transmission of genetic information, as well as their implications in medicine, biotechnology and molecular biology.