Spectroscopy study of 5-amino-1,10-phenanthroline.

Acidity constants for the 5-amino-1,10-phenanthroline (5-Aphen) were determined in aqueous media, using SQUAD and SUPERQUAD programs. Spectrophotometry and potentiometry data were fitted to the best model to enable correlation of the following acidity equilibria: 5-AphenH = 5-Aphen + H+ (-log K = 5.78 +/= 0.03) and 5-AphenH2 = 5-AphenH2 = 5-Aphen + 2H+ (-log K = 6.89 +/= 0.07). UV absorptivity coefficients obtained suggest that the first protonation takes place on the nitrogens of the heterocycle ring and the second protonation could take place on the amino group. As expected, the electrochemical evidence of the 5-Aphen species depends on the degree of protonation.