DIRECT DETECTION OF SINGLET OXYGEN SENSITIZED BY NALIDIXIC ACID: THE EFFECT OF pH AND MELANIN*

Abstract

Abstract— Singlet oxygen yields are reported for the antibiotic nalidixic acid in D 2 O at pH values above and below its pK., in water. The φ Δ increases on lowering the pH. The effect of eumelanin on the φ Δ values is shown to be substantial at pH 4.4, but virtually zero above the p K n value. Human serum albumin seems to have little effect on the singlet oxygen yield at high pH in the presence of melanin. The results are correlated with the experimental and clinical observations relating to the photosensitizing activity of the drug.