Effects of purines on fluorescent solutions

Abstract

The fluorescence of polycyclic aromatic hydrocarbons in aqueous caffeine soln. is quenched by acidification which is reversible upon neutralization. The active quenching agent is the caffeine-ion and not the H-ion. Other purine bases (hypoxanthine, xanthine and N-methylxanthines) behave similarly to caffeine. Uric acids quench even in pure water or in aqueous ethanol, while a 3d group of purines (guanine and adenine) quench without acidification but the effect is intensified by acid. Substances without the 4:5 double bond or the double bond adjacent to C8 do not quench. Quenching is strongest in water (decreases in less polar solvents) and is due to a reversible photochemical reaction and not to absorption of either primary or secondary radiation. Quenching was also observed with non-hydrocarbons (quinine, acridine, and quinaldine sulphates, thiochrome, riboflavin and fluores-cein). Neutral soln. of caffeine sometimes intensified the fluorescence of thiochrome, mepacrine, or eosin.