Rapid reaction of singlet molecular oxygen (1O2) with p-aminobenzoic acid (PABA) in aqueous solution.

The reaction of singlet molecular oxygen (1O2) with p-aminobenzoic acid (PABA) is quite rapid. The rate constant for reaction of 1O2 with PABA was measured in buffered aqueous solution by the method of competition kinetics and found to be 8.9 x 10(8) M-1 sec-1. The results of a Stern-Volmer analysis indicate that additional loss of 1O2 does not occur through physical quenching by PABA. Although illuminated PABA solutions are known to form 1O2, it appears that PABA is also a very efficient sink for 1O2.