Kinetic studies of the photoinitiated NO-releasing reactions of N,N′-bis-(carboxymethyl)-N,N′-dinitroso-1,4-phenylenediamine

Irradiation of N,N'-bis-(carboxymethyl)-N,N'-dinitroso- 1,4-phenylenediamine (1) with ultraviolet light (lambda = 308 nm) was previously shown to induce cleavage of 1 into NO and the N,N'-bis-(carboxymethyl)-N-nitroso-1,4-phenylenediamine radical (2). This paper provides a procedure for synthesizing 1, and a detailed kinetic re-investigation of the reactions that follow ns-pulse laser-flash photolysis of 1, under conditions that initially produce up to 10 muM of 2 and NO in situ. Under these conditions recombination of 2 with NO, and dissociation of an additional equivalent of NO from 2, appear to be the dominant pathways leading to the depletion of 2 in the ms that follows the initial photolysis. These reactions had been suggested in the initial study of the photolysis of 1; however, in the present study the rate constant k(I) that governs the recombination of 2 with NO to regenerate 1 was found to have a value of (1.1 +/- 0.1) x 10(9) M(-1)s(-1), while the rate constant k(d) governing the dissociation of the second equivalent of NO from 2 was found to be 500 +/- 50 s(-1). Both of these values are significantly different from the values (1.38 x 10(8) M-1 s(-1) and 2.96 x 10(4) s(-1)) reported in the earlier study. The present analysis also revealed the previously unreported presence of an absorbing species at too, that might be the doubly denitrosylated quinoimine derivative of 1 (3), or a charge-transfer complex of 1 and 3. (C) 2002 Elsevier Science B.V. All rights reserved.