Mechanisms of nitric oxide release from nitrovasodilators in aqueous solution:: reaction of the nitroprusside ion ([Fe(CN)5NO]2-) with L-ascorbic acid

Nitric Oxide (NO) is a very diverse endogenous molecule and is responsible for a number of mammalian physiological activities. Sodium nitroprusside (SNP) is a long known hypotensive agent due to its ability to produce NO in situ. In this study, we have carried out a detailed investigation on the kinetics and mechanism of the decomposition of SNP by L-ascorbic acid to afford NO in aqueous medium. Spectrophotometric and electrochemical methods were employed in these studies. Experiments were performed under an argon atmosphere and reaction rates were strongly pH dependent and increases with pH. NO release increases up to about pH 7 after which it decreases at higher pHs. The two ionized forms of ascorbate present in aqueous solution reduce SNP in the order A(2-) much greater than HA(-) much greater than H(2)A (H(2)A = L-ascorbic acid) to release NO. The outer-sphere reduction of SNP by ascorbate involved three clear stages with NO being released in the last stage. Our kinetic results also show catalysis by group I alkali metal ions to increase down the group from Li+ to Cs+. A detail study presented here, strongly illustrate the possibility of the biological antioxidant, L-ascorbic acid, to play a vital role in the in situ metabolism of nitrosocompounds such as SNP to produce NO. (C) 2001 Elsevier Science BY. All rights reserved.