Study of the reaction between nitric oxide and dithionite

PAOLA VARGAS; AGOSTINA MAZZEO; JULIO CRISTALDI; CARLOS BRONDINO; SEBASTIAN SUAREZ; FABIO DOCTOROVICH

Buenos Aires

Simposio; o Exploring the Frontiers of Chemistry: Challenges for the 21st Century; 2019

Exactas UBA / Ben-Gurion University

Study of the reaction between nitric oxide and dithioniteSodium dithionite is the most widely used reducing agent for inorganic complexes, bioinorganic compounds and certain organic species. In most cases, the main reducing agent is the SO 2 - radical, which arises from the dissociation of S2O4-2 . The strong reducing potential of this compound makes it very air sensitive and unstable, particularly in solution; therefore, it must be strictly manipulated in oxygen-free conditions. The principal impurity is the sulfite ion (SO3 -2 ), which is known to react with nitric oxide giving N-nitrosohydroxylamine-N- sulfonate (NHAS), evidenced by a characteristic UV absorption band at 260nm. For these reasons, commercially available sodium dithionite must be purified by recrystallization before employing it in the study ofthis reaction.Evidence of the reactivity between dithionite and nitric oxide (NO) has been found during enzyme-reducing studies. 1 The kinetics of this reaction have even been followed spectrophotometrically 2, although the mechanism remains unknown. In this work, we study the reaction mechanism between dithionite and NO using UV-vis spectrophotometry, following the dithionite absorbance traces (Ɛ 315nm = 8000 M -1 cm -1 ), IR spectroscopy, EPR and ionic chromatography for nitrite quantification. Our results show that the studied reaction is first-order in dithionite and zero-order in NO when an impure dithionite sample is used. Suprisingly, this reactivity decreases when purified dithionite was used instead.Dithionite (impure) + NO -> ReactionDithionite (pure) + NO -> slow reactionAccordingly, we propose that the sulfite ion traces present in the impure solid initiate the reaction with NO giving an intermediate that reacts subsequently with dithionite. The final nitrogen product is N 2 O, as evidenced by IR measurements. 1- Carballal S., Cuevasanta E., Yadav P., Gherasim C., Ballou D., Alvarez B., and Banerjee R. (2016) Kinetics ofNitrite Reduction and Peroxynitrite Formation by Ferrous Heme in Human Cystathionine β-Synthase J. Biol. Chem.291, 8004?80132- Moore, E. G., and Gibson, Q. H. (1976) Cooperativity in the dissociation of nitric oxide from hemoglobin. J. Biol.Chem. 251, 2788?2794