34 - The Kinetic Study on the Reactivity of HNO (Azanone) Towards Nitrite Ions, Hydroxylamine, Selected Nitrosocompounds and Selected Phosphines

Abstract

Nitroxyl (HNO, IUPAC name azanone), being formally the protonated product of one-electron reduction of nitric oxide (NO), is an elusive reactive nitrogen species possessing interesting biological chemistry and high pharmacological importance. 1,2 Contrary to nitric oxide, HNO is a strong electrophile highly reactive towards nucleophiles. Here, we present the study on the kinetics of HNO reaction with nitrate ions, hydroxylamine, selected nitrosocompounds and selected phosphines. In this study we applied previously described 4 competition kinetics method based on two parallel, competing HNO reactions – with thiol and with molecular oxygen. The latter, relatively fast reaction (k = (1.8 ± 0.3) ∙ 10 4 M -1 s -1 ), 3 results in the formation of peroxynitrite, 3 that can be easily detected fluorometrically with the use of fluorogenic boronate derivative of resorufin, PC1. PC1 reacts rapidly and directly with ONOO – (k = 1∙10 6 M -1 s -1 ) with the formation of fluorescent resorufin as the major product. In this study the formation of resorufin was monitored by Applied Photophysics SX20 stopped-flow spectrophotometer equipped with a fluorescence detector. HNO released from Angeli's salt (3 μM) reacts either with the azanone scavenger, or with molecular oxygen (225 μM) forming peroxynitrite detected by PC1 (25 μM). Table 1. The determined values of the second-order rate constant of HNO reaction. HNO scavenger k (M -1 s -1 ) Nitrite ions (4,8 ± 0,2) × 10 3 Hydroxyloamine (2,0 ± 0,1) × 10 4 2-Nitroso-1-naphtol (9,8 ± 0,2) × 10 5 Nitrosobenzene >1,1× 10 5 S-Nitrosoglutathione 2,9 × 10 5 Triphenylophosphine > 6,1 × 10 6 Triphenylphosphine-3,3′,3′′-trisulfonic acid trisodium salt (1,5 ± 0,1) × 10 7 References 1: J. M. Fukuto, M. D. Bartberger et al., Chem. Res. Toxicol., 2005, 18 , 790. 2: N. Paolocci, M. I. Jackson et al. , Pharmacol. Ther. , 2007, 113 , 442. 3: R. Smulik, D. Debski et al. , J. Biol. Chem., 2014, 289 , 35570.