Mechanistic Studies on the Reaction between Aquacobalamin and the HNO Donor Piloty's Acid over a Wide pH Range in Aqueous Solution

Polaczek J, Subedi H, Orzeł Ł, Lisboa LS, Cink RB, Stochel G, Brasch NE, van Eldik R (2021)

Publication Type: Journal article

Publication year: 2021

Journal

Inorganic Chemistry American Chemical Society

DOI: 10.1021/acs.inorgchem.0c02968

Abstract

Detailed kinetic and mechanistic studies have been carried out on the reaction between aquacobalamin/hydroxocobalamin (CblOH2+/CblOH) and nitroxyl (HNO) generated by Piloty's acid (PA, N-hydroxybenzenesulfonamide) over a wide pH range (3.5-13). The resulting data showed that in a basic solution HNO can react with hydroxocobalamin to form nitrosylcobalamin despite the inert nature of CblOH. It was shown that at low PA concentrations the rate-determining step is the decomposition of PhSO2NHO- to release HNO, whereas the reaction between CblOH and HNO becomes the rate-determining step at high PA concentrations. Data from kinetic studies on the reaction of CblOH with an excess of HNO enabled us to experimentally determine the pKa(HNO) value from initial rate data as a function of pH, giving pKa(HNO) = 11.47 ± 0.04. An especially interesting observation was made in the neutral pH range, where PA is stable and does not produce HNO. Under such conditions, rapid formation of CblNO was observed in the studied system. The obtained data suggest that CblOH2+ reacts directly with PA to form a Piloty's acid-bound cobalamin intermediate, which deprotonates rapidly at neutral pH followed by rate-determining S-N bond cleavage to give CblNO and release PhSO2-.

Authors with CRIS profile

Rudi van Eldik Naturwissenschaftliche Fakultät

Involved external institutions

Jagiellonian University / Uniwersytet Jagielloński (UJ) PL Poland (PL) Piedmont Virginia Community College US United States (USA) (US) Auckland University of Technology / Te Wānanga Aronui o Tāmaki Makau Rau NZ New Zealand (NZ)

How to cite

APA:

Polaczek, J., Subedi, H., Orzeł, Ł., Lisboa, L.S., Cink, R.B., Stochel, G.,... van Eldik, R. (2021). Mechanistic Studies on the Reaction between Aquacobalamin and the HNO Donor Piloty's Acid over a Wide pH Range in Aqueous Solution. Inorganic Chemistry. https://doi.org/10.1021/acs.inorgchem.0c02968

MLA:

Polaczek, Justyna, et al. "Mechanistic Studies on the Reaction between Aquacobalamin and the HNO Donor Piloty's Acid over a Wide pH Range in Aqueous Solution." Inorganic Chemistry (2021).

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