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Kinetics and Mechanism of the Reaction of Hydrogen Sulfide with Cobalamin in Aqueous Solution
Author(s) -
Salnikov Denis S.,
Kucherenko Poli.,
Dereven'kov Ilia A.,
Makarov Sergei V.,
van Eldik Rudi
Publication year - 2014
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201301340
Subject(s) - chemistry , cobalamin , hydrogen sulfide , inorganic chemistry , aqueous solution , sulfide , kinetics , reaction mechanism , molecule , photochemistry , organic chemistry , catalysis , sulfur , biochemistry , physics , quantum mechanics , vitamin b12
A detailed kinetic study of the reaction of aquacobalamin [H 2 OCbl(III)] with hydrogen sulfide in water at pH 1 to 10 was carried out using conventional spectrophotometric, stopped‐flow, and high‐pressure stopped‐flow techniques. The reaction proceeds in three steps: formation of the complex between aquacobalamin and hydrogen sulfide, inner‐sphere electron transfer, and addition of a second molecule of hydrogen sulfide to the reduced cobalamin. Kinetic parameters for the different reaction steps of the studied process were determined. The final products of the reaction between aquacobalamin and hydrogen sulfide were found to depend on pH. The main reaction product is five‐coordinate base‐on reduced cobalamin(II) [B 12r , Cbl(II)] in alkaline medium and six‐coordinate cobalamin(II) with the anion‐radical SSH 2 – in acidic medium.