Reduction of RuVIºN to RuIII-NH3 by Cysteine in Aqueous Solution

Document Type

Journal Article

Publication Date

2018

Keywords

Redox reactions, Solution chemistry, Peptides and proteins, Reaction mechanisms, Monomers

DOI

10.1021/acs.inorgchem.8b00238

Abstract

The reduction of metal nitride to ammonia is a key step in biological and chemical nitrogen fixation. We report herein the facile reduction of a ruthenium(VI) nitrido complex [(L)RuVI(N)(OH2)]+ (1, L = N,N′-bis(salicylidene)-o-cyclohexyldiamine dianion) to [(L)RuIII(NH3)(OH2)]+ by l-cysteine (Cys), an ubiquitous biological reductant, in aqueous solution. At pH 1.0–5.3, the reaction has the following stoichiometry: [(L)RuVI(N)(OH2)]+ + 3HSCH2CH(NH3)CO2 → [(L)RuIII(NH3)(OH2)]+ + 1.5(SCH2CH(NH3)CO2)2. Kinetic studies show that at pH 1 the reaction consists of two phases, while at pH 5 there are three distinct phases. For all phases the rate law is rate = k2[1][Cys]. Studies on the effects of acidity indicate that both HSCH2CH(NH3+)CO2– and –SCH2CH(NH3+)CO2– are kinetically active species. At pH 1, the reaction is proposed to go through [(L)RuIV(NHSCH2CHNH3CO2H)(OH2)]2+ (2a), [(L)RuIII(NH2SCH2CHNH3CO2H)(OH2)]2+ (3), and [(L)RuIV(NH2)(OH2)]+ (4) intermediates. On the other hand, at pH around 5, the proposed intermediates are [(L)RuIV(NHSCH2CHNH3CO2)(OH2)]+ (2b) and [(L)RuIV(NH2)(OH2)]+ (4). The intermediate ruthenium(IV) sulfilamido species, [(L)RuIV(NHSCH2CHNH3CO2H)(OH2)]2+ (2a) and the final ruthenium(III) ammine species, [(L)RuIII(NH3)(MeOH)]+ (5) (where H2O was replaced by MeOH) have been isolated and characterized by various spectroscopic methods.

Source Publication

Inorganic Chemistry

Volume Number

57

Issue Number

10

ISSN

0020-1669

First Page

5850

Last Page

5858

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