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Proton affinity of [Fe4S4{SCH2CH(OH)Me}4] 2- in methanol: Relevance to hydrogen bonding of Fe-S clusters in proteins

Lookup NU author(s): Professor Richard Henderson


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The reaction between PhS- and [Fe4S4{SCH2CH(OH)Me}4] 2- to form [Fe4S4(SPH)4]2- has been studied in methanol, and in the presence of the weak acid, [NHEt3]+. The kinetics are similar to those observed earlier for a variety of Fe-S-based clusters studied in MeCN. A major difference between the studies in the two solvents concerns the identity of the solution species. In MeCN, [NHEt3]+ is a sufficiently strong acid to convert all PhS- to PhSH. However, in MeOH, PhSH is a comparatively stronger acid and consequently PhS- is little protonated by [NHEt3]+. The rate law for the reaction in MeOH is consistent with a mechanism in which initial protonation of a thiolate ligand is followed by protonation of the cluster core (presumably a μ3-S) which labilises the terminal thiol ligand. Subsequent attack of PhS- at the vacant site thus created on one of the Fe atoms completes the first act of substitution. Analysis of the data yields pKa = 8.5 for [Fe4S3(μ-SH){SCH2CH(OH)Me}4] -. The relevance of this result to hydrogen bonding interactions of Fe-S-based clusters in proteins is discussed. The X-ray crystal structure of [NMe4]2[Fe4S4{SCH 2CH(OH)Me}4] is also reported, and the arrangement of the ligands is consistent with an extensive hydrogen bonding network between some of the hydroxyl groups.

Publication metadata

Author(s): Davies SC, Evans DJ, Henderson RA, Hughes DL, Longhurst S

Publication type: Article

Publication status: Published

Journal: Journal of the Chemical Society, Dalton Transactions

Year: 2001

Issue: 23

Pages: 3470-3477

ISSN (print): 1472-7773

ISSN (electronic): 1364-5447

Publisher: Royal Society of Chemistry


DOI: 10.1039/b105075n


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