Models of Amide-Cysteine Hydrogen Bonding in Rubredoxin: Hydrogen Bonding between Amide and Benzenethiolate in [(CH3)3NCH2CONH2]2[Co(SC6H5)4]· 1/2 CH3CN and [(CH3)3NCH2CONH2][SC6H5]

Marc Anton Walters, John C. Dewan, Caroline Min, Shirley Pinto

Research output: Contribution to journalArticlepeer-review

Abstract

Amide-thiolate hydrogen-bonding interactions are described for the cobalt complex [(CH3)3NCH2CONH2]2[CoCSC6H5)4]· 1/2 CH3CN (1) and the metal-free salt [(CH3)3NCH2CONH2] [SC6H5] (2). Complex 1 has a triclinic cell with space group [formula omitted], a= 16.960 (5) Å, b = 17.874 (6) Å, c = 14.184 (6) Å, α = 111.47 (3)°, β = 94.34 (3)°, γ = 70.50 (2)°, and Z = 4. Complex 2 has a monoclinic cell with space group P21/n, a = 12.847 (9) Å, b = 6.730 (5) Å, c = 29.268 (4) Å, β = 95.65 (2)°, and Z = 8. Compound 1 serves to model amide-cysteine hydrogen bonding and its effect on metal coordination in rubredoxin. Average N-H⋯S hydrogen bond lengths are 3.356 (7) and 3.306 (3) Å for 1 and 2, respectively. In 1 the average Co-SN bond length (SN = non-hydrogen-bonding sulfur) is 2.294 (2) Å, shorter by 0.034 Å than the average Co-S bond length of 2.328 (4) Å in the complex [(C6H5)4P]2[Co(SC6H5)4], in which hydrogen bonding is absent. The average Co-SH bond length (SH = hydrogen-bonded sulfur) in 1 is 2.320 (2) Å, equivalent to that in [(C6H5)4P]2[Co(SC6H5)4]. More generally the average Co-S(N+H) bond length in 1, 2.302 (1) Å, is 0.026 Å shorter than that of the non-hydrogen-bonding complex. These results suggest that a local stabilization of the [Co(SC6H5)4]2- complex results from hydrogen bonding. Vibrational bands assigned to metal-ligand modes of approximate T2 and A1 symmetry are observed at 237, 231, 218, and 204 cm−1, respectively, for 1 as compared with 235, 228, 220, and 201 cm−1 in [(CH3)4N]2[Co(SC6H5)4], a non-hydrogen-bonding complex. The direction of the metal-ligand vibrational frequency shifts with hydrogen bonding is in agreement with X-ray crystallographic data. These results suggest that amide-cysteine hydrogen bonding may stabilize the iron-containing redox center in rubredoxin and thereby account for its relatively high redox potential.

Original languageEnglish (US)
Pages (from-to)2656-2662
Number of pages7
JournalInorganic Chemistry
Volume30
Issue number12
DOIs
StatePublished - Jun 1 1991

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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