A reversible proton relay process mediated by hydrogen-bonding interactions in [FeFe]hydrogenase modeling

Kai-Ti Chu; Yu-Chiao Liu; Yi-Lan Huang; Cheng-Huey Hsu; Gene-Hsiang Lee; Ming-Hsi Chiang

doi:10.1002/chem.201501114

A reversible proton relay process mediated by hydrogen-bonding interactions in [FeFe]hydrogenase modeling

Chemistry. 2015 Jul 27;21(31):10978-82. doi: 10.1002/chem.201501114. Epub 2015 Jun 26.

Authors

Kai-Ti Chu^{1

2

3}, Yu-Chiao Liu¹, Yi-Lan Huang¹, Cheng-Huey Hsu¹, Gene-Hsiang Lee⁴, Ming-Hsi Chiang^{5

6}

Affiliations

¹ Institute of Chemistry, Academia Sinica, Nankang, Taipei 115 (Taiwan).
² Molecular Science and Technology Program, TIGP, Institute of Chemistry, Academia Sinica, Nankang, Taipei 115 (Taiwan).
³ Department of Chemistry, National Tsing Hua University, Hsinchu 300 (Taiwan).
⁴ Instrumentation Center, National Taiwan University, Taipei 106 (Taiwan).
⁵ Institute of Chemistry, Academia Sinica, Nankang, Taipei 115 (Taiwan). mhchiang@chem.sinica.edu.tw.
⁶ Molecular Science and Technology Program, TIGP, Institute of Chemistry, Academia Sinica, Nankang, Taipei 115 (Taiwan). mhchiang@chem.sinica.edu.tw.

PMID: 26118674
DOI: 10.1002/chem.201501114

Abstract

A reversible and temperature-dependent proton-relay process is demonstrated for a Fe2 complex possessing a terminal thiolate in the presence of nitrogen-based acids. The terminal sulfur site (S(t) ) of the complex forms a hydrogen-bond interaction with N,N-dimethylanilinium acid at 183 K. The Fe2 core, instead, is protonated to generate a bridging hydride at 298 K. Reversibility is observed for the tautomerization between the hydrogen-bonded pair and the Fe-hydride species. X-ray structural analysis of the hydrogen-bonded species at 193 K reveals a short N(H)⋅⋅⋅S(t) contact. Employment of pyridinium acid also results in similar behavior, with reversible proton-hydride interconversion. DFT investigation of the proton-transfer pathways indicates that the pKa value of the hydrogen-bonded species is enhanced by 3.2 pKa units when the temperature is decreased from 298 K to 183 K.

Keywords: S ligands; [FeFe]hydrogenase; hydrogen bonds; iron; proton transfer.