Faculty Collaboration Database

Substrate binding preferences and pka determinations of a nitrile hydratase model complex: variable solvent coordination to [(bmmp-TASN)Fe]OTf. Inorg Chem 2009 Mar 02;48(5):2300-8

Date

01/27/2009

Pubmed ID

19166306

Pubmed Central ID

PMC2754792

DOI

10.1021/ic802180d

Scopus ID

2-s2.0-64549133423 (requires institutional sign-in at Scopus site)   12 Citations

Abstract

The five-coordinate iron-dithiolate complex (N,N'-4,7-bis-(2'-methyl-2'-mercatopropyl)-1-thia-4,7-diazacyclononane)iron(III), [LFe]+, has been isolated as the triflate salt from reaction of the previously reported LFeCl with thallium triflate. Spectroscopic characterization confirms an S = 1/2 ground state in non-coordinating solvents with room temperature microeff = 1.78 microB and electron paramagnetic resonance (EPR) derived g-values of g1 = 2.04, g2 = 2.02 and g3 = 2.01. [LFe]+ binds a variety of coordinating solvents resulting in six-coordinate complexes [LFe-solvent]+. In acetonitrile the low-spin [LFe-NCMe]+ (g1 = 2.27, g2 = 2.18, and g3 = 1.98) is in equilibrium with [LFe]+ with a binding constant of Keq = 4.7 at room temperature. Binding of H2O, DMF, methanol, DMSO, and pyridine to [LFe]+ yields high-spin six-coordinate complexes with EPR spectra that display significant strain in the rhombic zero-field splitting term E/D. Addition of 1 equiv of triflic acid to the previously reported diiron species (LFe)2O results in the formation of [(LFe)2OH]OTf, which has been characterized by X-ray crystallography. The aqueous chemistry of [LFe]+ reveals three distinct species as a function of pH: [LFe-OH2]+, [(LFe)2OH]OTf, and (LFe)2O. The pKa values for [LFe-OH2]+ and [(LFe)2OH]OTf are 5.4 +/- 0.1 and 6.52 +/- 0.05, respectively.

Author List

O'Toole MG, Bennett B, Mashuta MS, Grapperhaus CA

Author

Brian Bennett D.Phil. Professor and Chair in the Physics department at Marquette University

MESH terms used to index this publication - Major topics in bold

Amides
Catalytic Domain
Electron Spin Resonance Spectroscopy
Ferric Compounds
Hydro-Lyases
Hydroxides
Imines
Models, Molecular
Nitriles
Nitrogen
Solvents
Substrate Specificity
Temperature
Water