%0 Journal Article
%A Noveron, Juan C.
%A Olmstead, Marilyn M.
%A Mascharak, Pradip K.
%D 2001
%T A Synthetic Analogue of the Active Site of Fe-Containing Nitrile
Hydratase with Carboxamido N and Thiolato S as Donors: Synthesis,
Structure, and Reactivities
%U https://acs.figshare.com/articles/journal_contribution/A_Synthetic_Analogue_of_the_Active_Site_of_Fe-Containing_Nitrile_Hydratase_with_Carboxamido_N_and_Thiolato_S_as_Donors_Synthesis_Structure_and_Reactivities/3629304
%R 10.1021/ja001253v.s001
%2 https://ndownloader.figshare.com/files/5718054
%K deprotonated carboxamido nitrogens
%K Fe III
%K ligand PyPSH 4
%K thiolate donor groups
%K S O 2
%K thiolato sulfurs
%K DMF
%K exhibit EPR spectra
%K CN
%K nitrile
%K Et 4 N
%K site
%K ligated carboxamido nitrogens
%K center
%X As part of our work on models of the iron(III) site of Fe-containing nitrile hydratase, a designed
ligand PyPSH4 with two carboxamide and two thiolate donor groups has been synthesized. Reaction of (Et4N)[FeCl4] with the deprotonated form of the ligand in DMF affords the mononuclear iron(III) complex (Et4N)[FeIII(PyPS)] (1) in high yield. The iron(III) center is in a trigonal bipyramidal geometry with two deprotonated
carboxamido nitrogens, one pyridine nitrogen, and two thiolato sulfurs as donors. Complex 1 is stable in
water and binds a variety of Lewis bases at the sixth site at low temperature to afford green solutions with a
band around 700 nm. The iron(III) centers in these six-coordinate species are low-spin and exhibit EPR spectra
much like the enzyme. The pKa of the water molecule in [FeIII(PyPS)(H2O)]- is 6.3 ± 0.4. The iron(III) site
in 1 with ligated carboxamido nitrogens and thiolato sulfurs does not show any affinity toward nitriles. It thus
appears that at physiological pH, a metal-bound hydroxide promotes hydration of nitriles nested in close
proximity of the iron center in the enzyme. Redox measurements demonstrate that the carboxamido nitrogens
prefer Fe(III) to Fe(II) centers. This fact explains the absence of any redox behavior at the iron site in nitrile
hydratase. Upon exposure to limited amount of dioxygen, 1 is converted to the bis-sulfinic species. The structure
of the more stable O-bonded sulfinato complex (Et4N)[FeIII(PyP{SO2}2)] (2) has been determined. Six-coordinated low-spin cyanide adducts of the S-bonded and the O-bonded sulfinato complexes, namely, Na2[FeIII(PyP{SO2}2)(CN)] (4) and (Et4N)2[FeIII(PyP{SO2}2)(CN)] (5), afford green solutions in water and other
solvents. The iron(II) complex (Et4N)2[FeII(PyPS)] (3) has also been isolated and structurally characterized.
%I ACS Publications