Co(III) Complexes with Coordinated Carboxamido Nitrogens and Thiolato Sulfurs as Models for Co-Containing Nitrile Hydratase and Their Conversion to the Corresponding Sulfinato Species

Abstract

Recent spectroscopic data suggest that the Co(III) site in Co-containing nitrile hydratase is ligated to carboxamido nitrogens and thiolato sulfurs and most possibly one or more of the bound thiolates exist as sulfenato and/or sulfinato groups. The absence of any Co(III) complex with such coordination makes it quite difficult to predict the reactivity of this kind of Co(III) site. In this paper, the Co(III) complexes of two designed ligands PyPepSH2 (1) and PyPepRSH2 (2) have been reported. The two complexes, namely, (Et4N)[Co(PyPepS)2] (3) and Na[Co(PyPepRS)2] (4) are the first examples of Co(III) complexes with carboxamido nitrogens and thiolato sulfurs as donors. The average Co(III)-Namido and Co(III)-S distances in these complexes lie in the range 1.90-1.92 and 2.22-2.24 A, respectively. Reaction of H2O2 with both complexes readily affords Na[Co(PyPepSO2)2] (5) and Na[Co(PyPepRSO2)2] (6), species in which the thiolato sulfurs are converted to sulfinato (SO2) groups. Such conversion also occurs when solutions of 3 and 4 are exposed to dioxygen in the presence of activated charcoal. These reactions are clean and the S --> SO2 transformation does not introduce significant changes in the metric parameters of these complexes. The reactivity of 3 and 4 indicates that the bound Cys-sulfurs around the biological Co(III) site could be oxidized to sulfinato groups.

New members of a class of dinitrosyliron complexes (DNICs): The characteristic EPR signal of the six-coordinate and five-coordinate {Fe(NO)2}9 DNICs

“…The reagents iron pentacarbonyl, bis(obenzamidophenyl) disulfide, 18-crown-6-ether (TCI), and nitrosonium tetrafluroborate ( [NO][BF 4 ]) (Aldrich) were used as received. Compounds [Fe(CO) 2 (NO) 2 ], N-2-mercaptophenyl-2′-pyridinecarboxamide disulfide ((PyPepS) 2 ), (N-2-mercaptophenyl-2′-pyridin-2-yl)ethylimino disulfide ((PyImiS) 2 ), tris(2-methylpyridine)amine (TPA) and 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine ( iPr PDI) were synthesized by published procedures [39][40][41][42][43]. Infrared spectra of the ν(NO) and ν(CO) stretching frequencies were recorded on a PerkinElmer model spectrum one B spectrophotometer with sealed solution cells (0.1 mm, CaF 2 windows).…”

Spectroscopic differences between heterocyclic benzothiazoline, -thiazole and imine containing ligands and comparison of the Co and Cu pyridine benzothiazole and imine complexes

“…First, bis-aminothiophenol disulfide was prepared following published procedure [25]. Next, a batch of the disulfide, (2 equiv, $2 mmol scale) was dissolved in a minimum amount of EtOH and was then added to one equiv of the corresponding aldehyde dissolved in $25 mL of EtOH (2-pyridinecarboxaldehyde for (PyIS) 2 , 2-thiophenecarboxaldehyde for (ThIS) 2 ).…”

Use of Metallopeptide Based Mimics Demonstrates That the Metalloprotein Nitrile Hydratase Requires Two Oxidized Cysteinates for Catalytic Activity

“…32,41,87–90 The spectrum is relatively featureless with a gradual increase in absorbance from 11,500 to 20,000 cm −1 (870 – 500 nm), shoulders at 22,125 (452 nm) and 28,735 cm −1 (348 nm), and a defined peak at 35,460 −1 (282 nm). The CD spectrum (Figure 5) of the oxidized Co-metallopeptide is also consistent with CoNHase, however, the signs of the resulting low energy bands are different than observed in the metalloenzyme.…”