Intermolecular Interactions and Intramolecular Couplings of Binuclear Porphyrin Models for Cytochrome c Oxidase

Abstract

Cytochrome c oxidase (CcO) has a binuclear active site composed of a high-spin heme group and a tris-histidine-ligated copper ion (CuB). By using two different porphyrin models derived by Gunter (H2TPyPP) and us (H2TImPP), we have isolated several mono- and binuclear complexes including one carbonyl and three chloride derivatives which are determined by 100 K single-crystal X-ray. Low-temperature (4 K) EPR and multitemperature (295–25 K) Mössbauer investigations on the products not only confirmed the spin states of the two metal ions (S = 5/2 Fe3+ and S = 1/2 Cu2+) but also revealed the intermolecular interactions and intramolecular couplings which are in accordance with the crystal structural features.

d‐Orbital Reconstructions Forced by Double Bow‐Shaped Deformations and Second Coordination Sphere Effects of Cu(II) Heme Analogs in HER**

“…EPR measurements: X-band continuous wave EPR measurements were obtained on a Bruker EMX plus 10/12 EPR spectrometer at a microwave frequency of 9.45 GHz using a liquid helium cooling system. [47] The EPR spectra were measured with a modulation amplitude 0.3 mT, a modulation frequency of 100 kHz, and a microwave power of 10.02 mW at ~4.0 K. Relative computer simulations were performed with EasySpin. [48] Electronic structure calculation: Density functional theory (DFT) calculations were performed using M06 functional [49] with a mixed basis set of SDD (for Cu) and 6-31G(d,p) (for all other atoms) [50] on ground-state spin multiplicity.…”

“…EPR measurements : X‐band continuous wave EPR measurements were obtained on a Bruker EMX plus 10/12 EPR spectrometer at a microwave frequency of 9.45 GHz using a liquid helium cooling system [47] . The EPR spectra were measured with a modulation amplitude 0.3 mT, a modulation frequency of 100 kHz, and a microwave power of 10.02 mW at ∼4.0 K. Relative computer simulations were performed with EasySpin [48]…”

Chlorido[5,10,15,20-tetrakis(quinoline-7-carboxamido)porphinato]iron(III)

“…The Gunter group devised a model compound, 5,10,15,20-tetrakis(o-nicotinamidophenyl)porphyrin, modeled after the classical picket-fence porphyrin, with the substitution of the tert-butyl group at the terminus by a pyridine group (Gunter et al, 1980). Similarly, 10,15,porphyrin by substituting the tert-butyl group at the terminus with an imidazole group (Yao et al, 2020). In this study, we replaced the terminal tert-butyl group with a 7-quinoline group, and determined the crystal structure of the title compound [Fe(C 84 H 52 N 12 O 4 )Cl].…”

“…Solvents utilized within the anhydrous and anaerobic operations (Schlenk system) underwent the freeze-pump-thaw method three times prior to utilization. The synthesis of the precursor 5,10,15,20-tetrakis-(quinoline-7-carboxamide)porphyrin followed the procedures outlined in a previous publication (Yao et al, 2020). Initially, oxalyl chloride (2.2 mmol) was added to a suspension of 7-quinolinecarboxylic acid (1 mmol) in a solvent mixture of 15 ml dichloromethane (DCM) and 10 ml N,N-dimethylformamide in a nitrogen-protected atmosphere.…”