Computational studies of modified [Fe3S4] clusters: Why iron is optimal

Redox Potentials and Electronic States of Iron Porphyrin IX Adsorbed on Single Crystal Gold Electrode Surfaces

“…HS and LS FePPIX with the four ligations were combined with the Au(111)- and C-surface models, altogether 60 models, and the structure as optimized at the BP86/def2-SVP level including the Cosmo solvation model with static dielectric constant 80 . Vertical ionization energies and electron affinities were computed for each ground state to obtain reorganization energies − (section ).…”

“…They have similar energies with a small preference for antiferromagnetic coupling; i.e., this coupling is well-behaved and does not produce artifacts. All geometries were optimized at the BP86/def2-SVP level using the Cosmo solvation model with a static dielectric constant of 80, as condensed phase screening is known to improve the accuracy of charged metal cluster geometries . The solvent probe radii were 2.0 Å for C, 1.83 Å for N, 1.72 Å for O, 1.3 Å for H, 2.0 Å for Fe, and 2.5 Å for Au.…”

Characterization of the [3Fe–4S]0/1+cluster from the D14C variant of Pyrococcus furiosus ferredoxin via combined NRVS and DFT analyses

“…In semi-classical Marcus theory of electron transfer, the activation barrier for electron transfer ΔG ‡ is predicted to depend on λ and the driving force ΔG o (difference in reduction potentials) by the relationship ΔG ‡ = ( λ + ΔG o ) 2 /4 λ . 34 Our computed inner-sphere contribution to reorganization energy λ i (see ESI † discussion on reorganization energy, Table S2 † , and earlier theoretical works 19, 25, 35–38 ) of the [3Fe-4S] 0/1+ redox couple is 111.3 kJ/mol, which is about 6 times higher than the 18.8 kJ/mol value 19 obtained for the [4Fe-4S] 1+/2+ variant within the same Pf Fd D14C protein framework. The significantly higher reorganization energy of [3Fe-4S] explains its less frequent occurrence in electron-transfer proteins as compared to [4Fe-4S].…”

“…16–22 Density functional theory (DFT) has a long history of successful applications to Fe-S clusters, including those to Pf Fd and [3Fe-4S]. 19, 23–25 In this study, we use 57 Fe-NRVS together with DFT to probe vibrational dynamics of the [3Fe-4S] cluster in Pf Fd D14C at two oxidation levels, and compare our results to those from an earlier account on the [4Fe-4S] variant from the same protein. 19 …”

Heme: From quantum spin crossover to oxygen manager of life

“…The iron(II)-iron(III) redox couple can produce fast electron transfer in both high-spin and lowspin octahedral ligand fields, as the sixth redox-active electron shuffles between low-lying t2g-orbitals that point away from the metal-ligand bonds: this minimizes the change in metal-ligand bond lengths upon electron transfer and reduces reorganization energies. This advantage of the d 5 Incidentally, this design principle also defines the Td-symmetric iron-sulfur clusters, which are high-spin and thus transfer electrons in the low-lying degenerate e level [50] [51]. These circumstances are arguably a major reason why iron(II/III) is nature's predominant redox couple.…”