Ferric–Thiolate Bond Dissociation Studied with Electronic Structure Calculations

Abstract

The stability and reactivity of iron-sulfur clusters are fundamental properties for the biological function of these prosthetic groups. Here, we investigate the ferric-thiolate bond dissociation of model iron-sulfur tetrahedral complexes with high-level ab initio multiconfigurational electronic structure calculations. We find that the reaction mechanism is homolytic with a spin-crossing from the sextet state in the reactant to quartet state in the product. We also compare several density functionals and semiempirical configuration interaction with the high-level ab initio results to find an accurate but computationally more efficient method to describe the reaction. The functionals M06 and those based on the OPTX exchange functional show the best performance and may reasonably describe the various electron correlation effects involved in ferric-thiolate bond dissociation.

Modelling the Hydrolysis of Iron-Sulfur Clusters

“…The MAE observed for all functionals tested correspond to the TS of reactions C and E where left-right (multi-configurational) correlation is significant. 27 The performance of B3LYP-D3 and M06L is also good. Comparison with B3LYP shows that addition of dispersion corrections is important and justifies the good performance of M06 and M06L which account for dispersion in the original parametrizations.…”

“…Several molecular electronic structure methods were compared with the the CCSD(T) goldstandard level of theory in order to find suitable descriptions of FeS reactivity, following our previous studies. 12,13,16,17,27 Solvation and free energy contributions were evaluated with an all-atom hybrid QM/MM potential giving an accomplished view of water substitution reactions on iron and allowing the calibration of more approximate implicit solvent models. We found that geometries determined by the OLYP functional with a split-valence basis set and energetics obtained with a hybrid functional such as M06 or ωB97X-D3 and a triple-zeta basis set, both together with implicit solvation, provide a reasonably reliable and efficient procedure to model FeS reactivity in solution.…”

“…26 Previous calculations showed this functional provides a reasonable description of Fe-S bond dissociation. 27 Two-dimensional scans were used to search for TS in substitution (AnDn) reactions, restraining a linear combination of forming (Fe-O) and breaking (Fe-S) bonds and the proton coordinate when this atom was transferred to the sulfur leaving group (see more details of reaction coordinates below). These scans were done with the pDynamo library 28 version 1.9 interfaced with ORCA program version 3.0.1, 29 the OLYP functional, the def2-SVP basis set 30 and the COSMO implicit water model.…”

Upcycling of Electroplating Sludge to Prepare Erdite-Bearing Nanorods for the Adsorption of Heavy Metals from Electroplating Wastewater Effluent

“…When the prepared SPs were introduced to the effluent, erdite was rich in SPs and spontaneously hydrolyzed and generated various Fe/S-bearing complexes and clusters, such as =Fe(SH) 2 , =Fe(OH)(SH) and =Fe(SH) + [47]. These products, which are metastable, were further converted to Fe/S-bearing oxyhydroxide (such as =Fe-SH and =Fe-OH) through the homolytic cleavage of Fe-S-Fe bonds [48] after the release of OH − and HS − to the effluent (Figure 14). This phenomenon corresponds to the increase in the treated effluent pH from 7.3 to 8.6.…”

Modelling the Hydrolysis of Iron-Sulfur Clusters

“…A semiempirical potential specifically parametrized to model Fe-S bond dissociation 27 based on the PM6 general parametrization 45 with d-orbitals was also tested. Complete active space configuration interaction calculations 46 with 7 electrons in 7 orbitals were performed with orbitals determined from restricted-open shell (ROHF) calculations with fractional occupation.…”