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1. Syntheses, Structures, and Magnetic Properties of a Novel mer -[(bbp)Fe III (CN) 3 ] 2– Building Block (bbp: bis(2-benzimidazolyl)pyridine dianion) and Its Related Heterobimetallic Fe(III)–Ni(II) Complexes

   https://doi.org/10.1021/ic301661x  

   Panja, Anangamohan ; Guionneau, Philippe ; Jeon, Ie-Rang ; Holmes, Stephen M. ; Clérac, Rodolphe ; Mathonière, Corine ( November 2012 , Inorganic Chemistry)
2. Assessment of electronic structure methods for the determination of the ground spin states of Fe( ii ), Fe( iii ) and Fe( iv ) complexes

   https://doi.org/10.1039/C7CP01263B  

   Verma, Pragya ; Varga, Zoltan ; Klein, Johannes E. ; Cramer, Christopher J. ; Que, Lawrence ; Truhlar, Donald G. ( January 2017 , Physical Chemistry Chemical Physics)

   Our ability to understand and simulate the reactions catalyzed by iron depends strongly on our ability to predict the relative energetics of spin states. In this work, we studied the electronic structures of Fe 2+ ion, gaseous FeO and 14 iron complexes using Kohn–Sham density functional theory with particular focus on determining the ground spin state of these species as well as the magnitudes of relevant spin-state energy splittings. The 14 iron complexes investigated in this work have hexacoordinate geometries of which seven are Fe( ii ), five are Fe( iii ) and two are Fe( iv ) complexes. These are calculated using 20 exchange–correlation functionals. In particular, we use a local spin density approximation (LSDA) – GVWN5, four generalized gradient approximations (GGAs) – BLYP, PBE, OPBE and OLYP, two non-separable gradient approximations (NGAs) – GAM and N12, two meta-GGAs – M06-L and M11-L, a meta-NGA – MN15-L, five hybrid GGAs – B3LYP, B3LYP*, PBE0, B97-3 and SOGGA11-X, four hybrid meta-GGAs – M06, PW6B95, MPW1B95 and M08-SO and a hybrid meta-NGA – MN15. The density functional results are compared to reference data, which include experimental results as well as the results of diffusion Monte Carlo (DMC) calculations and ligand field theory estimates from the literature. For the Fe 2+ ion, all functionals except M11-L correctly predict the ground spin state to be quintet. However, quantitatively, most of the functionals are not close to the experimentally determined spin-state splitting energies. For FeO all functionals predict quintet to be the ground spin state. For the 14 iron complexes, the hybrid functionals B3LYP, MPW1B95 and MN15 correctly predict the ground spin state of 13 out of 14 complexes and PW6B95 gets all the 14 complexes right. The local functionals, OPBE, OLYP and M06-L, predict the correct ground spin state for 12 out of 14 complexes. Two of the tested functionals are not recommended to be used for this type of study, in particular M08-SO and M11-L, because M08-SO systematically overstabilizes the high spin state, and M11-L systematically overstabilizes the low spin state. 

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3. A mixed-valent Fe(II)Fe(III) species converts cysteine to an oxazolone/thioamide pair in methanobactin biosynthesis

   https://doi.org/10.1073/pnas.2123566119  

   Park, Yun Ji ; Jodts, Richard J. ; Slater, Jeffrey W. ; Reyes, Reyvin M. ; Winton, Valerie J. ; Montaser, Rana A. ; Thomas, Paul M. ; Dowdle, William B. ; Ruiz, Anahi ; Kelleher, Neil L. ; et al ( March 2022 , Proceedings of the National Academy of Sciences)

   The iron-containing heterodimeric MbnBC enzyme complex plays a central role in the biosynthesis of methanobactins (Mbns), ribosomally synthesized, posttranslationally modified natural products that bind copper with high affinity. MbnBC catalyzes a four-electron oxidation of a cysteine residue in its precursor-peptide substrate, MbnA, to an oxazolone ring and an adjacent thioamide group. Initial studies of MbnBC indicated the presence of both diiron and triiron species, complicating identification of the catalytically active species. Here, we present evidence through activity assays combined with electron paramagnetic resonance (EPR) and Mössbauer spectroscopic analysis that the active species is a mixed-valent, antiferromagnetically coupled Fe(II)Fe(III) center. Consistent with this assignment, heterologous expression of the MbnBC complex in culture medium containing less iron yielded purified protein with less bound iron but greater activity in vitro. The maximally activated MbnBC prepared in this manner could modify both cysteine residues in MbnA, in contrast to prior findings that only the first cysteine could be processed. Site-directed mutagenesis and multiple crystal structures clearly identify the two essential Fe ions in the active cluster as well as the location of the previously detected third Fe site. Moreover, structural modeling indicates a role for MbnC in recognition of the MbnA leader peptide. These results add a biosynthetic oxidative rearrangement reaction to the repertoire of nonheme diiron enzymes and provide a foundation for elucidating the MbnBC mechanism. 

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4. Hematite/selenium disulfide hybrid catalyst for enhanced Fe(III)/Fe(II) redox cycling in advanced oxidation processes

   https://doi.org/10.1016/j.jhazmat.2021.127376  

   You, Yingying ; Huang, Shaobin ; Chen, Moshan ; Parker, Kimberly M. ; He, Zhen ( February 2022 , Journal of Hazardous Materials)
5. Enhanced terrestrial Fe(II) mobilization identified through a novel mechanism of microbially driven cave formation in Fe(III)-rich rocks

   https://doi.org/10.1038/s41598-022-21365-3  

   Parker, Ceth W. ; Senko, John M. ; Auler, Augusto S. ; Sasowsky, Ira D. ; Schulz, Frederik ; Woyke, Tanja ; Barton, Hazel A. ( October 2022 , Scientific Reports)

   Most cave formation requires mass separation from a host rock in a process that operates outward from permeable pathways to create the cave void. Given the poor solubility of Fe(III) phases, such processes are insufficient to account for the significant iron formation caves (IFCs) seen in Brazilian banded iron formations (BIF) and associated rock. In this study we demonstrate that microbially-mediated reductive Fe(III) dissolution is solubilizing the poorly soluble Fe(III) phases to soluble Fe(II) in the anoxic zone behind cave walls. The resultant Fe(III)-depleted material (termedsub muros) is unable to maintain the structural integrity of the walls and repeated rounds of wall collapse lead to formation of the cave void in an active, measurable process. This mechanism may move significant quantities of Fe(II) into ground water and may help to explain the mechanism of BIF dissolution and REE enrichment in the generation of canga. The role of Fe(III) reducing microorganism and mass separation behind the walls (outward-in, rather than inward-out) is not only a novel mechanism of speleogenesis, but it also may identify a previously overlooked source of continental Fe that may have contributed to Archaean BIF formation.

    

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