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Exposing the inadequacy of redox formalisms by resolving redox inequivalence within isovalent clusters.

ABSTRACT: In this report we examine a family of trinuclear iron complexes by multiple-wavelength, anomalous diffraction (MAD) to explore the redox load distribution within cluster materials by the free refinement of atomic scattering factors. Several effects were explored that can impact atomic scattering factors within clusters, including 1) metal atom primary coordination sphere, 2) M-M bonding, and 3) redox delocalization in formally mixed-valent species. Complexes were investigated which vary from highly symmetric to fully asymmetric by ⁵⁷Fe Mössbauer and X-ray diffraction to explore the relationship between MAD-derived data and the data available from these widely used characterization techniques. The compounds examined include the all-ferrous clusters [ ⁿ Bu₄N][(^tbsL)Fe₃(?³-Cl)] (1) ([^tbsL]^6- = [1,3,5-C₆H₉(NC₆H₄-o-NSi ^t BuMe₂)₃]^6-]), (^tbsL)Fe₃(py) (2), [K(C₂₂₂)]₂[(^tbsL)Fe₃(?³-NPh)] (4) (C₂₂₂ = 2,2,2-cryptand), and the mixed-valent (^tbsL)Fe₃(?³-NPh) (3). Redox delocalization in mixed-valent 3 was explored with cyclic voltammetry (CV), zero-field ⁵⁷Fe Mössbauer, near-infrared (NIR) spectroscopy, and X-ray crystallography techniques. We find that the MAD results show an excellent correspondence to ⁵⁷Fe Mössbauer data; yet also can distinguish between subtle changes in local coordination geometries where Mössbauer cannot. Differences within aggregate oxidation levels are evident by systematic shifts of scattering factor envelopes to increasingly higher energies. However, distinguishing local oxidation levels in iso- or mixed-valent materials can be dramatically obscured by the degree of covalent intracore bonding. MAD-derived atomic scattering factor data emphasize in-edge features that are often difficult to analyze by X-ray absorption near edge spectroscopy (XANES). Thus, relative oxidation levels within the cluster were most reliably ascertained from comparing the entire envelope of the atomic scattering factor data.

SUBMITTER: Bartholomew AK

PROVIDER: S-EPMC6690028 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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Exposing the inadequacy of redox formalisms by resolving redox inequivalence within isovalent clusters.

Bartholomew Amymarie K AK Teesdale Justin J JJ Hernández Sánchez Raúl R Malbrecht Brian J BJ Juda Cristin E CE Ménard Gabriel G Bu Wei W Iovan Diana A DA Mikhailine Alexandre A AA Zheng Shao-Liang SL Sarangi Ritimukta R Wang SuYin Grass SG Chen Yu-Sheng YS Betley Theodore A TA

Proceedings of the National Academy of Sciences of the United States of America 20190719 32

In this report we examine a family of trinuclear iron complexes by multiple-wavelength, anomalous diffraction (MAD) to explore the redox load distribution within cluster materials by the free refinement of atomic scattering factors. Several effects were explored that can impact atomic scattering factors within clusters, including 1) metal atom primary coordination sphere, 2) M-M bonding, and 3) redox delocalization in formally mixed-valent species. Complexes were investigated which vary from hig ...[more]

PMID: 31324742

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Project description:A novel bacterial behavior called congregation was recently described in Shewanella oneidensis MR-1 as the accumulation of cells around insoluble electron acceptors (IEA). It is the result of a series of "run-and-reversal" events enabled by modulation of swimming speed and direction. The model proposed that the swimming cells constantly sense their surroundings with specialized outer membrane cytochromes capable of extracellular electron transport (EET). Up to this point, neither the congregation nor attachment behavior have been studied in any other strains. In this study, the wild type of S. oneidensis MR-1 and several deletion mutants as well as eight other Shewanella strains (Shewanella putrefaciens CN32, S. sp. ANA-3, S. sp. W3-18-1, Shewanella amazonensis SB2B, Shewanella loihica PV-4, Shewanella denitrificans OS217, Shewanella baltica OS155, and Shewanella frigidimarina NCIMB400) were screened for the ability to congregate. To monitor congregation and attachment, specialized cell-tracking techniques, as well as a novel cell accumulation after photo-bleaching (CAAP) confocal microscopy technique were utilized in this study. We found a strong correlation between the ability of strain MR-1 to accumulate on mineral surface and the presence of key EET genes such as mtrBC/omcA (SO_1778, SO_1776, and SO_1779) and gene coding for methyl-accepting protein (MCPs) with Ca+ channel chemotaxis receptor (Cache) domain (SO_2240). These EET and taxis genes were previously identified as essential for characteristic run and reversal swimming around IEA surfaces. CN32, ANA-3, and PV-4 congregated around both Fe(OH)3 and MnO2. Two other Shewanella spp. showed preferences for one oxide over the other: preferences that correlated with the metal content of the environments from which the strains were isolated: e.g., W3-18-1, which was isolated from an iron-rich habitat congregated and attached preferentially to Fe(OH)3, while SB2B, which was isolated from a MnO2-rich environment, preferred MnO2.

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Exposing the inadequacy of redox formalisms by resolving redox inequivalence within isovalent clusters.

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Exposing the inadequacy of redox formalisms by resolving redox inequivalence within isovalent clusters.

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