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Insights into the Observed trans-Bond Length Variations upon NO Binding to Ferric and Ferrous Porphyrins with Neutral Axial Ligands.

ABSTRACT: NO is well-known for its trans effect. NO binding to ferrous hemes of the form (por)Fe(L) (L = neutral N-based ligand) to give the {FeNO}⁷ (por)Fe(NO)(L) product results in a lengthening of the axial trans Fe-L bond. In contrast, NO binding to the ferric center in [(por)Fe(L)]⁺ to give the {FeNO}⁶ [(por)Fe(NO)(L)]⁺ product results in a shortening of the trans Fe-L bond. NO binding to both ferrous and ferric centers involves the lowering of their spin states. Density functional theory (DFT) calculations were used to probe the experimentally observed trans-bond shortening in some NO adducts of ferric porphyrins. We show that the strong σ antibonding interaction of d _{z ²} and the axial (L) ligand p orbitals present in the Fe(II) systems is absent in the Fe(III) systems, as it is now in an unoccupied orbital. This feature, combined with a lowering of spin state upon NO binding, provides a rationale for the observed net trans-bond shortening in the {FeNO}⁶ but not the {FeNO}⁷ derivatives.

SUBMITTER: Khade RL

PROVIDER: S-EPMC8482462 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Evidence for microbial Fe redox cycling was documented in a circumneutral pH groundwater seep near Bloomington, Indiana. Geochemical and microbiological analyses were conducted at two sites, a semi-consolidated microbial mat and a floating puffball structure. In situ voltammetric microelectrode measurements revealed steep opposing gradients of O(2) and Fe(II) at both sites, similar to other groundwater seep and sedimentary environments known to support microbial Fe redox cycling. The puffball structure showed an abrupt increase in dissolved Fe(II) just at its surface (?5?cm depth), suggesting an internal Fe(II) source coupled to active Fe(III) reduction. Most probable number enumerations detected microaerophilic Fe(II)-oxidizing bacteria (FeOB) and dissimilatory Fe(III)-reducing bacteria (FeRB) at densities of 10(2) to 10(5)?cells?mL(-1) in samples from both sites. In vitro Fe(III) reduction experiments revealed the potential for immediate reduction (no lag period) of native Fe(III) oxides. Conventional full-length 16S rRNA gene clone libraries were compared with high throughput barcode sequencing of the V1, V4, or V6 variable regions of 16S rRNA genes in order to evaluate the extent to which new sequencing approaches could provide enhanced insight into the composition of Fe redox cycling microbial community structure. The composition of the clone libraries suggested a lithotroph-dominated microbial community centered around taxa related to known FeOB (e.g., Gallionella, Sideroxydans, Aquabacterium). Sequences related to recognized FeRB (e.g., Rhodoferax, Aeromonas, Geobacter, Desulfovibrio) were also well-represented. Overall, sequences related to known FeOB and FeRB accounted for 88 and 59% of total clone sequences in the mat and puffball libraries, respectively. Taxa identified in the barcode libraries showed partial overlap with the clone libraries, but were not always consistent across different variable regions and sequencing platforms. However, the barcode libraries provided confirmation of key clone library results (e.g., the predominance of Betaproteobacteria) and an expanded view of lithotrophic microbial community composition.

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Insights into the Observed trans-Bond Length Variations upon NO Binding to Ferric and Ferrous Porphyrins with Neutral Axial Ligands.

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