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Storing redox equivalent in the phenalenyl backbone towards catalytic multi-electron reduction.

ABSTRACT: Storing and transferring electrons for multi-electron reduction processes are considered to be the key steps in various important chemical and biological transformations. In this work, we accomplished multi-electron reduction of a carboxylic acid via a hydrosilylation pathway where a redox-active phenalenyl backbone in Co(PLY-O,O)2(THF)2, stores electrons and plays a preponderant role in the entire process. This reduction proceeds by single electron transfer (SET) from the mono-reduced ligand backbone leading to the cleavage of the Si-H bond. Several important intermediates along the catalytic reduction reaction have been isolated and well characterized to prove that the redox equivalent is stored in the form of a C-H bond in the PLY backbone via a ligand dearomatization process. The ligand's extensive participation in storing a hydride equivalent has been conclusively elucidated via a deuterium labelling experiment. This is a rare example where the ligand orchestrates the multielectron reduction process leaving only the metal to maintain the conformational requirements and fine tunes the electronics of the catalyst.

SUBMITTER: Bhunia M

PROVIDER: S-EPMC6713874 | biostudies-other | 2019 Aug

REPOSITORIES: biostudies-other

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Storing redox equivalent in the phenalenyl backbone towards catalytic multi-electron reduction.

Bhunia Mrinal M Sahoo Sumeet Ranjan SR Shaw Bikash Kumar BK Vaidya Shefali S Pariyar Anand A Vijaykumar Gonela G Adhikari Debashis D Mandal Swadhin K SK

Chemical science 20190610 31

Storing and transferring electrons for multi-electron reduction processes are considered to be the key steps in various important chemical and biological transformations. In this work, we accomplished multi-electron reduction of a carboxylic acid via a hydrosilylation pathway where a redox-active phenalenyl backbone in Co(PLY-O,O)2(THF)2, stores electrons and plays a preponderant role in the entire process. This reduction proceeds by single electron transfer (SET) fr ...[more]

PMID: 31489166

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Project description:UnlabelledDissimilatory metal-reducing bacteria, such as Geobacter sulfurreducens, transfer electrons beyond their outer membranes to Fe(III) and Mn(IV) oxides, heavy metals, and electrodes in electrochemical devices. In the environment, metal acceptors exist in multiple chelated and insoluble forms that span a range of redox potentials and offer different amounts of available energy. Despite this, metal-reducing bacteria have not been shown to alter their electron transfer strategies to take advantage of these energy differences. Disruption of imcH, encoding an inner membrane c-type cytochrome, eliminated the ability of G. sulfurreducens to reduce Fe(III) citrate, Fe(III)-EDTA, and insoluble Mn(IV) oxides, electron acceptors with potentials greater than 0.1 V versus the standard hydrogen electrode (SHE), but the imcH mutant retained the ability to reduce Fe(III) oxides with potentials of ≤-0.1 V versus SHE. The imcH mutant failed to grow on electrodes poised at +0.24 V versus SHE, but switching electrodes to -0.1 V versus SHE triggered exponential growth. At potentials of ≤-0.1 V versus SHE, both the wild type and the imcH mutant doubled 60% slower than at higher potentials. Electrodes poised even 100 mV higher (0.0 V versus SHE) could not trigger imcH mutant growth. These results demonstrate that G. sulfurreducens possesses multiple respiratory pathways, that some of these pathways are in operation only after exposure to low redox potentials, and that electron flow can be coupled to generation of different amounts of energy for growth. The redox potentials that trigger these behaviors mirror those of metal acceptors common in subsurface environments where Geobacter is found.ImportanceInsoluble metal oxides in the environment represent a common and vast reservoir of energy for respiratory microbes capable of transferring electrons across their insulating membranes to external acceptors, a process termed extracellular electron transfer. Despite the global biogeochemical importance of metal cycling and the ability of such organisms to produce electricity at electrodes, fundamental gaps in the understanding of extracellular electron transfer biochemistry exist. Here, we describe a conserved inner membrane redox protein in Geobacter sulfurreducens which is required only for electron transfer to high-potential compounds, and we show that G. sulfurreducens has the ability to utilize different electron transfer pathways in response to the amount of energy available in a metal or electrode distant from the cell.

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Storing redox equivalent in the phenalenyl backbone towards catalytic multi-electron reduction.

Publications

Storing redox equivalent in the phenalenyl backbone towards catalytic multi-electron reduction.

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