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Effect of Hydrogen Bonding on Innocent and Non-innocent Axial Ligands Bound to Iron Porphyrins

Abstract

Most known heme enzymes utilize hydrogen bonding interactions in their active site to control electronic and geometric structure and the ensuing reactivity. The details of these weak 2nd sphere interactions are slowly unravelling through spectroscopic and theoretical investigations in addition to biochemical studies. In synthetic Fe porphyrins H bonding is found to alter the nature of hydrogen bonding by iron bound hydroxide ligand (H bond acceptor or donor) in a series of hydroxide complexes. In this manuscript, a series of Fe porphyrins having triazole ring appended in the distal site of the porphyrin macrocycle are synthesized. The triazole rings are substituted to systematically alter its electron density which tunes its H bonding to water molecules trapped inside the distal cavity which in turn H bonds to the axial ligands bound to the iron porphyrin. Resonance Raman data indicate that metal ligand bond strength changes with change in substitution on triazole ring for innocent ligands like hydroxide as well as non-innocent ligands like oxygen; albeit the mechanism by which hydrogen bonding affects these are very different. Additionally, H bonding interaction is also found to alter the pKa of ferric hydroxide complexes.

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Publication details

The article was received on 24 Sep 2018, accepted on 03 Dec 2018 and first published on 07 Dec 2018


Article type: Paper
DOI: 10.1039/C8DT03852J
Citation: Dalton Trans., 2018, Accepted Manuscript
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    Effect of Hydrogen Bonding on Innocent and Non-innocent Axial Ligands Bound to Iron Porphyrins

    A. Singha, K. Mittra and A. Dey, Dalton Trans., 2018, Accepted Manuscript , DOI: 10.1039/C8DT03852J

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