Issue 28, 2012
From the journal:

Organic & Biomolecular Chemistry

Axial and equatorial ligand effects on biomimetic cysteine dioxygenase model complexes†

Luis E. Gonzalez-Ovalle,a   Matthew G. Quesne,a   Devesh Kumar,*b   David P. Goldberg*c  and  Sam P. de Visser*a  

* Corresponding authors

a Manchester Interdisciplinary Biocenter and School of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester M1 7DN, UK
E-mail: sam.devisser@manchester.ac.uk
Fax: +44 (0)161306 5201

b Department of Applied Physics, School of Physical Sciences, Babasaheb, Bhimrao Ambedkar University, Vidya Vihar, Rae Bareilly Road, Lucknow 226-025, India
E-mail: dkclcre@yahoo.com

c Department of Chemistry, The Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, USA
E-mail: dpg@jhu.edu

Abstract

Density functional theory (DFT) calculations are presented on biomimetic model complexes of cysteine dioxygenase and focus on the effect of axial and equatorial ligand placement. Recent studies by one of us [Y. M. Badiei, M. A. Siegler and D. P. Goldberg, J. Am. Chem. Soc. 2011, 133, 1274] gave evidence of a nonheme iron biomimetic model of cysteine dioxygenase using an i-propyl-bis(imino)pyridine, equatorial tridentate ligand. Addition of thiophenol, an anion – either chloride or triflate – and molecular oxygen, led to several possible stereoisomers of this cysteine dioxygenase biomimetic complex. Moreover, large differences in reactivity using chloride as compared to triflate as the binding anion were observed. Here we present a series of DFT calculations on the origin of these reactivity differences and show that it is caused by the preference of coordination site of anion versus thiophenol binding to the chemical system. Thus, stereochemical interactions of triflate and the bulky iso-propyl substituents of the ligand prevent binding of thiophenol in the trans position using triflate. By contrast, smaller anions, such as chloride, can bind in either cis or trans ligand positions and give isomers with similar stability. Our calculations help to explain the observance of thiophenol dioxygenation by this biomimetic system and gives details of the reactivity differences of ligated chloride versus triflate.

Graphical abstract: Axial and equatorial ligand effects on biomimetic cysteine dioxygenase model complexes

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Article information

DOI
https://doi.org/10.1039/C2OB25406A
Article type
Paper
Submitted
24 Feb 2012
Accepted
30 May 2012
First published
31 May 2012

Org. Biomol. Chem., 2012,10, 5401-5409

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Axial and equatorial ligand effects on biomimetic cysteine dioxygenase model complexes

L. E. Gonzalez-Ovalle, M. G. Quesne, D. Kumar, D. P. Goldberg and S. P. de Visser, Org. Biomol. Chem., 2012, 10, 5401 DOI: 10.1039/C2OB25406A

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