Axial and equatorial ligand effects on biomimetic cysteine dioxygenase model complexes.
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.
Manchester Interdisciplinary Biocenter and School of Chemical Engineering and Analytical Science, The University of Manchester, 131 Princess Street, Manchester M1 7DN, UK.
Luis E
LE
Gonzalez-Ovalle
Matthew G
MG
Quesne
Devesh
D
Kumar
David P
DP
Goldberg
Sam P
SP
de Visser
D040761:Biomimetic Materials / Q000737:chemistry*; D020134:Catalytic Domain; D050558:Cysteine Dioxygenase / Q000737:chemistry*; D058085:Iron Compounds / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D010100:Oxygen / Q000737:chemistry; D010636:Phenols / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry; D011789:Quantum Theory; D013237:Stereoisomerism; D013438:Sulfhydryl Compounds / Q000737:chemistry
D058085:Iron Compounds; D008024:Ligands; D010636:Phenols; D011725:Pyridines; D013438:Sulfhydryl Compounds; C042983:thiophenol; D050558:Cysteine Dioxygenase; D010100:Oxygen