Axial ligand exchange of N-heterocyclic cobalt(III) Schiff base complexes: molecular structure and NMR solution dynamics
| Autor: | Robert J. Holbrook, Marie C. Heffern, Amanda L. Eckermann, Allison S. Harney, Lisa M. Manus, Tulay A. Atesin, Thomas J. Meade |
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| Rok vydání: | 2013 |
| Předmět: |
Schiff base
Magnetic Resonance Spectroscopy Molecular Structure Stereochemistry Ligand Acetylacetone Rational design Nuclear magnetic resonance spectroscopy Cobalt Hydrogen-Ion Concentration Crystallography X-Ray Ligands Dissociation (chemistry) Article Inorganic Chemistry chemistry.chemical_compound chemistry Drug Stability Coordination Complexes Molecule Physical and Theoretical Chemistry Histidine Schiff Bases |
| Zdroj: | Inorganic chemistry. 52(2) |
| ISSN: | 1520-510X |
| Popis: | The kinetic and thermodynamic ligand exchange dynamics are important considerations in the rational design of metal-based therapeutics and therefore, require detailed investigation. Co(III) Schiff base complex derivatives of bis(acetylacetone) ethylenediimine [acacen] have been found to be potent enzyme and transcription factor inhibitors. These complexes undergo solution exchange of labile axial ligands. Upon dissociation, Co(III) irreversibly interacts with specific histidine residues of a protein, that alters structure and causes inhibition. In order to guide the rational design of next generation agents, understanding the mechanism and dynamics of the ligand exchange process is essential. To investigate the lability, pH stability, and axial ligand exchange of these complexes in the absence of proteins, the pD- and temperature-dependent axial ligand substitution dynamics of a series of N-heterocyclic [Co(acacen)(X)2]+ complexes [where X = 2-methylimidazole (2MeIm), 4-methylimidazole (4MeIm), ammine (NH3), N-methylimidazole (NMeIm), and pyridine (Py)] were prepared and characterized by NMR spectroscopy. The pD stability was shown to be closely related to the nature of the axial ligand with the following trend toward aquation: 2MeIm > NH3 >> 4MeIm > Py > Im > NMeIm. Reaction of each [Co(III)(acacen)(X)2]+ derivative with 4MeIm showed formation of a mixed ligand Co(III) intermediate via a dissociative ligand exchange mechanism. The stability of the mixed ligand adduct was directly correlated to the pD-dependent stability of the starting Co(III) Schiff base with respect to [Co(acacen)(4MeIm)2]+. Crystal structure analysis of the [Co(acacen)(X)2]+ derivatives confirmed the trends in stability observed by NMR spectroscopy. Bond distances between the Co(III) and the axial nitrogen atoms were longest in the 2MeIm derivative as a result of distortion in the planar tetradentate ligand, and this was directly correlated to axial ligand lability and propensity toward exchange. |
| Databáze: | OpenAIRE |
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