Document Detail

Axial ligand exchange of N-heterocyclic cobalt(III) Schiff base complexes: molecular structure and NMR solution dynamics.
MedLine Citation:
PMID:  23282130     Owner:  NLM     Status:  MEDLINE    
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, and consequently alters structure and causes inhibition. 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 (NH(3)), N-methylimidazole (NMeIm), and pyridine (Py)] were 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 > NH(3) ≫ 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.
Lisa M Manus; Robert J Holbrook; Tulay A Atesin; Marie C Heffern; Allison S Harney; Amanda L Eckermann; Thomas J Meade
Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.     Date:  2013-01-02
Journal Detail:
Title:  Inorganic chemistry     Volume:  52     ISSN:  1520-510X     ISO Abbreviation:  Inorg Chem     Publication Date:  2013 Jan 
Date Detail:
Created Date:  2013-01-18     Completed Date:  2013-08-12     Revised Date:  2014-01-24    
Medline Journal Info:
Nlm Unique ID:  0366543     Medline TA:  Inorg Chem     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1069-76     Citation Subset:  IM    
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MeSH Terms
Cobalt / chemistry*
Coordination Complexes / chemistry*,  classification
Crystallography, X-Ray
Drug Stability
Hydrogen-Ion Concentration
Magnetic Resonance Spectroscopy
Molecular Structure
Schiff Bases / chemistry*
Grant Support
Reg. No./Substance:
0/Coordination Complexes; 0/Ligands; 0/Schiff Bases; 3G0H8C9362/Cobalt

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