1. Energetics and Structural Consequences of Axial Ligand Coordination in Nonplanar Nickel Porphyrins
- Author
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Daniel J. Nurco, Jean-Claude Marchon, Jian-Guo Ma, Jun Zhang, Jacques Pécaut, Kevin M. Smith, Saphon Hok, Marilyn M. Olmstead, Stephanie Gazeau, Raid E. Haddad, Neal E. Schore, John A. Shelnutt, Song-Ling Jia, Yujiang Song, and Craig J. Medforth
- Subjects
Models, Molecular ,Absorption spectroscopy ,Metalloporphyrins ,Stereochemistry ,Resonance Raman spectroscopy ,Molecular Conformation ,chemistry.chemical_element ,Heme ,Crystallography, X-Ray ,Ligands ,Spectrum Analysis, Raman ,Biochemistry ,Catalysis ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Nickel ,polycyclic compounds ,Molecule ,heterocyclic compounds ,Chemistry ,General Chemistry ,Ligand (biochemistry) ,Porphyrin ,Binding constant ,Crystallography ,Thermodynamics ,Spectrophotometry, Ultraviolet ,Oxidoreductases - Abstract
The effects of ruffling on the axial ligation properties of a series of nickel(II) tetra(alkyl)porphyrins have been investigated with UV-visible absorption spectroscopy, resonance Raman spectroscopy, X-ray crystallography, classical molecular mechanics calculations, and normal-coordinate structural decomposition analysis. For the modestly nonplanar porphyrins, porphyrin ruffling is found to cause a decrease in binding affinity for pyrrolidine and piperidine, mainly caused by a decrease in the binding constant for addition of the first axial ligand; ligand binding is completely inhibited for the more nonplanar porphyrins. The lowered affinity, resulting from the large energies required to expand the core and flatten the porphyrin to accommodate the large high-spin nickel(II) ion, has implications for nickel porphyrin-based molecular devices and the function of heme proteins and methyl-coenzyme M reductase.
- Published
- 2005