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  • Title: Energetics and structural consequences of axial ligand coordination in nonplanar nickel porphyrins.
    Author: Song Y, Haddad RE, Jia SL, Hok S, Olmstead MM, Nurco DJ, Schore NE, Zhang J, Ma JG, Smith KM, Gazeau S, Pécaut J, Marchon JC, Medforth CJ, Shelnutt JA.
    Journal: J Am Chem Soc; 2005 Feb 02; 127(4):1179-92. PubMed ID: 15669857.
    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.
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