Functional mimics of copper enzymes. Synthesis and stereochemical properties of the copper(II) complexes of a trinucleating ligand derived from l-histidine |
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| Institution: | 1. Dipartimento di Chimica Inorganica, Metallorganica e Analitica, Università di Milano, Centro CNR, Via Venezian 21, 20133 Milano, Italy;2. Dipartimento di Chimica Organica e Industriale, Università di Milano, Via Venezian 21, 20133 Milano, Italy;3. Dipartimento di Chimica Generale, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy;1. School of resources and chemical engineering, Sanming University, Sanming, Fujian, 365004, China;2. College of Materials Science & Engineering, Huaqiao University, Xiamen, Fujian, 361021, China;3. School of Materials Science and Engineering, Xiamen University of Technology, Xiamen, 361021, China;4. Department of Chemistry, Southern Methodist University, 3215 Daniel Avenue, Dallas, Texas, 75275-0314, USA;1. Henan Key Laboratory of Functional Salt Materials, Center for Advanced Materials Research, Zhongyuan University of Technology, Zhengzhou 450007, China;2. College of Materials Engineering, Henan International Joint Laboratory of Rare Earth Composite Materials, Henan University of Engineering, Zhengzhou 451191, China;3. State Key Laboratory of Materials Processing and Die & Mould Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China;1. Research Institute for Science and Technology, Kindai University, 3-4-1 Kowakae, Higashi-Osaka, Osaka, 577-8502, Japan;2. Department of Chemistry, Kindai University, 3-4-1 Kowakae, Higashi-Osaka, Osaka, 577-8502, Japan;3. Diffraction & Scattering Division, Japan Synchrotron Radiation Research Institute, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan;1. G. A. Razuvaev Institute of Organometallic Chemistry of Russian Academy of Sciences, Russian Federation;2. Nizhny Novgorod State University, Russian Federation |
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| Abstract: | The ligand piperazine-1,4-bis4-(N-(1-acetoxy-3-(1-methyl-1H-imidazol-4-yl))-2-propyl)-N-(1-methyl-1H-imidazol-2-ylmethyl)aminobutyl] (PHI) was synthesized by a multistep procedure starting from Nτ-methyl-l-histidine, piperazine-1,4-bis4-(4-oxo-4-butanoic) acid] and 1-methyl-1H-imidazole-2-carbaldehyde. This ligand has two potential tridentate, aminobis(imidazole) (A sites), and one bidentate, piperazine (B site), binding sites for metal ions and was employed for the synthesis of the binuclear Cu2PHI]4+ and the trinuclear Cu3PHI]6+ complexes, the latter of which features a coordination environment mimicking that present in the trinuclear clusters of the blue copper oxidases. For comparison purposes, the mononucleating ligand l-Nα-(1-methyl-1H-imidazol-2-ylmethyl)-Nτ-methylhistidine methyl ester (IH) and its complex CuIH]2+ have been also prepared. These copper(II) model complexes are the first reported which are directly derived from chiral l-histidine residues. A detailed analysis of the UV–vis, CD and EPR spectra of the complexes has established that the Cu(II) centers bound to PHI A sites are square-pyramidal in solution, with the amino and one imidazole donor in the equatorial plane and the additional imidazole group bound axially. This arrangement implies the adoption of an unusual conformation of λ chirality by the l-histidine residue and is determined by the attempts to minimize steric interference between the substituents at the tertiary amine donor group and the histidine residue bearing the C-α substituent acetoxymethylene group of the bound PHI ligand. For the less sterically crowded secondary amine group of the bound IH ligand, the histidine C-α substituent can occupy a pseudoaxial position, so that in the complex CuIH]2+ the `normal' arrangement with three equatorial nitrogen donors and δ chirality in the l-histidine chelate ring occurs. |
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