| Summary: | 碩士 === 國立中興大學 === 化學系 === 91 === Nature uses a self-assembly principle building a supermolecular envelope around the metal center, to fine-tune the desired metal reactivity that can be adjusted as a function of coordination number, coordinate geometry, oxidation state, symmetry, chirality, and so on. Hence, metal ions in the active sites of many metalloenzymes exhibit distinctive spectral and chemical features. Here we describe a self-assembly methodology to synthesize a spiropentacopper (II) cluster self-enclosed by pyroglutamic acid ligands, K2Cu5(pGlu)6(OH)2．10H2O, namely Spiro-Cu5.
Spiro-Cu5, synthesized by one-step hydrothermal methods, contains square planar, square pyramidal, and distorted octahedral configurations being simultaneously present in three distinguish CuII (d9) ions of its asymmetric unit. The three mixed coordination geometries represent an entirely nature Jahn-Teller distortion of electronic Cu(II) configuration for the first time. The intra-cluster metal-metal separations are of 2.992(2), 3.185(2), and 3.549(3) Å. More interesting, the chiral pyroglutamic acid ligands for the first time reveal three different coordination preferences to encompass the novel spiropentacopper cluster within i-center.
In the presence of H2O2, Spiro-Cu5 can initiate hydroxy radicals ( ·OH ) and electron transfer to the phosphate backbone of nucleic acids, consequently cleave DNA. To our best knowledge, the spiropentacopper cluster is the first example capable of mediating DNA cleavage while in polynuclic species (M>3).
The present study illustrates the efficacy of the hydrothermal method to prepare nano-cluster systems in certain special situations containing amino acids, in which self-assembly metalosite processes may provide insights into related biological and catalytic processes. Spiro-Cu5 may open new perspectives for chiral catalysis, chiral memory, and magnetic bistability might also provide a pivotal role for the under- -standing of the mechanistic concepts of electron-transfer-communication in biological systems. Future work along these lines may lead us to as a whole new class of supramolecular nanoclusters related to metalloenzymes.
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