Modeling Tyrosinase and Catecholase Activity Using New m-Xylyl-Based Ligands with Bidentate Alkylamine Terminal Coordination

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• 作者：Sukanta Mandal ; Jhumpa Mukherjee ; Francesc Lloret ; Rabindranath Mukherjee
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：December 17, 2012
• 年：2012
• 卷：51
• 期：24
• 页码：13148-13161
• 全文大小：561K
• 年卷期：v.51,no.24(December 17, 2012)
• ISSN：1520-510X

文摘

Chemical model systems possessing the reactivity aspects of both tyrosinase and catechol oxidase are presented. Using two m-xylyl-based ligands providing bidentate alkylamine terminal coordination, 1,3-bis[(N,N-dimethylaminoethyl)aminomethyl]benzene (L^H,H) and 1,3-bis[(N,N,N鈥?trimethylaminoethyl)aminomethyl]benzene (L^Me,Me), four new dicopper(I) complexes, [Cu^I₂(L^H,H)(MeCN)₄][ClO₄]₂ (1), [Cu^I₂(L^H,H)(PPh₃)₂(MeCN)₂][ClO₄]₂ (2), [Cu^I₂(L^Me,Me)(MeCN)₂][ClO₄]₂ (3), and [Cu^I₂(L^Me,Me)(PPh₃)₂][ClO₄]₂ (4), have been synthesized and characterized. Complex 2 has been structurally characterized. Reaction of the dicopper(I) complex 3²⁺ with dioxygen at 183 K generates putative bis(渭鈥搊xo)dicopper(III) intermediate (absorption spectroscopy). Oxygenation of 1 and 3 brings about m-xylyl-ring hydroxylation (monooxygenase-like activity), with a noticeable color change from pale-yellow to dark green. The presence of phenoxo- and hydroxo-bridges in the end products [Cu^II₂(L^H,H鈥揙)(OH)(MeCN)₂][ClO₄]₂ (5) and [Cu^II₂(L^Me,Me鈥揙)(OH)(OClO₃)][ClO₄]路MeCN(6) has been authenticated by structural characterization. Oxygenation of 3 afforded not only the green complex 6 isolation but also a blue complex [Cu^II₂(L^Me,Me)(OH)₂][ClO₄]₂ (7). Variable temperature magnetic susceptibility measurements on 5 and 6 establish that the Cu^II centers are strongly antiferromagnetically coupled [singlet鈥搕riplet energy gap (J) = 鈭?28 cm^鈥? (5) and 鈭?05 cm^鈥? (6)]. The abilities of phenoxo- and hydroxo-bridged dicopper(II) complexes 5 and 6, the previously reported complex [Cu^II₂(L¹鈥揙)(OH)(OClO₃)₂]路1.5H₂O (8) (L¹鈥揙H = 1,3-bis[(2-dimethylaminoethyl)iminomethyl]phenol), and [Cu^II₂(L²鈥揙)(OH)(OClO₃)][ClO₄] (9) (L²鈥揙H = 1,3-[(2-dimethylaminoethyl)iminomethyl][(N,N,N鈥?trimethyl)aminoethyl]-4-methylphenol) have been examined to catalyze the oxidation of catechol to quinone (catecholase activity of tyrosinase and catechol oxidase-like activity) by employing the model substrate 3,5-di-tert-butylcatechol. Saturation kinetic studies have been performed on these systems to arrive at the following reactivity order [k_cat/K_M (catalytic efficiency) 脳 10^鈥? (M^鈥? h^鈥?)]: 470 (6) > 367 (5) > 128 (9) > 90 (8).