Highly Efficient Phosphodiester Hydrolysis Promoted by a Dinuclear Copper(II) Complex

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• 作者：Tamá ; s Gajda ; Yvonne Dü ; pre ; Ibolya Tö ; rö ; k ; Jeffrey Harmer ; Arthur Schweiger ; Jü ; rgen Sander ; Dirk Kuppert ; and Kaspar Hegetschweiler
• 刊名：Inorganic Chemistry
• 出版年：2001
• 出版时间：September 10, 2001
• 年：2001
• 卷：40
• 期：19
• 页码：4918 - 4927
• 全文大小：157K
• 年卷期：v.40,no.19(September 10, 2001)
• ISSN：1520-510X

文摘

The interaction of Cu^II with the ligand tdci (1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol) was studiedboth in the solid state and in solution. The complexes that were formed were also tested for phosphoesteraseactivity. The pentanuclear complex [Cu₅(tdciH_-2)(tdci)₂(OH)₂(NO₃)₂](NO₃)₄·6H₂O consists of two dinuclear unitsand one trinuclear unit, having two shared copper(II) ions. The metal centers within the pentanuclear structurehave three distinct coordination environments. All five copper(II) ions are linked by hydroxo/alkoxo bridgesforming a Cu₅O₆ cage. The Cu-Cu separations of the bridged centers are between 2.916 and 3.782 Å, whilethose of the nonbridged metal ions are 5.455-5.712 Å. The solution equilibria in the Cu^II-tdci system proved tobe extremely complicated. Depending on the pH and metal-to-ligand ratio, several differently deprotonated mono-,di-, and trinuclear complexes are formed. Their presence in solution was supported by mass, CW, and pulse EPRspectroscopic study, too. In these complexes, the metal ions are presumed to occupy tridentate {O_ax,N_eq,O_ax}coordination sites and the O-donors of tdci may serve as bridging units between two metal ions. Additionally,deprotonation of the metal-bound water molecules may occur. The dinuclear Cu₂LH_-3 species, formed aroundpH 8.5, provides outstanding rate acceleration for the hydrolysis of the activated phosphodiester bis(4-nitrophenyl)phosphate (BNPP). The second-order rate constant of BNPP hydrolysis promoted by the dinuclear complex (T =298 K) is 0.95 M^-1 s^-1, which is ca. 47600-fold higher than that of the hydroxide ion catalyzed hydrolysis (k_OH).Its activity is selective for the phosphodiester, and the hydrolysis was proved to be catalytic. The proposedbifunctional mechanism of the hydrolysis includes double Lewis acid activation and intramolecular nucleophiliccatalysis.