Hydroxylation of phenolic compounds by a peroxodicopper(II) complex: Further insight into the mechanism of tyrosinase
Hydroxylation of phenolic compounds by a peroxodicopper(II) complex: Further insight into the mechanism of tyrosinase
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DOI：
10.1021/ja0544298
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发表时间：
2005-12-28
影响因子：
15
通讯作者：
Casella, L
中科院分区：
文献类型：
--
作者：
Palavicini, S;Granata, A;Casella, L
双铜（I）配合物[Cu-2（MeL 66）]（2+）（其中MeL 66是六齿配体3，5-双-{双（2-（1-甲基-1H-苯并咪唑-2-基）-乙基]-氨基}-甲苯）在低温下与分子氧可逆反应形成μ-过氧加合物。在-80 ℃至-55 ℃的温度范围内，在丙酮中进行O-2结合的动力学研究，得到活化参数Δ H-1（不相等）= 40.4 +/- 2.2 kJ mol（-1），Delta S-1（不相等）= -41.4 +/- 10.8 J K-1 mol（-1）和Δ H-1（不相等）= 72.5 +/- 2.4 kJ mol（-1），Δ S--1（不相等）= 46.7 +/- 11.1 J K-1 mol（-1），分别用于正反应和逆反应，O-2 δ H度= -32.2 +/-2.2 U mol（-1），δ S度= -88.1 +/-10.7 J K-1 mol（-1）。在-55 ℃丙酮中研究了（Cu-2（MeL 66）O-2]（2+）对一系列对位取代苯酚盐的羟基化反应，结果表明该反应是以亲电芳香取代机理进行的，Hammett常数rho =-1.84。在-84 ° C和-70 ° C之间研究了对氰基苯酚钠浓度范围内苯酚羟基化的温度依赖性。速率曲线是双曲线的，能够导出单酚酶反应Δ H-ox的活化参数（不相等）= 29.1 +/- 3.0 kJ mol（-1），Δ S-ox（不相等）= -115 +/- 15 J K-1 mol-1，酚盐与μ-过氧物种的结合参数Δ H-b度= -8.1 +/-1.2kJ mol（-1），Δ S-b度= -8.9 +/-6.2JK-1 mol（-1）。因此，得到了[Cu-2（MeL 66）]（2+）的O-2结合和苯酚羟基化两个独立步骤的动力学和热力学参数。
The dicopper(l) complex [Cu-2(MeL66)](2+) (where MeL66 is the hexadentate ligand 3,5-bis-{bis(2-(1-methyl-1H-benzimidazol-2-yl)-ethyl]-amino}-methylbenzene) reacts reversibly with dioxygen at low temperature to form a mu-peroxo adduct. Kinetic studies of O-2 binding carried out in acetone in the temperature range from -80 to -55 degrees C yielded the activation parameters Delta H-1(not equal) = 40.4 +/- 2.2 kJ mol(-1), Delta S-1(not equal) = -41.4 +/- 10.8 J K-1 mol(-1) and Delta H--1(not equal) = 72.5 +/- 2.4 kJ mol(-1), Delta S--1(not equal) = 46.7 +/- 11.1 J K-1 mol(-1) for the forward and reverse reaction, respectively, and the binding parameters of O-2 Delta H degrees = -32.2 +/- 2.2 U mol(-1) and Delta S degrees = -88.1 +/- 10.7 J K-1 mol(-1). The hydroxylation of a series of p-substituted phenolate salts by (Cu-2(MeL66)O-2](2+) studied in acetone at -55 degrees C indicates that the reaction occurs with an electrophilic aromatic substitution mechanism, with a Hammett constant rho = -1.84. The temperature dependence of the phenol hydroxylation was studied between -84 and -70 degrees C for a range of sodium p-cyanophenolate concentrations. The rate plots were hyperbolic and enabled to derive the activation parameters for the monophenolase reaction Delta H-ox(not equal) = 29.1 +/- 3.0 kJ mol(-1), Delta S-ox(not equal) = -115 +/- 15 J K-1 mol-1, and the binding parameters of the phenolate to the mu-peroxo species Delta H-b degrees = -8.1 +/- 1.2 kJ mol(-1) and Delta S-b degrees = -8.9 +/- 6.2 J K-1 mol(-1). Thus, the complete set of kinetic and thermodynamic parameters for the two separate steps of O-2 binding and phenol hydroxylation have been obtained for [Cu-2(MeL66)](2+).