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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Pulse radiolysis investigation on the mechanism of the catalytic action of Mn(II) - Pentaazamacrocycle compounds as superoxide dismutase mimetics
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Pulse radiolysis investigation on the mechanism of the catalytic action of Mn(II) - Pentaazamacrocycle compounds as superoxide dismutase mimetics

机译：脉冲辐解研究Mn（II）-五氮杂cro环化合物作为超氧化物歧化酶模拟物的催化作用机理

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摘要

The mechanism for the catalytic dismutation of superoxide by the Mn(II) pentaazamacrocyclic compound M40403 ([manganese(II) dichloro-(4R,9R, 14R, 19R)-3,10,13,20,26 pentaazatetracyclo [20.3.1.0(4,9).0(14,9)] hexacosa-1(26),-22(23),24-triene], SODm1) and two 2,21-dimethyl analogues has been investigated using pulse radiolysis. The initial rate of reaction between superoxide and the manganese compounds was found to be dependent on structure and pH, with the resulting transient adducts possessing spectral characteristics of the metal center being oxidized to Mn(III). Values for the pK(a) of the transient adducts (pK(a) = 5.65 +/- 0.05; 5.3 +/- 0.1 and < 5 for SODm1, SODm2 and SODm3, respectively) were obtained from spectrophotometric and conductivity measurements. Reaction of these transient adducts with further superoxide was highly structure dependent with the 2S,21S-dimethyl derivative (SODm2) being highly catalytically active at pH 7.4 (k(cat) = 2.35 x 10(8) M-1 s(-1)) compared to SODm1 (k(cat) = 3.55 x 10(6) M-1 s(-1)). In contrast the 2R,21R-dimethyl derivative (SODm3) showed no dismutation catalysis at all. The reaction rates of the initial complexes with HO2 center dot were significantly lower than with O-2(center dot-), and it is proposed that O-2(center dot-) is the main reactant in the catalytic cycle at pH 7.4. Variable temperature studies revealed major differences in the thermodynamics of the catalytic cycles involving SODm2 or SODm1. In the case of SODm2, the observed high entropic contribution to the activation energy is indicative of ligand conformational changes during the catalytic step. These results have provided the basis for a new mechanism for the catalytic dismutation of superoxide by Mn(II)-pentaazamacrocycle SOD mimetics.
机译：锰（II）五氮杂大环化合物M40403（[锰（II）二氯-（4R，9R，14R，19R）-3,10,13,20,26五氮杂四环[20.3.1.0（ 4,9）.0（14,9）] hexacosa-1（26），-22（23），24-triene]，SODm1）和两个2,21-二甲基类似物已使用脉冲放射分解法进行了研究。发现超氧化物和锰化合物之间的初始反应速率取决于结构和pH，所得的具有金属中心光谱特征的瞬态加合物被氧化成Mn（III）。从分光光度法和电导率测量中获得了瞬态加合物的pK（a）值（pK（a）= 5.65 +/- 0.05; SODm1，SODm2和SODm3分别为5.3 +/- 0.1和<5）。这些瞬态加合物与其他超氧化物的反应高度依赖结构，2S，21S-二甲基衍生物（SODm2）在pH 7.4下具有高催化活性（k（cat）= 2.35 x 10（8）M-1 s（-1） ）相较于SODm1（k（cat）= 3.55 x 10（6）M-1 s（-1））。相反，2R，21R-二甲基衍生物（SODm3）根本没有显示出歧化催化作用。初始与HO2中心点的络合物的反应速率明显低于与O-2（中心点）的络合物，并提出在pH 7.4下，O-2（中心点）是催化反应的主要反应物。可变温度研究表明，涉及SODm2或SODm1的催化循环的热力学存在重大差异。在SODm2的情况下，观察到的高熵对活化能的贡献表明了催化步骤中配体的构象变化。这些结果为Mn（II）-五氮杂大环超氧化物歧化酶模拟物催化超氧化物歧化的新机理提供了基础。

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