Ghosh Anindya, Mitchell Douglas A, Chanda Arani, Ryabov Alexander D, Popescu Delia Laura, Upham Erin C, Collins Gregory J, Collins Terrence J
Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA.
J Am Chem Soc. 2008 Nov 12;130(45):15116-26. doi: 10.1021/ja8043689. Epub 2008 Oct 17.
Exceptionally high peroxidase-like and catalase-like activities of iron(III)-TAML activators of H 2O 2 ( 1: Tetra-Amidato-Macrocyclic-Ligand Fe (III) complexes [ F e{1,2-X 2C 6H 2-4,5-( NCOCMe 2 NCO) 2CR 2}(OH 2)] (-)) are reported from pH 6-12.4 and 25-45 degrees C. Oxidation of the cyclometalated 2-phenylpyridine organometallic complex, [Ru (II)( o-C 6H 4py)(phen) 2]PF 6 ( 2) or "ruthenium dye", occurs via the equation [ Ru II ] + 1/2 H 2 O 2 + H +-->(Fe III - TAML) [ Ru III ] + H 2 O, following a simple rate law rate = k obs (per)[ 1][H 2O 2], that is, the rate is independent of the concentration of 2 at all pHs and temperatures studied. The kinetics of the catalase-like activity (H 2 O 2 -->(Fe III - TAML) H 2 O + 1/2 O 2) obeys a similar rate law: rate = k obs (cat)[ 1][H 2O 2]). The rate constants, k obs (per) and k obs (cat), are strongly and similarly pH dependent, with a maximum around pH 10. Both bell-shaped pH profiles are quantitatively accounted for in terms of a common mechanism based on the known speciation of 1 and H 2O 2 in this pH range. Complexes 1 exist as axial diaqua species [FeL(H 2O) 2] (-) ( 1 aqua) which are deprotonated to afford [FeL(OH)(H 2O)] (2-) ( 1 OH) at pH 9-10. The pathways 1 aqua + H 2O 2 ( k 1), 1 OH + H 2O 2 ( k 2), and 1 OH + HO 2 (-) ( k 4) afford one or more oxidized Fe-TAML species that further rapidly oxidize the dye (peroxidase-like activity) or a second H 2O 2 molecule (catalase-like activity). This mechanism is supported by the observations that (i) the catalase-like activity of 1 is controllably retarded by addition of reducing agents into solution and (ii) second order kinetics in H 2O 2 has been observed when the rate of O 2 evolution was monitored in the presence of added reducing agents. The performances of the 1 complexes in catalyzing H 2O 2 oxidations are shown to compare favorably with the peroxidases further establishing Fe (III)-TAML activators as miniaturized enzyme replicas with the potential to greatly expand the technological utility of hydrogen peroxide.
据报道，在pH值为6 - 12.4以及温度为25 - 45摄氏度的条件下，过氧化氢（H₂O₂）的铁（III）- TAML活化剂（1：四酰胺基大环配体铁（III）配合物[Fe{1,2 - X₂C₆H₂ - 4,5 - (NCOCMe₂NCO)₂CR₂}(OH₂)]⁻）具有极高的类过氧化物酶和类过氧化氢酶活性。环金属化的2 - 苯基吡啶有机金属配合物[Ru(II)(o - C₆H₄py)(phen)₂]PF₆（2）或“钌染料”的氧化反应通过方程式[RuII] + 1/2H₂O₂ + H⁺ -->(FeIII - TAML)[RuIII] + H₂O进行，遵循简单的速率定律rate = kobs(per)[1][H₂O₂]，也就是说，在所研究的所有pH值和温度下，反应速率与2的浓度无关。类过氧化氢酶活性（H₂O₂ -->(FeIII - TAML)H₂O + 1/2O₂）的动力学遵循类似的速率定律：rate = kobs(cat)[1][H₂O₂]）。速率常数kobs(per)和kobs(cat)强烈且相似地依赖于pH值，在pH约为10时达到最大值。基于该pH范围内1和H₂O₂的已知物种形成情况，两种钟形pH曲线都可以通过一种通用机制进行定量解释。配合物1以轴向二水合物物种[FeL(H₂O)₂]⁻（1水合物）形式存在，在pH值为9 - 10时去质子化生成[FeL(OH)(H₂O)]²⁻（1 OH）。途径1水合物 + H₂O₂（k₁）、1 OH + H₂O₂（k₂）和1 OH + HO₂⁻（k₄）产生一种或多种氧化态的Fe - TAML物种，这些物种进一步快速氧化染料（类过氧化物酶活性）或第二个H₂O₂分子（类过氧化氢酶活性）。以下观察结果支持了这一机制：（i）向溶液中添加还原剂可可控地抑制1的类过氧化氢酶活性；（ii）在添加还原剂的情况下监测O₂释放速率时，观察到了H₂O₂的二级动力学。结果表明，1配合物催化H₂O₂氧化的性能与过氧化物酶相比具有优势，进一步确立了铁（III）- TAML活化剂作为小型化酶复制品的地位，具有极大扩展过氧化氢技术应用的潜力。
