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首页> 外文期刊>Chemical science >A designed second-sphere hydrogen-bond interaction that critically influences the O–O bond activation for heterolytic cleavage in ferric iron–porphyrin complexes
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A designed second-sphere hydrogen-bond interaction that critically influences the O–O bond activation for heterolytic cleavage in ferric iron–porphyrin complexes

机译：设计的第二球形氢键相互作用，对铁卟鸡卟啉复合物中的o-o键活化进行致密地影响O-O键活化

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Heme hydroperoxidases catalyze the oxidation of substrates by H _(2) O _(2) . The catalytic cycle involves the formation of a highly oxidizing species known as Compound I , resulting from the two-electron oxidation of the ferric heme in the active site of the resting enzyme. This high-valent intermediate is formed upon facile heterolysis of the O–O bond in the initial Fe ~(III) –OOH complex. Heterolysis is assisted by the histidine and arginine residues present in the heme distal cavity. This chemistry has not been successfully modeled in synthetic systems up to now. In this work, we have used a series of iron( III ) porphyrin complexes (Fe ~(III) L2(Br), Fe ~(III) L3(Br) and Fe ~(III) MPh(Br)) with covalently attached pendent basic groups (pyridine and primary amine) mimicking the histidine and arginine residues in the distal-pocket of natural heme enzymes. The presence of pendent basic groups, capable of 2 ~(nd) sphere hydrogen bonding interactions, leads to almost 1000-fold enhancement in the rate of Compound I formation from peracids relative to analogous complexes without these residues. The short-lived Compound I intermediate formed at cryogenic temperatures could be detected using UV-vis electronic absorption spectroscopy and also trapped to be unequivocally identified by 9 GHz EPR spectroscopy at 4 K. The broad (2000 G) and axial EPR spectrum of an exchange-coupled oxoferryl-porphyrin radical species, [Fe ~(IV) O Por˙ ~(+) ] with g ~(eff) _(⊥) = 3.80 and g ~(eff) _(‖) = 1.99, was observed upon a reaction of the Fe ~(III) L3(Br) porphyrin complex with m -CPBA. The characterization of the reactivity of the Fe ~(III) porphyrin complexes with a substrate in the presence of an oxidant like m -CPBA by UV-vis electronic absorption spectroscopy showed that they are capable of oxidizing two equivalents of inorganic and organic substrate(s) like ferrocene, 2,4,6-tritertiary butyl phenol and o -phenylenediamine. These oxidations are catalytic with a turnover number (TON) as high as 350. Density Functional Theory (DFT) calculations show that the mechanism of O–O bond activation by 2nd sphere hydrogen bonding interaction from these pendent basic groups, which are protonated by a peracid, involves polarization of the O–O σ-bond, leading to lowering of the O–O σ*-orbital allowing enhanced back bonding from the iron center. These results demonstrate how inclusion of 2 ~(nd) sphere hydrogen bonding interaction can play a critical role in O–O bond heterolysis.
机译：血红液过氧化物酶通过H _（2）O _（2）催化基质的氧化。催化周期涉及形成称为化合物I的高氧化物种，由静息酶的活性位点中的二氧化血红素的两电子氧化产生。在初始Fe〜（III）-OOH复合物中的O-O键的体内异溶解时形成该高价质的中间体。通过在血红素远侧腔中存在的组氨酸和精氨酸残基辅助异溶解。该化学尚未在综合系统中成功建模。在这项工作中，我们使用了一系列铁（III）卟啉络合物（Fe〜（III）L2（BR），Fe〜（III）L3（BR）和Fe〜（III）MPH（BR）），共价附加椎体基碱基（吡啶和初级胺）模仿天然血红素酶的远端袋中的组氨酸和精氨酸残基。具有2〜（Nd）球体氢键相互作用的底层基团的存在导致在没有这些残留物的类似络合物中从哌酸形成的化合物I的速率几乎1000倍。可以使用UV-Vis电子吸收光谱检测在低温温度下形成的短寿命化合物I中间体，并捕获在4K的9GHz EPR光谱法中捕获以明确鉴定。广泛的（2000g）和交换的轴向EPR谱 - 用G〜（Eff）_（⊥）= 3.80和g〜（eff）_（‖）= 1.99，[fe〜（iv）o porα〜（+）] [fe〜（iv）opor˙〜（+）]被观察到Fe〜（III）L3（BR）卟啉复合物与M-CPBA的反应。 Fe〜（III）卟啉复合物在uV-Vis电子吸收光谱如M-CPBA存在如下存在氧化剂存在的情况下，它们能够氧化两当量的无机和有机基质（S. ）与二茂铁，2,4,6-三替替替苯酚和邻苯二胺。这些氧化具有高达350的转档数（吨）的催化性理论（DFT）计算表明，O-O键活化由第二球体氢键相互作用的O-O键活化由这些底形基团的反相，其由A质量质原子化。 peracid，涉及O-OΣ - 键的偏振，导致O-OΣ* -Borbital允许从铁中心增强后粘合。这些结果表明了如何包含2〜（Nd）球体氢键相互作用可以在O-O键异水中发挥关键作用。

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