三價鐵超氧化物之反應性、熱力學及中間體探討
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2021
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Abstract
自然界中，細胞色素P450具有將烷類轉化成醇類的重要催化能力，在其反應機制中有許多不穩定的中間體。其中，鐵超氧化物及鐵氫過氧化物擔任極重要的角色。本研究使用實驗室先前所開發之 N3O2 五牙基 H2BDPＲP，將其苯環上𝜌-位置分別置換成溴、甲基與三級丁基。將配位基去質子化後與 FeCl2 反應可生成五配位二價鐵錯合物 Fe(BDPRP)。先與氧氣反應生成鐵超氧化物Fe(BDPRP)(O2•)。此時加入三氟甲磺酸（Trifluoromethanesulfonic acid, HOTf）會反應生成鐵氫過氧化物[Fe(BDPRP)(OOH)](OTf)。利用DBU滴定所確認的pKa值與循環伏安法（cyclic voltammetry, CV）測得的氧化還原半電位可定出三價鐵氫過氧化物 Fe(BDPRP)(OOH)的鍵能及其反應性。另外透過電子順磁共振光譜儀 (Electron Paramagnetic Resonance Spectrometer, EPR)及穆斯堡爾光譜儀 (Mössbauer Spectrometer)初步證明鐵氫過氧化物之鐵中心可能為正四價高自旋S = 2的電子組態。上述研究可幫助我們更詳細地了解由氧合酶之含金屬酵素進行氧氣活化時的反應機制，及所製備之仿生化合物的反應性探討。
In nature, cytochrome P450 possesses a very important catalytic ability of converting alkanes into alcohols. Two active intermediates, iron superoxide and iron hydroperoxide, are essential in the P450 catalytic cycle. In order to produce stable biomimetic intermediates, the N3O2 pentadentate ligand, H2BDPP, developed previously in our laboratory was modified to H2BDPRP (R = Br, Me, tBu). After deprotonation of H2BDPRP by NaH, the resulting ligands was reacted with FeCl2 forming the pentacoordinated Fe(II) complexes Fe(BDPRP).The Fe(III)-superoxo complexes, Fe(BDPRP)(O2•), were first generated by bubbling O2 into MeTHF solutions of Fe(BDPRP) at – 120 °C. Addition of 1 equiv of trifluoromethanesulfonic acid (HOTf) into the solution of Fe(BDPRP)(O2•) produced the Fe(IV)-hydroperoxo complexes, [Fe(BDPＲP)(OOH)](OTf). If Fe(BDPRP)(O2•) reacted with TEMPOH, the Fe(III)-hydroperoxo complexes, Fe(BDPRP)(OOH), were formed. The bond energies of the OO−H bond in Fe(BDPRP)(OOH) were determined by pKa values confirmed by DBU titration and redox potential (E1/2) obtained by cyclic voltammetry. In addition, Mössbauer and EPR studies on [Fe(BDPtBuP)(OOH)](OTf) preliminary indicate the high-spin (S = 2) FeIV center. The studies described above shed light on understanding more details of the mechanism proceeded in O2 activation carried out by metallo-enzymes of oxygenases and reactivity of our model compounds.
In nature, cytochrome P450 possesses a very important catalytic ability of converting alkanes into alcohols. Two active intermediates, iron superoxide and iron hydroperoxide, are essential in the P450 catalytic cycle. In order to produce stable biomimetic intermediates, the N3O2 pentadentate ligand, H2BDPP, developed previously in our laboratory was modified to H2BDPRP (R = Br, Me, tBu). After deprotonation of H2BDPRP by NaH, the resulting ligands was reacted with FeCl2 forming the pentacoordinated Fe(II) complexes Fe(BDPRP).The Fe(III)-superoxo complexes, Fe(BDPRP)(O2•), were first generated by bubbling O2 into MeTHF solutions of Fe(BDPRP) at – 120 °C. Addition of 1 equiv of trifluoromethanesulfonic acid (HOTf) into the solution of Fe(BDPRP)(O2•) produced the Fe(IV)-hydroperoxo complexes, [Fe(BDPＲP)(OOH)](OTf). If Fe(BDPRP)(O2•) reacted with TEMPOH, the Fe(III)-hydroperoxo complexes, Fe(BDPRP)(OOH), were formed. The bond energies of the OO−H bond in Fe(BDPRP)(OOH) were determined by pKa values confirmed by DBU titration and redox potential (E1/2) obtained by cyclic voltammetry. In addition, Mössbauer and EPR studies on [Fe(BDPtBuP)(OOH)](OTf) preliminary indicate the high-spin (S = 2) FeIV center. The studies described above shed light on understanding more details of the mechanism proceeded in O2 activation carried out by metallo-enzymes of oxygenases and reactivity of our model compounds.
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鐵超氧化物, 鐵氫過氧化物, iron superoxo, iron hydroperoxo