含錳超氧化物岐化酶之N3O2五牙配位基擬態化合物的合成、性質及超氧化物反應性探討
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2013
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為了模擬含錳過氧化物歧化酶(MnSOD)，本研究沿用之前本實驗所合成C2對稱的N3O2五牙配位基(H2BDPP)，經去質子化後與MnCl2反應可得五配位二價錳錯合物Mn(BDPP) (1)，錯合物1經氧化後可得穩定的三價錳錯合物Mn(BDPP)(OH) (2)、Mn(BDPP)(Cl) (3)及[Mn(BDPP)(H2O)](BF4) (4)，並利用紫外/可見光光譜、X光繞射結構解析以及循環伏安法，進行鑑定及探討。相對於Ag/Ag+參考電極，超氧離子歧化反應的還原電位應介於−0.24與+0.96伏特之間，使超氧離子的單電子氧化還原最好位於此範圍的中間值，錯合物1及4的還原電位分別為+0.125及−0.3伏特，有機會與KO2進行反應。當錯合物1與KO2於−80 ˚C下反應時，在UV/vis可見光譜上可以觀察到370, 447及720 nm處有特徵吸收峰，與過去文獻中MnIII-OOH中間態化合物的吸收光譜相似，就MnSOD的催化循環而言，MnIII-OOH確實參與反應機制當中。另一方面，錯合物4與KO2於室溫下反應，其紫外/可見光光譜與錯合物2相近，我們推測其反應過程為KO2將錯合物4去質子化後形成錯合物2。
In order to mimic the active site of MnSOD, a C2-symmetric N3O2 pentadentate ligand, H2BDPP prepared previously by our lab, was deprotonated and employed to react with MnCl2 to give a five-coordinate Mn(BDPP) (1). Complex 1 can be oxidized to form stable MnIII complexes, Mn(BDPP)(OH) (2), Mn(BDPP)(Cl) (3) and [Mn(BDPP) (H2O)](BF4) (4), which are characterized by UV/vis spectroscopy, X-ray crystallography and cyclic voltammetry. The reductive potential for dismutasing superoxide anion should be between −0.24 and +0.96 V (vs. Ag/Ag+), and preferentially near the middle of this range for one-electron oxidation and reduction of superoxide. The reductive potential of complexes 1 and 4 were +0.125 and −0.3 V, respectively. They have the potential to react with KO2. When complex 1 reacted with KO2 at −80 ˚C, three electronic absorptions (λmax = 370, 447, 720 nm) were observed. The UV/vis spectrum of the reaction mixture is similar to that of MnIII-OOH intermediate. According to the proposed MnSOD catalytic cycle, MnIII-OOH intermediate is certainly involved in the catalytic cycle. On the other hand, when complex 4 reacted with KO2 at room temperature, a UV/vis spectrum similar to that of complex 2 was obtained. We proposed that complex 4 was deprotonated by KO2 to form complex 2.
In order to mimic the active site of MnSOD, a C2-symmetric N3O2 pentadentate ligand, H2BDPP prepared previously by our lab, was deprotonated and employed to react with MnCl2 to give a five-coordinate Mn(BDPP) (1). Complex 1 can be oxidized to form stable MnIII complexes, Mn(BDPP)(OH) (2), Mn(BDPP)(Cl) (3) and [Mn(BDPP) (H2O)](BF4) (4), which are characterized by UV/vis spectroscopy, X-ray crystallography and cyclic voltammetry. The reductive potential for dismutasing superoxide anion should be between −0.24 and +0.96 V (vs. Ag/Ag+), and preferentially near the middle of this range for one-electron oxidation and reduction of superoxide. The reductive potential of complexes 1 and 4 were +0.125 and −0.3 V, respectively. They have the potential to react with KO2. When complex 1 reacted with KO2 at −80 ˚C, three electronic absorptions (λmax = 370, 447, 720 nm) were observed. The UV/vis spectrum of the reaction mixture is similar to that of MnIII-OOH intermediate. According to the proposed MnSOD catalytic cycle, MnIII-OOH intermediate is certainly involved in the catalytic cycle. On the other hand, when complex 4 reacted with KO2 at room temperature, a UV/vis spectrum similar to that of complex 2 was obtained. We proposed that complex 4 was deprotonated by KO2 to form complex 2.
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超氧化物歧化酶, 還原電位, superoxide dismutase, reductive potential