非血基質三價錳羥基錯合物之反應性研究

Abstract

在許多的酵素催化循環中，錳金屬羥基化合物被認為是可能存在的反應中間物之一，尤其是第二光系統(Photosystem II)中的氧釋放複合體(Oxygen-Evolving Complex)、核糖核苷酸還原酶(Ribonucleotide Reductase)和含錳脂氧合酶(Mn-Lipoxygenase)，為了能模擬這些存在酵素中的中間物，本研究利用實驗室所開發的三價錳錯合物：[MnIIIBDPP(H2O)]BF4 (2)、MnIIIBDPP(OH) (3)、MnIIIBDPP(Cl) (4)，透過Evans method和EPR光譜，來驗證其三價錳錯合物為高整自旋態(S = 2)。錯合物 3 加入TEMPOH會反應成二價錳錯合物MnIIBDPP (1)和一當量水分子。另一方面，將二氧化碳通入錯合物 3 會反應生成MnIIIBDPP(HCO3)，再通入氮氣會回到錯合物 3，錯合物 2 更可以透過氧化劑Magic Blue (Tris(4-bromophenyl) aminium hexachlorido antimonate)氧化成錯合物 5 ，再加入有機鹼DBU會反應成錯合物 6，錯合物 6 也可以藉由錯合物 3 加上氧化劑 Magic Blue 反應獲得，推測其錯合物 5 與6 分別為[MnIVBDPP(H2O)]2+和[MnIVBDPP(OH)]+，透過UV-vis光譜和EPR光譜來鑑定，錯合物 5 與 6 為高自旋四價錳錯合物(S = 3/2)。Manganese hydroxide species are proposed intermediates in the catalytic cycles of most manganese containing enzymes, especially for Photosystem II, Ribonucleotide Reductase and Mn-Lipoxygenase. In order to mimic these intermediates, A serial of MnIIIBDPP complexes: [MnIIIBDPP(H2O)]BF4 (2), MnIIIBDPP(OH) (3), MnIIIBDPP(Cl) (4), were prepared. Through Evans method or EPR spectra, the manganese(III) complexes are confirmed to be high integral spin complexes (S = 2). Complex 3 can react with TEMPOH to form MnIIBDPP (1) and H¬2O via hydrogen atom abstraction, and with CO2 to form MnIIIBDPP(HCO3). After bubbling nitrogen gas through the solution of MnIIIBDPP(HCO3), complex 3 will be regenerated. Complex 2 can be oxidized to manganese(IV) complex, [MnIVBDPP-H2O]2+ (5), at -80°C by Magic Blue (Tris(4-bromophenyl)aminium hexachloridoantimonate). Addition of one equiv of organic base DBU to the solution of 5 will form a manganese(IV) hydroxide [MnIVBDPP-OH]+ (6) which can also be produced from Complex 3 by adding one equiv of Magic Blue. Complexes 5 and 6 will convert to complex 2 by reacting with TEMPOH. The UV-vis and EPR spectra support that both complexes 5 and 6 are both high spin manganese(IV) complexes (S = 3/2).