非血基質的苯甲基取代三價鈷超氧化物之反應性和催化研究

Abstract

在自然界中，兒茶酸2,3-雙加氧酶 (Homoprotocatechuate 2,3-Dioxygenase)，可藉由氧氣將高原兒茶酸 (HPCA) 這種雙醇化合物切割，轉化為半醛的產物，在催化反應的進行中，Co中心會與氧氣活化形成超氧中間體，因此模擬這種自然酵素的活性位點與中間體的鑑定及後續反應是許多科學家致力研究的議題。因此本研究參考先前洪嘉伶學姊在2020年的研究，將H2BDPP修飾過後的新型配位基H2BDBP與金屬鍵結，合成出CoII(BDBP) (1)，與氧氣反應可形成三價鈷超氧化物CoIII(BDBP)(O2‧) (2)，並且與TEMPOH進行奪氫反應會生成CoIII(BDBP)(OOH) (3)，在學姊的研究下皆有良好的光譜表徵。這裡，針對上述做更深入的研究，將錯合物2與弱酸TFA (Trifluoroacetic acid) 進行質子轉移反應，質子化會發生於配位基上，氫原子會與超氧自由基團以氫鍵形式鍵結，形成中間體[CoIII(HBDBP)(O2‧)](OOCF3) (4)，隨後分別與Proton Sponge以及TEA (Triethylamine) 反應進行逆滴定，以判定是否反應去求出其pKa範圍，並且參考洪嘉伶學姊從循環伏安法得到的還原半電位E1/2，以及利用Bordwell方程式，求得錯合物3的OO-H鍵能範圍。此外，因為H2BDBP上甲苯基團的推電子特性會使中心金屬的電子密度比H2BDPP還要高，推測其反應性會有變化，因此嘗試與BDE較高的9,10-Dihydroacridine、9,10-Dihydroanthracene(DHA)等受質反應，發現能夠對其進行碳氫鍵的活化，並且進一步對9,10-Dihydroacridine進行酵素動力學的研究，發現其催化行為能擬合Michaelis-Menten kinetics，求得催化速率kcat/Km = 7.61×10-5 mM-1 h-1，對催化反應有更深入的研究。In nature, Homoprotocatechuate 2,3-Dioxygenase (HPCA), a diol compound, can be cleaved by oxygen and transformed into a semi-formaldehyde product by Homoprotocatechuate (HPCA). During the catalytic reaction, the Co center is activated with oxygen to form a superoxide intermediate. Therefore, the characterization of the active site and intermediate of natural enzyme and the subsequent reaction are the subject of many scientists' research. Therefore, in this study, CoII(BDBP) (1), which was synthesized by a new ligand H2BDBP modified with H2BDPP and successfully published by Chia-Ling Hung in 2020, reacts with oxygen to form CoIII(BDBP)(O2‧) (2), then a trivalent cobalt superoxide reacts with TEMPOH to form CoIII(BDBP)(OOH) (3), which has good spectroscopically characterization under her study. The protonation will occur on the ligand group and the hydrogen atom will bond with the superoxide radical in the form of hydrogen bond to form [CoIII(HBDBP)(O2‧)](OOCF3) (4), and then the inverse titration with Proton Sponge and TEA will be performed to find the pKa range, finally, the OO-H bonding energy range of the complex 3 was also obtained by using Bordwell's equation with reference to the reduced half potentials E1/2 obtained from cyclic voltammetry by Chia-Ling Hung. In addition, the electron density of the to benzyl group on H2BDBP is higher than that of H2BDPP, and the reactivity of H2BDBP is expected to change, so the reaction with 9,10-Dihydroacridine and 9,10-Dihydroanthracene (DHA) was found to be able to activate the hydrocarbon bond . Also, the catalytic behavior of 9,10-Dihydroacridine can fit with Michaelis-Menten kinetics, and the catalytic rate kcat/Km = 7.61×10-5 mM-1 h-1 was obtained, which led to a more in-depth study of the catalytic reaction.