配位三氟甲基修飾之三氮二氧配基的三價鐵超氧化物之反應性及光譜探討
No Thumbnail Available
Date
2023
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
自然界含有許多生物酵素，透過研究將其功能模仿並運用。而氧氣作為地球上含量豐富的分子，許多酵素透過氧氣活化進行受質轉化，以含鐵酵素，細胞色素 P450 為例，此酵素活化氧氣後，將受質之 C−H鍵轉換為C−OH鍵，此催化對於烷類轉換為醇類十分重要，由於酵素中含鐵超氧型式為催化步驟中重要步驟，因此含鐵酵素超氧型式之反應性研究十分重要。本次以本實驗室開發之三氮二氧五牙基配位基 (H2(BDPRP))做研究，並修飾三氟甲基以改變配位基之反應性，合成出非血基質二價鐵錯合物 (Fe(BDPCF3P))，並以氧氣活化得出其三價鐵超氧錯合物 (Fe(BDP CF3P)(O2·))，藉由不同功能的諸多化合物進行反應，並以UV-vis紫外線-可見光光譜儀、CV循環伏安法儀做反應之鑑定，以及光譜之探討。首先將三價超氧錯合物 (Fe(BDPCF3P)(O2·)) 與質子酸 HOTf 進行反應，將HOTf以滴定形式加入，並形成鐵氫過氧錯合物[Fe(BDPCF3P)(OOH)](OTf)，透過計算得出反應之 pKa 值為 10.12。以循環伏安法儀測量二價鐵錯合物 (Fe(BDPCF3P)) 之半電位，以及三價鐵超氧錯合物 (Fe(BDPCF3P)(O2·)) 加入氫原子給體TEMPOH得到之三價鐵氫過氧錯合物 [Fe(BDPCF3P)(OOH)] 之半電位 E1/2 0.122 V，代入Bordwell 方程式得出 Fe(BDP CF3P)(OOH) 之 O−H 鍵能 (BDFE) Bond Dissociation Free Energy為 77.07kcal/mol 。接著進行三價鐵超氧錯合物到三價鐵氫過氧錯合物之動力學探討。將三價鐵超氧錯合物 (Fe(BDPCF3P)(O2·)) 加入氫原子給體TEMPOH以及氘原子給體TEMPOD 形成(Fe(BDPCF3P)(OOH/D))。進行動力學同位素效應 (KIE)之反應鑑定。得出之值為 2.17。表示反應之速率決定步驟為氫原子轉移 (HAT) 。再將三價鐵超氧錯合物 (Fe(BDPCF3P)(O2·)) 與有不同推拉電子效應之4-R-phenol ( X = OMe、Me、H、Cl、CF3、CN、NO2 ) 進行反應，得出反應的二級速率常數 (k2) 並分析動力學。並求得Hammett plot，得知反應路徑有兩條路徑。並發現三價鐵超氧錯合物與4-R-phenol 形成另一產物(Fe(BDPCF3P)-(4-R-phenolate))而非單純(Fe(BDPCF3P)(OOH))，透過另一產物伴隨之過氧化氫副產物得知。透過以上研究以及光譜特徵，使非血基質三氟甲基三價鐵超氧化物的特性更加清晰，並且能完善各種取代基鐵錯合物之特性比對，並對於仿生鐵錯合物之超氧及氫過氧之機制有更深層的了解。
In nature, there are many biological enzymes that can be studied by humans. The goal is to mimic and utilize their function through research. Oxygen, as an abundant molecule on Earth, activate many biological enzymes. Here, we take the example of a heme-containing enzyme: cytochrome P450. This enzyme activate oxygen and convert C−H bond of the substrate into C−OH bond. This catalytic process is crucial for the transformation of alkane into alcohol. Due to the importance of the iron superoxo specie in the enzyme as a catalytic step, studying the reactivity of iron-containing superoxo enzymes is the key.In this study, we investigated the N3O2 ligand (H2(BDPRP)) developed in our lab and modified it by introducing trifluoromethyl group to alter the reactivity of the ligand. We synthesized a non-heme iron (II) complex (Fe(BDPCF3P)) and activated it with oxygen to obtain the iron (III) superoxo complex (Fe(BDPCF3P)(O2·)). Many of compounds with different functionalities were used for reaction, and the reaction were characterized using UV-vis spectroscopy, cyclic voltammetry.Firstly, the iron (III) superoxo complex (Fe(BDPCF3P)(O2·)) reacted with the acid (HOTf) by titration, forming the iron hydroperoxo complex Fe(BDPCF3P)(OOH). The pKa value of the reaction is 10.12.The half-potential,E1/2 of the iron (II) complex (Fe(BDPCF3P)) and the E1/2 of iron (III) superoxo complex (Fe(BDPCF3P)(O2·)) to iron (III) hydroperoxo Fe(BDPCF3P)(OOH) complex were measured using cyclic voltammetry. the E1/2 of the iron (III) hydroperoxo complex Fe(BDPCF3P)(OOH) obtained by adding hydrogen atom donor TEMPOH was 0.122 V. By applying the Bordwell equation, the O−H bond energy (BDFE) of Fe(BDPCF3P)(OOH) is 77.07 kcal/mol.Next, the kinetic study of the conversion from the iron (III) superoxo complex to the iron (III) hydroperoxo complex were investigated. The iron (III) superoxo complex (Fe(BDPCF3P)(O2·)) was reacted with the hydrogen atom donor TEMPOH and the deuterium atom donor TEMPOD to form (Fe(BDPCF3P)(OOH/D)). The reaction was identified using kinetic isotope effect (KIE), and the value is 2.17, indicating that the rate-determining step of the reaction is hydrogen atom transfer (HAT).Furthermore, the reaction of the iron (III) superoxo complex (Fe(BDPCF3P)(O2·)) with different substituent of 4-R-phenols (X = OMe, Me, H, Cl, CF3, CN, NO2) was studied. The second-order rate constant (k2) of the reaction were determined, and the kinetic study were analyzed. A Hammett plot was constructed, revealing two reaction pathways. It was found that the iron (III) superoxo complex formed another product (Fe(BDPCF3P)−(4-R-phenolate)) with 4-R-phenols, not the pure (Fe(BDPCF3P)(OOH)). This was determined through the accompanying hydrogen peroxide byproduct.We analyzing the non-heme trifluoromethyl iron (III) superoxo by kinetic study and spectroscopics. Furthermore, a comprehensive comparison of the properties of substituted iron complexes was achieved, leading to a deeper understanding of the mechanism of biomimetic iron catalyst involving superoxo and hydroperoxo.
In nature, there are many biological enzymes that can be studied by humans. The goal is to mimic and utilize their function through research. Oxygen, as an abundant molecule on Earth, activate many biological enzymes. Here, we take the example of a heme-containing enzyme: cytochrome P450. This enzyme activate oxygen and convert C−H bond of the substrate into C−OH bond. This catalytic process is crucial for the transformation of alkane into alcohol. Due to the importance of the iron superoxo specie in the enzyme as a catalytic step, studying the reactivity of iron-containing superoxo enzymes is the key.In this study, we investigated the N3O2 ligand (H2(BDPRP)) developed in our lab and modified it by introducing trifluoromethyl group to alter the reactivity of the ligand. We synthesized a non-heme iron (II) complex (Fe(BDPCF3P)) and activated it with oxygen to obtain the iron (III) superoxo complex (Fe(BDPCF3P)(O2·)). Many of compounds with different functionalities were used for reaction, and the reaction were characterized using UV-vis spectroscopy, cyclic voltammetry.Firstly, the iron (III) superoxo complex (Fe(BDPCF3P)(O2·)) reacted with the acid (HOTf) by titration, forming the iron hydroperoxo complex Fe(BDPCF3P)(OOH). The pKa value of the reaction is 10.12.The half-potential,E1/2 of the iron (II) complex (Fe(BDPCF3P)) and the E1/2 of iron (III) superoxo complex (Fe(BDPCF3P)(O2·)) to iron (III) hydroperoxo Fe(BDPCF3P)(OOH) complex were measured using cyclic voltammetry. the E1/2 of the iron (III) hydroperoxo complex Fe(BDPCF3P)(OOH) obtained by adding hydrogen atom donor TEMPOH was 0.122 V. By applying the Bordwell equation, the O−H bond energy (BDFE) of Fe(BDPCF3P)(OOH) is 77.07 kcal/mol.Next, the kinetic study of the conversion from the iron (III) superoxo complex to the iron (III) hydroperoxo complex were investigated. The iron (III) superoxo complex (Fe(BDPCF3P)(O2·)) was reacted with the hydrogen atom donor TEMPOH and the deuterium atom donor TEMPOD to form (Fe(BDPCF3P)(OOH/D)). The reaction was identified using kinetic isotope effect (KIE), and the value is 2.17, indicating that the rate-determining step of the reaction is hydrogen atom transfer (HAT).Furthermore, the reaction of the iron (III) superoxo complex (Fe(BDPCF3P)(O2·)) with different substituent of 4-R-phenols (X = OMe, Me, H, Cl, CF3, CN, NO2) was studied. The second-order rate constant (k2) of the reaction were determined, and the kinetic study were analyzed. A Hammett plot was constructed, revealing two reaction pathways. It was found that the iron (III) superoxo complex formed another product (Fe(BDPCF3P)−(4-R-phenolate)) with 4-R-phenols, not the pure (Fe(BDPCF3P)(OOH)). This was determined through the accompanying hydrogen peroxide byproduct.We analyzing the non-heme trifluoromethyl iron (III) superoxo by kinetic study and spectroscopics. Furthermore, a comprehensive comparison of the properties of substituted iron complexes was achieved, leading to a deeper understanding of the mechanism of biomimetic iron catalyst involving superoxo and hydroperoxo.
Description
Keywords
含鐵超氧化物, 含鐵氫過氧化物, 氫氧鍵鍵能測定, 反應性測定, Iron superoxo, Iron hydroperoxo, BDFE of Iron hydroperoxo, Kinetic Analysis