碳氮異位紫質鐵錯合物之亞硝酸鹽還原反應 及其相關錯合物之電子組態研究

Iron N-confused Porphyrin Complexes for Nitrite Reduction and Studies on Their Electronic Structures

荊偉民

指導教授 ： 洪政雄 ； 李位仁

國立臺灣師範大學/理學院/化學系/博士(2011年)

摘要

一氧化氮分子在生物系統中扮演著相當重要的角色，在無氧的條件下，亞硝酸環原酶利用周遭環境的質子及本身活性中心的電子，將亞硝酸鹽還原成一氧化氮分子。我們利用實驗室所發展含有環內碳上氫原子及環外氮上氫原子的金屬錯合物FeII(HCTPPH)Br (1a)，能成功的模擬亞硝酸鹽還原反應；在與一當量的亞硝酸鹽反應可獲得產物Fe(CTPP)NO (1d) {FeNO}6，而在半當量亞硝酸鹽的反應中則可獲得產物Fe(HCTPP)NO (1g) {FeNO}7；除此之外，藉由碳氮異位紫質環本身具有可變的共軛式，也可獲得一質子化產物[Fe(HCTPP)NO][ClO4] (1j) {FeNO}6。
在環內碳上甲基化的FeII(HCTPPCH3)Br (2a)與一氧化氮分子的反應中，可以得到與一氧化氮分子鍵結的產物Fe(CTPPCH3)NO (2d) {FeNO}7，若氧化此(2d)產物，則可獲得環內甲基中碳氫鍵被活化的產物[Fe(HCTPPCH2)NO][BF4] (2g) {FeNO}6；然而在無一氧化氮分子配位的幫助下，直接氧化FeII(HCTPPCH3)Br (2a)僅能獲得中心金屬鐵氧化後的產物{[FeIII(HCTPPCH3)]2O}[BF4]2 (2h)。
含有環內碳上甲基的FeII(HCTPPCH3)Br (2a) 除了能進行亞硝酸鹽還原反應外，反應的結果能獲得甲基碳氫鍵活化的產物Fe(CTPPCH2)NO (3b){FeNO}6，而與亞硝酸鹽進行還原反應的過程中，經過一甲基碳氫鍵未被活化的產物Fe(CTPPCH3)NO (2d) {FeNO}7；此產物會被反應過程中所產生的氫氧自由基氧化，而形成含有環內甲基碳氫鍵活化的產物Fe(CTPPCH2)NO (3b){FeNO}6。
分析FeII(MeCTPPMe)Br (3a)及FeII(MeCTPPH)Br (1c)與亞酸鹽反應的結果，可推得FeII(HCTPPH)Br (1a)與亞硝酸鹽的反應機制；FeII(HCTPPH)Br (1a)與亞硝酸鹽反應會先產生半當量的Fe(HCTPP)NO (1g) {FeNO}7及半當量的FeIII(HCTPP)Br，而FeIII(HCTPP)Br再與剩餘的亞硝酸鹽進行反應，形成最後產物Fe(CTPP)NO (1d) {FeNO}6，此時反應所生成的氫氧自由基會將Fe(HCTPP)NO (1g) {FeNO}7氧化獲得Fe(CTPP)NO (1d)。
結合EPR光譜、NMR光譜及理論計算的分析，我們成功的分析Fe(TPP)NO，Fe(HCTPP)NO (1g)、Fe(CTPPCH3)NO (2d)、Fe(CTPPCF3)NO (4k)及Fe(CTPPCN)NO (4p)等{FeNO}7的電子組態；其未偶電子在中心金屬鐵所佔的比例依次Fe(CTPPCH3)NO (2d)為0.99、Fe(CTPPCF3)NO (4k)為0.98、Fe(TPP)NO為0.91及Fe(HCTPP)NO (1g)為0.87。同時也成功的解釋Fe(CTPPCH3)NO (2d) 及Fe(CTPPCF3)NO (4k)在順磁13C NMR光譜中，中心金屬鐵將未偶電子傳遞至環內氮原子及meso碳原子的機制，以及室溫EPR光譜所觀察到的現象。

關鍵字

紫質 ； 碳氮異位紫質 ； 亞硝酸鹽 ； 一氧化氮

並列摘要

Nitric oxide plays an important role in biological system. In the hypoxia conditions, nitrite reductase uses the protons from active site surrounding amino acid residues and the electron shuttles to convert nitrite to nitric oxide and water. Herein, we use the FeII(HCTPPH)Br (1a) complex with an inner proton and an outer proton to minic the nitrite reduction reaction successfully. The reaction of complex 1a with 1 equiv of nitrite obtained Fe(CTPP)NO (1d) {FeNO}6. In additional, the reaction of complex 1a with 0.5 equiv of nitrite obtained Fe(HCTPP)NO (1g) {FeNO}7. Moreover, we also obtained the protonate complex [Fe(HCTPP)NO][ClO4] (1j) {FeNO}6 from the treatment of 1d with HClO4.
In the reaction of the FeII(HCTPPCH3)Br (2a) with nitric oxide, we can obtain the nitric oxide coordinated complex Fe(CTPPCH3)NO (2d), a {FeNO}7 complex. The oxidation of the complex 2d, result a C-H bond activated product [Fe(HCTPPCH2)NO][BF4] (2g) {FeNO}6. However, only the oxidized product {[FeIII(HCTPPCH3)]2O}[BF4]2 (2h) was obtained, if we oxidize the FeII(HCTPPCH3)Br (2a) without the presence of nitric oxide as the axial ligand.
FeII(HCTPPCH3)Br (2a) reacts with nitrite resulting C-H bond activated {FeNO}6 product, Fe(CTPPCH2)NO (3b), through nitrite reduction. It is confirmed that nitrite reduction proceeds through the formation of a C-H bond unactivated {FeNO}7 product, Fe(CTPPCH3)NO (2d). The complex 2d will further oxidize by the hydroxyl radical which is generated from hemolytic cleavage of the nitrite N-OH bond after nitrite protonation and the C-H bond activation product Fe(CTPPCH2)NO (3b) will obtain finally.
Analysis the reactions of the FeII(MeCTPPMe)Br (3a) and FeII(MeCTPPH)Br (1c) with nitrite, we can conclude that the overall nitrite reduction reaction mechanism in FeII(HCTPPH)Br (1a) is : (1) FeII(HCTPPH)Br (1a) reacts with nitrite to generate a half equiv Fe(HCTPP)NO (1g) {FeNO}7and half equiv FeIII(HCTPP)Br; (2).The half equiv FeIII(HCTPP)Br further reacts with the residual nitrite to form the final product Fe(CTPP)NO (1d) {FeNO}6and generates the hydroxyl radical; (3) The hydroxyl radical then oxidizes the Fe(HCTPP)NO (1g) {FeNO}7 to the final product Fe(CTPP)NO (1d) to complete the reaction.
According to the EPR spectra, NMR spectra and theoretiacl calculation, we successfully analyzed the electronic structure of {FeNO}7 complexes, Fe(TPP)NO, Fe(HCTPP)NO (1g), Fe(CTPPCH3)NO (2d), Fe(CTPPCF3)NO (4k) and Fe(CTPPCN)NO (4p). The unpaired electron spin density population on the iron center in Fe(CTPPCH3)NO (2d) is 0.99, and Fe(CTPPCF3)NO (4k) is 0.98, and Fe(TPP)NO is 0.91, and Fe(HCTPP)NO (1g) is 0.87. the higer population of unpaired spin on iron center rather than NO explains the absence of three-line pattern EPR spectrum at room temperature for 2d and 4k. Forthermore, using the paramegnetic 13C NMR spectra, we also porposed a mechanism for the unpair electron spin density to transfer from iron center to the carbon atom and nitrogen atom in Fe(CTPPCH3)NO (2d) and Fe(CTPPCF3)NO (4k).

並列關鍵字

porphyrin ； N-confused porphyrin ； nitrite ； Nitric oxide

參考文獻

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