以鐵鐵氫化酶為基礎仿生合成金屬氫簇族並進行光催化產氫研究

Abstract

在自然界，氫氣的產生可藉由氫化酶的催化生成。氫化酶可藉由活性位金屬中心的不同分成三大類，分別為鐵-鐵氫化酶、鎳-鐵氫化酶及單鐵氫化酶 。而其中的鐵-鐵氫化酶的催化中心主要為二鐵二硫的結構，並主要用於氫氣的生成。而研究的目的主要為模仿此結構合成以不同金屬為中心的氫簇族並用於催化氫氣的生成。我的研究目標為合成此類蛋白的二鐵二硫中心並以共價連結具有不同官能基的膦，以及將中心的鐵原子置換成錸原子並研究其在不同溫度及不同相的光催化產氫性質。在此研究中，首先我合成以鐵做為仿生的鐵-鐵氫化酵素，並將之共價連結具有不同官能基的膦，分別於水相及有機相下做光催化產氫的研究，接著合成以錸金屬為中心的二錸二硫結構並添加不同的膦研究其催化效率。研究中所合成的化合物利用質譜儀測定其分子量,及利用單晶X光繞射鑑定其結構並利用紫外光-可見光光譜儀及循環伏安法測試其光學及電化學特性。在計算化學上，所使用的軟體為Gaussian09，而計算的分子結構來自於單晶繞射的結構，並做結構優化分析化合物的最低電子未占有軌域(LUMO)、最高電子占有軌域(HOMO)、電量分布及紅外光譜震動圖譜。在產氫系統上分成有機相及水相,在有機相中主要以甲酸作為氫氣的來源，並分別以二鐵二硫的氫簇族及二錸二硫的氫簇族作為催化劑，在以二鐵二硫當催化劑的實驗中發現到在添加推電子基的膦化合物其催化效果優於拉電子基，因此接著將其與膦化合物進行共價方式連接後，發現到在接上膦衍生物後其催化效率降低，而將中心金屬置換成錸之後，其催化效率也沒有以鐵為中心金屬好。在水相中,以共價性連接三(4-甲氧基苯基)膦P(p-C6H4OMe)3二鐵二硫結構為最佳,而在未來將進一步研究其產氫的反應機制。 在DFT 理論計算上，主要以釕的金屬簇族作為計算的目標，在比較其不同的配體的衍生物後其HOMO及LUMO的變化，以及紅外光譜圖譜的模擬，並用於解釋產氫的結果，在結果上發現到當共價連接上膦衍生物後，其HOMO及LUMO的能量上具有向上提升，並降低其軌域能接的能隙，在未來可用於比較其產氫的結果。

In nature, hydrogen production is catalyzed by hydrogenases (H2ase). Hydrogenases can be classified into three types depending on different central metals, [Fe-Fe], [Fe-Ni] or [Fe] within the enzymes. The study of the active site of [Fe-Fe] hydrogenase, diiron carbonyl sulfur cluster (also named H-cluster), provides a structural basis for hydrogen generation. The aim of the research is to mimic the structure of H-cluster with different metals and apply it as a catalyst for hydrogen production. My goal is to synthesize artificial [Fe-Fe] H-cluster and covalent link to different phosphine ligands and I also replaces the iron metal centers with rhenium and study their catalytic activity for photocatalytic hydrogen production at different temperatures and different phases. In this study, we first synthesize iron-sulfur cluster ([Fe2(CO)6(μ-pdt)]) and covalent link P-ligabds ([Fe2(CO)5(μ-pdt)(P-ligand)]) and rhenium (Re)-substituted H-cluster mimics complex ([Re2(CO)6(μ-pdt)]). Then the synthesized metal-sulfur clusters were subjected to photocatalytic hydrogen production studies in organic phase and aqueous phase. In addition, different P-ligands were added into the system to study the efficiency. All the synthetic compounds were checked by MS spectra and the characteristics of the complex was analyzed by UV-Vis spectrum and cyclic voltammetry. The experimental structures here elucidated by DFT calculations, and the orbital analyses optimized the analyzed the LUMO, HUMO, charge distribution and IR spectra were performed based on the optimized geometries. Hydrogen generation could proceed in organic phase and aqueous phase. In organic phase, formic acid is the hydrogen source. For iron-sulfur clusters, additional added P-ligand with electron donating functional group are better than electron withdrawing. And the covalent link P-ligand to iron-sulfur clusters are worse than without linking to P-ligand. And the replaced the center iron into rhenium is also worse than it. In aqueous phase system, covalent link P(p-C6H4OMe)3 to iron-sulfur cluster is the best. The mechanism of hydrogen evolution by various metal sulfur clusters will be elucidated in the future. In DFT calculations, the ruthenium-sulfur clusters are modeled to calculate energy level of HOMO and LUMO and the IR spectroscopy. And using these data to explain the hydrogen generation results. According to the energetics, we found that the energy level increased after covalent link to P-ligand, and the band gap between HOMO-LUMO is decreased. The computational results could be further used to predict the hydrogen generation process.