重組金屬乙炔苯酸紫質之人工肌紅蛋白系統對於光激發電子轉移機制的研究與其在生物性太陽能電池的應用

Abstract

肌紅蛋白是一個很適合用來了解光物理以及探討光催化電子轉移機制的生物系統，因為肌紅蛋白的血色素基口袋可以有效穩定中間輔基的氧化或還原態。而將人工合成的輔基重組進入肌紅蛋白中是一個嶄新的方式為蛋白質注入新的功能。為了模擬光合作用的機轉，我們設計一個更簡單的系統來模擬光合作用。我們將一系列不同金屬的光敏劑 metallo-5-(4-carboxy-phenylethynyl)-10,20-biphenylporphines (簡稱MtPE1)重組到肌紅蛋白中防止自身聚集的現象以及延長在激發態的生命期。我們進行紫外光-可見光光譜、循環伏安法、螢光光譜、時間-解析螢光光譜、光化學還原法、光電流等的研究。在螢光生命期的比較，ZnPE1-Mb 以及H2PE1-Mb 在緩衝溶液中的生命期比起在有機溶劑四氫呋喃 (THF) 中的ZnPE1、H2PE1 有些微的增加。光化學還原是利用以肌紅蛋白重組MtPE1 做為光敏劑，TEA做為電子提供者，NADP+為電子接受者所組成的簡單系統來比較不同金屬MtPE1 以及MtPE1-Mb 的轉換效率。在將NADP+還原成NADPH 的效率上，以H2PE1 與ZnPE1 重組的肌紅蛋白相對於只以H2PE1 與ZnPE1 為光敏劑的轉換效率來說，約可提升兩倍的效率，我們推測蛋白質能有效穩定光敏劑的激發態並延長處於激發態的時間而提高轉換效率。我們也利用循環伏安法確認重組之MtPE1-Mb 具有和TEA 及NADP+ 可適當轉移電子的能階。最後，也試著建構一個以MtPE1-Mb、TiO2 導電玻璃、電解液組合成能將光能轉成電能的生物太陽能電池。

Myoglobin (Mb) is a suitable model to understand the photophysical properties and photoinduced electron transfer mechanism, because of the heme pocket of Mb can stabilize the reduced and oxidized state of the prosthetic group. Reconstitution of an artificial prosthetic group into apo-myoglobin (apo-Mb) is a unique method for introducing a new chemical function into the protein. To mimic the function of photosynthetic system, we design a simple system. A series of different metallo-5-(4-carboxy-phenylethynyl)-10, 20-biphenylporphines, denoted as MtPE1(used as photo-sensitizers) were reconstituted with apo-Mb to avoid self-aggregation and extend the lifetime of excited state. The photophysical properties of reconstituted Mb were examined by UV-Vis, CV, fluorescence spectra, time-resolved fluorescence spectroscopy, photochemical reduction, and photocurrent study. Fluorescence decay profiles of ZnPE1-Mb and H2PE1-Mb showed slightly increase by comparing with ZnPE1 and H2PE1 in THF. Photochemical reduction of nicotinamide adenine dinucleotide phosphate (NADP+) was studied by using MtPE1 reconstituted myoglobin (MtPE1-Mb) as a photosensitizer, and triethanolamine (TEA) as a sacrificial donor. This simple model system can let us to compare the conversion efficiency of MtPE1 and MtPE1-Mbs. H2PE1-Mb and ZnPE1-Mb exhibited 2-folds of photo-induced electron transfer efficiency than H2PE1 and ZnPE1 for converting NADP+ to NADPH. The results showed that MtPE1 reconstituted with apo-Mb can stabilize the excited state and increase the conversion efficiency. We also confirmed that MtPE1-Mb have well-matched energy level of TEA and NADP+ by CV analysis. At last, we try to combine MtPE1-Mb, TiO2 film, and electrolyte to construct a biosolar cell with solar-electric energy converting ability.