The Purple Bacterial Photosynthetic Protein Nano Bionic Membrane And Device Research

Creation and exploitation of stable, high-efficient, and also environmentally friendly photoelectric materials or devices for a better utilization of solar energy is one of the long-term pursuits for human beings that might suffer from the serious problems of oil exhaustion. Photosynthesis, which has played an important role as both bio-energy source and life basis, is much more superior to the artificial apparatus on photoelectric conversion performance and has attracted great concerns. Recently, significant advancements have been achieved on both the structural and functional research of the purple bacteria photosynthetic reaction center (RC), a transmembrane pigment-protein complex that is the smallest unit in bacteria photosynthetic membrane able to perform a light-driven charge separation. It is with great value for both the theoretical study and applicable try to design effective photoelectric apparatus based on RC and fully reveal the excitation relaxation processes of the proteins encased within the functionalized films, which depends on the preparation of advanced electrode materials, introduction of site-directed protein mutation as well as genetic engineering, and establishment of new methodology for analysis and probing.Aimed at exploiting and developing the stable, high-efficient novel RC-functionalized nanofilms, a series of original work has been done especially on increasing the protein loading, promoting the photo-induced electron injection, manipulating the favorable protein orientation, and revealing the complex, ultrafast, and effective photo-induced energy/electron transfer:1. A new kind of bio-nanocomposite photoelectrode (PE) was fabricated through direct immobilization of RC on a porous nanocrystalline TiO₂ matrix prepared by the anodic oxidative hydrolysis method. Combination of the high-efficient near-infrared (NIR) light-harvesting faculty of RC and the well performance of TiO₂ on the photo-induced charge separation led to a better photoelectric conversion efficiency of the derived bio-photoelectrode (Bio-PE) as compared with that of the separate component.2. Novel 3D-worm-like mesoporous WO₃-TiO₂ films with tailored pore size were synthesized and applied to prepare the Bio-PEs through direct entrapping the RC molecules. These mesoporous WO₃-TiO₂ films exhibited unique characteristics, e.g. opened mesostructure, narrow-distributed pore size well-matching one 2D dimension of RC, and ideal hydrophilicity, in the specific loading of RC with high activityretained. Thanks to the higher capability of WO₃-TiO₂ in splitting photo-induced electron hole pairs than that of the single oxide, enhanced photo-induced electron injection from photo-excited RC to the WO₃-TiO₂ matrix decreased the disadvantages of electron transfer and charge recombination within the proteins.3. The disadvantages of electron transfer and charge recombination within RC itself were further conquered by means of the specific protein pigment exchange, which resulted in energy level change of the protein charge-separated state. The prepared Bio-PE composed of the pigment-exchanged proteins and the mesoporous WO₃-TiO₂ matrix exhibited remarkably enhanced photoelectric performances as compared with those RC PEs reported before.4. Successful modification of RC was achieved on the surface of functionalized Au colloid through self-assembling. Favorable protein orientation manipulated and the unique property of Au colloid in storing and shuttling the electrons contributed to the new concept of research and development of high-efficient Bio-PE materials.5. In situ femtosecond (fs) pump-probe spectroelectrochemistry methodology was developed for the first time for probing the ultrafast energy/electron transfer process inside the pigment-protein complex. The ultrafast excitation energy trapping dynamics of purple bacteria peripheral light-harvesting complexes (LH2) induced by electrochemical oxidation was investigated and reported particularly.Detailedly, the dissertation consists of 6 chapters that tightly relate to the main topic.1) IntroductionIn this chapter, firstly, significance of the topic discussed here was briefly described. Then, the research background about the structure and function of RC was introduced and illustrated. After that, strategies for construction and fabrication of well-defined RC-functionalized nanocomposite films for probing and exploiting the photo-induced electron transfer of RC were classified and summarized mainly including five categories, and the related literatures were well-reviewed. Finally, the main novelty and innovation of the study were provided.2) Bio-PE composed of the RC proteins adsorbed on a nanocrystalline TiO₂ film prepared by anodic electrodepositionIn this part, RC-functionalized nanocomposite PE prepared through adsorption ofthe photosensitive proteins on a porous nanocrystalline TiO₂ film synthesized by the anodic oxidative hydrolysis method was studied and reported. The NIR-visible (Vis) absorption spectra and fluorescence emission spectra displayed that the native activity was well-remained for RC immobilized on the TiO₂ matrix. Obvious reproducible photoelectric responses dominated by the adsorbed RC proteins were observed when the composite PE was illuminated. The high-efficient light-harvesting faculty of RC at long wavelength region compensated the negligible NIR-light absorption of TiO₂, which enabled the fabricated composite PE to capture the light energy more effectively. Combination of RC and the nanocrystalline TiO₂ led to a better photoelectric conversion efficiency of the Bio-PE resulted from the enhanced utilization of solar energy and promoted photo-induced charge separation, which might open a new perspective to develop versatile biomimic energy convertors or photoelectric sensors. However, the dramatically different photoelectric responses of the eight ITO/TiO₂/RC PEs prepared simultaneously strongly implied that the widely distributed nanopores derived from the inter-crystalline voids of TiO₂ may dampen the high-efficient immobilization of proteins with a certain specific dimensional size.3) Bio-PE composed of the RC proteins entrapped on a tailor-made mesoporous WO3-TiO₂ matrixIn this chapter, novel 3D-worm-like mesoporous WO₃-TiO₂ films with tailored pore size were applied to entrap the RC proteins for obtaining increased protein loading as well as promoted charge separation. By analyzing the relationship between the matrix properties (pore size, structural topology, and composing) and the immobilized protein amount, the optimized RC entrapment was obtained for the tailor-made 3D-worm-like mesoporous WO₃-TiO₂ with opened pore structure, narrow-distributed and matched pore size (- 7.1 nm), and ideal hydrophilicity. The fluorescence and photoelectric measurements of the ITO/WO₃-TiO₂/RC PE confirmed the improved photo-induced electron injection from the photo-excited proteins to the matrix as compared with that for the ITO/TiO₂/RC PE mentioned above, thanks to the higher capability of WO₃-TiO₂ in splitting photo-induced electron hole pairs than that of single TiO₂ or WO₃ as well as the matched energy level between the mesoporous semiconductor and RC. Such strategy for fabricating PE based on well-designed mesoporous metal oxides and RC contributed to a better utilization of solar energy, which might open a new perspective to develop versatile bio-photoelectric devices.4) Bio-PE composed of the pigment-exchanged RC mutant (containing Phe instead of BPhe) entrapped on the mesoporous WO₃-TiO₂ filmsWith the aim at well probing the photo-induced multiple-pathway electron transfer and further promoting the photoelectric performances of the photosensitive proteins entrapped on the above-mentioned mesoporous WO₃-TiO₂ films, a RC mutant (containing plant pheophytin (Phe) instead of bacteriopheophytin (BPhe), termed as Phe-RC) was introduced here for replacement of native-RC adsorbed. The NIR-Vis absorption and circular dichroism (CD) spectra displayed the successful replacement of BPhe by Phe with a high yield of more than 95%. The fluorescence emission, fs pump-probe and electrochemical experiments indicated that the free energy level of P⁺Phe" is higher than that of P⁺BPhe", which resulted in 1) the deferred evolution of ultrafast excited-state dynamics of Phe-RC; 2) increased life time of B* (excited-state of bacteriochlorophyll (BChl) monomer), P* (excited-state of BChl dimer), and P⁺ (oxidated-state of BChl dimer) in the RC mutant as compared with that in its native counterpart. The photoelectric measurements further demonstrated that the delayed electron transfer as well as the matched energy level between RC and the WO₃-TiO₂ matrix contributed to the further enhanced electron injection intensity, and thus the promoted electron-hole pair separation. Accordingly, remarkably improved photoelectric performance of the ITO/WO₃-TiO₂/Phe-RC PE was clearly observed(IPCE_800nm=-23%)5) Manipulating the favorable RC orientation on functionalized Au colloidsIn this chapter, RC-capped functionalized Au colloids were prepared for controlling the favorable protein orientation. Dramatically different protein orientations were achieved on Au colloids derivated with different bifunctional reagents (P or the neighborhood/primary quinone (Q_A) facing to the Au colloids). The ultraviolet (UV)-Vis absorption, X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) measurements reflected the structural properties of the functionalized Au colloids, which suggested the successful derivation of Au colloids with the selected bifunctional reagents. The NIR absorption and CD spectra showed that both the native structure and function of RC assembled on the derivative Au colloids remained unaltered. The fluorescence emission and fs pump-probe spectra results revealed the significantly different excitation relaxation pathway and dynamics of different RC/Aucolloid systems, and the existence of photo-induced electron injection from the photo-excited proteins to the Au colloids, which suggested the successful manipulation of favorable RC orientation. Combination of the favorable protein orientation and the unique properties of Au colloids in storing and shuttling the electrons provided a potential strategy for research and development of high-efficient Bio-PE materials.6) Ultrafast excitation energy relaxation of electrochemical-oxidized LH2Herein, in situ fs pump-probe spectroelectrochemistry methodology was established for probing the ultrafast energy entrapment dynamics resulted from electrochemical oxidation of LH2 from purple bacteria. Fs pump-probe spectroelectrochemical techniques coupled with NIR absorption spectroelectrochemical and fluorescence emission spectroelectrochemical methods were employed to investigate the different electrochemical oxidative behaviors of B800 (BChl monomer) and B850 (BChl dimer), address the change of pigment-pigment, pigment-protein arrangements during the oxidation, and reveal the effect of oxidation on the ultrafast energy transfer. The results showed that 1) Although the degradation of both B800 and B850 Qy bands took place at practically the same potential, yet the B800 band bleached faster as compared with the B850 band. 2) Dramatically quenching of the fluorescence emission from the B850 ring was observed during the electrochemical oxidation and the peak decrease rate was much faster as compared with the bleaching rate of absorption. 3) The BChl-B850 radical cation might act as an additional channel to compete with the unoxidized BChl-B850 molecules for rapidly releasing the excitation energy, however the B800-B850 energy transfer rate remained almost unchanged during the oxidation process. The development of in situ fs pump-probe spectroelectrochemical method might not only supply a new approach for monitoring and analysis of the ultrafast energy/electron transfer inside the photosynthetic proteins but also inspire more concerns on study and probing of various ultrafast excited-state dynamics with electrochemical oxidation concomitantly occurring.