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Self-assembly and excited energy transfer in bacteriochlorophyll aggregates
Pospíšil, Petr ; Pšenčík, Jakub (advisor) ; Vácha, František (referee)
Bacteriochlorophyll c (BChl c) belongs among photosynthetic pigments. It is found in lightharvesting complexes of green photosynthetic bacteria in the form of self-assembled aggregates. It is possible to prepare BChl c aggregates also in vitro in aqueous solutions, in the presence of certain non-polar molecules (e.g. lipids or carotenoids). In this work, artificial light-harvesting antenna was prepared composed of BChl c and selected azulene derivative. The aggregation of BChl c with azulene enhances the absorption in the near UV region compared to BChl c. Fluorescence spectroscopy was used to study an efficiency of energy transfer from azulene to BChl c. The procedure used was based on fluorencence excitation spectra measurement, and a comparison with absorption 1-T spectra. The measurements were complicated by anomalous fluorencence of azulene, which occurs from the S2 state. Furthermore, the reference diode in the fluorescence spectrometer did not correct properly the signal in the near UV region, where azulene absorbs. The problem was partially solved by preparing the new correction files using selected laser dyes. Excitation spectra demonstrate the presence of the energy transfer from azulene to BChl c, however, it was not yet possible to satisfactorily quantify its efficiency.
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Interaction of bacteriochlorophyll c and its derivative with titanium dioxide
Ridzoňová, Katarína ; Pšenčík, Jakub (advisor) ; Alster, Jan (referee)
Dye-sensitized solar cells (DSSC) are promising low-cost molecular photovoltaic devices that have a good chance to become a competitor for solar cells based on technology of p-n junction. One of the key components of DSSC is a dye, which is responsible for the capture of light. The main goal of this bachelor thesis is to compare adsorption properties of bacteriochlorophyll c (BChl c) and its modified version referred as bacteriochlorophyllide c (BChlide c) on titanium dioxide (TiO2). In the experimental part of this work interaction of these two sensitizing dyes with TiO2 were investigated by several different methods, including absorption spectroscopy and measuring photo-induced current and current-voltage characteristics of the fabricated DSSC. It has been shown, that BChlide c adsorbs better on the TiO2 layer presumably due to the presence of a carboxylate group. Also the performance of the DSSC based on BChlide c was better than with BChl c.
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Temperature dependence of the triplet-triplet energy transfer in photosynthetic light-harvesting complexes
Vinklárek, Ivo ; Pšenčík, Jakub (advisor)
Toxic singlet oxygen can be populated by the quenching of triplet states of chlorophyll (Chl). In photosynthetic light-harvesting complexes (LHCs), the gen- eration of singlet oxygen is prevented by a photoprotective mechanism based on an energy transfer from Chl triplets to carotenoids, which occurs via a Dexter mechanism (DET). The temperature dependence of the DET was studied in three selected LHCs by means of transient absorption spectroscopy. The emphasis was on a chlorophyll a-chlorophyll c2-peridinin-protein complex (acpPC) of Dinoflagel- late Amphidinium carterae. The results obtained from acpPC were compared with those for LHC-II from pea and chlorosomes of Chloroflexus aurantiacus. All three antennas exhibit high efficiency and fast rate of chlorophyll triplet quenching by carotenoids at room temperature, which prevents the accumulation of Chl triplets. The fast rate of quenching persists at low temperatures (≥77 K) in the case of LHC-II. However, the efficiency of the Chl triplets quenching is lower as proved by a detection of long-lived Chl triplets with a millisecond lifetime. These triplets were assigned to peripheral Chls that are not neighbouring with carotenoids active at 77 K. A similar population of long-lived Chl triplets was detected in the acpPC complex. In acpPC, the rate of the...
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Spectroelectrochemical study of porphyrin derivatives in non-aqueous solvents
Povišer, Martin ; Dian, Juraj (advisor) ; Pšenčík, Jakub (referee)
Porphyrins and their derivatives constitute an important group of com- pounds taking part in vital biological processes such as transport of oxygen in blood and in photosynthesis. Electrochemical experiments such as cyclic volta- mmetry allow to examine the energetic balance of oxidation and reduction pro- cesses of particles under study. In spectroelectrochemical studies, the experiment is extended with optical characterization of the arising oxidized or reduced spe- cies. These are means to study of electronic structure of species and available electron transitions. Such studies are especially interesting in case of porphyrins due to possible elucidation of electron transfer in photosynthetic chains. This work presents: (a) an elementary theoretical treatment of electrode reactions fun- damental for electrochemical experiments, (b) description of the experimental realization of spectroelectrochemical study of porphyrins and derivatives in non- aqueous solvents, and (c) results of original spectroelectrochemical measurements on protoporphyrin IX in medium dimethylformamide. 1
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Artificial light-harvesting antenna based on an aggregation of bacteriochlorophyll c with selected pigments
Malina, Tomáš ; Pšenčík, Jakub (advisor) ; Litvín, Radek (referee)
Title: Artificial light-harvesting antenna based on an aggregation of bacteriochlorophyll c with selected pigments Author: Tomáš Malina Department: Department of Chemical Physics and Optics Supervisor of the master thesis: doc. RNDr. Jakub Pšenčík, Ph.D., KCHFO MFF UK Abstract: Solar energy is one of the most important energy sources for all living organisms. The light harvesting takes place in specialised photosynthetic complexes called antennas; they typically contain pigments held by a protein scaffold. Antennas of green bacteria, chlorosomes, are unique in this respect, for they do not need proteins to organise the pigments. The pigments contained in chlorosomes, bacteriochlorophyll (BChl) c, d or e, aggregate spontaneously. This self-aggregation can be used to form an artificial light-harvesting antenna the absorption spectrum of which can be extended by addition of other pigments. Antennas based on aggregation of BChl c with β-carotene and BChl a were prepared by a fast and slow method. The excitation energy transfer efficiency between these pigments was studied. The efficiency of energy transfer from BChl c to BChl a reached up to 95 %, the efficiency of energy transfer from β-carotene to BChl c was lower. An important role of β- carotene in artificial aggregates as well as in chlorosomes is its...
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Preparation and characterization of photovoltaic cells based on photosystem I
Kuižová, Alžbeta ; Pšenčík, Jakub (advisor) ; Alster, Jan (referee)
Photosystem I is increasingly used for new types of photovoltaic devices because of high stability. The goal of this thesis was to characterize organic photovoltaic cells based on photosystem I. Our task was to compare three electron mediators, namely TMPD, DCIP and cytochome c, and to choose the best one. In the experimental part of thesis, TMPD was selected as the most effective electron mediator. Subsequent measurements were performed to optimize the thickness of the cell and the concentration of photosystem I and TMPD in a final solution. Solar cells have been characterized by absorption and action spectra, and current-voltage characteristics were used to determine the overall power. It was found out that thinner photovoltaic cells work better and that the use of more concentrated solutions of photosystem I and TMPD leads to more efficient cells.
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Temperature dependence of the triplet-triplet energy transfer in photosynthetic light-harvesting complexes
Vinklárek, Ivo ; Pšenčík, Jakub (advisor) ; Polívka, Tomáš (referee)
Toxic singlet oxygen can be populated by the quenching of triplet states of chlorophyll (Chl). In photosynthetic light-harvesting complexes (LHCs), the gen- eration of singlet oxygen is prevented by a photoprotective mechanism based on an energy transfer from Chl triplets to carotenoids, which occurs via a Dexter mechanism (DET). The temperature dependence of the DET was studied in three selected LHCs by means of transient absorption spectroscopy. The emphasis was on a chlorophyll a-chlorophyll c2-peridinin-protein complex (acpPC) of Dinoflagel- late Amphidinium carterae. The results obtained from acpPC were compared with those for LHC-II from pea and chlorosomes of Chloroflexus aurantiacus. All three antennas exhibit high efficiency and fast rate of chlorophyll triplet quenching by carotenoids at room temperature, which prevents the accumulation of Chl triplets. The fast rate of quenching persists at low temperatures (≥77 K) in the case of LHC-II. However, the efficiency of the Chl triplets quenching is lower as proved by a detection of long-lived Chl triplets with a millisecond lifetime. These triplets were assigned to peripheral Chls that are not neighbouring with carotenoids active at 77 K. A similar population of long-lived Chl triplets was detected in the acpPC complex. In acpPC, the rate of the...
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Quenching of chlorophyll triplet states by carotenoids in thylakoid membranes
Vahalová, Petra ; Pšenčík, Jakub (advisor) ; Vácha, František (referee)
Photosynthesis is one of the most important biological processes. The photosynthetic apparatus is protected against formation of reactive singlet oxygen by carotenoids. In this work, thylakoid membranes from spinach were studied, and the main aim was to explore the effect of a partial carotenoid removal on the protective function. Carotenes, which are nonpolar carotenoids, were removed from a part of the sample by hexane. About 90 % of carotenes were removed, as revealed by liquid chromatography. However, the high efficiency of chlorophyll triplet state quenching was not affected by the carotene removal. Therefore, it was concluded that the remaining carotenes are probably localized around reaction centres, where they are not accessible to hexane and where their protective function is the most important. At the same time, changes in optical spectra were observed, which were ascribed to structural modifications caused by the carotene removal from the outer parts of the complexes. The carotenoids removal probably caused detachment of outer light-harvesting complexes. This interpretation is supported by the fact that similar changes were observed in experiments with a detergent dodecyl maltoside. 1
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Photosynthetic Apparatus of Green Sulfur Bacteria Studied by Coherent Two-Dimensional Electronic Spectroscopy
Dostál, Jakub ; Pšenčík, Jakub (advisor) ; Polívka, Tomáš (referee) ; Ihalainen, Janne (referee)
The process of photosynthesis begins with a capture of sunlight and its quick conversion into the chemical energy. Both these primary processes take place in a specially designed photosynthetic apparatus that is present in cells of all photosynthetic organisms. In green sulfur bacteria the apparatus consists of a massive light-harvesting antenna (chlorosome), intermediate antennas (baseplate complex and FMO proteins) and of the reaction center, where the conversion into the chemical energy occurs. The energy flow through the apparatus can be monitored by time-resolved spectroscopy techniques. Coherent two-dimensional electronic spectroscopy (2DES) in one of such techniques, which combines high temporal and spectral resolution, and therefore it is especially well suited for studying multichromophoric systems such as photosynthetic apparatus. This thesis describes the principles of the 2DES technique and outlines the basic facts about the photosynthetic apparatus of green sulfur bacterium Chlorobaculum tepidum. Finally, it summarizes the investigation of the photosynthetic machinery using 2DES. Results presented in this thesis provide new insights into the exciton diffusion and vibrational coherences within chlorosomes, excitonic structure of the baseplate and the overall energy flow through the entire...
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