Freestanding sample holder for ultrafast optical spectroscopy at low temperatures.

Ultrafast optical spectroscopy techniques are often employed to gain information about samples that are liquid at room temperature and frozen at cryogenic temperatures. However, the measurements suffer from the presence of unwanted, non-resonant signals originating in the sample cell walls. Most of these artifacts can be avoided in the measurements performed at room temperature by using liquid jet systems, i.e., by removing the sample cell. However, these systems cannot be used in low temperature measurements, when the sample is frozen. Herein we describe a freestanding sample holder that allows low temperature ultrafast spectroscopy measurements free of artifacts caused by the sample cell

Self-assembly and energy transfer in artificial light-harvesting complexes of bacteriochlorophyll c with astaxanthin

Chlorosomes, the light-harvesting antennae of green photosynthetic bacteria, are based on large aggregates of bacteriochlorophyll molecules. Aggregates with similar properties to those in chlorosomes can also be prepared in vitro. Several agents were shown to induce aggregation of bacteriochlorophyll c in aqueous environments, including certain lipids, carotenes, and quinones. A key distinguishing feature of bacteriochlorophyll c aggregates, both in vitro and in chlorosomes, is a large (>60 nm) red shift of their Qy absorption band compared with that of the monomers. In this study, we investigate the self-assembly of bacteriochlorophyll c with the xanthophyll astaxanthin, which leads to the formation of a new type of complexes. Our results indicate that, due to its specific structure, astaxanthin molecules competes with bacteriochlorophylls for the bonds involved in the aggregation, thus preventing the formation of any significant red shift compared with pure bacteriochlorophyll c in aqueous buffer. A strong interaction between both the types of pigments in the developed assemblies, is manifested by a rather efficient (~40%) excitation energy transfer from astaxanthin to bacteriochlorophyll c, as revealed by fluorescence excitation spectroscopy. Results of transient absorption spectroscopy show that the energy transfer is very fast (<500 fs) and proceeds through the S2 state of astaxanthin.This study was supported by the Czech Ministry of Education, Youth and Sports (projects MSM0021620835, MSM6007665808, AV0Z50510513), Czech Science Foundation (projects 206/09/0375, 202/09/H041, 202/09/1330), and Spanish Ministry of Science and Innovation (AVCR-CSIC joint project 2008CZ0004).Peer reviewe

Study of light-harvesting antennae based on bacteriochlorophyll aggregates

Title: Study of light-harvesting antennae based on bacteriolorophyll aggregates Author: Jan Alster Department: Department of Chemical Physics and Optics Supervisor of the doctoral thesis: doc. RNDr. Jakub Pšenčík, Ph.D. Abstract: Artificial photosynthesis is a potential future source of renewable energy. e light-to-emical energy conversion process starts with capturing light. Chlorosomes of green phototropic bacteria are probably the most efficient light-harvesting antenna found in the Nature. Moreover, their unique structure based on a self-organised ag- gregate of pigment molecules makes them relatively easy to mimic in vitro. is work explores formation and properties of self-assembled aggregates of bacteriolorophyll molecules in aqueous solvents by means of steady state and time resolved optical spec- troscopy with time resolution in the microsecond to femtosecond range. Various ag- gregation inducing agents have been tested. Isoprenoid quinones introduce a redox- dependent excitation energy quening meanism into the bacteriolorophyll aggre- gates. Carotenoids enhance the light-harvesting properties of the aggregates by cap- turing light in the spectral region where bacteriolorophyll does not and transferring the excitation energy to bacteriolorophyll. e results indicate that self-assembled..

Relaxace excitonových stavů v umělé fotosyntetické anténě

Katedra chemické fyziky a optikyDepartment of Chemical Physics and OpticsMatematicko-fyzikální fakultaFaculty of Mathematics and Physic

Studium světlosběrných antén na bázi bakteriochlorofylových agregátů

Název práce: Studium světlosběrný antén na bázi bakteriolorofylový agregátů Autor: Jan Alster Katedra: Katedra emié fyziky a optiky Vedoucí doktorské práce: doc. RNDr. Jakub Pšenčík, Ph.D. Abstrakt: Umělá fotosyntéza je jeden z možný budoucí zdrojů obnovitelné energie. Prvním krokem procesu konverze energie záření na emiou energii je záyt světla. Chlorosomy zelený fototrofní bakterií jsou jednou z nejúčinnější světlosběrný antén vyskytující se v přírodě. Jeji unikátní struktura, založená na samoorganizo- vaný agregáte pigmentový molekul, je navíc dovoluje poměrně snadno napodobit v laboratoři. Tato práce zkoumá formování a vlastnosti agregátů molekul bakteriolo- rofylu ve vodný prostředí za pomoci tenik optié spektroskopie ustáleného stavu a s časovým rozlišením v řádu mikrosekund až femtosekund. Bylo otestováno něko- lik látek indukující agregaci. Chinony s nepolárním postranním řetězcem zavádí do agregátů bakteriolorofylu meanismus zhášející excitační energii řízený redoxním potenciálem. Karotenoidy zlepšují záyt světla ve spektrální oblaste, kde bakterio- lorofyl absorbuje slabě, a zaycenou excitační energii přenáší na bakteriolorofyl. Výsledky naznačují, že samoorganizované agregáty molekul bakteriolorofylu jsou do- brým kandidátem na světlosběrnou anténu pro umělou...Title: Study of light-harvesting antennae based on bacteriolorophyll aggregates Author: Jan Alster Department: Department of Chemical Physics and Optics Supervisor of the doctoral thesis: doc. RNDr. Jakub Pšenčík, Ph.D. Abstract: Artificial photosynthesis is a potential future source of renewable energy. e light-to-emical energy conversion process starts with capturing light. Chlorosomes of green phototropic bacteria are probably the most efficient light-harvesting antenna found in the Nature. Moreover, their unique structure based on a self-organised ag- gregate of pigment molecules makes them relatively easy to mimic in vitro. is work explores formation and properties of self-assembled aggregates of bacteriolorophyll molecules in aqueous solvents by means of steady state and time resolved optical spec- troscopy with time resolution in the microsecond to femtosecond range. Various ag- gregation inducing agents have been tested. Isoprenoid quinones introduce a redox- dependent excitation energy quening meanism into the bacteriolorophyll aggre- gates. Carotenoids enhance the light-harvesting properties of the aggregates by cap- turing light in the spectral region where bacteriolorophyll does not and transferring the excitation energy to bacteriolorophyll. e results indicate that self-assembled...Department of Chemical Physics and OpticsKatedra chemické fyziky a optikyFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult

Relaxace excitonových stavů v umělé fotosyntetické anténě

Katedra chemické fyziky a optikyDepartment of Chemical Physics and OpticsMatematicko-fyzikální fakultaFaculty of Mathematics and Physic

Self-assembly and energy transfer in artificial light-harvesting complexes of bacteriochlorophyll c with astaxanthin

Chlorosomes, the light-harvesting antennae of green photosynthetic bacteria, are based on large aggregates of bacteriochlorophyll molecules. Aggregates with similar properties to those in chlorosomes can also be prepared in vitro. Several agents were shown to induce aggregation of bacteriochlorophyll c in aqueous environments, including certain lipids, carotenes, and quinones. A key distinguishing feature of bacteriochlorophyll c aggregates, both in vitro and in chlorosomes, is a large (>60 nm) red shift of their Qy absorption band compared with that of the monomers. In this study, we investigate the self-assembly of bacteriochlorophyll c with the xanthophyll astaxanthin, which leads to the formation of a new type of complexes. Our results indicate that, due to its specific structure, astaxanthin molecules competes with bacteriochlorophylls for the bonds involved in the aggregation, thus preventing the formation of any significant red shift compared with pure bacteriochlorophyll c in aqueous buffer. A strong interaction between both the types of pigments in the developed assemblies, is manifested by a rather efficient (~40%) excitation energy transfer from astaxanthin to bacteriochlorophyll c, as revealed by fluorescence excitation spectroscopy. Results of transient absorption spectroscopy show that the energy transfer is very fast (<500 fs) and proceeds through the S2 state of astaxanthin.This study was supported by the Czech Ministry of Education, Youth and Sports (projects MSM0021620835, MSM6007665808, AV0Z50510513), Czech Science Foundation (projects 206/09/0375, 202/09/H041, 202/09/1330), and Spanish Ministry of Science and Innovation (AVCR-CSIC joint project 2008CZ0004).Peer reviewe

Low-temperature spectroscopy of bacteriochlorophyll c aggregates

Chlorosomes from green photosynthetic bacteria belong to the most effective light-harvesting antennas found in nature. Quinones incorporated in bacterichlorophyll (BChl) c aggregates inside chlorosomes play an important redox-dependent photo-protection role against oxidative damage of bacterial reaction centers. Artificial BChl c aggregates with and without quinones were prepared. We applied hole-burning spectroscopy and steady-state absorption and emission techniques at 1.9 K and two different redox potentials to investigate the role of quinones and redox potential on BChl c aggregates at low temperatures. We show that quinones quench the excitation energy in a similar manner as at room temperature, yet the quenching process is not as efficient as for chlorosomes. Interestingly, our data suggest that excitation quenching partially proceeds from higher excitonic states competing with ultrafast exciton relaxation. Moreover, we obtained structure-related parameters such as reorganization energies and inhomogeneous broadening of the lowest excited state, providing experimental ground for theoretical studies aiming at designing plausible large-scale model for BChl c aggregates including disorder

β-carotene to bacteriochlorophyll c energy transfer in self-assembled aggregates

Carotenoids are together with bacteriochlorophylls important constituents of chlorosomes, the light-harvesting antennae of green photosynthetic bacteria. Majority of bacteriochlorophyll molecules form self-assembling aggregates inside the chlorosomes. Aggregates of bacteriochlorophylls with optical properties similar to those of chlorosomes can also be prepared in non-polar organic solvents or in aqueous environments when a suitable non-polar molecule is added. In this work, the ability of β-carotene to induce aggregation of bacteriochlorophyll c in aqueous buffer was studied. Excitation relaxation and energy transfer in the carotenoid-bacteriochlorophyll assemblies were measured using femtosecond and nanosecond transient absorption spectroscopy. A fast, approx. 100-fs energy transfer from the S2 state of β-carotene to bacteriochlorophyll c was revealed, while no evidence for significant energy transfer from the S1 state was found. Picosecond formation of the carotenoid triplet state (T1) was observed, which was likely generated by singlet homo-fission from the S1 state of β-carotene.This study was supported by Czech Ministry of Education, Youth and Sports (projects MSM0021620835, MSM6007665808 and AV0Z50510513), Czech Science Foundation (projects 206/09/0375, 202/09/1330 and 202/09/H041), Spanish Ministry of Education and Science (project BF2007-68107-C02-02/BMC), and AVCR-CSIC joint project (project 2008CZ0004). The authors would like to thank Marcel Fuciman and Petr Hribek for technical assistance with femtosecond spectroscopy measurements, and Ivana Hunalova, Frantisek Matousek and Anita Zupcanova for their help with pigment isolation.Peer reviewe