Photosynthetic apparatus of Rhodobacter sphaeroides exhibits prolonged charge storage (original) (raw)
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TURKISH JOURNAL OF BIOLOGY, 2015
The light phase of photosynthesis is considered a joint operation of 2 functional pigment-protein complexes: a light harvesting antenna, absorbing sunlight in a wide spectral range, and a reaction center, utilizing the energy of absorbed light quanta in photochemical charge separation reactions. These complexes allow converting solar energy to the energy of specific biomolecules with high quantum efficiency. However, before being transferred to reaction centers, the solar energy is stored in the lowest excited state of pigment molecules of the light harvesting antenna that partially convert light quantum energy into heat. These energy losses bring a significant reduction of energy efficiency of photosynthesis in view of a very wide spectral range of photosynthetically active sunlight. In the current study we analyzed the energy efficiency of sunlight harvesting and storing in different photosynthetic bacteria with different absorption bands. We showed that simultaneous exploitation of several such photosynthetic organisms leads to an increased total energy efficiency in terms of harvesting sunlight of the wider spectra. Maximal values of energy efficiencies of the sunlight harvesting and storing system in photosynthetic bacteria and semiconductor photovoltaic cells are compared, and perspectives on practical use of photosynthetic bacteria as solar energy converters are discussed.
ACS nano, 2012
The innately highly efficient light-powered separation of charge that underpins natural photosynthesis can be exploited for applications in photoelectrochemistry by coupling nanoscale protein photoreaction centers to man-made electrodes. Planar photoelectrochemical cells employing purple bacterial reaction centers have been constructed that produce a direct current under continuous illumination and an alternating current in response to discontinuous illumination. The present work explored the basis of the open-circuit voltage (V OC ) produced by such cells with reaction center/antenna (RC-LH1) proteins as the photovoltaic component. It was established that an up to ∼30-fold increase in V OC could be achieved by simple manipulation of the electrolyte connecting the protein to the counter electrode, with an approximately linear relationship being observed between the vacuum potential of the electrolyte and the resulting V OC . We conclude that the V OC of such a cell is dependent on the potential difference between the electrolyte and the photo-oxidized bacteriochlorophylls in the reaction center. The steady-state short-circuit current (J SC ) obtained under continuous illumination also varied with different electrolytes by a factor of ∼6-fold. The findings demonstrate a simple way to boost the voltage output of such protein-based cells into the hundreds of millivolts range typical of dye-sensitized and polymer-blend solar cells, while maintaining or improving the J SC .
The Journal of Physical Chemistry B, 2013
Owing to the considerable current interest in replacing fossil fuels with solar radiation as a clean, renewable, and secure energy source, light-driven electron transport in natural photosynthetic systems offers a valuable blueprint for conversion of sunlight to useful energy forms. In particular, intracytoplasmic membrane vesicles (chromatophores) from the purple bacterium Rhodospirillum rubrum provide a fully functional and robust photosynthetic apparatus, ideal for biophysical investigations of energy transduction and incorporation into biohybrid photoelectrochemical devices. These vesicular organelles, which arise by invagination of the cytoplasmic membrane, are the sites of the photochemical reaction centers and the light harvesting 1 (LH1) complex. The LH1 protein is responsible for collecting visible and near-IR radiant energy and funneling these excitations to the reaction center for conversion into a transmembrane charge separation. Here, we have investigated the morphology, fluorescence kinetics and photocurrent generation of chromatophores from Rsp. rubrum deposited directly onto gold surfaces in the absence of chemical surface modifications. Atomic force microscopy showed a significant coverage of the gold electrode surface by Rsp. rubrum chromatophores. By in situ fluorescence induction/relaxation measurements, a high retention of the quantum yield of photochemistry was demonstrated in the photoactive films. Chronoamperometric measurements showed that the assembled bioelectrodes were capable of generating sustained photocurrent under white light illumination at 220 mW/cm 2 with a maximum current of 1.5 μA/cm 2 , which slowly declines in about 1 week. This study demonstrates the possibility of photoelectrochemical control of robust chromatophore preparations from Rsp. rubrum that paves the way for future incorporation into functional solar cells.
Nano Letters, 2011
b S Supporting Information B acteriorhodopsin (bR), the other natural photosynthetic system, is the light transducing membrane protein usually found in two-dimensional crystalline patches (purple membrane, PM) of Halobacterium halobium. 1À3 These patches make up the PM, which is composed of mainly protein (75% by wt.) and lipid (∼25%). 4À6 The lattice parameters of crystallized PM have been investigated extensively, showing bR to be composed of seven helices with one interior retinal chromophore in a two-dimensional hexagonal structure. 1À6 This light-driven proton pump moves protons from the cytoplasmic to the extracellular side of its membrane. 7 Under continuous wavelength (cw) illumination, bR exhibits a stationary photocurrent as it transforms light energy into electrochemical energy in the form of a proton gradient across its membrane. 8À10 It offers advantages for its ease of generation and handling, as well as for its durability over a wide range of temperature, 11 pH, 12 and salt concentration ranges. 11,12 These unique characteristics make bR promising for applications in solar energy; however, a limitation arises from its relatively poor native solar energy conversion efficiency 10 compared to other materials, such as semiconducting metal oxides. 13 Indeed, the photocurrent density values reported so far in bR thin film systems are only 0.2À40 pA cm À2 per monolayer even with the use of an applied bias. Recently, our group constructed a solution-based electrochemical cell that has no need for an external bias and does not
Biochemical and Biophysical Research Communications, 2006
The oxidation of bacteriochlorophylls (BChls) in peripheral light-harvesting complexes (LH2) from Rhodobacter sphaeroides was investigated by spectroelectrochemistry of absorption, fluorescence emission, and femtosecond (fs) pump-probe, with the aim obtaining information about the effect of in situ electrochemical oxidation on the pigment-protein arrangement and energy transfer within LH2. The experimental results revealed that: (a) the generation of the BChl radical cation in both B800 and B850 rings dramatically induced bleaching of the characteristic absorption in the NIR region and quenching of the fluorescence emission from the B850 ring for the electrochemical oxidized LH2; (b) 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.
Photovoltage generation in enzymatic bio-hybrid architectures
MRS Advances
Most of the photochemical activity of bacterial photosynthetic apparatuses occurs in the reaction center, a transmembrane protein complex which converts photons into charge-separated states across the membrane with a quantum yield close to unity, fuelling the metabolism of the organism. Integrating the reaction center from the bacterium Rhodobacter sphaeroides onto electroactive surfaces, it is possible to technologically exploit the efficiency of this natural machinery to generate a photovoltage upon Near Infra-Red illumination, which can be used in electronic architectures working in the electrolytic environment such as electrolyte-gated organic transistors and bio-photonic power cells. Here, photovoltage generation in reaction center-based bio-hybrid architectures is investigated by means of chronopotentiometry, isolating the contribution of the functionalisation layers and defining novel surface functionalization strategies for photovoltage tuning.