Photobiological process

Flavins (152), benzoamielated derivatives of lumazine (145), are implicated in a variety of photobiological processes such as photodynamic action, phototropism, phototaxis, and photosynthesis. The biologically active H form 152a of alloxazine (R = R = R = = H) is less stable in... 

M. Brouers, F. Collard, J. Jeanfils, R. Loudeche (1983) Long term stabilization of photobiological activities of immobilized algae photoproduction of hydrogen by immobilized adapted Scenedesmus cells. In Photochemical, Photoelectrochemical and Photobiological Processes. Hall D.O et al eds. Reidel Pul. Dordrecht. 170-178... 

Eventually, hydrogen could also be produced directly from renewable sources through photoelectrochemical or photobiological processes, but these are still at an early stage of research and development. 

Knowledge of the dynamics of excited states is of major importance in understanding photophysical, photochemical and photobiological processes. Two time-resolved techniques, pulse fluorometry and phase-modulation fluorometry, are commonly used to recover the lifetimes, or more generally the parameters characterizing the S-pulse response of a fluorescent sample (i.e. the response to an infinitely short pulse of light expressed as the Dirac function S). 

Ochsner M (1997) Photophysical and photobiological processes in the photodynamic therapy of tumours. J Photochem Photobiol B 39 1-18. 

Because of this difference in electron-donorand electron-acceptor properties, excited states have very different redox properties from those of related ground states. The effect is so marked that many photochemical processes begin with a complete transfer of an electron from (or to) an excited state (1.2), and the subsequent chemistry is that of radical cations and radical anions, species that are regarded as unusual in ground-state organic reactions. The importance of photochemical electron transfer is underlined by its extensive involvement in photobiological processes such as photosynthesis. 

This Workshop is on Photochemical and Photobiological processes for producing energy rich compounds and more specifically we are part of the sub-programme Energy from biomass . 

E.C. Workshop on Photochemical and Photobiological Processes for the Production of Energy-rich Compounds 2nd (1987), Seville, Spain. 

Quantum Yield Efficiency of fluorescence percentage of incident energy emitted after absorption. The higher the quantum yield, the greater the intensity of the fluorescence, luminescence, or phosphorescence. See Papp, S. and Vanderkooi, J.M., Tryptophan phosphorescence at room temperature as a tool to study protein structure and dynamics, Photochem. Photobiol. 49, 775-784, 1989 Plasek, J. and Sigler, K Slow fluorescent indicators of membrane potential a survey of different approaches to probe response analysis, J. Photochem. Photobiol. 33, 101-124, 1996 Vladimirov, Y.A., Free radicals in primary photobiological processes, Membr. Cell Biol. 12, 645-663, 1998 Maeda, M., New label enzymes for bioluminescent enzyme immunoassay, J. Pharm. Biomed. Anal. 30, 1725-1734, 2003 Imahori, H., Porphyrin-fullerene linked systems as artificial photosynthetic mimics, Org. Biomol. Chem. 2, 1425-1433, 2004 Katerinopoulos, H.E., The coumarin moiety as chromophore of fluorescent ion indicators in biological systems, Curr. Pharm. Des. 10, 3835-3852, 2004. 

Biological Hj production is expected to be one of many processes that contribute to the ultimate supply of H2. But it is useful to consider that in an area of less than 5,000 square miles (about 0.12% of the U.S. land area) of bioreactor footprint in the desert southwest, photobiological processes could in principle produce enough H2 to displace all of the gasoline currently used in the U.S. (236 million vehicles). The underlying assumptions are that H2 could be produced from water at 10% efficiency (the maximum theoretical efficiency of an algal H2 production system is about 13%) and that fuel cell-powered vehicles could get 60 miles/kg of H2 (M. Mann, personal communication). 

Many operating costs are the same as those for any conventional chemical production process, such as operating labor, raw materials, and equipment maintenance. However, some expenses, such as cleaning optical surfaces or preventing biofilm growth on the photobioreactor surfaces, are unique to photobiological processes. 

Covers gasification, electrolysis, thermochemical, and photobiological processes for generating hydrogen... 

Fig. 4. Time scales of photophysical and photobiological processes with the range of pulsed lasers...

Halocarbon concentrations in natural waters are typically very low. At such low concentrations and with constant irradiance, the rate is usually directly proportional to halocarbon concentration that is, a pseudo-first-order rate expression applies. The kinetic data sometimes are expressed as half-lives that equal 0.693/fcp (where /cp is the pseudo-first-order rate constant). More references and a detailed discussion of the modeling of aquatic photochemical and photobiological processes, including the effects of vertical mixing, were given by Plane et al. (23), Smith (24), Zepp and Cline (25), and Sikorski and Zika (26). 

The Physics section provides information and discussions on global UVR climatology at the Earth s surface level and the factors controlling the transmittance of UVR through the atmosphere (Chapter 2), and the penetration into the water column (Chapter 3). The last chapter within this section (Chapter 4) introduces basic notions of mixing and advection and outlines the implications of vertical water motion for photochemical and photobiological processes. 

Alternative methods of hydrogen production are thermochemical water decomposition, photoconversions, photobiological processes, production from biomass, and various industrial processes where it is a by-product. 

A plate loop or sandwich reactor for photobiological processes using purple nonsulfur bacteria has been designed at the RWTH Aachen (Fig. 5-12, right). The reactor is separated by a central plate on which the bacteria are growing. Solar insulation triggers a natural convection of the nutrition suspension to flush around the bacteria. In outdoor experiments, a hydrogen production rate of 2 l/(h m ) was achieved [63]. 

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