Biological systems photosynthesis

Many of the simplest chemical reactions involve only an interchange of atoms or ions between reactants, or perhaps only the dissociation of one reactant into two parts. In such reactions, there is no change in the electrical charge of any of the atoms involved. This chapter deals with another type of reaction, in which one or more electrons are transferred between atoms, with the result that some of the atoms involved do have their electrical charges changed. These reactions are known as electron-transfer reactions. You can appreciate their importance when you realize that every battery used in electronic devices and machines, every impulse involved in nerve transmission, every metabolic reaction that produces energy in biological systems, photosynthesis, and combustion processes (to mention but a few examples) requires electron-transfer reactions. 

Electron transfer reactions constitute an ubiquitous class of chemical reactions. This is particularly true in biological systems where these reactions often occur at interfaces, in photosynthesis for instance. It is therefore challenging to use the surface specificity and the time resolution of the SHG technique to investigate these processes. At liquid-liquid interfaces, these processes are mimicked through the following scheme ... 

In the course of evolution, the importance of particular metal ions in biological systems has ebbed and flowed, as a function of environmental conditions. Before the arrival of photosynthesis, when there was no oxygen, elements like Fe and Ni were extremely important, whereas, for example, Cu was virtually inaccessible for reasons of solubility. With the arrival of an oxidizing environment, Ni virtually disappeared from the equation, Cu became bioavailable, and Fe, although it was now insoluble and poorly available, had proved of such fundamental importance in biological catalysis that specific systems were developed for its uptake from the environment, such that it continues to play a key role in life as we know it today. 

Recently it has been reported (3 ) that in a triad molecule where a porphyrin is juxtaposed between a carotenoid and a quinone, a charge transfer donor-acceptor pair with a lifetime similar to that found experimentally in biological systems was produced on light irradiation. It was suggested that an electrical potential similar to the type developed in this donor-acceptor pair may be important in driving the chemical reactions in natural photosynthesis. 

Intermolecular electron transfer plays an important role in the operation of biological systems. For example, electron transfer from one biological molecule to another is the primary act of energy conversion in the processes of respiration and photosynthesis. Despite a large number of works dedicated to the study of intermolecular electron transfer in biological systems, the mechanisms of these reactions have been insufficiently elucidated. This is due to great difficulties in the interpretation of experimental results which are in their turn explained by the very intricate structure of biological systems. 

The approach for this system is the mimicry of the highly efficient photosynthesis process in biological systems, by which an antenna device collects the light energy before a series of exciton, energy, and electron transfers, which lead to the synthesis of the plant s fuel.70-73... 

Photosynthesis, another potential target of bioconjugation, is one of the most important processes in nature. In photosynthesis, photoelectric conversion with nearly 100% efficiency is involved in the primary process.47-48 Such a high performance of photosystem I (PSI) is due to its well-designed spatial configuration. A large number of trials have applied such biological systems to electronic devices. For example, chloroplasts coated on an SnC>2 electrode have been examined as photoelectrochemical cells.49-53... 

G. Charles Dismukes is professor of chemistry at Princeton University and an affiliated member of the Princeton Environmental Institute and the Princeton Materials Institute. His research interests focus on biological and chemical methods for solar-based fuel production, photosynthesis, metals in biological systems, and tools for investigating these systems. His published works describe the biology and chemistry of oxygen production in natural photosynthetic systems, the synthesis and characterization of bioinspired catalysts for renewable energy production, the use of microorganisms... 

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