Biological chemical reactions photosynthesis

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 ... 

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. 

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. 

One problem that is amenable to this technique is transition metal-mediated chemical reactions. They range from industrial processes such as petroleum refinery to biological cycles such as nitrogen fixation and photosynthesis. These reactions have been thought to take place at an unsaturated metal site, for example, the kinks or step edges on a metal surface. Ideally, one would like to observe the chemical events that evolve... 

Although such a 2-MHz ESR apparatus was very sophisticated, its time resolution was not enough for measurement of CIDEP. In 1973, Fessenden [5] found that the direct ESR measurement without field modulation improved the time resolution, observing CIDEP signals in solution with pulse radiolysis. This method was applied for laser-photolysis measurements in solids [6] and in solution [7]. A spin-echo ESR technique was also found to be useful for CIDEP [8]. Since then, CIDEP experiments with cw-ESR and pulsed-ESR spectrometers without field modulation have become much more popular than before. Through such transient ESR measurements, CIDEP due to not only the radical pair mechanism but also several other mechanisms have been observed in many chemical reactions including biologically important ones such as photosynthesis reactions. In this chapter, we will show several mechanisms for CIDEP with several typical examples. 

Biological cell membranes are multi-component systems consisting of a fluid bilayer lipid membrane (BLM) and integrated membrane proteins. The main structural features of the BLMs are determined by a wide variety of amphiphilic lipids whose polar head groups are exposed to water while hydrocarbon tails form the nonpolar interior. The BLMs act as the medium for biochemical vectorial membrane processes such as photosynthesis, respiration and active ion transport. However, they do not participate in the corresponding chemical reactions which occur in membrane-dissolved proteins and often need redox-active cofactors. BLMs were therefore mostly investigated by physical chemists who studied their thermodynamics and kinetic behaviour . ... 

A long time contact of the dissolved fraction with particulate matter can produce changes in the distribution of chemical forms of heavy metals in solution. Any change in the equilibrium conditions after collection can promote or remove dissolved metals (54) or desorption of adsorbed metals operated by particulate. Biological activity involves photosynthesis and respiration which will change the carbon dioxide content of the water and its pH. All the equilibrium reactions affected by pH will be altered, e.g., the reactions of precipitation, complexation and redox involving heavy metals. 

Free energy used by most biological systems originates from solar energy stored by photosyndiesis in green plants, algae, or photosynthetic bacteria. The fundamental process of photosynthesis(l) may be represented by one deceptively simple chemical reaction ... 

The concentrations of inorganic carbon species in sea water are controlled not only by the chemical reactions outlined above (i.e., eqn [I]) but also by various physical and biological processes, including the exchange of CO2 between ocean and atmosphere the solubility of CO2 photosynthesis and respiration and the formation and dissolution of calcium carbonate (CaC03). 

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