Photosynthetic process

Berry, J.A. 1975 Adaptation of photosynthetic processes to stress. Science 188 644-650. 

Genty, B., Briantais, J.M. Da Silva, J.B.V. (1987). Effects of drought on primary photosynthetic processes of cotton leaves. Plant Physiology, 83, 360-4. 

Chemical models of photosynthesis have been used to investigate two types of reactions photosynthesis and photocatalysis. In photosynthetic processes the standard Gibbs free energy of the reaction is positive, and solar energy is utilized to perform work. In photocatalytic processes the free energy is negative and solar energy is used to overcome the activation barrier. 

FIG. 4 (a) Latimer diagram of the water soluble zinc tetra-Af-methyl-4-pyridium porphyrin (ZnTMPyP ). (Reprinted with permission from Ref. 47.) (b) Schematic representation of a photosynthetic process based on porphyrin sensitized water-organic interface. Dotted line corresponds to the back electron-transfer process. (Reprinted from Ref. 51 with permission from Elsevier Science.)... 

As mentioned earlier, a great deal of literature has dealt with the properties of heterogeneous liquid systems such as microemulsions, micelles, vesicles, and lipid bilayers in photosynthetic processes [114,115,119]. At externally polarizable ITIES, the control on the Galvani potential difference offers an extra variable, which allows tuning reaction paths and rates. For instance, the rather high interfacial reactivity of photoexcited porphyrin species has proved to be able to promote processes such as the one shown in Fig. 3(b). The inhibition of back ET upon addition of hexacyanoferrate in the photoreaction of Fig. 17 is an example of a photosynthetic reaction at polarizable ITIES [87,166]. At Galvani potential differences close to 0 V, a direct redox reaction involving an equimolar ratio of the hexacyanoferrate couple and TCNQ features an uphill ET of approximately 0.10 eV (see Fig. 4). However, the excited state of the porphyrin heterodimer can readily inject an electron into TCNQ and subsequently receive an electron from ferrocyanide. For illumination at 543 nm (2.3 eV), the overall photoprocess corresponds to a 4% conversion efficiency. 

The lack of understanding of the effect of the allelopathic agents on whole plant photosynthetic processes, namely, changes in stanatal opening, membrane permeability, water content and marry other processes that affect the overall photosynthetic processes. 

However, process (6.5.5) cannot be a universal photosynthetic process because H2S is unstable and is not available in sufficient quantities in nature. Water is the only substance that can be used in the reduction of carbon dioxide whose presence in nature is independent of biological processes. 

There have been many attempts to mimic some features of photosynthesis with abiotic systems for purposes of artificial solar energy conversion. Ideally a fuel, e.g., H2, is formed through a photosynthetic process. Photolysis of water is a highly endergonic process ... 

In addition to photocleavage of water with photocatalysts, other photosynthetic processes such as photochemical C02 reduction, resulting in the formation of CO or methane, and the photochemical fixation of nitrogen are of great interest ... 

Photosynthetic processes involving some inorganic iron-bearing minerals (semiconductors) and dissolved Fe-species may be looked at as "primitive alternatives or precursors to biological photosynthesis. 

Outline the essential features of the photosynthetic process in green plants and in photosynthetic bacteria. 

Thermodynamically, since the free-energy change has a positive value it can only proceed when energy is supplied from the sun. The photosynthetic process occurs on a vast scale, fixing 2 x 1011 tonnes per annum of carbon as carbohydrate, representing 10 times the energy consumption of the entire human race. 

The photosynthetic process thus provides us with an example of a complex, light-powered photochemical molecular device which uses light as an energy supply in order to facilitate energy conversion. In green plants, this molecular device is located within a specially-adapted photosynthetic membrane. 

Of course, natural systems do not operate outside of the laws of thermodynamics. The process of assimilating atoms to form organized structures requires energy, and this energy is derived (with a few exceptions) from the sun, via photosynthetic processes. 

Liquid-crystalline media are important especially for technical and biomedical applications of electron-transfer reactions. Molecular electronic systems, photosynthetic processes, and some... 

Table 8.30 shows the chemistry of seawater compiled by Turekian (1969) for major, minor, and trace constituents, expressed in parts per billion (ppb) at a mean salinity of 35. The listed values are estimates of mean amounts in solution, whereas elemental concentrations actually vary with depth. The most conspicuous variations are observed in the first 200 m from the surface, where photosynthetic processes are dominant and phosphorus and nitrogen are fixed by plankton and benthos, as well as silica and calcium, which constitute, respectively, the skeletons of planktonic algae (diatom) and the shells of foraminifera and mollusks. 

Reaction of 217 with Cjq leads to the amino-protected porphyrin-fulleropyrroli-dine, which can easily be deprotected to the corresponding amine [229, 277]. By further functionalization via amide coupling an easy access to extended donor-acceptor systems is possible. A carotene-porphyrin-fullerene triad was prepared by reaction of the amine with the appropriate carotene acid chloride. The motivation for the synthesis of all these donor-acceptor systems is the attempt to understand and imitate the photosynthetic process. On that score, a model for an artificial photosynthetic antenna-reaction center complex has been achieved by attaching five porphyrin cores in a dendrimer-like fashion to the fullerene [242]. 

---