Processes in biological systems

Radical chemistry has undergone something of a renaissance in recent years. The phenomenon of CIDNP has played an important part in this. The growing interest in the role of radical processes in biological systems may stimulate the application of CIDNP in even wider fields in the future. The development of a practical device for radiofrequency amplification by the stimulated emission of radiation (RASER) may well be one such application. 

As mentioned previously, siderophores must selectively bind iron tightly in order to solubilize the metal ion and prevent hydrolysis, as well as effectively compete with other chelators in the system. The following discussion will address in more detail the effect of siderophore structure on the thermodynamics of iron binding, as well as different methods for measuring and comparing iron-siderophore complex stability. The redox potentials of the ferri-siderophore complexes will also be addressed, as ferri-siderophore reduction may be important in the iron uptake process in biological systems. 

Lipid peroxidation is probably the most studied oxidative process in biological systems. At present, Medline cites about 30,000 publications on lipid peroxidation, but the total number of studies must be much more because Medline does not include publications before 1970. Most of the earlier studies are in vitro studies, in which lipid peroxidation is carried out in lipid suspensions, cellular organelles (mitochondria and microsomes), or cells and initiated by simple chemical free radical-produced systems (the Fenton reaction, ferrous ions + ascorbate, carbon tetrachloride, etc). In these in vitro experiments reaction products (mainly, malon-dialdehyde (MDA), lipid hydroperoxides, and diene conjugates) were analyzed by physicochemical methods (optical spectroscopy and later on, HPLC and EPR spectroscopies). These studies gave the important information concerning the mechanism of lipid peroxidation, the structures of reaction products, etc. 

Figure 1.27 Double-walled silica nanotubes with monodisperse diameters self-orga-nize into highly ordered centimetre-sized fibres, using a synthetic octa-peptide as a template. The growth mechanism is proposed to be the fundamental mechanism for growth processes in biological systems. (Reproduced from ref. 53, with permission.)...

A number of publications in recent years have demonstrated an active interest in the theoretical aspects of electron transfer (ET) processes in biological systems (1.-9). This interest was stimulated by the extensive experimental information regarding the temperature dependence of ET rates measured over a broad range of temperatures (10-16). The unimolecular rate of cyto-chrome-c oxidation in Chromatium (10-12), for example, exhibits the Arrhenius type dependence and changes by three orders of... 

This expression constitutes the basis of current interpretations of electron transfer processes in biological systems. From Eq. (9), the functions Hg, (Q) and Hbb (Q) represent potential energy surfaces for the nuclear motion described by Xav and Xbw respectively, if the weak diagonal corrections Taa and T b are neglected. Then, the region Q Q where Xav and Xbw overlap significantly corresponds to the minimum of the intersection hypersurface between Hga (Q) and Hbb (Q)- Referring to definition (5), this implies ... 

There is experimental evidence for the dependence of efficiency of transport or chemical processes in biological systems. Many studies have... 

Since the initial observation of flavin radical species by Michaelis and coworkers the involvement of flavins in one-electron oxidation-reduction processes in biological systems has occupied the attention of workers in the field of redox enzymology up to the present time. Flavin coenzymes occupy a unique role in biological oxidations in that they are capable of functioning in either one-electron or two-electron transfer reactions. Due to this amphibolic reactivity, they have been termed in a recent review to be at the crossroads of biological redox processes. 

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... 

The construction of an artificial protein-protein complex is an attractive subject to elucidate the electron-transfer process in biological systems. To convert Mb into an electron-transfer protein such as cytochromes, Hayashi and Ogoshi (101) prepared a new zinc Mb having a unique interface on the protein surface by the reconstitutional method as shown in Fig. 27. The modified zinc protoporphyrin has multiple functional groups, carboxylates, or ammonium groups, at the terminal of the two propionates. Thus, the incorporation of the... 

Mason, R. Charge transfer processes in biological systems. Pis. Faraday Society, 27 129-133, 1959. 

The use of the equilibrium constant Pow (the octanol-water partition coefficient) as a descriptor of chemical processes in biological systems is well known the study of kinetics is more general than that of the special case of equilibrium, but is more difficult. The emphasis here will be on pesticides and model compounds, but is relevant to other systems. 

In order for the color state to persist for an extended time, a charge separation of the photogenerated ions must be produced such as that in a photosynthetic process in biological systems. Also, the rate of reverse electron transfer can be retarded by the presence of an external field. 

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