Oxidation-reduction potential factors influencing

Eugenol, like other phenolic compounds, is a structurally non-specific drug. The pharmacological action is not directly subordinated to chemical structure, except to the extent that structure affects physicochemical properties, as adsorption, solubility, pKa, and oxidation-reduction potential, factors which influence permeability, depolarization of the membrane and protein coagulation [34],... 

A characteristic of the cytochromes c3 is a very low oxidation-reduction potential. Moreover, it is obvious from the multiheme nature of these cytochromes that the redox properties should be complex. In the simplest situation, four individual redox potentials could be expected, one for each heme. In addition to the axial ligands on the hemes, a number of factors are anticipated to influence the individual heme redox potentials. First and foremost, the environment of each heme can exert an influence on its oxidation-reduction potential. This influence will be manifested in two ways the packing of the specific amino acid side chains about each heme and the extent of solvent exposure of each heme. It is quite apparent from the structural data (Figures 1 and 2) that the four hemes, which are in nonequivalent environments, are expected to have different oxidation-reduction potentials. Moreover, at least with Miyazaki cytochrome c3> one of the hemes (heme II) is substantially more exposed to solvent, which may result in a lower oxidation-reduction potential (13). Finally, it is apparent that in a small molecule that contains four hemes within close proximity (< 18 A), heme-heme interactions, principally as a result of electrostatic interactions, are likely to influence oxidation-reduction potentials (14). Indeed, on electrostatic grounds the redox state of one heme should influence another. This influence results from the fact that addition of electrons changes the formal... 

The functionality of a protein is dictated by the molecular properties of the protein as modified by processing treatments, environmental factors, and interactions with other components. Environmental conditions, such as pH, ionic strength, type of salts, moisture content, and oxidation-reduction potential, may alter the functional properties of a protein in a food. Protein functional properties are also influenced by unit operations during processing... 

The factors that influence corrosion of steels in soils are the type of soil moisture content and the position of the water table soil resistivity and soluble ion content soil pH oxidation-reduction potential and the role of microbes present in soil. The exposure of a buried pipe to the soil environment is illustrated in Figure 4.2. The steel pipe is exposed to both meteoric water passing through ground surface and the water in the ground. The meteoric water may be acidic due to the presence of carbon dioxide and sulfur dioxide in the atmosphere. The soil water may be acidic in addition to some dissolved minerals. The steel pipe is partially above the water table with the rest below the water. The pH and the dissolved ions in the ground water provide a corrosive environment. 

For most oxidation-reduction systems z — zl is relatively high, e.g., 7 for the Fe(CN)o, Fe(CN)F system, and so the last terra in equation (7), which represents the activity coefficient factor, may be quite considerable further, the terms in the ionic strength involve the square of the valence and hence t will be large even for relatively dilute solutions. In any case, the presence of neutral salts, w hich were frequently added to the solution in the earlier studies of oxidation-reduction potentials, increases the ionic strength they will consequently have an appreciable influence on the potential, although the ratio of the amounts of oxidized to reduced forms remains constant. 

Influence of various factors on the oxidation-reduction potential 393... 

INFLUENCE OF VARIOUS FACTORS ON THE OXIDATION-REDUCTION POTENTIAL... 

Perhaps the most fundamental fimctional property of a heme prosthetic group at the active site of a heme protein is the relative stability of the reduced and oxidized states of the heme iron. A number of structural characteristics of the heme binding environment provided by the apo-protein have been identified as contributing to the regulation of this equilibrium and have been reviewed elsewhere 82-84). Although a comprehensive discussion of these factors is not possible in the space available here, they can be summarized briefly. The two most significant influences of the reduction potential of the heme iron appear to be the dielectric constant of the heme environment 81, 83) and the chemical... 

Oxidation-reduction (redox) reactions, along with hydrolysis and acid-base reactions, account for the vast majority of chemical reactions that occur in aquatic environmental systems. Factors that affect redox kinetics include environmental redox conditions, ionic strength, pH-value, temperature, speciation, and sorption (Tratnyek and Macalady, 2000). Sediment and particulate matter in water bodies may influence greatly the efficacy of abiotic transformations by altering the truly dissolved (i.e., non-sorbed) fraction of the compounds — the only fraction available for reactions (Weber and Wolfe, 1987). Among the possible abiotic transformation pathways, hydrolysis has received the most attention, though only some compound classes are potentially hydrolyzable (e.g., alkyl halides, amides, amines, carbamates, esters, epoxides, and nitriles [Harris, 1990 Peijnenburg, 1991]). Current efforts to incorporate reaction kinetics and pathways for reductive transformations into environmental exposure models are due to the fact that many of them result in reaction products that may be of more concern than the parent compounds (Tratnyek et al., 2003). 

Both empirical and rational methods have been successful in developing novel fluorescent sensors. However, on the one hand, empirical design and synthesis may require considerable trial and error. On the other hand, the rational design approach described above is limited to analytes that can sufficiently change the oxidation or reduction potential. Further, even in the case of theoretically designed molecules, the fluorescence properties may be unexpectedly influenced by environmental factors. The construction of libraries of fluorescent molecules is one way to overcome some of these problems in the development of novel fluorescent sensors. 

The reduction potentials of Cua centers are influenced by the same factors that contribute to those of mononuclear cupredoxins discussed above, including hydrophobic encapsulation and axial ligand interactions from a weak methionine and a backbone carbonyl oxygen. However, the presence of two covalent Scys ligands would significantly stabilize the oxidized center and further lower the reduction potentials. This effect is believed to be countered by the presence of a Cu—Cu bond in the oxidized Cua the presence of a second copper ion in close proximity would tend to increase the effective nuclear charge felt by the redox active electron and thus would increase the reduction potentials of the Cua centers. ... 

In the designing new molecular architectures, one preliminary objective is finding the relationships among the factors which affect the electronic properties of the final materials. Specifically, the properties one may wish to control in the starting monomer are (i) symmetry, to influence the HOMO bandwidth of the polymer, and hence the mobility of the charge carriers, (ii) 7C-electron conjugation, which should be maintained in the polymer backbone, (iii) oxidation or reduction potential, to favor desired reactions for polymer synthesis, (iv) positional selectivity, to prevent the formation of defects that may interrupt the 7C-conjugation. 

A second factor influencing the distribution of cofactor forms is solvent acidity. With one exception, the principal 2 1 distribution is uninfluenced by this variable. Thus, changes in solvent acidity appear to produce subsets of cofactor species with the following properties (1) Different reduction potentials for the major fraction of oxidized cofactor in acid (E a = -0.36 V) solution (2) changes in the number (Rs-r versus Ns-r and Ws-r) and EPR spectroscopic properties of semi-reduced cofactor species (3) formation of additional forms (Aox, Aox", Aox" ) of electroactive FeMoco(ox). These observations are summarized in Scheme 1. 

The factors which influence the rate of dissolution of iron oxides are the properties of the overall system (e. g. temperature, UV light), the composition of the solution phase (e.g. pH, redox potential, concentration of acids, reductants and complexing agents) and the properties of the oxide (e. g. specific surface area, stoichiometry, crystal chemistry, crystal habit and presence of defects or guest ions). Models which take all of these factors into account are not available. In general, only the specific surface area, the composition of the solution and in some cases the tendency of ions in solution to form surface complexes are considered. 

Brett etal. [103] have studied selfassembling of 1-decanethiol at the fixed positive potentials of pc-Au electrode in chronoamperometry and quartz crystal microgravimetry. The obtained layers appeared to have improved quality and were produced faster than in the open-circuit deposition. The factors possibly influencing the fine structure of monolayers observed in voltammetric reductive desorption and oxidative redeposition of long-chain alka-nethiolates, for example, hexadecanethiol (HT) and octadecanethiol on smooth Au electrodes have been discussed [104]. It has been shown that the local order of adlayer has a role to play in the formation of that fine structure. 

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