Redox potential

Redox potential (synonym redox potential; from lat. reductio - restoration and oxydatio - oxidation) - potential arising on inert (usually platinum) electrode immersed in a solution containing one or more reversible oxidation-reduction systems.
Reversible oxidation-reduction system (redox system) is a solution containing oxidized and reduced forms of substances, each of which is derived from another by means of reversible oxidation-reduction reactions.
The composition of the simplest redox systems are cations of the same metal various valence, for example

or anions of the same composition, but different valence, for example

In such systems the redox process is carried out by transfer of electrons from a restored form to oxidized. These redox systems include a number of respiratory enzymes, containing in its composition geminus, for example cytochromes. The redox potential of such systems can be calculated by the formula Peters:

where e - Acting-VP in volts, T - absolute temperature scale, n is the number of electrons lose a single molecule or ion restored form when moving it in the oxidized form; [Oh] and [Red] - molar concentration (or rather activity), oxidized and reduced forms, respectively; E0 normal O.-century I. this system is equal to its About.-VP, provided that [Ox]=[Red]. Normal O.-VP many redox systems can be found in physical-chemical and biochemical directories.
In many biological oxidation-reduction reactions are carried out by transfer from restored form to oxidized not only electrons, but also equal number of protons, for example

The value of the redox potential of such systems is determined not only by the attitude of [Oh] : [Red), but the pH of the environment and can be calculated by the formula

where pH pH environment, E0-normal redox potential of the system, equal O.-B. N. it provided that [Oh] = = [Red] and pH = 0;other values have the same meaning as in equation (1). O.-VP of biological systems, typically set at pH 7 and the value E0-1,984·10-4·T·rn denote through e0. In this case the equation (2) becomes:

Experimentally redox potential define potentiometric (see Potentiometry). O.-VP isolated cells and other biological objects is often measured colorimetrically using redox indicators (see). The value of O.-VP is a measure of oxidative or resilience of the system. Redox system with a higher O.-VP, oxidizes system with a lower O.-B. N. Thus, knowing the magnitude of O.-VP biological redox systems, you can determine the direction and sequence of redox reactions in them. Knowledge O.-VP makes it possible to calculate the amount of energy, which is released at a certain stage of oxidative processes in biological systems. Cm. also the biological Oxidation.