Redox energies

Since World War 11, the U.S. space program and the military have used small amounts of insoluble chromates, largely barium and calcium chromates, as activators and depolarizers in fused-salt batteries (214,244). The National Aeronautics and Space Administration (NASA) has also used chromium (111) chloride as an electrolyte for redox energy storage cells (245). 

In the case of either eq. 2 or eq. 3, even though excited state energy has been converted into stored chemical redox energy, the storage is temporary because of back electron transfer between the separated redox products, e.g., eq. 4. 

Global geochemical cycle of solar redox energy. Note that no reaction stoichiometry Is shown In this schematic depiction. 

The phototrophs that assimilate fixed nitrogen preferentially utilize ammonium over nitrate or nitrite. (Some phototrophs assimilate DON, such as urea, to meet their nitrogen needs, and, hence, are not strict autotrophs.) Ammonia is fevored over the more oxidized forms of DIN as less redox energy is required to incorporate its nitrogen into biomolecules, primarily amino acids and the nucleotide bases. 

In some cases, mixed valence states may appear simultaneously on two different atoms because of an overlap of the redox energies associated with the two atoms. In the ilmenite FeTi03, the valence states Fe " and Ti are stabilized with an ordering of Fe and Ti on crystallographically inequivalent sites FeV03, on the other hand, has the corundum structure with Fe and V randomly distributed on equivalent sites with the valence states Fe and This observation places the top of the Fe " 3d band (level) below the bottom of the Ti 3 d band, but above the top of the 3 d band, so charge transfers of the type... 

Support for this tentative interpretation comes from a study by Tricker et al. on the system 2 [Zn(ilxV2Sn(i x)/2Fci-xFci ] in which they also find evidence from Mossbauer data for thermal excitation of the mobile ferrous electron to an unspecified conduction band. In this case the conduction band is probably associated with the Shb ions, which would have a 5s band edge close to the Fel 3d redox energy. 

Further there are some other correlations between the characteristic energy terms E, the equilibrium redox energy levels °E and the reorganization energies L which read as follows ... 

The oxide redox energy levels for all elements except gold are cathodic to the redox level of the H2O/O2 couple. Gold, however, is an impractical component for compound semiconductors. All other compound semiconductors employed as electrolysis photoanodes will undergo surface oxidation in aqueous electrolytes to produce a surface oxide film which normally constitutes the stable surface of the photoelectrode. Our proposed mechanism indicates that the proton induced oxide dissolution reaction arises from product ir ion interactions with the oxide anion (0=). 

LC levels are either unaffected or slightly red-shifted under the same conditions, and (iii) the validity for 3MLCT emissions, of a linear relationship between emission levels and redox energies, AEi/2 = e(E0X - red) eV (e is the elementary charge), see the equation below [3],... 

In reaction centers, this energy drives an electron transfer reaction, which in turn initiates a series of slower chemical reactions. Energy is saved as redox energy,29,30 inducing a charge separation in a chlorophyll dimer called the special... 

Fig. 4. Schematic one-electron energies for Nd-5d, 6s and 0-2p bands of NdMnC>3 and redox energies of Nd(III) and Mn(III) in NdMn03.

The transition from localized to itinerant electronic behavior occurs where the interatomic interactions become greater than the intraatomic interactions. A measure of the strength of the interatomic interactions is the bandwidth W and of the strength of the intraatomic interactions is the energy C/eff that separates successive redox energies. The transition from localized to itinerant electronic behavior occurs where... 

CYTOCHROME b-559 AS A TRANSDUCER OF REDOX ENERGY INTO ACID-BASE ENERGY IN PHOTOSYNTHESIS... 

Transduction of light energy into redox energy... 

Transduction of redox energy into acid-base energy... 

Thus, light energy is eventually transduced not only into redox energy, but also into acid-base energy ... 

Fig. 1. Diagrammatic representation of the reversible transduction of redox energy into acid-base energy by the cytochrome b-559 system (Losada et al., 1987 Ortega et al., 1987).

---