Thermodynamic oxygen transfer potential

FIGURE 3.1 Thermodynamic oxygen transfer potentials. DMDO, dimethyldioxirane Ac, CH3C(0) DMSO, dimethyl sulfoxide DMS, dimethyl sulfide. 

TOP Thermodynamic oxygen transfer potential, according to J Am Chem Soc 2004 126 996 TS Transition state... 

The need for quantitative bond energy data for oxygen-containing molecules in the condensed phase has prompted the development of an evaluation procedure that is based on electron-transfer thermodynamics. The approach is illustrated for H-O bonds and for Fe-0 bonds, but is applicable to any X-O bond for which appropriate electron-transfer potentials are available. Table 6(a) summarizes the one-electron standard reduction potentials for H3O+, HO-, HOH, O2, HOO-, 02 % -O-, and in aqueous solutions (see Table 1). 

The hydrolysis of a thioester is thermodynamically more favorable than thai of an oxygen ester because the electrons of the C=0 bond cannot form resonance structures with the C—S bond that are as stable as those that they can form with the C—O bond. Consequently, acetyl CoA has a high acetyl group-transfer potential because transfer of the acetyl group is exergonic. Acetyl CoA carries an activated acetyl group, just as ATP carries an activated phosphoryl group. 

The reason for the exponential increase in the electron transfer rate with increasing electrode potential at the ZnO/electrolyte interface must be further explored. A possible explanation is provided in a recent study on water photoelectrolysis which describes the mechanism of water oxidation to molecular oxygen as one of strong molecular interaction with nonisoenergetic electron transfer subject to irreversible thermodynamics.48 Under such conditions, the rate of electron transfer will depend on the thermodynamic force in the semiconductor/electrolyte interface to... 

Now, we may consider in detail the mechanism of oxygen radical production by mitochondria. There are definite thermodynamic conditions, which regulate one-electron transfer from the electron carriers of mitochondrial respiratory chain to dioxygen these components must have the one-electron reduction potentials more negative than that of dioxygen Eq( 02 /02]) = —0.16 V. As the reduction potentials of components of respiratory chain are changed from 0.320 to +0.380 V, it is obvious that various sources of superoxide production may exist in mitochondria. As already noted earlier, the two main sources of superoxide are present in Complexes I and III of the respiratory chain in both of them, the role of ubiquinone seems to be dominant. Although superoxide may be formed by the one-electron oxidation of ubisemiquinone radical anion (Reaction (1)) [10,22] or even neutral semiquinone radical [9], the efficiency of these ways of superoxide formation in mitochondria is doubtful. 

Equation (8.14) demonstrates once more that the cation flux caused by the oxygen potential gradient consists of two terms 1) the well known diffusional term, and 2) a drift term which is induced by the vacancy flux and weighted by the cation transference number. We note the equivalence of the formulations which led to Eqns. (8.2) and (8.14). Since vb = jv - Vm, we may express the drift term by the shift velocity vb of the crystal. Let us finally point out that this segregation and demixing effect is purely kinetic. Its magnitude depends on ft = bB/bA, the cation mobility ratio. It is in no way related to the thermodynamic stability (AC 0, AG go) of the component oxides AO and BO. This will become even clearer in the next section when we discuss the kinetic decomposition of stoichiometric compounds. 

Much has been written about solid metal electrodes, which have now largely displaced liquid mercury. Those most often used as redox ( inert ) electrodes for studying electron transfer kinetics and mechanism, and determining thermodynamic parameters are platinum, gold, and silver. However, it should be remembered that their inertness is relative at certain values of applied potential bonds are formed between the metal and oxygen or hydrogen in aqueous and some non-aqueous solutions. Platinum also exhibits catalytic properties. 

Chapter 2 appears on the ESS-RGN of VRB Power Systems, Vancouver, formerly the Regenesys power storage system, both for its own sake and for the thermodynamic points it enables the author to make, reiterate or emphasise in relation to his thermodynamic theories. Here are fuel cells without oxygen, and certainly without combustion, but undoubtedly with charge transfer reactions separated by a potential difference. Moreover, here are fuel cells with incompressible liquid reactants and products. 

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