Protonic Carriers

These equations and the symbols are in accordance with Kroger-Vink notation [27]. V is an oxygen vacancy, is the lattice oxygen, h is an electronic hole, OHq is a hydroxyl ion, which represents an interstitial proton associating strongly with a neighboring oxygen ion. From the equilibrium of reactions (2.1) and (2.2), the activity of electronic-holes and protons can be described as  

From Eq. (2.3) and (2.4) it is apparent that protonic and p-type electronic conduction depend respectively, on the H2O partial pressure and O2 partial pressure. 

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Transition states for betaine isomerization to ylides via the intramolecular mechanism were not localized. We believe that these processes are intermolecular and involve donor solvent molecules or the second betaine molecule as a proton carrier. 

Deng, W., Molinero, V. and Goddard, W. A., III. 2004. Fluorinated imidazoles as proton carriers for water-free fuel cell membranes. Journal of the American Chemical Society 126 15644-15645. 

Uncoupling of phosphorylation from electron transfer FCCP DNP Hydrophobic proton carriers... 

What is the nature of the proton-translocating pumps that link Ap with electron transport In his earliest proposals Mitchell suggested that electron carriers, such as flavins and ubiquinones, each of which accepts two protons as well as two electrons upon reduction, could serve as the proton carriers. Each pump would consist of a pair of oxidoreductases. One, on the inside (matrix side) of the coupling membrane, would deliver two electrons (but no protons) to the carrier (B in Fig. 18-13). The two protons needed for the reduction would be taken from the solvent in the matrix. The second oxidoreductase would be located on the outside of the membrane and would accept two electrons from the reduced carrier (BH2 in Fig. 18-13) leaving the two released protons on the outside of the membrane. To complete a "loop" that would allow the next carrier to be reduced, electrons would have to be transferred through fixed electron carriers embedded in the... 

The above results indicate that in order to maintain the high rate of transmembrane electron transfer, it is necessary to provide efficient neutralization of the arising polarization. For this purpose lipophilic ions and proton carriers were successfully used (see Table 1). These compounds are known to act as the uncouplers of the mitochondrial oxidative phosphorylation and are able to remove the gradients of electric fields across lipid membranes. 

In mitochondria there are two types of mechanisms for coupling the electron transport to the movement of protons across the membrane. The first is based on anisotropic reduction and oxidation of a lipid-soluble quinone inside the membrane. The quinone, coenzyme Q, becomes protonated upon reduction and diffuses to an oxidation site on the other side of the membrane where removal of electrons leads to proton release. This is essentially a proton carrier system with the hydroquinone acting as the proton carrier in the lipid phase of the membrane. A further refinement of this system in mitochondria provides for a coenzyme Q redox cycle where the movement of one electron through the chain allows for two protons to cross the... 

As the last contribution in this Section, DFT cluster studies and AIMD methods considered the role of water as proton carrier in the OOH formation step on Pt(lll) and Au surfaces. These works considered Hs02 in the presence and absence of surrounding water molecules. 

Owing to the importance of the amine, probably acting as a ligand of lithium or a proton carrier [ammonium salt of (2R,3R)-DPTA], a process was proposed allowing the introduction of different amines and consequently a modification of the selectivity of the protonation after deprotonation of a Schiff base of methyl valinate with Lithium Hexamethyldisilazide (LHMDS), the liberated HMDS was replaced by a more basic primary, secondary, or tertiary amine prior to the addition of (2R,3R)-DPTA (eq 5) (Table 3). In some cases, higher ee were observed compared to the classical procedure with LHMDS (34% ee) or LDA (47% ee). ... 

One-electron reduction of (NH3)5Ru-4-(l 1 -dodecenyl)py + by externally added reductants followed biphasic kinetics when the complex was bound at both interfaces of PC liposomes, but only the fast step was observed when binding was limited to the external surface [111]. The slow step was first order and independent of the identity and concentrations of added reductants. The rate constant, k = 10 s", was unchanged upon adding either the potassium ionophore, valinomycin, or the proton carrier, carbonyl cyanide m-chlorophenylhydrazone, to the medium, indicating that, although electrogenic, the transmembrane reduction step was not rate-... 

More difficult in BLMs, refined HPTS assays exist to address the special cases of selective transport of protons [11] and electrons [17] in LUVs. In the conventional HPTS assay (Fig. 11.5c), the apparent activity of proton channels decreases with increasing proton selectivity because the rate ofthe disfavored cation (M ) influx influences the detected velocity more than the favored proton efflux. Disfavored potassium influx can, however, be accelerated with the potassium carrier vaiinomycin (Fig. 11.8). Increasing activity in the presence of vaiinomycin identifies proton channels with H > K+ selectivity being at least as high as the maximal measurable increase (in unpolarized LUVs of course, compare Section 11.3.4). Important controls include evidence for low enough vaiinomycin concentrations to exclude activity without the proton channel (due to disfavored H+ efflux). The proton carrier FCCP is often used as complementary additive to confirm M+ > H+ selectivity (e.g. amphotericin B). 

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