Proton switch mechanism

Electrical properties of liquids and solids are sometimes crucially influenced by H bonding. The ionic mobility and conductance of H30 and OH in aqueous solutions are substantially greater than those of other univalent ions due to a proton-switch mechanism in the H-bonded associated solvent, water. For example, at 25°C the conductance of H3O+ and OH are 350 and 192ohm cm mol , whereas for other (viscosity-controlled) ions the values fall... 

H2SO4.Z2H2O, are known with = 1, 2, 3, 4 (mps 8.5", -39.5". -36.4" and -28.3% respectively). Other compounds in the H2O/SO3 system are H2S2O7 (mp 36") and H2S4O13 (mp 4"). Anhydrous H2SO4 is a remarkable compound with an unusually high dielectric constant, and a very high electrical conductivity which results from the ionic self-dissociation (autoprotolysis) of the compound coupled with a proton-switch mechanism for the rapid... 

Push-pull acid-base catalysis has been proposed to account for the proton switch mechanism which occurs in the methoxyaminolysis of phenyl acetate (Scheme 11.14) where a bifunctional catalyst traps the zwitterionic intermediate. A requirement of efficient bi-functional catalysis is that the reaction should proceed through an unstable intermediate which has p values permitting conversion to the stable intermediate or product by two proton transfers after encounter with the bifunctional catalyst the proton transfer with monofunctional catalysts should also be weak. 

Despite this enormous viscosity, fused H3PO4 (and D3PO4) conduct electricity extremely well and this has been shown to arise from extensive self-ionization (autoprotolysis) coupled with a proton-switch conduction mechanism for the... 

Figure 12.17 Schematic representation of proton-switch conduction mechanism involving [U2PO4I phosphoric acid.

How is the sequence driven by the absorbed light energy Protons must enter the pump from the cytosol and exit on the exterior (periplasmic) side, flowing out against a concentration gradient. There must be a "gating" or "switch" mechanism that ensures that protons enter and leave the pump in the correct direction.586... 

Brandt U (1999) Proton translocation in the respiratory chain involving ubiquinone - a hypothetical semiquinone switch mechanism for complex I. Biofactors 9,95-101. 

Figure 14. Protonation-deprotonation switching mechanism of quadratic NLO response.

The PA-ET mechanism just described is formally plausible, since all the nuclear configurations involved in its steps obey to the formal rules of the valency. As mentioned above, a major problem is the proof that chemical events, such as oxidation or reduction, can produce the driving force for proton switching in a structure of the appropriate type. Such a problem is not easy to handle in a real system, especially because the electrostatic field of the protein backbone, which... 

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