Proton transport rate constant

Methods similar to those discussed in this chapter have been applied to determine free energies of activation in enzyme kinetics and quantum effects on proton transport. They hold promise to be coupled with QM/MM and ab initio simulations to compute accurate estimates of nulcear quantum effects on rate constants in TST and proton transport rates through membranes. 

There are several variants of this method for more complicated reactions. If the reacting species is produced by a preceding chemical reaction, deviations from Eq. (14.6) may be observed for large in, when the reaction is slower than mass transport. From these deviations the rate constant of the chemical reaction can be determined. As an example we consider hydrogen evolution from a weak acid HA, where the reacting protons are formed by a preceding dissociation reaction ... 

Blue copper proteins, 36 323, 377-378, see also Azurin Plastocyanin active site protonations, 36 396-398 charge, 36 398-401 classification, 36 378-379 comparison with rubredoxin, 36 404 coordinated amino acid spacing, 36 399 cucumber basic protein, 36 390 electron transfer routes, 36 403-404 electron transport, 36 378 EXAFS studies, 36 390-391 functional role, 36 382-383 occurrence, 36 379-382 properties, 36 380 pseudoazurin, 36 389-390 reduction potentials, 36 393-396 self-exchange rate constants, 36 401-403 UV-VIS spectra, 36 391-393 Blue species... 

The functional form of the triggers ate based on transition state, as determined by the quantum mechanical calculation and their numerical values are parameterized to satisfy the macroscopically determined rate constant and activation energy. Local equilibration at the end of the reaction helps in maintaining the correct heat of reaction and structure. For the vahdation of the algorithm, it has been implemented to study proton transport in bulk water. In bulk water the two components of the total diffusivity were found to be uncorrelated. 

Changes in moisture content affect charged species in foods that are not part of the chemical equation, but that may impart their own effects upon reaction rate. Reactions that involve proton and electron transport, which include hydrolysis, Maillard browning, oxidation, and almost every critical shelf-life-limiting reaction in foods, will be affected by the presence of ions. This is part of the theory behind the Debye-Hiickel equation. This model describes the effect of ionic strength on the reaction rate constant in dilute solutions ... 

Carbanion protonation in water is a two-step reaction (i) movement of a Bronsted acid into a reactive position, and (ii) proton transfer to carbon. The overall rate constant for carbanion protonation may be limited by either the rate constant for formation of the reactive complex, in which case the overall rate constant for proton transfer can be estimated by using a representative rate constant for the rate-determining transport step, or by the rate constant for proton transfer to carbon. 

Proton transport in the gA channel was also simulated with a kinetic model (see section 16.3.5.3). " Each H2O molecule was allowed to take six orientations and each HsO molecule, four orientations, so that the chain of eleven H2O molecules could take 10 states. Three types of transitions were allowed rotation of H2O and HsO" proton transfer from HsO to a neighbouring H2O molecule when they form a hydrogen bond and proton uptake and release for water molecules located at the channel ends. The rate constants were taken of the TST type, with Ag values calculated by continuum electrostatics or deduced from data about proton transfer in water. For the proton uptake and release steps, the Ag value depended explicitly on the pH. The master equation was solved by a sequential dynamical Monte Carlo algorithm and the PMF was deduced from the probability of occupancy of the various sites. When no voltage was applied, the PMF was a symmetrical barrier with a maximum at 3.4 kcal mol . Stationary proton ffuxes calculated for various pH and voltages values were in reasonable agreement with the conductance data. Despite the simplified description of electrostatic interactions and the questionable... 

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