Rate limiting factors

The construction, meaning and uses of such maps has been explained with great clarity in a monograph by Frost and Ashby (1982). The various mechanisms and rate-limiting factors (such as lattice friction or dislocation climb combined... 

Pressure is similar to temperature as a rate limiting factor since the diffusibility of a gas is inversely related to its pressure. For instance, loweringthe pressure 760 Torr(l atm)to 1 Torr increases the gas-phase transfer of reactants to the deposition surface and the... 

When a limiting current is encountered, it is almost always caused by the slowness of transport of charged (ionic) or uncharged (molecular) species through the solution.1 These species move toward the appropriate electrodes, where they are consumed in the electrode reaction, or in a reaction coupled with it. Whenever the supply of a dissolved species from the solution to the electrode surface becomes a rate-limiting factor, limiting-current phenomena may be observed. 

Rau, M., Ohlmann, T., Morley, S. J., and Pain, V. M. (1996). A reevaluation of the capbinding protein, eIF4E, as a rate-limiting factor for initiation of translation in reticulocyte lysate. J. Biol. Chem. 271, 8983—8990. 

Mechsner K, Wuhrmann K (1982) Cell permeability as a rate limiting factor in the microbial reduction of sulfonated azo dyes. Eur J Appl Microbiol Biotechnol 15(2) 123-126... 

If the neurotoxicity of /7-hexane was potentiated in this study by co-exposure to acetone, the level of n-hexane alone required to produce these effects would be higher than 58 ppm and the MRL level would be higher. Results from simulations with a PBPK model that accurately predicted /7-hexane blood and 2,5-hexanedione urine levels (Perbellini et al. 1986, 1990a) indicate that at concentrations of 50 ppm, the rate-limiting factor in /7-hexane metabolism is delivery to the liver, not metabolic activity. This suggests that at this concentration (and at the MRL concentration of 0.6 ppm), induction of P-450 enzymes in the liver by acetone or other chemicals would not affect the rate at which 2,5-hexanedione was produced. 

If, instead of contracting out, one is concerned with managing a testing laboratory, then the situation is considerably more complex. The factors and activities involved are outlined below. Within these steps are rate-limiting factors that are invariably due to some critical point or pathway. Identification of such critical factors is one of the first steps for a manager to take to establish effective control over either a facility or program. 

Particle size of chemical in solid dosage form smaller particle sizes will increase the rate and/or degree of absorption if dissolution of the chemical is the rate-limiting factor in absorption. Chemicals that have a low dissolution rate may be made in a micronized form to increase their rate of dissolution. 

We start with the case where the initial electron transfer reaction is fast enough not to interfere kinetically in the electrochemical response.1 Under these conditions, the follow-up reaction is the only possible rate-limiting factor other than diffusion. The electrochemical response is a function of two parameters, the first-order (or pseudo-first-order) equilibrium constant, K, and a dimensionless kinetic parameter, 2, that measures the competition between chemical reaction and diffusion. In cyclic voltammetry,... 

The three terms on the left-hand side of equation (2.10) correspond to each of the three rate-limiting factors successively electron transfer, followup reaction, and diffusion (the parameters Af and 2 measure the competition between each of the first two factors with the third). 

The next step consists of assembling these various rate-limiting factors so as to provide a description of the resulting catalytic responses of these multilayered coatings. 

The plateau currents are thus a function of two dimensionless parameters, Jis/ik and 4/4(1 — k/i )- On this basis, a kinetic zone diagram may be established (Figure 4.19) as well as the expressions of the plateau currents pertaining to each kinetic zone (Table 4.1).17 Derivation of these expressions is described in Section 6.4.4. There are in most cases two successive waves, and the expressions of both limiting currents are given in Table 4.1. The general case corresponds to a situation where none of the rate-limiting factors... 

In the monomolecular layer systems described so far, diffusion of the cosubstrate through the film is not a rate-limiting factor. This is true in the case of a free-moving cosubstrate, but also, at least at low scan rates, with cosubstrates attached to the structure. When several layers are coated on the electrode, diffusion of the cosubstrate may become rate limiting even if it is not attached to the structure. The diffusion rate of the two cosubstrate forms increases with its concentration. One may thus expect that the enzymatic reaction, rather than diffusion, tends to be the rate-determining step upon raising the cosubstrate concentration and that this situation is reached all the more easily that the number of layers is small. Under such conditions, the separation of the cyclic voltammetric current in two independent contributions [equation (5.29)] is still valid. icat is thus proportional to the total amount of enzyme contained in the film per unit surface area and therefore to the number, N, of monomolecular layers deposited on the electrode ... 

A. Laisk and D. A. Walker, Control of phosphate turnover as a rate limiting factor and possible source of oscillations in photosynthesis, a mathematical model. Proc. R. Soc. London B 227,... 

The only rate-limiting factor in a coupled assay should be the concentration of the initial and linking products and all other reagents should be in excess. The role of the auxiliary and indicator enzymes is essentially that of a substrate assay system and under optimum assay conditions the rate of the indicator reaction should be equal to the rate of formation of the initial product. The indicator reaction must be capable of matching the different test reaction rates and its velocity can be defined by the Michaelis-Menten equation in the usual way ... 

It is found that the diffusion of the tributyltin species in the matrix is the rate limiting factor the highly crosslinked epoxy matrix offers great resistance for the diffusion of the large molecule. 

The mode of action of the antifouling polymers thus conforms to the bulk abiotic bond cleavage model. All the controlling factors, viz., diffusion of water into the polymer matrix, hydrolysis of the tributyltin carboxylate, diffusion of tributyltin species from the matrix to the surface, phase transfer of the organotin species, and its migration across the boundary layer, are analyzed. It is found that the transport of the mobile tributyltin species in the matrix is the rate limiting factor. 

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