Initiation reaction, definition

The Q (initial reaction rate) plots were presented in Fig. 19. Note again that the data may be correlated well by straight lines for both models. The C2 values are correlated by the solid lines of Fig 20. Note that the dual-site values can again be correlated by a straight line, but that the single-site values of C2 show a definite curvature. Alternatively, the 0.975 atm value of the single-site C2 could be rejected, and the three high-pressure points... 

Norbert Berkowitz. I suggest that initial reaction data cannot justify the author s rather definite conclusions since a diffusion-controlled component of the overall reaction would be relatively slow compared with an initial surface reaction and therefore more or less completely masked by it. Moreover, if the oxidation reaction were carried out in a liquid medium, swelling and dispersion of the solid reactant would accompany it, and in a dry (gaseous) medium, oxidation is known to cause some eating out of pores, etc. In both cases, therefore, continuous changes in reactant geometry accompany the reaction, and the critique applying to Hill et al. applies to Kapo. 

The Michaelis constant, KM, for an enzyme-substrate interaction has two meanings (1) Ku is the substrate concentration that leads to an initial reaction velocity of V" /2 or, in other words, the substrate concentration that results in the filling of one-half of the enzyme active sites, and (2) KM = (k2 + ki)/kv The second definition of Ku has special significance in certain... 

Some comments on and explanations of the applications listed are in place here. As is seen below, not all applications are of the solvents as such in many cases they are added to other materials to improve their properties, to initiate reactions and accelerate their rates, and as reagents that are consumed by transforming other compounds to more useful ones. Following is an alphabetical lexicon with brief definitions of the key words used in Table 5.1. 

Gilman catalyst, 57-58 Grignard reaction definition and scope, 1-6 first reported. 2 initiation of. 9 effect of oxygen on. 10 effect of water oil. 10 iodine used for. 145-146 (.w aiw Gilman catalyst)... 

It should be noted that to date one more question related to the kinetics of the chain termination reaction in radical polymerization has not yet been conclusively solved. The diffusive nature of termination presupposes a quite definite, non-random distribution of radicals the number of radicals located close to one another must be smaller than that which corresponds to the random law of particle distribution in space. The initiation reaction, i.e., that of the formation of radicals, does not depend on their location in space. This reaction will, therefore, distort the distribution of radicals in space that corresponds to the diffusive termination and will tend to make... 

It is obvious from Figures 4 and 5 that for mentioned monomer salts AG and MAG the non-linear increase of relative viscosity (r rei) is naturally observed with the rise of monomer concentration in initial reaction solution. (As it was already mentioned the solution remained transparent.) Thus, there is definite correlation in the character of polymerization initial rate change and values of r rei.. 

However, the practice of investigations of acid-base equilibria consists in studies of the reactions with the transfer of definite particles (acid or base) in different solvents, irrespective of the fact whether they are prone to dissociation with the formation of given acid (base), or not. In order to give the most general formulation of the solvosystem concept we should divide the solvent in relation to the initially chosen definition of acids and bases (definition of acidic and basic particles). 

Additional data on hydroformylation of 1-pentene, 1-octene and ethyl acrylate are provided in Table 1. In all the runs, the solutions became clear and yellow after a period of 10 minutes, which indicated the formation of the microemulsion with the catalyst formed in situ inside the water droplets. The solutions were clear and homogeneous during the entire run, which definitely excludes reaction via a biphasic pathway. Because of equipment limitations, the highest reaction temperature we investigated was 87.1 C. The stability of the W/CO2 microemulsion system at such a high temperature is remarkable. At the conditions employed, conversions ranged from 6 to 75%. The increase of temperature and the addition of NaOH were found to increase the reaction rate. The initial reaction rate for 1-pentene is about two times higher than that of 1-octene. In studies on hydroformylation of different olefins in aqueous biphasic systems, Brady et al. [2/] found that there is a marked dependence of the reaction rate on the solubility of the terminal olefins in water. The data shown in... 

Atmospheric Reaction Mechanisms. There is no definitive Information as to the subsequent reaction steps after this Initial reaction, and hence the following mechanism for C2H2 la completely speculative ... 

Many of the early studies were conducted with enzymes from fermentation, particularly invertase, which catalyzes the hydrolysis of sucrose to monosaccharides D-glucose and D-fmctose. With the introduction of the concept of hydrogen ion concentration, expressed by the logarithmic scale of pH (Sorensen, 1909), Michaelis and Menten (1913) realized the necessity for carrying out definitive experiments with invertase. They controlled the pH of the reaction medium by using acetate buffer, allowed for the mutarotation of the product and measured initial reaction rates at different substrate concentrations. Michaelis and Menten described their experiments by a simple kinetic law which afforded a foundation for a subsequent rapid development of numerous kinetic models for enzyme-catalyzed reactions. Although the contribution of previous workers, especially Henri (1902, 1903), was substantial, Michaelis and Menten are regarded as the founders of modern enzyme kinetics due to the definitive nature of their experiments and the viability of their kinetic theory. 

In order to discuss the physical meaning of a, we need to introduce the concept of early and late transition states. In the previous section we discussed in detail the transition state for CO dissociation over transition-metal surfaces and described the reaction as an example of a late transition state. The transition state is late along the reaction coordinate since the transition-state structure is close to the final dissociated state. Transition states which are early along the reaction coordinate are called early transition states and thus resemble the initial reaction states (see Chapters 4 and 7 for the definition of the pretransition state). The activation energies for the protonic zeolite reactions correlate with deprotonation energies (see Fig. 2.9) and are examples of intermediate transition states that also vary with the energies of the initial states . When a 0.5 (a 0), the transition state is early AS fv 0... 

Apart from substrates with photolabile groups blocking the function, there are several other types of compounds and systems which permit the photochemical initiation of reactions with precise temporal and/or spatial definition. Montal, Lester and others (see for instance Gurney Lester, 1987) have used photoisomerization of an inactive isomer to the active form of a substrate (messenger) to initiate reactions. The reviews by McCray Trentham (1989), Corrie Trentham (1993) and others quoted below, will complement the present discussion of the development of this subject. Trentham and his colleagues treat in particular detail the kinetics of the liberation of phosphate compounds from their inactive precursor. 

Unit definition One restriction unit is usually defined as the amount of enzyme required to digest completely 1 fig of DNA (typically phage A) in 1 hr. Because the definition relies on the activity at an end point of the reaction, it is distinguished from the usual kinetic definition of enzyme units based on the initial reaction rate. 

The results of electrostatic potential calculations can be used to predict initial attack positions of protons (or other ions) during a reaction. You can use the Contour Plot dialog box to request a plot of the contour map of the electrostatic potential of a molecular system after you done a semi-empirical or ab initio calculation. By definition, the electrostatic potential is calculated using the following expression ... 

These definitions are valid only when the concentration of the enzyme is very small compared with that of the substrate. Moreover, they apply only to the initial rate of formation of products in other words, the rate of formation of the first few percent of the product, before the substrate has been depleted and products that can interfere with the catalytic reaction have accumulated. 

---