Direct reaction mechanism

Miller W H 1976 Unified statistical model for complex and direct reaction mechanisms J. Chem. Rhys. 65 2216-23... 

As shown in Table 3-1, ozone can destroy other disinfectants. This should be avoided by dosing them not ahead of ozonation stages, but rather at the end of the total treatment before the distribution of water to the supply-net. A special case is the reaction of ozone with H202 (correctly with the species H02 ), which is used as an advanced oxidation process (AOP) for intensified formation of hydroxyl radicals and their oxidative attack on persistent organic target compounds (persistent against ozone in the direct reaction mechanism) (see Chapter A 2). 

The absorption of ozone from the gas occurred simultaneously with the reaction of the PAH inside the oil droplets. In order to prove that the mass transfer rates of ozone were not limiting in this case, the mass transfer gas/water was optimized and the influence of the mass transfer water/oil was studied by ozonating various oil/water-emulsions with defined oil droplet size distributions. No influence of the mean droplet diameter (1.2 15 pm) on the reaction rate of PAH was observed, consequently the chemical reaction was not controlled by mass transfer at the water/oil interface or diffusion inside the oil droplets. Therefore, a microkinetic description was possible by a first order reaction with regard to the PAH concentration (Kornmuller et al., 1997 a). The effects of pH variation and addition of scavengers indicated a selective direct reaction mechanism of PAH inside the oil droplets... 

Ec is rather flat, yet hot, extending up to about/ = 10. By contrast, the higher Ec results show the more usual envelop peaking at much lower values off. Nesbitt and coworkers [95] measured the product distribution in a "crossed jet" experiment, and obtained results are consistent with Figure 3.5. Again, the result is consistent with a resonance state picture in that the low Ec distribution is entirely due to a resonance decay mechanism that is expected to be quite different from the direct reaction mechanism that dominates at higher Ec. 

Here we will discuss the progress achieved so far in our mechanistic understanding of peptide hydrolysis reactions by metalloproteinases. We will focus on the need for comparative structure-function analyses of individual metalloproteinases to reveal the reaction mechanisms. Finally, we will describe new frontiers in the biophysics and chemistry of metalloproteinases and the application of such studies to reveal directly reaction mechanisms and their relevance to dmg discovery. 

Just like a direct reaction mechanism discussed in Section II, a pathway is not merely a set of reactions, because many distinct pathways can be constructed to include the same reactions but achieve different transformations. A pathway must include a coefficient (denoted by in Section II) for each reaction, indicating the proportions in which the stoichiometries are combined. In this section, we will call these coefficients the reaction stoichiometry of the pathway. The overall transformation of net reactants to net products will be called the molecular stoichiometry of the pathway, and was denoted by in Section II. 

So far, we have presented evidence for direct reaction mechanisms and shown that various dynamic aspects of reactions can be interpreted in terms of these mechanisms. From what has been described in the previous sections and other related experiments, we see that the stripping mechanism is rather widespread, if not universal. 

E. PoUak, P. Pechukas, Unified statistical model for "complex" and "direct" reaction mechanisms A test on the collinear H + H2 exchange reaction, J. Chem. Phys. 70 (1) (1979) 325-333. 

The methoxy species formed by the dissociation of methanol can react with a second methanol molecule to give dimethyl ether and a proton. This is termed the alkoxy intermediate for the consecutive direct reaction mechanism. Alternative reaction paths exist which can be described as associative reaction mechanisms in which the product of an association reaction is formed without the formation of an alkoxy intermediate species . For two coadsorbed methanol molecules, the most stable adsorption mode does... 

The creation of a new bond between two different molecules or molecular fragments through consecutive reaction steps is typically called a direct reaction mechanism. In each individual reaction step, a chemical bond between the molecule or molecular fragment and the catalyst surface is formed. The molecular fragments bonded to the catalyst surface can subsequently react with a second adsorbed molecule. In an associative reaction mechanism, a cluster of at least two molecules adsorbs at the reaction center. Bond formation and cleavage reaction, now occur as a single event within the adsorbate cluster consisting of several molecules. This is assisted by transient chemical bond formation with the catalyst surface. 

The "unified" statistical model was introduced originally in order to reconcile, or unify, two different kinds of statistical theories, transition state theory which is appropriate for reactions proceeding via a direct" reaction mechanism, and the phase space theory of Lightand Nikitin which is designed to describe reactions proceeding via a long-lived collision complex. It is particularly straightforward to apply this theory within the framework of the reaction path Hamiltonian. 

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