Catalyzed reactions, mechanisms

The two rate laws given by equations 8.4-24 and -26 (Types I and II) are used extensively to correlate experimental data on surface-catalyzed reactions. Nevertheless, there are many surface-catalyzed reaction mechanisms which have features not covered by LH kinetics. 

J. L. Boucher, M. Delaforge, D. Mansuy, Dehydration of Alkyl- and Arylaldoximes as a New Cytochrome P450-Catalyzed Reaction Mechanism and Stereochemical Characteristics , Biochemistry 1994, 33, 7811. 7818. 

Catalytic titration, 27 114-118 gas-liquid chromatography, 27 115, 116 pulse reactors, 27 115, 116 Catalyzed reactions, mechanisms, 38 234-236 Catenanes, 24 135 Cathodes... 

All the available data supports the HDV ribozyme-catalyzed reaction mechanism shown in Fig. 9C. In this model, the donation of a proton is favored and the model involves an acid with an optimal pKa of 7 under physi-... 

A ping pong enzyme-catalyzed reaction mechanism in which three substrates react to form three products " ... 

A sequential enzyme-catalyzed reaction mechanism in which two substrates react to form two products and in which there is a preferred order in the binding of substrates and release of products. Several enzymes have been reported to have this type of binding mechanism, including alcohol dehydrogenase , carbamate kinase , lactate dehydrogenase , and ribitol dehydrogenase. ... 

Multisubstrate or multiproduct enzyme-catalyzed reaction mechanisms in which one or more substrates and/ or products bind and/or are released in a random fashion. Note that this definition does not imply that there has to be an equal preference for any particular binding sequence. The flux through the different binding sequences could very easily be different. However, in rapid equilibrium random mechanisms, the flux rates are equivalent. See Multisubstrate Mechanisms... 

Scheme 10.2 Homogeneous acid-catalyzed reaction mechanism for the transesterification of triglycerides (1) protonation of the carbonyl group by the acid catalyst (2) nucleophilic attack of the alcohol, forming a tetrahedral intermediate (3) proton migration and breakdown of the intermediate. The sequence is repeated twice.

Figure 4 Homogeneous base-catalyzed reaction mechanism for the transesterification of triglycerides...

In isomerization reactions, an alkene is deprotonated to form an allyl anion, which is reprotonated to give the more stable alkene (double-bond migration). The most simple example is the isomerization of 1-butene producing a mixture of cis- and trans-2-butene (Scheme 3). Because the stability of the cis-allyl anion formed as an intermediate is greater than for the trans form, a high cis/trans ratio is observed for base-catalyzed reactions whereas for acid-catalyzed reactions the ratio is close to unity. Thus, the cis/trans ratio of the products has frequently been used as an indication of base-catalyzed reaction mechanisms. The carbanions formed in the course of such superbase reactions are not freely mobile in solution,... 

Mulholland AJ, GH Grant, WG Richards (1993) Computer Modeling of Enzyme Catalyzed Reaction-Mechanisms. Protein Eng. 6 (2) 133—147... 

They found that at room temperature using benzene as the solvent only 3% consisted of the diketone 25 and mainly the ring-contracted products were obtained 33% of keto aldehyde 24 and 28% of ketone 26. From an industrial point of view the desired compound is the keto aldehyde 24, which is an interesting intermediate for the synthesis of other cyclopentanone derivatives with floral and fruity smells. The acid catalyzed reaction mechanism leading to the synthesis of keto aldehyde 24 had been discussed earlier (25). Therefore, it is of interest whether the product distribution changes in the presence of a heterogeneous catalyst system and also whether the decarbonylation of the compound 24 to compound 26 can be suppressed. 

Figure 10 Proposed pathways in the lactoperoxidase-catalyzed reaction mechanism (LPO system)...

Boucher, J.-L., M. Delaforge, and D. Mansuy (1994). Dehydration of alkyl- and arylaldoximes as a new cytochrome P450-catalyzed reaction Mechanism and stereochemical characteristics. Biochemistry 33, 7811—7818. 

The catalytic destruction of ozone in the stratosphere involves reactions between gases there, so it is an example of homogeneous catalysis. The most important catalyst for this process is chlorine. Much of the chlorine present in the stratosphere comes from CFC molecules that were released in the troposphere and slowly migrated to the stratosphere. (Because they are very unreactive at ground level, nearly all CFCs that are released into the atmosphere eventually find their way to the stratosphere.) Upon absorption of UV light, the CFCs initiate a catalyzed reaction mechanism ... 

Saldccioli, M., M. Stamatakis, S. Caratzoulas D. G. Vlachos (2011) A review of multiscale modeling of metal-catalyzed reactions Mechanism development for complexity and emergent behavior. Chemical Engineering Science, 66, 4319-4355,1SSN 00092509. 

Kinetic models to describe lipase-catalyzed reaction mechanisms have been proposed, and most have been extensions of the model developed by Michaelis and Menten (1913). However, normal Michaelis-Menten kinetics do not apply to lipase-induced changes, because the substrates (lipids) are not water-soluble and the enzyme operates at an interface (Brockman, 1984). However, rate expressions for the hydrolysis of emulsified lipids catalyzed by immobilized lipases resemble the rate expressions modeled with Michaelis-Menten mechanisms (Benzonana and Desnuelle, 1965). The kinetics and mechanisms of reactions catalyzed by immobilized lipases have been reviewed by Malcata et al. (1990 1992). 

Chemistry of naphthoquinone diazide was reviewed on the three different types of its reactions i.c., photochemical, thermal and base catalyzed reactions. Mechanisms of the several novel resist processes were elucidated based on these reactions. 

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