Catalytic Requirements

Rahmatullah, M. and Roche, T.E. (1987) The catalytic requirements for reduction and acetylation of protein X and the related regulation of various forms of resolved pyruvate dehydrogenase kinase. Journal of Biological Chemistry 262, 10265-10271. 

The difficult task of examining the role of catalysis in coal liquefaction has been taken on by Mochida and Sakanishi. They show the catalytic requirements in various stages of coal conversion and the many complex interactions of the catalyst with coal constituents. They also point out directions for future catalysis research needed for more economical coal liquefaction, a commendable feature for processes requiring a long lead time. 

The structural studies have given a clear and chemically satisfying description of the stereochemical and catalytic requirements of the hydride transfer reaction. In three of the examples, there is an acid-base catalyst that forms a hydrogen bond with the carbonyl or alcohol group of the substrate, helps orient it correctly, and stabilizes the transition state for the reaction (equation 16.18). 

On the basis of the structure of their active site, catalases may be classified as heme or nonheme enzymes. Those that contain heme iron are efficient catalysts, operating close to the diffusion limit, 108M 1sec 1. In iron catalases the metal is coordinated by four heme nitrogens and a proximal Tyr residue, which occupies the fifth coordination site. A catalytically required His is found on the distal side of the heme. In addition, a water molecule has also been observed close to the iron sixth coordination site. 

ECB deacylase is an 81-83-kDa heterodimer consisting of 63- and 18-20-kDa subunits. Penicillin G acylase from Escherichia coli is an 87-kDa heterodimer with 65- and 22-kDa subunits [32], For comparison, cephalosporin acylase from a Pseudomonas strain is an 83-kDa heterodimer consisting of 57- and 26-kDa subunits [33], The essential absence of any external catalytic requirement, cofactor stimulation, or product inhibition of ECB deacylase is also an intrinsic property of penicillin acylase [34], Based on the amino-terminal sequences of the two subunits of ECB deacylase, a 48% sequence similarity has been observed between the small subunit of ECB deacylase and a penicillin acylase [25]. This statistically significant albeit moderate sequence similarity from two short segments of the enzymes suggests an evolutionary relationship between ECB deacylase and peni-... 

If nitrogen oxide control is one of the catalytic requirements, the stoichiometry of air-to-fuel ratio must be kept nearly stoichiometric to reduce NO then air must be added and CO and hydrocarbons oxidized in a second part of the catalyst bed. 

The analysis of adsorption, electronic, mechanical, and thermal properties of CNTs and CNFs, with respect to catalytic requirements, is needed to evaluate their stability and to predict how the metallic particles could anchor to the support and how the reagents could interact with these metal-supported catalysts, and to understand what such novel carbon forms could bring to catalysis. The possibility of nanofilamentous carbon shaping and sizing to prevent handling problems is also discussed. 

Considerable research has been carried out on the short chain isoprenyl diphosphate synthases of plants, though our knowledge of these enzymes in conifers is restricted to work on just two species, Abies grandis and Taxus canadensis.All short-chain isoprenyl diphosphate synthases share some basic properties, including an absolute catalytic requirement for a divalent metal ion (usually Mg " ), a pFl optimum near neutrality, K values for both substrates in the 1 -100 pM range and a homodimeric architecture with subunits of 30-50 kDa (except... 

In terms of additional catalytic requirements a catalyst might be required to promote the controlled hydrolysis of urea to generate NH. Lewis acids such as TiO are effective catalysts for this reaction [49]. The use of other materials (e.g. Bronsted acids) can result in unselec-tive hydrolyses with side products such as melamine being formed [50]. In more cases, however, the urea solution is injected into a heated zone where thermal hydrolysis generates 2 equivalents of NH and 1 CO for each urea molecule [51]. 

Most forming processes involve the use of suspensions, sols or gels (pastes). In order to solve hcindling problems or to tailor the rheological properties of these media to suit a particular forming process, one can act on mechanical parameters (choice and operation of equipments), modify the surface chemistry of the suspended or gcJled particles ( ect of pH, additives) or use a binder (colloidal silica, alumina,...). Such actions generally affect the final properties that the catalyst has to meet (textural, mechanical and catalytic requirements). 

From these basic structures, numerous other phosphites have been derived over the last 30 years. Several of them are characterized by the phenolic ester backbone and bulky substituents in the ortho position of each or of selected aryl rings. In several instances, also /)-aryl substituents can be found. Both features are consequences of the intention to have the simplest and unambiguous synthetic access and/or they are motivated by catalytic requirements. 

Kim G, Lee S, Shin JY, Crare G, Irvine JTS, Vohs JM, Gorte RJ (2009) Investigation of the structural and catalytic requirements for high-performance SOFC anodes formed by infiltration of LSCM. Electrochem Solid State Lett 12 B48-B52... 

It should be apparent from an examination of the reaction sequence that the preparation of these compounds, although not complicated, is cumbersome. There are differences in the methods by which these and related compounds are prepared, but they all require two ring formation steps and the second of these (5 6, 1.21) has generally been accomplished at high dilution. As a consequence, these compounds remain expensive (even for catalytic requirements) and their use is still infrequent despite their obvious importance and potential. 

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