Catalytic schematic model

Fig. 2.4. Schematic model of the molecular polymorphism of acetylcholinesterase and cholinesterase [110][112a]. Open circles represent the globular (G) catalytic subunits. Disulfide bonds are indicated by S-S. The homomeric class exists as monomers (Gl), dimers (G2), and tetramers (G4) and can be subdivided into hydrophilic (water-soluble) and amphiphilic (membrane-bound) forms. The G2 amphiphilic forms of erythrocytes have a glycophospholipid anchor. The heteromeric class exists as amphiphilic G4 and as asymmetric forms (A) containing one to three tetramers. Thus, heteromeric G4 forms found in brain are anchored into a phospholipid membrane through a 20 kDa anchor. The asymmetric A12 forms have three hydrophilic G4 heads linked to a collagen tail via disulfide bonds.

Asymmetric diarylmethanes, hydrogenolytic behaviors, 29 229-270, 247-252 catalytic hydrogenolysis, 29 243-258 kinetics and scheme, 29 252-258 M0O3-AI2O3 catalyst, 29 259-269 relative reactivity, 29 255-257 schematic model, 29 254 Asymmetric hydrogenations, 42 490-491 Asymmetric synthesis, 25 82, 83 examples of, 25 82 Asymmetry factor, 42 123-124 Atom-by-species matrix, 32 302-303, 318-319 Atomic absorption, 27 317 Atomic catalytic activities of sites, 34 183 Atomic displacements, induced by adsorption, 21 212, 213 Atomic rate or reaction definition, 36 72-73 structure sensitivity and, 36 86-87 Atomic species, see also specific elements adsorbed... 

Catalytic hydrogenolysis (continued) M0O3-AI2O3 catalyst, 29 258-269 relative reactivity, 29 255-257 schematic model, 29 254 diphenylmethane kinetics, 29 241-243 reaction mechanism, 29 267 Catalytic oxidation,... 

A FIGURE 23-24 Schematic model of the proofreading function of DNA polymerases. All DNA polymerases have a similar three-dimensional structure, which resembles a half-opened right hand. The "fingers" bind the single-stranded segment of the template strand, and the polymerase catalytic activity (Pol) lies in the junction between the fingers and palm. 

FIG. 18 Schematic model of catalytic oxidation of substrate, S, using an electron acceptor, Mqx, by an intact enzyme, DHase, in the C5doplasmic membrane of a micro-organism. (From Ref. 47.)... 

Figure 17 A schematic model of enzymatic hydrolysis of P(3HB) single crystals by PHA depolymerase consisting of binding and catalytic domains. Reproduced with permission from Iwata, T. Doi, Y. Kasuya, K. Inoue, Y. Macromolecules l, 30, 833. ° Copyright 1997 American Chemical Society.

Figure 11.14 I A schematic model of the steps involved in the catalytic removal of NO from exhaust gas.

Figure 1 Schematic model for the functioning of (a) an autocatalytic replication system, in which Tab copies itself, and (b) a cross-catalytic system, in which Ten and Tef copies each other.

Figure 11.16 Substrate-assisted catalysis. Schematic diagram from model building of a substrate, NHa-Phe-Ala-His-Tyr-Gly-COOH (red), bound to the subtilisin mutant His 64-Ala. The diagram illustrates that the His residue of the substrate can occupy roughly the same position in this mutant as His 64 in wild-type subtilisin (see Figure 11.14) and thereby partly restore the catalytic triad.

As the crystal surface exposed to the atmosphere is usually not ideal, specific sites exist with even much lower co-ordination numbers. This is shown schematically in Fig. 3.5, which gives a model comprising so-called step, kink and terrace sites (Morrison, 1982). This analysis suggests that even pure metal surfaces contain a wide variety of active sites, which indeed has been confirmed by surface science studies. Nevertheless, catalytic surfaces often behave rather homogeneously. Later it will be discussed why this is the case. In short, the most active sites deactivate easiest and the poorest active sites do not contribute much to the catalytic activity, leaving the average activity sites to play the major role. 

FIGURE 1 2-2 Schematic diagram of the phosphorylation sites on each of the four 60kDa subunits of tyrosine hydroxylase (TOHase). Serine residues at the N-terminus of each of the four subunits of TOHase can be phosphorylated by at least five protein kinases. (J), Calcium/calmodulin-dependent protein kinase II (CaM KII) phosphorylates serine residue 19 and to a lesser extent serine 40. (2), cAMP-dependent protein kinase (PKA) phosphorylates serine residue 40. (3), Calcium/phosphatidylserine-activated protein kinase (PKC) phosphorylates serine 40. (4), Extracellular receptor-activated protein kinase (ERK) phosphorylates serine 31. (5), A cdc-like protein kinase phosphorylates serine 8. Phosphorylation on either serine 19 or 40 increases the activity of TOHase. Serine 19 phosphorylation requires the presence of an activator protein , also known as 14-3-3 protein, for the expression of increased activity. Phosphorylation of serines 8 and 31 has little effect on catalytic activity. The model shown includes the activation of ERK by an ERK kinase. The ERK kinase is activated by phosphorylation by PKC. (With permission from reference [72].)... 

A schematic of the proposed growth model is shown in Fig. 10.23. In this model, Co nanoparticles play a dual catalytic role. On the one hand, they catalyze silane formation by reacting first with silicon to form Co silicides, and then react with hydrogen to form silane while being reduced to Co metal. The second role of Co nanoparticles is their classic catalytic ability of making nanowires by first dissolving the silane and precipitating out Si nanowires. 

The fulvene route was also successfully employed in the preparation of a compound, which can be regarded as one of the most advanced molecular models for a catalytically active titanium center on a silica surface. When Cp Ti(C5Me4CH2) was reacted with the monosilylated silsesquioxane precursor 12 in refluxing toluene a color change from deep purple to amber was observed. Crystallization afforded a bright-yellow material, which was subsequently shown to be the novel mo o(pentamethyleyclopentadienyl) titanium(IV) silsesquioxane complex 126 (69% yield). Its formation is illustrated schematically in Scheme 42. 

Figure 1. Schematic illustrations of a functionality-oriented strategy in applied catalysis research (panel A) and a catalytic insight-driven strategy in fundamental model studies (panel B).

Scheme 3.4-1. Simulated titration curves for the catalytic model system described above. The change in the steady-state concentrations following the ligand association process is schematically depicted (the species present at relatively high concentration is underlined).

We now can prepare, in principle, enzyme models by use of the concept of host design, where artificial enzymes are so designed as multiple recognition hosts schematically shown in Fig. 20. Although unsubstituted cyclodextrins are well known to catalyze some organic reactions such as ester hydrolysis, their catalytic activities are relatively small. Recent progress in cyclodextrin chemistry has shown that it is possible to enhance the catalytic... 

It is evident that the simple model of heterogeneous catalytic eliminations assumes the same adsorption complex for all mechanisms, written schematically as... 

Enzymological and redox potentiometric studies by EPR have indicated that the catalytic sites of the oxygen-stable [Ni-Fe] hydrogenases exhibit at least six enzy-mologically distinct states [75-78], These are schematically represented in Figure 3, which depicts a speculative model for the hydrogenase redox cycle, as discussed later. 

The Monsanto carbonylation of methanol to acetic acid catalyzed by Rh/H is a well-understood example of an organometallic catalytic cycle and can act as a good model with well defined steps (shown schematically in Chapter 4, Section 4.2.4). The starting material is the square planar Rh(I) complex, [Rh(CO)2l2] which is easily accessible by reaction of rhodium trichloride in solution with CO in the presence of iodide. This undergoes oxidative addition with Mel very readily to give the methyl-Rh(III) complex [Rh(Me)(CO)2l3] as an unstable... 

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