Maximum catalytic activity

The working conditions of the immunosensor (enzyme and antigen concentrations, dilutions of the antibodies, pH of the buffer solution) were found. The cholinesterase immobilized demonstrated the maximum catalytic activity in phosphate buffer solution with pH 8.0. The analytical chai acteristics of the sensor - the interval of the working concentrations and detection limit - have been obtained. The proposed approach of immunoassay made possible to detect 5T0 mg/ml of the bacterial antigen. 

Table II represents the data on the reactivity of the propagation centers and their number corresponding to the maximum catalytic activity observed for three typical one-component catalysts. These data were ob-...

For the purpose of demonstrating the effects of surface coverage by Pd, 0pd, on the rate of electro-oxidation of formic acid and the ORR, Fig. 8.17 reveals that the i versus 0Pd relationship again has a volcano-like form, with the maximum catalytic activity being exhibited for 1 ML of Pd. The examples that we have given indicate that volcano relationships are the rule rather than the exception, emphasizing the importance of a systematic evaluation of the catalyst factors that control catalytic activity. A thorough... 

Chitwood (2) found that copper compounds exhibited only a short period of maximum catalytic activity for the dehydrogenation of ethanolamine to glycine salt. In this study, the catalytic activity of a skeletal copper catalyst was tested in repeated use. The catalyst used was prepared by selectively leaching CuAl2 particles in a 6.1 M NaOH solution at 293 K for 24 hours. Figure 1 shows the profiles of hydrogen evolved versus reaction time. 

The catalytic activities of Cu(II), Co(II) and Mn(II) are considerably enhanced by sodium dodecyl sulfate (SDS) in the autoxidation of H2DTBC (51). The maximum catalytic activity was found in the CMC region. It was assumed that the micelles incorporate the catalysts and the short metal-metal distances increase the activity in accordance with the kinetic model discussed above. The concentration of the micelles increases at higher SDS concentrations. Thus, the concentrations of the catalyst and the substrate decrease in the micellar region and, as a consequence, the catalytic reaction becomes slower again. 

In 1971, LDHs containing different metal cations (such as Mg, Zn, Ni, Cr, Co, Mn and Al) with carbonate as interlayer anions, calcined at 473-723 K and partially or completely chlorinated, were reported to be effective as supports for Ziegler catalysts in the polymerization of olefins [8], with the maximum catalytic activity of polyethylene production observed for Mg/Mn/Al - CO3 LDH calcined at 473 K. Even earher, calcined Mg/Al LDHs were used to support Ce02 for SO removal from the emissions from fluidized catalytic cracking units (FCCU) [9,10]. Some transition metal oxides have also been... 

Surface acidity and catalytic activity develop only after heat treatment of a coprecipitated mixture of amorphous silicon and aluminum oxides. Similar catalysts can be prepared by acid treatment of clay minerals, e.g., bentonite. The acidity is much stronger with silica-alumina than with either of the pure oxides. Maximum catalytic activity is usually observed after activation at 500-600°. At higher temperatures, the catalytic activity decreases again but can be restored by rehydration, as was shown by Holm et al. (347). The maximum of activity was repeatedly reported for compositions containing 20-40% of alumina. 

The maximum catalytic activity (Vmax) is measured at saturating concentrations of substrate and in the presence of activators and in the absence of inhibitors of the enzyme. It is the values of V ax of the enzymes that are obtained in extracts of cells, tissues or organs that are of importance in physiology for example to establish or confirm (i) the role of an enzyme in a particular pathway, in vivo ... 

A reaction in a metabolic pathway is likely to be nonequilibrium if the maximum catalytic activity of the enzyme that catalyses the reaction is low in comparison with those of other enzymes in the pathway. In consequence, the concentration of substrate of this reaction is likely to be high whereas that of the product is likely to be low, since the next enzyme in the sequence readily catalyses its removal. Because the concentration of this product is low, the rate of the reverse component of the reaction is very much less than the rate of the forward component. This situation characterises a non-equilibrium process. Conversely, a reaction is near-equiUbrium if the maximum catalytic activity of the enzyme is high in relation to those of other enzymes in the pathway in this case, the rates of the forward and the reverse components of the reaction are similar and both are much greater than the overall flux... 

Table 9.6 Flux through Krebs cycle as calculated from the maximum catalytic activity of oxoglutarate dehydrogenase, measured in extracts of muscle, and from oxygen consumption by muscles working maximally...

Thus it is seen that Cu(II) does not catalyze the hydrolysis of the mononegative ion, as probably would be expected because this form of the substrate would have little affinity for the metal ion. Maximum catalytic activity is realized in structure XXIII rather than XXI, because the former is in equilibrium with a smaller concentration of inactive forms analogous to XX and with a relatively higher concentration of the inactive tautomeric form of XXI. 

Analysis of structure-activity relationships shows that various species characterized by different reactivities exist on the surface of vanadium oxide-based catalysts.339 The redox cycle between V5+ and V4+ is generally accepted to play a key role in the reaction mechanism, although opposite relationships between activity and selectivity, and reducibility were established. More recent studies with zirconia-supported vanadium oxide catalysts showed that vanadium is present in the form of isolated vanadyl species or oligomeric vanadates depending on the loading.345,346 The maximum catalytic activity was observed for catalysts with vanadia content of 3-5 mol% for which highly dispersed polyvanadate species are dominant. 

How does ATP hydrolysis turn the shaft Are four H+ pumped for each step, or are there smaller single proton substeps Is the simple picture in Fig. 18-15 correct or, as proposed by some investigators,263-265 must all three p subunits be occupied for maximum catalytic activity 266 How is the coupling of H+ transport to mechanical motion accomplished 267 2673 1... 

For maximum catalytic activity, the metal usually is prepared in a finely divided state. This is achieved for platinum and palladium by reducing the metal oxides with hydrogen prior to hydrogenation of the alkene. A specially active form of nickel ( Raney nickel ) is prepared from a nickel-aluminum alloy. Sodium hydroxide is added to the alloy to dissolve the aluminum. The nickel remains as a black powder which is pyrophoric (bums in air) if not kept moist ... 

Fig. 24. Maximum catalytic activity for CO oxidation as a function of alloy composition for Pt-Cu (A), Pt-Ni (O, ), and Pt-Fe ( ) systems. [From Bonzel and Wynblatt (707).] (Reprinted with permission of North-Holland Publishing Company.)...

Catalytic activity in zeolitic materials is strongly influenced by the type of alkali metal cations, and maximum catalytic activity, e.g, in isomerization reactions, is explained by the formation of an imide species EuNH [305]. Synergetic effects were observed in bimetallic supported Si02 which showed considerable hydrogen uptake during hydrogenation reactions [307]. The formation of Ln-NH2, -NH, -N species seemed to be suppressed in the presence of transition metal powders and precipitation of elemental lanthanides is favored [309]. Lanthanide imides were favored as active species in the Ln/AC-mediated cyclization of ethyne and propyne [310]. 

Metals frequently used as catalysts are Fe, Ru, Pt, Pd, Ni, Ag, Cu, W, Mn, and Cr and some of their alloys and intermetallic compounds, such as Pt-Ir, Pt-Re, and Pt-Sn [5], These metals are applied as catalysts because of their ability to chemisorb atoms, given an important function of these metals is to atomize molecules, such as H2, 02, N2, and CO, and supply the produced atoms to other reactants and reaction intermediates [3], The heat of chemisorption in transition metals increases from right to left in the periodic table. Consequently, since the catalytic activity of metallic catalysts is connected with their ability to chemisorb atoms, the catalytic activity should increase from right to left [4], A Balandin volcano plot (see Figure 2.7) [3] indicates apeak of maximum catalytic activity for metals located in the middle of the periodic table. This effect occurs because of the action of two competing effects. On the one hand, the increase of the catalytic activity with the heat of chemisorption, and on the other the increase of the time of residence of a molecule on the surface because of the increase of the adsorption energy, decrease the catalytic activity since the desorption of these molecules is necessary to liberate the active sites and continue the catalytic process. As a result of the action of both effects, the catalytic activity has a peak (see Figure 2.7). 

The Fe(II)/Fe(III)-H202 system has its maximum catalytic activity at a pH of 2.8-3.0. Any increase or decrease in the pH sharply reduces the catalytic activity of the metal ion. At high pH, the ferric ion precipitates as ferric hydroxide, whilst at low pH, the complexation of Fe(III) with hydrogen peroxide is inhibited. To overcome this problem, Sun and co-workers have used Fe(III) chelates in place of Fe(II)/Fe(III).21 Sun has shown that a variety of herbicides and pesticides can be transformed and practically mineralized by Fe(II) chelates at neutral pH. 

Newsholme, E. A., and Crabtree, B. (1986). Maximum catalytic activity of some key enzymes in provision of physiologicaUy useful information about metaboUc fluxes. f. Exp. Zool. 239, 159—167. 

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