Activation curves

Volter and Alsdorf (52) obtained a relation of a very similar character for the dependence of the catalytic activity in formic acid decomposition on the composition of the nickel-copper alloys. However, extending the times of the alloy annealing for their better homogenization caused the maxima on the catalytic activity curves to disappear. 

Figure 1. Activity curves showing substituent effect with MAO and EAS, in turn.

It should be observed that curve C (Fig. 31) which characterizes the steady activity of the catalyst surface may be directly compared to activity curves obtained by other techniques. The evolutions of heat as a function of time produced by the reaction of doses of reaction mixture at the surface of four different nickel oxide catalysts are, for instance, plotted on Fig. 32. These curves are very similar indeed to the kinetic curves obtained with the same catalysts in a classical static reactor (Fig. 33) (8). 

It was found that, in a nonpolar medium, the crotyl rhodium complex 1 is relatively inactive as a codimerization catalyst. However, it becomes very active in the presence of a small amount of donors such as alcohol. The activity generally increases linearly with the amount of the added donors and then depends on the strength of the donors, either leveling off or decreasing with further increases in the donor concentration. Strong donors improve the activity at lower concentration but inhibit the reaction at higher concentration. Some representative donors and their rate enhancement efficiency are shown in Table VI. The relationships between the concentrations of various donors and the reaction rates are summarized in Figure 5. The rate enhancement efficiency (expressed as relative reactivity) of a donor was measured based on the maximum rate attainable by addition of a suitable quantity of the donor to the reaction mixture, i.e., the maximum in the activity curve of Fig. 5. The results in Table VI show that those donors with p Ka values (25) between -5 and... 

There have been two independent mutagenesis studies that have been directed toward probing the role of E4 in the PLCB(. reaction [36, 94]. In the first of these, the kinetic parameters kcM and Km of the E4L, E4D, and E4Q mutants, which each gave CD spectra similar to wild-type, were determined by the choline quantitation method [33], and these mutants were found to retain 6-60% of the catalytic efficiency (i.e., kcat/iCm) of wild-type [36, 64]. Furthermore, the pH-dependence with activity curve of the E4L mutant was virtually identical with that for E146Q (Fig. 13) and similar to that of wild-type. In the other inves-... 

A solute B obeys Henry s law at infinite dilution if the slope of the activity curve aB versus xB has a nonzero finite value when xB - 0 ... 

An extensive study of the effect of salts on the pH-activity curves of PM was made on alfalfa49 and on orange21 and tomatoes.44 In general, the effect of salts is to lower the pH at which maximum activity is attained and to extend the activity into lower pH regions. At the higher pH values (7-8), salts have practically no activating effect. The main usefulness of salt activation of PM seems to lie in counteracting adverse pH conditions. 

Hepatic elimination obeys exponential kinetics because metabolizing enzymes operate in the quasilinear region of their concentration-activity curve hence the amount of drug metabolized per unit of time diminishes with decreasing blood concentration. 

A very shallow maximum in activity for both n-heptane and gasoil cracking is observed for Beta zeolites (with nominal framework Si/Al ratio of 20-40), while for Y zeolite a clear maximum is located at values between 10 and 20. In any case, a partial dealumination takes place when the TEA-3 zeolites are NHj-exchanged and calcined. Consequently, the activity curve for Beta zeolites should be shifted to higher framework Si/Al with respect to those plotted in Figures 6 and 7a. 

Each point on the activity curve of a test compound represented the average of the results of each concentration tested in triplicate, air-induction was strongly pH dependent (24, our results, data not shown), so the buffer system was used to minimize variation in pH. Standard deviations rarely reached 10%, the average being 4.7% (n = 92) for results of 100 Miller units and above. 

Figure 2.3 Schematic dose-response curves. Curves a and b (with different values) show the actions of drugs in the same series acting on the same receptor site with different intrinsic activities. Curve c represents a partial agonist of the same series. Thus, a and b are agonists c is a partial agonist. Curve d is the action of a in the presence of a competitive antagonist. Compounds represented by curves a and b have the same efficacy.

With the exception of the enzyme from the limpet, P. vulgata, a-D-mannosidase from most of the important sources shows optimal activity at pH values lying between 4 and 5. For the enzyme from jack-bean meal39 and that from rat epididymis,80 we employed a pH of 5 for routine assays. If this is not the actual optimum, it is close to it on the broad pH-activity curves, and, at this pH, the addition of Zn2+ and other cations has relatively little effect in the assay, thus simplifying the study of the various metal complexes that can be formed by the enzyme protein. 

The dissociation of the active protein-Zn2+ complex at low pH can be seen from the pH-activity curves shown in Fig. 1. This Figure also shows the effect of Cl-. Chloride ion not only accelerates hy-... 

Figure 2. Deconvoluted time-activity curve of right lung of patient in Figure 1. Secondary curves are least squares fits from which the Qp Qs values are derived. Region A - normal pulmonary perfusion. Region - early recirculation due to left-to-right shunt.

Figure 2b. Activity curve for concentrations of Cs absorbed on a column of Selma chalk. Two series of samples of chalk were analyzed after the experiment and their radioactivities are indicated by the histograms. The smooth curve is the distribution inferred from these results. Column 24-3, selma chalk, Cs-134. (---------------), First series of samples (----), second series of samples.

FIGURE 6-29 Substrate-activity curves for representative allosteric enzymes. Three examples of complex responses of allosteric enzymes to their modulators, (a) The sigmoid curve of a homotropic enzyme, in which the substrate also serves as a positive (stimulatory) modulator, or activator. Note the resemblance to the oxygen-saturation curve of hemoglobin (see Fig. 5-12). (b) The effects of a positive modulator (+) and a negative modulator (—) on an allosteric enzyme in which K0 5 is altered without a change in Zmax. The central curve shows the substrate-activity relationship without a modulator, (c) A less common type of modulation, in which Vmax is altered and /C0.sis nearly constant. 

In 1959, H. Beuther et al. (8) of Gulf Oil Company published the first systematic study of the HDS activity of CoMo and NiMo supported on alumina as a function of the atomic ratio Co(Ni)/Mo. As a result, they showed what they called a promoter effect of the cobalt (or nickel) on the molybdenum for atomic ratios Co/Mo = 0.3 and Ni/Mo = 0.6. This publication was preceded by several patents proposing similar atomic ratios for cobalt by Union Oil of California (1948) (9) and Shell Oil Company (1954) (10) and for nickel by Union Oil of California (1954)(/7). Figure 1 shows a typical activity curve of NiMo/Al203 catalysts as a function of the value of the atomic ratio Ni/Mo (12). 

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