Reaction conditions choosing optimum

Also, before one can choose the substrate concentration for a particular method, the Michaelis constant must be determined. Usually, if the enzyme does not exhibit inhibition at high substrate concentration, it may be reasonable to use a working molar concentration of the substrate equal to 3 or 4 times the Km value so that the enzyme can manifest its highest activity. As in the case of j8-glucuronidase (F17), the conditions developed for a particular isoenzyme (of alkaline phosphatase) in one tissue may not be applicable for another isoenzyme in another tissue or for those present in serum. Hence reevaluation of every reaction condition (e.g., substrate concentration, optimum pH) is necessary for each isoenzyme. Vide infra 2.1.1. 

The chemical shift differences between reactants and products permit NMR to be used to follow the course of a reaction and to choose the optimum reaction conditions. In Fig. 3.53, the Si NMR spectra show that NMR can follow the process of making fS-SiC, a refractory ceramic, from polymethylvinylsilane and silicon metal. The NMR spectmm of the product silicon carbide (top spectmm) is clearly different from the spectmm of the starting mixture (bottom spectmm). In the bottom spectmm, the resonance at —18 ppm is due to the organo-silane the resonance at — 82 ppm is the elemental silicon signal. All reactant and product signals are well separated in chemical shift, so any unreacted starting material can be measured in the product and the production process can be optimized. 

With many redox systems, coupled reactions take place that make it necessary to choose the appropriate system in accordance with the monomer and the polymerization conditions. If the redox reaction is slow, there will be a low yield of radicals and therefore a low polymerization rate. On the other hand, if the redox reaction is fast compared with the initiation step, the majority of initiating radicals will be consumed by radical termination reactions. Therefore, redox systems are modified by further additives. For example, heavy metal ions may be complexed with substances such as citrates, which adjust their reactivity to a reduced level. Hence, redox systems for technical polymerization are complex formulations which enable one to obtain optimum results at well-defined reaction conditions. 

Many variables are of importance in determining the course of an electrode reaction. In order to determine the optimum conditions for an electrosynthesis the use of current-voltage curves obtained at microelectrodes is of great value. A series of such curves are produced using different electrode materials, solvents, and pH when mercury is used as the electrode material, the ordinary polarographic technique8-10 is applied. With some experience it is possible from such a series of experiments to choose conditions suitable for the reaction. 

Results show that when the in situ polymerization of pyrrole monomer was happened at 3 hr, the electrical conductivity of PPy coated fabric pretreated increased more than other conditions, so this reaction time can be choose as optimum. 

The pH of the buffer solution in which the analysis takes place must also be controlled. Most enzymes have a pH dependence of their activity of the type shown in Figure 4 B, and pH should be controlled to within 0.02. The optimum pH, and the range over which the enzyme is active, vary widely from one enzyme to another. These phenomena arise from the effects of pH on the structure of the enzyme itself, on the affinity constant between the enzyme and the substrate, on V ax. and also on any coupled indicator reaction that is used. The choice of buffer recipe for any given pH may be important. The ionic strength of the buffer and the salts contained in it can influence the rate and mechanism of the main and coupled reactions, sometimes with unpredictable results. It may be necessary to choose a buffer whose properties represent a compromise between the ideal conditions for the main reaction, and the ideal conditions for the indicator leaction(s). Immobilized enzymes (Section 9.1.7) often have pH (and temperature) dependence significantly different from their soluble counterparts. This all points to the value of establishing and maintaining a well-defined buffer system for enzymatic analyses. 

This step is the most important part of carbon fibers and nanofibers formation and has been attracted a lot of attentions [6, 14,20,]. It has been shown that thermal stabilization conditions have considerable effect on the properties of the resulting carbon fiber [14]. It is necessary to choose the optimum conditions of temperature, heating rate and oxidation duration. Studies showed that optimal stabilization conditions lead to high modulus carbon fibers. Too low temperatures lead to slow reactions and incomplete stabilization, whereas too high temperatures can fuse or even bum the fibers [6, 9]. 

The ammonia synthesis reaction is affected by many factors. The fundamental basis of choosing process conditions is the thermodynamics and kinetics of the ammonia synthesis reaction, and the activity of the catalyst. In selecting the optimum conditions, it is necessary to consider many factors including thermodynamics, reaction kinetics, yields, and energy consumption. Both the process and the equipment need to be considered, all of which must be subjected to the constraints of the catalyst. ... 

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