Efficiency of the inhibitor

This problem was first approached in the work of Denisov [59] dealing with the autoxidation of hydrocarbon in the presence of an inhibitor, which was able to break chains in reactions with peroxyl radicals, while the radicals produced failed to contribute to chain propagation (see Chapter 5). The kinetics of inhibitor consumption and hydroperoxide accumulation were elucidated by a computer-aided numerical solution of a set of differential equations. In full agreement with the experiment, the induction period increased with the efficiency of the inhibitor characterized by the ratio of rate constants [59], An initiated inhibited reaction (vi = vi0 = const.) transforms into the autoinitiated chain reaction (vi = vio + k3[ROOH] > vi0) if the following condition is satisfied. 

When amines are added to the acetaldehyde-oxygen and ethyl ether-oxygen systems, a period of time elapses before oxidation of the fuel begins. The length of this induction period is dependent on the amount of amine added and the structure of the amine. Detailed analysis has shown that the length of the induction period can be used as a parameter for the efficiency of the inhibitor, for it is only when the amine has been consumed that oxidation of the fuel can take place (28). 

In all cases, the efficiency of the inhibitor may be obtained by determining Km and u,lulI from a control experiment with uninhibited enzyme and then repeating the experiment with a known concentration of inhibitor. From the slope and y-intercept of the Lineweaver-Burk plot for the inhibited enzyme (eqn 23.27), the mode of inhibition, the values of a or a, and the values of K, or K[ may be obtained. 

An interesting effect is observed, Fig.12, when the six normal hydrochloric acid solution is deaerated with nitrogen. It is seen that the absence of oxygen reduces the efficiency of the inhibitor considerably. 

In a preliminary study on the inactivation of -trypsin by a preparation of 2% p-NOo-ZACK and 98% of the inactive cyclic compound (Fig. Ic), Shaw and Glover were able to show the high efficiency of the inhibitor. They estimated that pure p-NO -ZACK should be orders of magnitude more rapid than the lysine derivative, TLCK. From their data it could be deduced that the impure inhibitor preparation totally eliminates the activity of trypsin within 10 min at pH 7 and 25° at an inhibitor-enzyme ratio of 50 1. They have also shown that a histidine residue is replaced by a 3-carboxymethylhistidine residue in the total hydrolyzate of the inactivated trypsin, which proves the active site-oriented action of the inhibitor. 

In terms of the efficiency of the inhibitor effect of salts during combustion, these metals are ranked in the following order [101] Li < Na < K < Rb. It was concluded that the ability to form active intermediates during decomposition of alkali metal salts is a function of the nature of the anion [102]. The effectiveness of flame inhibition decreases in the order oxalates > cyanides > carbonates > iodides > bromides > chlorides sulphates > phosphates. Consequently, alkali and alkali earth salts of organic acids are more effective catalysts of active center recombination during the combustion process. 

Radiolytic oxidation is important to the design and operation of reactors because it adversely affects key graphite properties and, by removing moderator material, may bring about the need for increased fuel enrichment. As mentioned earlier, an inhibitor (methane) is added to the coolant to reduce radiolytic oxidation to acceptable levels. However, access of the inhibitor to the inner portions of the moderator brick must be assured. Two approaches have been adopted in the AGRs to provide this access. Vertical methane access holes are provided in the fuel bricks and in the later stations, Heysham II and Tomess, a pressure drop from outside to inside the brick was established to cause an enhanced flow through the brick. The amount of inhibitor added must be restricted, however, because the carbon inhibition reaction product deposits on the fuel pin and restricts heat transfer to the coolant, thus reducing reactor efficiency. 

At 300°C and in the presence of KOH an increase in the molecular weight is observed, i.e., the reaction of macropolymerization is realized [38,39]. Potassium hydroxide is effectively inhibiting thermal destruction of polyethylene at temperatures from 350-375°C. The per cent change in molecular weight is half or one-third as high as that without the use of an inhibitor. At 400°C the efficiency of inhibition is insignificant. Potassium hydroxide with an ABC carrier is effective up to the temperature of 440°C due to the increased contact surface of the inhibitor with macroradicals. 

Inhibitor Efficiency. The value of corrosion inhibitors can be compared on the basis of inhibitor efficiency. Inhibitor efficiency indicates the percentage that corrosion is lowered in the presence of the inhibitor as compared to that in its absence. Inhibitor efficiency can be calculated by using the formula... 

In situations such as the acid pickling of steel or the use of steel pipes to handle sour oil streams, the use of suitable inhibitors can give a significant reduction in hydrogen entry. In this context it is important to emphasise that the efficiency of an inhibitor in reducing hydrogen entry is not the same as its efficiency in reducing corrosion. Thus arsenic and antimony compounds... 

The efficiency of an inhibitor under a given set of conditions is expressed by the formula... 

The potency of the inhibitors is affected by the pH. Changes in pH affect the protonation state of the guanidine. In conditions of low pH, such as in ischemia-reperfusion, some dtugs such as cariporide work more efficiently because they are on average more positively charged. 

The efficiency of these inhibitors may depend on reaction conditions. For example the reaction of radicals with stable radicals (e.g. nitroxides) may be reversible at elevated temperatures (Section 7.5.3) triphenylmethyl may initiate polymerizations (Section 7.5.2). A further complication is that the products may be capable of undergoing further radical chemistry. In the case of DPPH (22) this is attributed to the fact that the product is an aromatic nitro-compound (Section 5.3.7). Certain adducts may undergo induced decomposition to form a stable radical which can then scavenge further. 

Certain substances known as competitive inhibitors, symbolized I, may lower the catalytic efficiency of the enzyme (or other catalyst) by binding to it. Consider that the E I complex has a dissociation constant K. ... 

In noncompetitive inhibition, binding of the inhibitor does not affect binding of substrate. Formation of both EI and EIS complexes is therefore possible. However, while the enzyme-inhibitor complex can still bind substrate, its efficiency at transforming substrate to product, reflected by is decreased. Noncompetitive... 

The processes by which unsaturated monomers are converted to polymers of high molecular weight exhibit the characteristics of typical chain reactions. They are readily susceptible to catalysis, photoactivation, and inhibition. The quantum yield in a photoactivated polymerization in the liquid phase may be of the order of 10 or more, expressed as the number of monomer molecules polymerized per quantum absorbed. The efficiency of certain inhibitors is of a similar magnitude, thousands of monomer molecules being prevented from polymerizing by a single molecule of the inhibitor. ... 

If the rate constant kd for the spontaneous decomposition of the inhibitor is known, and its efficiency has been established, the important ratio kl/kt may then be evaluated. With greater generality, Eq. (8) may be combined with (12) to give... 

Inhibitors of swelling act in a chemical manner rather than in a mechanical manner. They change the ionic strength and the transport behavior of the fluids into the clays. Both the cations and the anions are important for the efficiency of the inhibition of swelling of clays [503]. 

In stimulation fluids containing concentrated HCl, the partial substitution of water by alcohols such as methanol, ethanol, and glycerol increases the corrosivity of the acid fluids and reduces the efficiency of the corrosion inhibitors [1148]. This effect is especially important for fatty amine-based inhibitors. For products containing acetylenic-type inhibitors the detrimental effect is less important and a weight loss may be maintained within acceptable limits using slightly higher, but still reasonable, levels of inhibitor. 

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