Inhibition, and poisoning

Recent developments in analytical and experimental techniques have made it possible to identify the individual species in FCC feeds and products, to determine the strength and distribution of the catalytic active centres (acid sites) and to study the structure and composition of deactivating coke. In addition, for a variety of model compounds, a wealth of published qualitative and semi-empirical data exists that highlight some of the key features of FCC catalysts. This includes the inhibiting and poisoning effects of various species and deactivation by the progressive reduction in the number and changing distribution of acid sites. 

Previously, for 2-methyl pentane cracking we have used Eley-Rideal kinetic rate expressions to describe the inhibition and poisoning effects of species in the feed, as well as intermediate and product species. In order to utilise such kinetic expressions values for the adsorption equilibrium constants are required. A method for estimating adsorption equilibrium constants has been proposed that uses an integrated form of van t Hoff equation. The heats of adsorption have been calculated using proton affinities and heats of condensation. The entropy of adsorption has been calculated using the Sackur-Tetrode expression. 

Both the inhibition and poisoning of topoisomerases are deleterious to cells. The collision of a transcription complex or a replication fork against a topoisomer-ase-associated DNA break interrupts RNA or DNA synthesis, and can lead to real (nontopoisomerase-bound) double-strand breaks and to gene translocations, which can trigger apoptosis and/or cancer (Li and Liu 2001). 

Elucidating Mechanisms for the Inhibition of Enzyme Catalysis An inhibitor interacts with an enzyme in a manner that decreases the enzyme s catalytic efficiency. Examples of inhibitors include some drugs and poisons. Irreversible inhibitors covalently bind to the enzyme s active site, producing a permanent loss in catalytic efficiency even when the inhibitor s concentration is decreased. Reversible inhibitors form noncovalent complexes with the enzyme, thereby causing a temporary de-... 

The second behavior observed in the results plotted in Fig. 7.13 is that of Bi-Pt(lll) electrodes. In this case, a very small amount of adatom on the surface can produce a significant effect on the amount of poison formed. In fact, no poison can be detected when the Bi coverage is as low as 0.04. It has been calculated that if this effect were due to an extended electronic modification, it would mean that one adatom inhibits the poison formation in the surrounding Pt atoms, extending its influence as far as to 7 neighbors. This is quite unexpected, and contrary to theoretical... 

In technical hydrocarbon reforming processes using platinum catalysts, high hydrogen pressures are usually used to inhibit catalyst poisoning and coke formation as far as possible, for instance a total pressure of several atmospheres to several tens of atmospheres, with a several-fold excess of hydrogen in the reactant mixture. 

Activators and inhibitors regulate not the amount of enzyme protein but the activity ( efficiency ) of that which is present. Two principal mechanisms of control are (i) competitive and (ii) allosteric. Competitive control (inhibition) occurs when a compound which is structurally similar to the true substrate binds to the active site of the enzyme. This is how a number of drugs and poisons bring about their effect. For example, a group of therapeutic drugs called statins are used to treat heart disease because by inhibiting a key enzyme called HMGCoA reductase, they reduce the hepatic synthesis of cholesterol and therefore the plasma concentration of that lipid. 

CASRN 107-02-8 DOT 1092 (inhibited), 2607 (stabilized dimer) DOT label Flammable liquid and poison molecular formula C3H4O FW 56.06 RTECS AS1050000 Merck Index 12, 130... 

If a methionine auxotroph is not used, the methionine within the culture can be replaced by SeMet using a methionine biosynthesis inhibition or poisoning method such as that outlined in Protocol 2.7. This method has the advantage of using any E. coli strain available and thus the initial growth of the culture is not reduced, however the method is more laborious than using the methionine auxotroph. 

Alcohols. Methyl alcohol, and to a lesser extent ethyl alcohol, were used as freezing point depressants for many years. Their use now is minimal. When properly inhibited, alcohol-water solutions can be satisfactory coolants only under restricted conditions. Alcohol antifreezes fell into disuse because of their low boiling point (lower than that of water) and the danger of loss from boiling or evaporation. Alcohol volatilizes from hot surfaces much more readily than glycol coolant and can be a potential fire hazard. Methyl alcohol liquids are both flammable and poisonous. Methyl alcohol vapors are toxic when inhaled at high concentrations. 

The toxicology and pharmacology of esters of the type 126 have been studied in some detail, both because of their commercial importance and their close structural relationship to some nerve gases. They are poisonous compounds which act, like the related alkyl dithionophosphate esters, by cholinesterase inhibition, and their misuse has been associated with certain mental disorders. As a consequence of this pronounced biological activity, much attention has been directed to both the detection and isolation of the compounds as such, ... 

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