Use of Inhibitors

First of all, it should be noted that there is no such thing as a universal inhibitor capable of protecting all metals in a single medium. Some inhibitors may protect several metals, while others are highly specific to one metal or alloy (Table B.5.4). 

Each metal or alloy in a multi-metal circuit must be protected by its own inhibitor(s). This explains the complexity of certain formulations of liquid inhibitors used for certain circuits. 

Inhibitors can also be used in very specific cases such as in protecting aircraft against corrosion during cleaning operations [45]. Inhibitors are very rarely used in open systems, because of their cost and environmental problems. 

It is impossible to list all the inhibitors that have been proposed for protecting aluminium. Specialised publications should be studied for this purpose [46]. The inhibitors most commonly mentioned for aluminium [47-49] are listed in Table B.5.5. It should be noted that inhibitors may be subject to ageing, and that their effectiveness is not always total. 

Diluted nitric acid 10% 0.1% alkali chromate, 0.50% hexamethylene tetramine 

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Myrcene Manufacture. An important commercial source for mycene is its manufacture by pyrolysis of p-piaene at 550—600°C (87). The thermal isomerization produces a mixture of about 75—77 wt % myrcene, 9% limonene, a small amount of T -limonene [499-97-8] and some decomposition products and dimers. The cmde mixture is usually used without purification for the production of the important alcohols nerol and geraniol. Myrcene may be purified by distillation but every precaution must be taken to prevent polymerization. The use of inhibitors and distillation at reduced pressures and moderate temperatures is recommended. Storage or shipment of myrcene in any purity should also include the addition of a polymerization inhibitor. 

The use of inhibitors is not limited to controlling corrosion of iron and steel. They frequently are effective with stainless steel and other aUoy materials. The addition of copper sulfate to dilute sulfuric acid will sometimes control corrosion of stainless steels in hot dilute solutions of this acid, whereas the uninhibited acid causes rapid corrosion. 

In some instances the amount of inhibitor present is critical in that a deficiency may result in localized or pitting attack, with the overall results being more destructive than when none of the inhibitor is present. Considerations for the use of inhibitors should therefore include review of experience in similar systems or investigation of requirements and limitations in new systems. 

Use of inhibitors. Because corrosion is such a vital aspect of the erosion-corrosion process, inhibitors that will reduce corrosion under conditions of high fluid velocity have been a cost-effective method of dealing with erosion-corrosion. For example, injection of ferrous sulfate either intermittently or continuously has been successful in inhibiting erosion-corrosion, especially with copper-base alloys. 

FIGURE 18.12 The use of inhibitors to reveal the sequence of reactions in a metabolic pathway, (a) Control Under normal conditions, the steady-state concentrations of a series of intermediates will be determined by the relative activities of the enzymes in the pathway, (b) Plus inhibitor In the presence of an inhibitor (in this case, an inhibitor of enzyme 4), intermediates upstream of the metabolic block (B, C, and D) accumulate, revealing themselves as intermediates in the pathway. The concentration of intermediates lying downstream (E and F) will fall. 

The inhibitive efficiency of alkali metal hydroxides increases with increased branching of polyethylene. This is confirmed by more pronounced effect of these hydroxides diminishing the yield of propane and propylene than in case of ethane and ethylene. The decreased yield of propane and propylene is also conditioned by more efficient inhibition of the macroradical isomerization stage by alkali metal hydroxides. Upon thermal destruction of polyethylene with the use of inhibitors the... 

Besides the measures described in the main part of this paper, significant improvement of the corrosion resistance of a material can be obtained by use of inhibitors. In this case, good results seem to be achieved with rare earths employed in low amounts as alloying metals or as protective dense oxide coatings. The use of coatings often means the research into the best compromise between mechanical properties and corrosion resistance of the material. 

In some circumstances, use of inhibitors may be a desirable remedial measure. For instance, benzotriazole has been found of considerable value... 

Complete inhibition of corrosion in waters containing high concentrations of chloride is difficult, if not impossible to achieve economically. Despite this, many such systems make use of inhibitors to give marked reductions in corrosion rates. 

Probably the major use of inhibitors in acid solutions is in pickling processes. The chief requirements of the inhibitor are that it should not decompose during the life of the pickle, not increase hydrogen absorption by the metal... 

Although chemicals in closed circulation systems do not generally come into contact with the environment - except perhaps on disposal - problems can exist with safety in handling. A particular example is the need for caution in the mixing of coolants containing nitrites with those containing amines because of the possible production of carcinogenic nitrosoamines. This caution has been expressed in other fields of use of inhibitors (see below). 

The very wide use of inhibitors is obvious, but emphasis must always be placed on the factors affecting their performance and on the specific circumstances and other requirements relating to particular applications. 

Here, the use of inhibitor formulations having a less dramatic effect on TDS (such as certain tannins) may be extremely beneficial. Formulations are available that are based on tannin chemistry and contain blends that act as oxygen scavengers and metal passivators, with additional sludge dispersant and antifoam properties. 

Abstract This review provides an overview of the development of viral protease inhibitors as antiviral drugs. We concentrate on HlV-1 protease inhibitors, as these have made the most significant advances in the recent past. Thus, we discuss the biochemistry of HlV-1 protease, inhibitor development, clinical use of inhibitors, and evolution of resistance. Since many different viruses encode essential proteases, it is possible to envision the development of a potent protease inhibitor for other viruses if the processing site sequence and the catalytic mechanism are known. At this time, interest in developing inhibitors is Umited to viruses that cause chronic disease, viruses that have the potential to cause large-scale epidemics, or viruses that are sufQciently ubiquitous that treating an acute infection would be... 

Much information about the respiratory chain has been obtained by the use of inhibitors, and, conversely, this has provided knowledge about the mechanism of action of several poisons (Figure 12-7). They may be classified as inhibitors of the respiratory chain, inhibitors of oxidative phosphorylation, and uncouplers of oxidative phosphorylation. 

Catalysts that decrease reaction rates are usually referred to as inhibitors. They usually act by interfering with the free radical processes involved in chain reactions, and the mechanism differs from that involved in accelerating a reaction. The most familiar example of the use of inhibitors is the addition of tetraethyl lead to gasoline to improve its antiknock properties. 

Cell lysis When studying signaling components, it is important that the integrity and phosphorylation states of proteins of interest are not altered during cell lysis and the subsequent preparation of the samples prior to analysis. The principal precautions include the use of inhibitors of protein phosphatases and of proteases, in addition to working speedily and keeping samples cold (0 to 4°). 

Identification of the energy source for muscle contraction and determination of the order in which the phosphate esters were metabolized was helped by the use of inhibitors. These inhibitors blocked different stages in glycolysis and caused preceding substrates to accumulate in quantities which could greatly exceed those normally present. The compounds were then isolated, identified, and used as specific substrates to identify the enzymes involved in their metabolism. Iodoacetic acid (IAc) was one of the most important inhibitors used to analyze glycolysis. 

When in later years Krebs reviewed the major points which had to be established if the cycle was to be shown to be operative in cells, the obvious needs were to find the presence of the required enzymes and to detect their substrates. As the substrates are present in the cycle in catalytic amounts their accumulation required the use of inhibitors. Krebs also stressed that rates of oxidation of the individual substrates must be at least as fast as the established rates of oxygen uptake in vivo, an argument first used by Slator (1907) with reference to fermentation A postulated intermediate must be fermented at least as rapidly as glucose is. (See Holmes, 1991). This requirement did not always appear to be met. In the early 1950s there were reports that acetate was oxidized by fresh yeast appreciably more slowly than the overall rate of yeast respiration. It was soon observed that if acetone-dried or freeze-dried yeasts were used in place of fresh yeast, rates of acetate oxidation were increased more than enough to meet the criterion. Acetate could not penetrate fresh yeast cell walls sufficiently rapidly to maintain maximum rates of respiration. If the cell walls were disrupted by drying this limitation was overcome, i.e. if rates of reaction are to be... 

Percutaneous absorption is another route of interest for the administration of peptides [158], with metabolism being a complicating factor [159]. Thus, [Leu5]enkephalin and Tyr-Pro-Leu-Gly-NH2 were rapidly degraded on the dermal side after penetration through rat skin preparations [160]. The use of inhibitors confirmed the involvement of serine proteases and metalloenzymes. 

The intrusive hydrogen probe (IHP-200) shown in Fig. 29 can be placed in access fittings in industrial plants (pressure vessels, pipelines) and withstands pressures up to 200 bar. It is typically used to monitor the efficiency of measures taken to diminish the risks of hydrogen damage (use of inhibitors, H2S scavengers, etc.). 

Xylose isomerases (EC 5.3.1.5), often referred to as glucose isomerase, have been studied extensively, in large part because of their use in the conversion of glucose to fructose for high-fructose corn syrup (HFCS). The world market for HFCS is expected to reach a total of 7.9 million metric tons in 1990 which, at a cost of 0.20/LB, would amount to 3.2 billion (i), and sales of xylose isomerase is expected to be about 15 million (T. Wallace, International Biosynthetics, personal communication). Research on xylose isomerase has produced DNA sequences of the gene from a number of bacterial strains, including the detailed structure of the xylose operon (2-7). In addition, x-ray crystallographic studies (8), kinetic measurements (9), and the use of inhibitors (10,11) have led to descriptions of the location of the active site and mechanistic models of its activity. 

Rationale for the Use of Inhibitors of Releasing Hormones in Cancer Treatment... 

K. Osiecki-Newman, D. Fabbro, G. Legler, R. J. Desnick, and G. A. Grabowski, Human acid P-glucosidase Use of inhibitors, alternative substrates and amphiphiles to investigate the properties of the normal and Gaucher disease active sites, Biochim. Biophys. Acta, 915 (1987) 87-100. 

Because of the complex structure and the insolubility of cellulose, the precise mechanism of recognition and action of cellulases have been examined by the use of inhibitors and artificial substrates. Cellulases have been found, so far, in 11 families of glycosyl hydrolases [65]. 

Resell, C., Femandez-Lafuente, R. and Gnisan, J.M. (1995) Modification of enzyme properties by the use of inhibitors dnring their stabilisation by multipoint covalent attachment. Biocatalysis and Biotransformation, 12, 67-76. 

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