Chemical inhibition

As shown in Chap. 7, shock compression introduces large numbers of defects which in turn cause substantial increases in solid state reactivity. Such shock activation is obviously critical to the process. One of the most direct effects of the mechanical deformation is the removal of oxides or other surface films from the surfaces of the powders. It is well recognized that such surface films can greatly inhibit chemical reaction. The very large mechanical deformation would be expected to substantially damage, if not completely remove, such films. Other manifestations of shock activation are shown in the next chapter. Effects have been shown that represent many orders of magnitude of change in solid state reactivity. 

Scale Inhibitors. When scaling conditions exist, scale inhibitors can be used to control the scaling tendencies, and keep metal surfaces free of scale deposits. Scale inhibitors are chemicals that interrupt and deform the normal crystalline growth pattern of carbonate scales. The three most commonly used classes of scale-inhibiting chemicals used in drilling fluid are [191,197] ... 

A common feature of both these methods is that the quantity of treatment chemical can be calculated from stoichiometric relationships in the reactions involved. This is not so with conventional inhibitor treatments. With these the concentration of inhibitive chemicals can only be determined on the basis of experimental laboratory studies, service trials and overall practical experience. 

Stabilizer These are agents or materials present in or added into practically all different plastics to improve their performances that range in the many different requirements needed in the fabricated product to meet performance requirements. They basically inhibit chemical reactions that bring about undesirable chemical degradation. 

CLA, the acronym for a series of conjugated dienoic isomers of linoleic acid, occurs naturally in many foods, particularly dairy products and other foods derived from ruminant animals (6). Synthetically prepared CLA inhibits chemically-induced mouse epidermal and forestomach neoplasia (7,8) and rat mammary neoplasia (9). Hence, the effect of CLA on carcinogenesis is opposite that of linoleic acid. 

Spamins, V.L., Venegas, P.L. Wattenberg, L.W. (1982) Glutathione S-transferase achvity enhancement by compormds inhibiting chemical carcinogenesis and by dietary conshtuents. J. natl Cancer Inst, 68, 493 96... 

Chen, J., Tan, K.P., Ward, W.E., and Thompson, L.U. 2003. Exposure to flaxseed or its purified lignan during suckling inhibits chemically induced rat mammary tumorigenesis. Exp. Biol. Med 228, 951-958. 

Thompson, H.J., N.D. Chasteen, and L.D. Meeker. 1984. Dietary vanadyl (IV) sulfate inhibits chemically-induced mammary carinogenesis. Carcinogenesis 5 849-851. 

Water-soluble vitamins and co-factors also appear to elicit an effect on xenobiotic metabolism. Ascorbic acid has been shown to inhibit chemically induced chemical carcinogenesis in test systems (Shamberger, ( ). When diets are deficient in choline, the animals appear to become much more susceptible to chemically-... 

Fat-soluble vitamins, in addition to their antioxidative effects on lipids, appear to exert a general protective effect in animals. Vitamin A and beta-carotenes protect lab animals from toxicity of citral, cyclophosphamide and some hydrocarbons (Seifter et al, (A2.) In related but independent studies, it was observed that high levels of vitamin A inhibit tumorogenesis and that low levels of vitamin A appear to enhance tumorogenesis (Baird, (1 ). vitamin E inhibited chemically-induced carcinogenesis in test systems (Shamberger, ) and also reduced the susceptibility of rats to cigarette smoke (Chow,... 

Numerous scientists have also demonstrated that dietary selenium supplementation can inhibit chemical carcinogen induced tumorigenesis in skin, liver, colon and mammary tissue (19-45)... 

OH)2D3 inhibited proliferation and induced differentiation and apoptosis in human colon, breast, prostate and gynecological cancers as well as several forms of hematopoietic cancer (Studzinski and Moore, 1995 van Leeuwen and Pols, 1997). Experimental animal studies show that 1, 25(OH)2D3 inhibited chemically-induced breast, colon, and skin tumors. The growth of colon, breast and prostate cancer cells, as well as melanoma and retinoblastoma cells implanted into rodents was retarded by treatment with 1, 25(OH)2D3 (Studzinski and Moore, 1995 van den Bemd et al, 2000). 

Micro emulsion droplets and micellar aggregates can catalyse or inhibit chemical reactions by compartmentalization and by concentration of reactants and products. The catalytic effect in micelles has been widely studied, a typical reaction being base catalysed hydrolysis of lipophilic esters. This rate enhancement is normally referred to as micellar catalysis. The analogous effect occurring in microemulsions may be called microemulsion catalysis. 

How heavy metals, arsenate, and azide inhibit chemical reactions induced by iron stress. 

Voziyan PA, Metz TO, Baynes JW, and Hudson BG (2002) A post-Amadori inhibitor pyri-doxamine also inhibits chemical modification of proteins by scavenging carbonyl intermediates of carbohydrate and lipid degradation. Journal of Biological Chemistry 277, 3397- 03. 

Research in our laboratory has focused on cancer prevention in colon and skin by phytochemicals. We have recently studied apigenin, a tri-hydroxy flavone that is widely distributed in plants and resveratrol, a phytoalexin that is found in grapes, wine, peanuts, and Asian herbs. We initially found that topical apigenin inhibited chemically and ultraviolet (UV)-light induced skin cancer and that it was most effective in preventing cancer promotion. 

Examples of enzyme-inhibiting chemicals are disulfiram, metyrapone, diethyl maleate, and 1-aminobenzotriazole. 

An inhibiting chemical slows the enzymatic metabolism of a toxic chemical. In this instance, if the uptaken chemical itself is the toxin, inhibition will slow the metabolism and intensify its action. If the metabolite of the absorbed xenobiotic is the toxic agent, inhibition will decrease the toxic affect. Vinyl chloride uptake in rats results in the lowering of cytochrome P450 and a corresponding loss of ability to metabolize other xenobiotics. Other inhibitors include diethyl maleate, which inhibits glutathione s-transferase and 1-aminobenzotriazole, which inhibits P450. 

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