Inhibition acetylenes

Nitrogenase catalyzes the reduction of many substrates (Table IV) and there are several lines of evidence to suggest that these are reduced at different sites or by different forms of the enzyme. Kinetic studies of interactions between pairs of substrates (Hwang ef al., J973 Rivera-Ortiz and Burris, 1975) show that Ng inhibits acetylene reduction competitively whereas the reverse inhibition is noncompetitive azide and acetylene are mutually noncompetitive and azide and cyanide inhibit each other competitively. HCN inhibits Nj reduction competitively whereas Nj inhibits HCN reduction in an undetermined manner. N2O inhibits Nj reduction competitively and acetylene reduction noncompetitively. ATP-dependent evolution by nitrogenase is inhibited by all the other reducible substrates and CO inhibits all substrate reductions except H2 evolution in a noncompetitive manner. Table V summarizes these results. The simplest interpretation of these results is that the N2-reducing site reduces N2 and possibly N2O but no other substrate azide, HCN, and methyl isocyanide are reduced at the same site... 

Following the action of extraordinary stimulants (hypoxic hypoxia, hypoxia + hyperoxia, hypodynamia + hyperthermia), animals demonstrate an accumulation of malonic dialdehyde with a simultaneous fall of antiradical activity of the liver tissue. A preliminary introduction to rats of acetylene amine 3,4,5-tris(morpho-linopropynyl)-l-methylpyrazole 103 and also of tocopherol antioxidant and gutumine antihypoxant averts activation of the lipid peroxidation processes. The inhibition of peroxidation with this agent is mediated by stabilization of ly-zosomal and mitochondrial membranes. Unsaturated amines prevent destruction of the organelle membranes provoked by UV irradiation and incubation at 37°C (pH4.7)(78MIl). 

The acetylene aminopyrazole 103 was capable of inhibiting the processes of lipid peroxidation both in the enzymatic and nonenzymatic peroxidation system (76MI2). Finally, 4-[3-(l-methyl-l//-pyrazol-3-yl)-prop-2-ynyl]morpholine hydrochloride 104 was patented as a compound with high hypoxic activity (93MIP1). 

Acetylenic compounds have been described for inhibition in acid solutionsTypical inhibitors include 2-butyne-l,4-diol, l-hexyne-3-ol and 4-ethyl-l-octyne-3-ol. 

Reaction of adsorbed inhibitors In some cases, the adsorbed corrosion inhibitor may react, usually by electro-chemical reduction, to form a product which may also be inhibitive. Inhibition due to the added substance has been termed primary inhibition and that due to the reaction product secondary inhibition " . In such cases, the inhibitive efficiency may increase or decrease with time according to whether the secondary inhibition is more or less effective than the primary inhibition. Some examples of inhibitors which react to give secondary inhibition are the following. Sulphoxides can be reduced to sulphides, which are more efficient inhibitorsQuaternary phosphonium and arsonium compounds can be reduced to the corresponding phosphine or arsine compounds, with little change in inhibitive efficiency . Acetylene compounds can undergo reduction followed by polymerisation to form a multimolecular protective film . Thioureas can be reduced to produce HS ions, which may act as stimulators of... 

Corrosion inhibition is primarily associated with acidizing. Buffered hydrofluoric acid compositions have been shown to be less corrosive (147). Corrosion inhibitors are designed to reduce the rate of reaction of fluid with metal surfaces, generally by forming films on the surfaces. Acetylenic alcohols and amines are frequently components of corrosion inhibitor blends. Other compounds that have been used include nitrogen heterocyclics, substituted thioureas, thiophenols, and alpha-aminoalkyl thioethers (148). 

The possible mechanisms of inhibition of flavin by (—)-deprenyl, as an irreversible acetylenic inhibitor, were studied by ab initio methods with the 6-31G basis set using simplified model compounds, 3-formyl-2-imino-l-hydroxypyrazine, and propargylamine. The formation of two energetically stable cyclic adducts, the 0,N adduct 286 and a C,N adduct, was shown <1999THA147>. 

N. A. Zorin, B. Dimon, J. Gagnon, J. Gaillard, P. Carrier, P. M. Vignais (1996) Inhibition by iodoacetamide and acetylene of the H-D exchange reaction catalyzed by Thiocapsa roseopersicina hydrogenase. Eur. J. Biochem., 241 675-681... 

Fowler CJ, Mantle TJ, Tipton KF. The nature of the inhibition of rat liver monoamine oxidase types A and B by the acetylenic inhibitors clorgyline, 1-deprenyl and pargyline. Biochem Pharmacol 1982 31(22) 3555-3561. 

Pharmacologically active allenic steroids have already been examined intensively for about 30 years [5], Thus, the only naturally occurring allenic steroid 107 had been synthesized 3 years before its isolation from Callyspongia diffusa and it had been identified as an inhibitor of the sterol biosynthesis of the silkworm Bombyx mori (Scheme 18.34) [86d], At this early stage, allenic 3-oxo-5,10-secosteroids of type 108 were also used for the irreversible inhibition of ketosteroid isomerases in bacteria, assuming that their activity is probably caused by Michael addition of a nucleophilic amino acid side chain of the enzyme at the 5-position of the steroid [103, 104]. Since this activity is also observed in the corresponding /3,y-acetylenic ketones, it can be rationalized that the latter are converted in vivo into the allenic steroids 108 by enzymatic isomerization [104, 105],... 

Although HR-600/Thermid-600 provided promising neat resin and composite properties, major processing problems have plagued these as well as other acetylene-terminated oligomers. Resin flow and wetting is inhibited due to the reaction of the terminal ethynyl groups prior to the formation of a complete melt or soft state. This becomes even more severe due to heat transfer problems as... 

Much early effort in 5-LO inhibition centered on substrate and product analogues. One goal, especially of the Corey group at Harvard, was to study the 5-LO reaction by creating mechanism-based irreversible inhibitors, or by removing the substrate protons which are abstracted by the enzyme. These approaches, which included preparation of acetylenic, methylated, cyclized, or thia-analogues of arachidonic acid, and cyclopropyl analogues... 

Pharmacology Selegiline hydrochloride is a levorotatory acetylenic derivative of phenethylamine. Although the mechanism of action is not fully understood, inhibition of monoamine oxidase (MAO) type B activity is of primary importance and selegiline... 

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