Coupling agents action mechanism

Fujino, M., T. Arima, Y. Sato, and H. Tako. 1985. Suppression of action of some excitation-contraction (E-C) uncoupling agents and mechanism in E-C coupling in single skeletal muscle fibers of frog, R. japonica. Jour. Physiol. Soc. Japan 47 519. 

The chemical structure and mechanism of action of the coupling agent... 

The question regarding the mechanism(s) of the action of maleated coupling agents was approached via studying the crystallization kinetics in wood-fiber-filled polypropylene in the presence and the absence of a maleated polypropylene copolymer... 

Plueddemann has recently published a book on the subject of silane coupling agents. According to Plueddemann and references cited in his book, the mechanism of action of silane coupling agents involves not just interfacial reactivity, but also the formation of an interpenetrating polymer network between a polysiloxane surface layer and the overlying polymer. 

Probably the most efficient flame retardant system ever discovered for a polymer is platinum, which at 1 ppm flame retards silica-filled silicones and increases unbumed residue (Fig. 6). In a very thorough study by MacLaury at GE (37), platinum was shown to exert a catalytic action to induce coupling between chains and with the filler. The detailed mechanism is still uncertain nevertheless, the remarkable efficacy of platinum in this system supports the idea that very efficient f.r. agents may be designed by using catalysis principles. 

The available agents with antithyroid activity are the thioamides propylthiouracil, carbimazole and methimazole also known as thiamazole. Their thio-carbamide group is indispensable for antithyroid activity. The mechanism of action is complex. The most important action is the prevention of hormone synthesis by an inhibition of the thyroid peroxidase-catalyzed reactions involved in iodine organification. These agents also block the coupling of the iodoty-rosines. 

Incorporation of a benzylic halide into the structure of the alternate-substrate lactone (12-4) led to the bifunctional lactones (13-1, Table 2.13), and (13-2), which showed rapid and irreversible inactivation of a-chymotrypsin and PPE [178]. It was postulated that the intermediate acyl-enzyme formed from attack of Ser-195 on the lactone carbonyl dehydrohalogenated to form a reactive quinone methide that coupled with His-57. If this mechanism were followed, then lactone (13-2) would be an example of a mechanism-activated inhibitor. However, lactone (13-2) is sufficiently reactive as an alkylating agent to directly couple with imidazole while the lactone ring is intact. Because of this, it is not clear, from the published data, whether acylation of Ser-195 precedes alkylation, a prerequisite for this compound to be confirmed as a mechanism-activated inhibitor. Interestingly, the corresponding coumarin (13-3) was both less potent and only provided partial inactivation of a-chymotrypsin [179, 180]. It was shown that the lactone linkage in this coumarin was stable in the presence of a-chymotrypsin and that the modified enzyme retained its intact active-site. These facts led to the postulate that, like the action of phenacyl bromides or benzyl bromides on a-chymotrypsin, the partial inactivation by (13-3) involves alkylation of Met-192 [179]. 

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