Initiation-promotion system

Figure 1. A generalized schematic of the two-step initiation-promotion system of...

Materials and additives that are chemically basic in nature have a detrimental effect on the curing of cationic-initiated epoxy systems. These substances can either stop the curing mechanism completely or produce under-cured polymers. Therefore such additives as amines or imides that are known to be adhesion promoters cannot be used in the EB-curable epoxy adhesive formulations. 

In the newborn mouse system (Table II), the (+) anti dihydrodiol epoxide is clearly more effective than benzo[ajpyrene but this is not the case in initiation-promotion studies or in complete carcinogenesis studies on mouse skin. Nevertheless, there is always... 

The route to carbene initiation for systems catalyzed solely by transition metal salts (55, 54), or their combinations with Lewis acids such as A1C13 (55), is not well established. Nevertheless, some evidence suggests reduction of the metal by the olefinic substrate (55). Zero-valent (56) and hexavalent (57, 55) tungsten complexes that promote metathesis when activated by UV radiation are the least-understood metathesis systems. 

Lindane, a widespread insecticide constituted of technical mixtures of hexa-chlorocyclohexane (HCH), was dechlorinated using Pd/C, Pt/C, or Raney-Ni. The product using the multiphasic system was benzene, obtained within 1 hour. The base initially promoted HCl ehmination from HCH to yield trichlorobenzene, which then underwent the usual hydrodechlorination reaction. 

TABLE 27.11 Critical review of in vivo initiation-promotion model systems for identification and characterization of atypical tumor promoters and tumor progression... 

CuCb/Sitech/Zn the reaction rate reaches stationarity at a high level immediately after the short induction period. Hence, it would be wrong to state that the non-promoted system was of low reactivity. Rather, it seems that its reactivity was temporarily even higher than of the zinc-promoted system in the very beginning. (The frequency of GC analysis might have been to low in order to catch the real maximum of reactivity.) But, there must have been a mechanism responsible for the detrimental loss of activity observed and, possibly, there is even a connection between the high initial activity and the following activity decline. 

In an initiation-promotion skin bioassay conducted at New York University Medical Center (12), 69.0 mg of DBCP was applied to the skin of female mice, followedTy repeated application of phorbol myri state acetate three times weekly for 499 days. The most significant finding from this study was the occurrence of lung papillomas and squamous cell carcinomas of the forestomach indicating that the occurrence of stomach tumors in the oral studies may be systemic and not merely related to an irritant effect at the site of application. 

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