Autoinhibition effect

The autoinhibiting effect which was apparent in the later stages, particularly for thicker films, was attributed to the formation of charge transfer complexes between HC1 and polyenes. These complexes were assumed to be photochemically inert as far as further dehydrochlorination of the polymer was concerned but may be involved in the reverse process of re-addition of HC1 to the polyenes. The balance between the two effects depends on the ease of diffusion of HC1 out of the film. 

Increasing reaction temperature results in a smaller fraction of amine to become associated with the hydroxyl groups and, hence, in an increase in conversion at which the process becomes inhibited291. The reaction at adiabatic conditions gives a 100% conversion of the epoxide groups without any autoinhibition effect involved291. 

Autoinhibiting effects of the SCOC oxidation products resulted in characteristic shapes... 

Short electrolysis times in pulse voltammetric techniques limit autoinhibiting effects of SCOC oxidation products. 

At present, it is difficult to provide an unambiguous interpretation of this phenomenon. One of the most plausible explanations may be that, in the course of the reaction, at least in the transition state, the area occupied by the molecule increases or its reorientation is considerable. All this requires a certain free area near the reacting particle therefore, the high degree of coverage produces an autoinhibiting effect on the reaction. 

Many of the neuroleptics are a-adrenoceptor antagonists. Some, like chlorpromazine, block d postsynaptic receptors while clozapine (and risperidone) are as potent at 2 as D2 receptors. There is no evidence that either of these actions could influence striatal or mesolimbic function but NA is considered important for function of the prefrontal cortex and any increase in its release, achieved by blocking a2-mediated autoinhibition, might contribute to a reduction in negative symptoms and provide a further plus for clozapine (see Nutt et al. 1997). Centrally, however, most a2-receptors are found postsynaptically and their function, and the effect of blocking them, is uncertain. 

Kinetic studies of the acetylation of several arylethers were carried out over HBEA zeolites. The main conclusion is that the rate and stability of the reactions are determined by the competition between reactant(s) and product(s) molecules for adsorption within the zeolite micropores. This competition shows that the autoinhibition of arene acetylation, that is, the inhibition by the acetylated products, and also by the very polar acetic acid product is generally observed. This effect is much more pronounced with hydrophobic substrates such as methyl and fluoro aromatics than with hydrophilic substrates because of the larger difference in polarities between substrate and product molecules. 

An especially interesting case of inhibition is the internal or autoinhibition of allylic monomers (CH2=CH—CH2Y). Allylic monomers such as allyl acetate polymerize at abnormally low rates with the unexpected dependence of the rate on the first power of the initiator concentration. Further, the degree of polymerization, which is independent of the polymerization rate, is very low—only 14 for allyl acetate. These effects are the consequence of degradative chain transfer (case 4 in Table 3-3). The propagating radical in such a polymerization is very reactive, while the allylic C—H (the C—H bond alpha to the double bond) in the monomer is quite weak—resulting in facile chain transfer to monomer... 

Additionally, it has been hypothesized that the anxiolytic effects of NKi receptor antagonists are a result of a reduced autoinhibition of the LC. 

The idea of the decisive role of complexing reactions makes possible to unterstand such peculiarities of epoxy compound reactions with primary and secondary amines as a rather unusual, from the kinetic point of view, simultaneous occurrence of the autoacceleration and autoinhibition reactions, catalytic and inhibitive effects of various solvents, and obvious ortho-effect of a number of substituents in aromatic amines, the influence of tertiary amines as additives and some other 5,6,13.14.30,... 

Thus the above data point to the fact that in such systems the reaction mechanism of the epoxy compounds with amines involves not only autocatalysis, but also autoinhibition of the reaction in its deep stages. However, this effect can only be observed if the relative concentration of the free hydroxyl groups decreases due to an increase in hydroxyl-amine complexing as a result of the conversion of the primary into the secondary and then to the tertiary amino group. For the real epoxy-amine compositions, the diffusion mechanism of the reaction inhibition at the deep stages is still the most typical. 

This equation was used to calculate the reaction rates as a function of temperature and rongalite/Ni(II) concentration ratio, and Table 11.6 shows the results for a ratio of 1.5/0.5. The data in this table confirm the previous conclusion that a temperature of about 333 K should be used in order to have an economical and technologically acceptable reaction rate for the reduction of Ni(II) by rongalite and to avoid the large influence of autoinhibition by formaldehyde, an unfavourable effect that increases with temperature. 

In the peripheral (Wessler 1989) as well as central (Wonnacott 1997) nervous system, presynaptic nicotinic autoreceptors were reported to control the release of acetylcholine. In both locations, the consequence of presynaptic nAChR activation most commonly is an increase in both spontaneous and evoked acetylcholine release (MacDermott et al. 1999), whereas presynaptic muscarinic receptors mediate the opposite effect, an autoinhibition. Recent studies have focused on the composition of presynaptic nAChRs (Table 2). In the hippocampus, nicotinic autoreceptors were suggested to be a3/p4 receptors (Tani et al. 1998), but a role of p2 subunits has also been implicated (Lloyd et al. 1998). Likewise, in the neocortex, presynaptic nicotinic autoreceptors are likely to be 04/ p2 receptors (Marchi et al. 2002). In contrast, in the interpeduncular nucleus the autoreceptors were suggested to mainly contain a3 and p4 subunits (Grady et al. 2001). 

Mode of Action DCA induces tumor by nongeno-toxic mechanisms. Most data now suggest that it is the parent compound that is responsible for the effects related to carcinogenicity by interfering with the cellular signaling mechanisms. This, in addition to autoinhibition of its metabolism, suggests that the actual mechanism is by tumor promotion rather than by cytotoxicity and reparative hyperplasia. 

Some selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine, fluvoxamine, and paroxetine, are potent inhibitors of CYP2D6 activity. Therefore, multiple dosing causes autoinhibition of CYP2D6 and conversion from extensive to slow metabolizer phenotype and from ultrafast to extensive metabolism [16,17]. In the case of fluvoxamine, diflerences in areas under the curve (AUCs) were described after single doses [18,19], whereas multiple doses result in similar AUCs in PMs and EMs, indicating a strong inhibitory effect on CYP2D6 in EMs [20]. 

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