Apparent effect site

Halogenated Butyl Rubber. Halogenation at the isoprene site ia butyl mbber proceeds by a halonium ion mechanism leading to a double-bond shift and formation of an exomethylene alkyl haUde. Both chlorinated and brominated mbber show the predominate stmcture (1) (>80%), by nmr, as described eadier (33,34). Halogenation of the unsaturation has no apparent effect on the isobutylene backbone chains. Cross-linked samples do not crystallize on extension due to the chain irregularities introduced by the halogenated isoprene units. 

Data from the reconnaissance survey indicated that bulk sediment concentrations of all COPCs were greater than apparent effect levels (AELs Environment Canada, 1995), indicating that contamination was widespread. A 20% reduction in toxicity test endpoint performance (relative to the negative control) was used to evaluate toxicity data. Such a reduction typically indicates real differences from the control. All samples demonstrated greater than a 20% reduction in bivalve normal development, however, similar reductions in amphipod survival were not observed, with the exception of one marginal hit for a single sample. As a result of the bivalve toxicity and elevated COPC concentrations observed in the reconnaissance survey, a full SQT was considered necessary for the site. 

Unit cancer risk (UCR) is defined as the sum of the slopes of lines drawn from the lowest apparent effective dose of the chemical throngh zero for each tnmor site... 

Moreover, adding small amounts of water to the solvent had no apparent effect on the spin label s mobility, as evidenced by the spectra in Figure 2. EPR spectra recorded in butyl acetate with and without 1% water revealed that the active site conformation was unchanged by water addition even though the enzyme s activity was much higher when 1% water was present. Thus, the increase in activity upon water addition cannot be attributed to a loosening up of the active-site conformation. This result differs from a proposed model of the sequential hydration of dry lysozyme (19), in which restoration of enzyme activity followed a hydration-induced flexibility increase. 

Conjugate addition of the y-butyrolactam to enals was promoted by diphenyl-prolinol trimethylsilyl ether 12 via the iminium activation process (Scheme 32, second hne) [53]. A satisfactory level of enantioselectivity was generally observed irrespective of the solvent polarity, although the use of aqueous acetonitrile was superior for optimizing the chemical yield and enantioselectivity. In addition, acidic additives had apparent effects on the reaction profile and the highest diastereoselectivity was attained with 2-fluorobenzoic acid. The synthetic utility of this site- and stereoselective transformation was demonstrated in a series of product derivatizations, including the three-step synthesis of a cAMP-specific phosphodiesterase (PDE IV) inhibitor (Scheme 32, third hne). 

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