Hydrolytic conformational effects

These effects result from the impact of fluorination on the properties of the peptide at the level of (1) the lipophilicity/hydrophobicity balance and p faJ (2) the conformation, because of the more demanding volume of the fluorinated moiety and (3) the hydrolytic and metabolic stability. 

Micromolar to 10-4 M levels affect hydrolytic and synthetic activities in an activity-discriminating, pH- and concentration-dependent manner Millimolar—10-2 M levels also exert activity-discriminating effects The former activates all activities, the latter are necessaiy for enzymic activity and appear to maintain enzyme in a stable, active conformational state... 

The correlation between primary (n-v interactions) and secondary (n-o ) electronic effects in the cleavage of tetrahedral intermediates has now been explained in detail. Before attempting the rationalization of experiments which could potentially support the importance of the stereoelectronic principle in hydrolytic reactions, the energy barrier for the breakdown of a tetrahedral intermediate relative to that for conformational change must be considered. This is essential in cases where the tetrahedral inter-... 

Influence of Physical Structure. The hydrolytic behavior of cellulose is much influenced by its physical structure and lateral order [121-132]. Wood cellulose was hydrolyzed twice as fast as cotton [125]. Hydrolysis rate was significantly increased by physical or chemical pretreatment, with the effect depending on the source of cellulose. Hill and coworkers [127,128] reported that mercerization increased the hydrolysis rate of cotton (by 40%) and of ramie (7%), whereas the opposite effect was observed for linen and a-cellulose samples showing an approximately 30% reduction. Based on kinetic analysis, they concluded that the end-attach model proposed by Sharpies [121] can only be applied to the cellulose II structure and not to the cellulose I crystallite. Thus, the conformation of cellulose is also a significant factor affecting its reactivity and possibly the hydrolytic mechanism as well. 

When using (rac)-vinylcyclohexane epoxide as a standard substrate (Scheme 4.24), the dendrimer catalysts exhibited significantly higher catalytic activities in the hydrolytic kinetic resolution of terminal epoxides as compared to the monomer or the dimer catalysts. Among the dendrimer catalysts, the first-generation dendrimer catalyst gave the best results and the efficiency of the catalyst on a per-metal basis was in the following order 4-Co(salen)-PAMAM > 8-Co(salen)-PAMAM > 16-Co(salen)-PAMAM. This dendrimer effect was considered to arise from the restricted conformation imposed by the dendrimer structure, which enhanced the... 

The reason for this pattern is not yet clear. As seen in the data presented in Table III, there is no strong correlation between the final cure temperature and the degree of hydrolysis after long-term exposure. Similarly, films of different thicknesses do not show significant differences in the amount of imide eventually hydrolyzed, suggesting that hydrolytic susceptibility is not related to surface effects. One possibility still under consideration is that different conformations of the benzophenone moieties result in different hydrolytic susceptibilities. 

The ac" C nucleoside is found at the wobble position of methionine tRNA from E. coli as well as glutamine, glutamate, lysine, proline, and serine tRNAs in archaea. Kawai et al showed that ac" C strongly favors the 3 -endo conformation, and that this conformational preference is reinforced by simultaneous 2 -OMe to form the ac Cm nucleoside found in tRNAs from hyperthermophilic archaea. The presence of N-acetylated cytidine in organisms growing above 100 °C is somewhat remarkable given the hydrolytic lability of this functionality. In light of the dramatic effects that ac" and f modifications have on the cytidine conformational preference, these modifications could have applications for RNA duplex stabilization similar to that shown recently for s U. ... 

Micrococcal nuclease is an extracellular enzyme of Staphylococcus aureus that hydrolyzes specific phosphodiester bonds of both RNA and DNA. The protein is a convenient model for studies of conformational stability, effects of ligand binding, chemical modification, hydrolytic mechanism, and X-ray crystallographic analyses. ... 

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