Chaperone effect

Examples of the so-called chaperon effect involving interaction between the electrophile and an appropriate substituent at the a-position in an alkyl chain prior to ring substitution at the ortAo-position have been explored in nitrations involving dilute solutions of nitric acid in dichloromethane. Aldehydic or ketonic carbonyl groups are most effective, but carboxyl, alkoxycarboxyl, and amide groups also work well. l-Phenylpropan-2-one, for example, forms 85% of l-(2-nitrophenyl)propan-2-one (5). 

The overall activation energy was reported to be 18.7 0.8 kcal.mole that of the initiating reaction was calculated from the activation energies for reactions (28), (29) and (38) which had earlier been estimated very crudely by Bodenstein et This scheme satisfactorily accounts for all the facts except the chaperone effect reported by Rollefson and Byrns . That effect can be incorporated by including reactions (28 ), (29 ), (34) and (35). 

Finally, a group of mild phenylketonuric patients with autosomal recessive mutations in the gene encoding PAH but with normal BH4 metabohsm respond to treatment with oral BH4 as an alternative to a low-phenylalanine diet. " " Recent investigations on the mechanism of this BH4-responsive PKU revealed a multifactorial basis, including a chemical chaperon effect of BH4 that prevents degradation of mutant PAH proteins and protection from... 

Wiebe and Heicklen (1973) argued that the pressure dependence that they saw on 4> N20 in the photolysis of CH3ONO at 366 nm probably was due to decay of energetic CH3O produced in the primary process. However, a more likely explanation is that the pressure effect seen in their studies was due to the chaperone effect in the recombination of CH3O and NO. There is no evidence that hot CH3O radicals are formed with 366-nm photolysis. 

As for neat IPDI-BD(40)-P[3F-co-BrOx-l l-(4.7)], the observed atom% Br for 0.5 wt% IPDI-BD(40)-P[3F-co-BrOx-l l-(4.7)l is about half (2.2%) that calculated for the soft block alone (4.7%). While the surface concentration of Br shows the chaperone effect of fluorous side chains, near-surface partitioning of the —CH2Br groups is proposed to explain the low atom% Br compared to the soft-block-alone value. 

However, when the proteins fall on tiie 2D surface of the membrane, tiiis distance is significantly decreased. The effect is potentiated by tiie fact that the attachment of the amyloid protein on the membrane is not stochastic. Indeed, a common feature of amyloid proteins is that they have a marked preference for glycosphingolipids (e.g., gangliosides) that are concentrated in relatively small microdomains of tiie plasma membrane (lipid rafts). Thus, landing on a lipid raft will result in an important concentration of the amyloid protein, and this effect is potentiated by the reduction of dimensionality (Fig. 8.5). Moreover, the head groups of glycolipid clusters will exert a chaperone effect that forces the amyloid protein to adopt a secondary structure, which, depending on the protein-lipid stoichiome, can be either an a-helix or a (3-rich stmcture. ... 

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