Shielding, hydrophobic

The M to N and the N to O reactions both occur on the millisecond time scale, yet Asp-96 cannot be in communication with the cytoplasmic surface at the time its protonation equilibrium with the Schiff base is established. It is likely that this is ensured by the hydrophobic shield between Asp-96 and the aqueous interface that contains the side chains of Phe-42, Leu-100, Phe-171, and Leu-223. At the time Asp-96 is repro-tonated from the bulk in the N to O reaction, this shield must be made permeable, while the pathway between Asp-96 and the Schiff base is abolished. The crystal structure of the O-like state suggests how these two goals are accomplished (Fig. 6, see color insert Rouhani et al., 2001). 

A somewhat different aspect of the hydrophobic shielding effect of alkyl substituents was reflected in the relative hydrophilicity of aliphatic amine-cured resins. A standard room temperature-curing polyamine, triethylenetetramine (TETA), was used to cure a series of resins at room temperature. The... 

The hydrophobic shielding of the hydantoin ring by alkyl substituents affected all the solvent-solute interactions of cured resins. Two of the resins and the DMH-based resin mixture were cured with a commercially available aromatic amine mixture derived from aniline-formaldehyde condensation, identified in Table VII. Weight gain and solvent plasticization were followed in a number of solvents and aqueous media. Some of the exposure was at 60 C as well as at room temperature. 

Peroxo-diiron(III) complexes can undergo not only redox but also ligand substitution reactions. Liberation of H202 was observed in the reactions with phenols and carboxylic acids leading also to the respective phenolate or carboxylate iron(III) complexes.86 Hydrolysis of a peroxo-diiron(III) complex results in an oxo-diiron(III) species and hydrogen peroxide. Such reaction is responsible for the autoxidation of hemerythrin, but is very slow for the native protein due to hydrophobic shielding of the active site (Section 4.2.3).20 The hydrolysis of iron(III) peroxides is reversible, and the reverse reaction, the formation of peroxo intermediates from H202 and the (di)iron(III), is often referred to as peroxide shunt and is much better studied for model complexes. 

WF decompose, both materials emit oxide gases and radicals, which initiate the degradation of PLA to break down the chain. PLA blended with WF is more resistant to decomposition due to the complex lignin structure, which acts as a hydrophobic shield protecting the PLA chains from direct attack of the volatiles. This observation can be further justified by the work of Tao et al. (2009) who compared PLA blended with jute and ramie fibers they found that there was a lack of significant difference in thermal decomposition for both natural fibers (see Figure 3.13). 

Addition of aqueous HBr to hydrophobically shielded aiylallgmes HC=C-aiyl and HgC-C C-aiyl, cariying 2,6-di- and 2,4,6-tri-tert-butyl-phenyl as the aryl group has been studied by Knorr et The strongly retarded HBr addition to HsC-CsC-aryl in moist chloroform produced more E than Z product, whereas a thermodynamic E/Z ratio of 10 87 was found in moist acetic acid. The E/Z configurational assignments of the obtained products have been deduced from the /hc couplings of C-1 to... 

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