Hydrophobic interaction between bulky molecules

the final configuration of, say, a biphenyl molecule is not much different from the configuration of two benzene molecules at contact distance (as in Fig. 8.16). Hence, the HI for the reaction 

we expect the function ((r ) to be a decreasing function of a [see Fig. (8.15)]. Therefore, as n increases, a increases and approaches unity (for n - oo), and (or ) will reach its lowest value. Translating this in terms of we conclude that will decrease with n, in accord with the 

A different way of gaining information on the HI at more realistic distances is provided by molecules such as neopentane (2,2-dimethylpro-pane). In Section 8.7, we gave the value of the HI for five methane molecules brought to the final configuration of neopentane. The reaction is 

Before turning to a different way of processing the same experimental data, it is worth noting that the validity of the replacement approximation discussed in Section 5 differs in this case from that in the case 

We now consider a novel way of extracting information on the HI from the same data. Consider the process of bringing four methane molecules from infinity to the final configuration of the four peripheral methyl groups in neopentane, as indicated schematically in Fig. 8.18. The reaction is 

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The hydrolyses of the neutral substrates by partially alkylated poly(4-vinyl-pyridine) (I) were studied (63, 64). The rate enhancement is attributed to the hydrophobic interaction between the substrate and the polymer. In this hydrolysis, the rate of the substrate decomposition and the rate of the catalysis hold almost constant. It was explained that the deacylation step in the hydrolysis is affected by the bulkiness of the alkyl group in the polymer in which the alkyl group interferes an attack of water molecule on the acylated intermediate. 

A n.m.r. spectroscopic study of 1 1 complexes between cycloamyloses and azo dyes having a naphthalene nucleus has been reported.Almost all carbons of the guest molecules showed low field shifts on inclusion, consistent with n.m.r. spectroscopic results. The shift may be due not to a simple steric polarization but to hydrophobic interaction with the host molecule, whose cavity uniformly affects the guest molecule as if it is dissolved in a hydrophobic solvent. The host molecule was shown to be deformed by the bulky naphthalene nucleus at the glycosidic linkage rather than at the small diameter side of the cavity. 

Elastin is a macromolecule synthesized as a 70,000 single peptide chain, termed tropoelastin and secreted into the extracellular matrix where it is rapidly crosslinked to form mature elastin. The carboxy-terminal end of elastin is highly conserved with the sequence Gly-Gly-Ala-Cys-Leu-Gly-Leu-Ala-Cys-Gly-Arg-Lys-Arg-Lys. The two Cys residues that form disulfide crosslinks are found in this region as well as a positively charged pocket of residues that is believed to be the site of interaction with microfibrillar protein residues. Hydrophobic alanine-rich sequences are known to form a helices in elastin these sequences are found near lysine residues that form crosslinks between two or more chains. Alanine residues not adjacent to lysine residues found near proline and other bulky hydrophobic amino acids inhibit a helix formation. Additional evidence exists for (3 structures and 3 turns within elastin thereby giving an overall model of the molecule that contains helical stiff segments connected by flexible segments. 

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