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Proton magnetic resonance studies on conformation and association of oligo-γ-benzyl-L-glutamates in solution

✍ Scribed by Toyoko Imae; Shoichi Ikeda; Yuji Kobayashi; Yoshimasa Kyogoku

Publisher
Wiley (John Wiley & Sons)
Year
1985
Tongue
English
Weight
970 KB
Volume
24
Category
Article
ISSN
0006-3525

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✦ Synopsis

The proton magnetic resonance spectra of enitrophenylthio-tetra-and hexa-y-benzyl-L-glutamate ethylamides have been measured at different concentrations in CDC1, and CD,,Cl. The N H and a-CH resonances of the tetrapeptide show downfield shifts with increasing concentration, accompanying disappearance of their fine structure and line broadening. The apparent feature of chemical shifts against concentration is sigmoidal, and it can be interpreted by assuming the presence of a step or more of associationdissociation equilibria of tetrapeptide. With increasing concentration, small aggregates are formed by intermolecular hydrogen bonding, the size of which is not sufficiently large to exhibit critical micelle concentrations. In contrast to the tetrapeptide, the hexapeptide has constant chemical shifts of the NH and a-CH resonances, independent of concentration, which implies that only the unassociated molecules show observable sharp resonances. In the hexapeptide, the phenyl CH and benzyl CH2 groups of the side chains exhibit new resonances above certain critical concentrations, indicating the restriction of rotational freedom of the side chains in the aggregated states.

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