The solid-state conformation of copolymers of oxidized L-methionine [~-Met(O)l with L-methionine (L-Met) and/or L-alanine (L-Ala) was studied by IR spectroscopy and circular dichroism (CD). The results from the IR spectra in the region of 900-330 cm-' are compared with data obtained by CD experiments. A film cast from the solution of a copolymer containing L-Met(0) had a new trough between 205 and 210 nm in the solid-state CD spectra and new IR absorption bands at 815 and 680 cm-', while oxidizing the film of an L-Met containing copolymer after casting did not induce a significant change in IR and CD spectra. It seems that the film cast from the solution of an L-Met(0) containing copolymer exhibits the feature of a random coil as well as of an a-helix. From the CD spectra of the film on immersion in water, it was deduced that the helix of the film became gradually disordered and hence the film was dissolved in water.

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SUMMARY: A new poly(carboxybetaine) whose main chain is composed of peptide bonds was synthesized from poly(c-methyl L-glutamate). The side chains of poly(c-methyl L-glutamate) were exchanged to carboxybetaine structures by three reactions. Our new poly(carboxybetaine) has 84% carboxybetaine structures in the side chains, as determined by 1 H NMR measurements. The presence of betaine structures in the side chains was confirmed by viscosity measurements.

We prepared a photoresponsive polypeptide, M n = 10 630, composed of two amphiphilic α-helical copolypeptides, poly[(γ-methyl l-glutamate)-co-(l-glutamic acid)], joined by an azobenzene (am.-MAzoM) as a molecular photoreceptor. Dipalmitoylphosphatidylcholine monolayers containing the am.-MAzoM were formed at the air−water interface. We investigated photoinduced changes in the structure of the polypeptide−lipid monolayer systems. The α-helical rod of am.-MAzoM was laid at the air−water interface when the monolayer was in a liquid state. While in the solid condensed monolayer, the polypeptide molecules arranged perpendicular to the membrane (the air−water interface) and formed a bundle by self-association. The bundle of am.-MAzoM could be observed as an intramembranous particle ca. 4 nm in diameter with atomic force microscopy. UV light irradiation induced the destabilization of the bundle structure in the monolayer. This behavior arose from the photoinduced denaturation of the amphiphilic character of the polypeptide owing to a bending of the polypeptide in the main chain by a cis−trans photoisomerization of the azobenzene moiety. After removal of the light, the am.-MAzoM in the solid condensed monolayer returned to the original bundle structure.

Poly(γ-methyl l-glutamate-co-l-glutamic acid) containing a β-cyclodextrin at the terminal (MG/GA-CyD) was prepared and the relationship investigated between the conformation of the polypeptide and inclusion capability of the β-cyclodextrin by circular dichroism and fluorescence spectroscopy in aqueous solution containing 8-anilino-1-naphthalenesulfonate (ANS) as a guest molecule. The terminal β-cyclodextrin of MG/GA-CyD could not include ANS at higher pH, where the polypeptide almost formed a random coil. This was attributed to the terminal β-cyclodextrin being concealed in the random coil of the polypeptide. At low pH, however, random coil-to-α-helix transition of the polypeptide exposed the terminal β-cyclodextrin to the aqueous phase resulting in the ANS-inclusion capability. These results imply that control of the polypeptide conformation leads to conformational switched guest binding of the terminal cyclodextrin.