Akira Takizawa

Characterization of copolyaspartates containing a long alkyl side chain

Abstract Copoly(β-stearyl l -aspartate-β-benzyl l -aspartate) with various degrees of stearylation was synthesized and secondary and higher ordered structure in solid state was examined from the standpoint of composition and temperature of the copolyaspartates. Copolyaspartate with degree of stearylation 30% caused the reverse transformation, from right-handed α helix to left-handed α helix. The transition from α helix to β form was observed at higher temperature for all copolyaspartates studied. The transitions of helix sense and α helix to β form were irreversible. Copolyaspartate with degree of stearylation > 20% could furthermore cause an intramolecular side chain crystallization of a long alkyl chain. The side chain crystal of such a copolyaspartate melted but a helix backbone was still stable. The helix surrounded by a molten long side chain which plays a role as a solvent could be considered for construction of a thermotropic liquid crystalline phase. Copolyaspartate with a long alkyl side chain was compared with copolyglutamate and the difference of helix stability and side chain crystalline part was interpreted in terms of the competitive hydrogen bonding between NH groups in the backbone and CO groups in the side chain formed in the copolyaspartate.

Circular dichroism on copolyaspartates containing a long alkyl side chain

Abstract Copoly(β-stearyl l -aspartate-β-benzyl l -aspartate)s (copoly(SLAsp-BLAsp)s) with various compositions were synthesized by ester exchange reaction of parent poly(β-benzyl l -aspartate) (PBLAsp). Circular dichroism (c.d.) studies were performed in chloroform solutions and for solid films as a function of degree of stearylation and temperature. The left-handed α helix of copoly(SLAsp-BLAsp) transformed to right-handed with increasing degree of stearylation at room temperature. A temperature-induced reversal of α helix sense from right to left was observed in chloroform solution of copoly(SLAsp-BLAsp) of certain composition, e.g. degree of stearylation 41 and 63%. On the other hand, two kinds of conformational behaviour were observed in solid films with respect to composition. At low degree of stearylation (0–30%), and α–ω transition occurred, while at degree higher than 40%, the α helix sense reversed from right-handed to left-handed as the temperature increased. All the conformational behaviours observed in solid films were irreversible, but they were reversible in solution.

Ionic salt permeabilities and membrane potentials of glutamic acid-methyl-L-glutamate copolymer membranes

Abstract The ionic salt permeabilities and membrane potentials of charged polypeptide membranes of glutamic acid-methyl-L-glutamate co-polymers were studied as a function of glutamic acid content of the membranes. The basic membrane properties of the copolymer, such as fixed-charge concentration and water-containing capacity, could be controlled by adjusting the glutamic acid content of the membranes. The observed concentration dependences of ionic permeability and membrane potential in the external concentration range from 10−4 mol/liter to 10−1 mol/liters were interpreted on the basis of the Nernst-Planck flux equation and the Donnan distribution. In this interpretation, to obtain a satisfactory agreement between experimental results and theoretical predictions, it was necessary to introduce the standard chemical potential difference of the ion between the membrane and external solution phase, and the concentration dependence of the effective charge density of the membrane. Applying the free-volume theo...

Photocontrol of polypeptide membrane permeabilities by cis–trans isomerism in side chain azobenzene groups

The ion permeabilities of solid membranes of poly(L-glutamic acid) with azobenzene groups in the polymer side chains can be reversibly controlled by photo-irradiation.