On the Differences in Monolayer Properties of Poly-γ-benzyl-l-glutamate and Poly-β-benzyl-l-aspartate

Abstract

Abstract In view of the marked differences of PBLG and PBLA in crystals and in solutions, we have investigated their differences in monolayer states and further examined the monolayers of CP(BLG, BLA) and of the equimolar mixture of PBLG and PBLA. All these polymers were found to be of condensed type and their limiting areas to be about 22Å2. The surface compressibility at the region of rise of surface pressure was in the order: PBLA>CP(BLG, BLA)>PBLG. The surface moments of all these polymers were considerably higher than those of non-polar polypeptides. The surface moment of PBLA was 50 mD higher than that of PBLG, and that of CP(BLG, BLA) gave a value intermediate between them. PBLG and CP(BLG, BLA) exhibited high surface viscosities at a very low surface pressure region, but, in spite of the condensed nature of the monolayer, PBLA showed appreciable surface viscosity first at a high surface pressure region. The surface viscosities of PBLG and PBLA were higher at higher temperatures. From the data on surface pressure and surface moment, all these polymers were considered to have a configuration similar to the β-form in the spread state and possible configurations of side chains of PBLG and PBLA were deduced. It was found that the carbonyl group on the side chain of PBLG is far from the aqueous surface but that of PBLA is in contact with the surface and scarcely distinguishable from the carbonyl group on the main chain. Accordingly, PBLG can take a stable configuration like the β-form in monolayer, but the correspounding configuration of PBLA will be less stable owing to possible hydrogen bonding of the carbonyl group on the side chain with the imino group on the main chain and the resulting enhanced hydrophility of the side chain. This might be ascribed to the differences in surface compressibility and surface viscosity of PBLG and PBLA. The surface pressure behavior of the mixed monolayer of PBLG and PBLA was such as was expected, but its behavior in surface potential and viscosity was very anomalous.