Compression/Expansion Hysteresis of Poly(l-glutamic acid) Monolayers Spread at the Air/Water Interface

Abstract

In order to study the conformational behavior of poly(L-glutamic acid) (PGA) at the air/water interface under the influence of compression and expansion forces, PGA was spread on an aqueous acidic subphase and studied by the Langmuir technique. Several distinct regions of the first compression surface pressure/ area (π/A) isotherm could be identified by the starting and inflection point of the isotherm and by the beginning and the center of the pseudoplateau. The interpretation of the characteristic shape of the π/A isotherms in the sense of a side-by-side and an interdigitated organization of helical rods is strongly supported by molecular modeling calculations. But the helical surface layer is sensitive to repeated expansion and compression. A well-defined and reaction-kinetic demonstrable change occurs. The reasons for this transformation are discussed. Solidified regions are forming in the layer. Finally, after several compression/ expansion cycles a more rigid monolayer results than that formed by helical rods exclusively. These monolayer ruptures on expansion and clods of PGA molecules were observed using Brewster angle microscopy and ellipsometry.

Mixed films of poly(n-hexyl isocyanate) and poly(vinyl acetate) at the air–water interface

“…With a decrease in the area the surface pressure increases and attains a plateau region, where PHIC chains form a bilayer [12,13], and beyond the plateau region the surface pressure monotonically increases. Similar shapes of the π-A isotherms were ob- served for several polypeptide monolayers in the α-helix state [2,[4][5][6][7][8]. At the areas where the surface pressure is almost zero, the surface pressure gain by hydrogen bonding between the isocyanate group and water is compensated for by the surface pressure loss by cohesive interaction among the hexyl groups.…”

“…Polypeptides are typical rigid-rod-like polymers spread at the air-water interface and their interfacial properties have been investigated in depth [2,[4][5][6][7][8]. Recently, we reported that a rigid-rod-like poly(n-hexyl isocyanate) (PHIC) [9,10] was formed as a stable polymer film spread at the air-water interface, as shown by surface pressure and fluorescence microscopy studies [11][12][13].…”

The complexation mode of metal ions with Langmuir monolayers of nitrogen-containing flavonoid glycoside-based surfactants derived from rutin

“…Although the hysteresis occurred was independent of the surface pressures according to Reda et al [26], however, it was strongly dependent on the cycling periodicity and the lipid chain length. Fig.…”

Langmuir-Blodgett films of cellulose ethers containing carbazole

“…(1). The temperature dependence of the surface tension of water [18] , (dc 0 /dT) was taken as -0.16 mN N m -1 K -1 .…”

“…Similar transitions have been observed in the compression isotherms of a number of cellulose derivatives [15,16] and other rigid polymers. [17][18][19] From Fig. 2, one can see that the plateau pressure increases slightly, from 11 to 13 mN N m -1 with the incorporation of carbazole groups, possibly as the result of a corresponding increase in monolayer rigidity.…”