The collapse of monolayers of 2-hydroxytetracosanoic acid at the air/water interface has been examined by measurements of surface pressure-area isotherms and imaging with light scattering microscopy. Topographic images of films transferred to mica by the Langmuir-Blodgett technique have also been obtained. At low pressures, the films undergo "slow collapse" by the formation of multilayer islands. Folding occurs at highpressure plateaus. At low compression rates, "giant folds" into the subphase arise at defects. They are composed of bilayers that remain suspended beneath the film and open reversibly during expansion. At higher rates of compression, the dominant collapse mechanism is by the formation of small-amplitude "multiple folds" that extend across the trough and are perpendicular to the compression direction.

A surface with photocontrollable wetting behavior is introduced. A monolayer of a polymeric material containing 4‘-[trifluormethoxy-4,4‘-dibenzoazo] dyes in the side chains has been transferred on quartz slides and silicon wafer. The azobenzene chromophore possesses two distinct isomers, cis and trans. Transition between these states can be triggered by illumination with light of two different wavelengths. It will be demonstrated that with the use of light and a mask, fine cis−trans patterns on the order of micrometers can be written in the monolayer. The corresponding interface exhibits different wetting behavior. This is visualized by a surface decoration with water droplets. The formation of water microdroplets on the patterned monolayer can be controlled by light. Writing and erasing of patterns is completely reversible. The system has potential for studying wetting behavior on microstructured surfaces.

Molecular systems composed of peptides or proteins can be programmed to yield intriguing and potentially useful supramolecular architectures. 1 The surfaces of solid or liquid substrates may induce conformational, orientational, and positional order in molecular assemblies, 2 and peptides composed of alternating hydrophilic and hydrophobic amino acids have been shown by spectroscopic and scanning probe techniques to form β-sheet assemblies at interfaces. 3 Recently, two-dimensional (2D) order in β-sheet monolayers has been demonstrated by grazing incidence X-ray diffraction (GIXD). 4 Long-range order has also been inferred from the preferred orientation of nanocrystals nucleated under β-sheet monolayers at the air-water solution interface. 5 Langmuir films of β-sheet peptides differ from many ordered molecular assemblies 2,6 in that peptide side chains can be engineered to provide scaffolds for further organization of the interface. Here we aimed at generating an ordered 2D molecular assembly composed of triplestranded amphiphilic peptides arrayed at the air-water interface.Progress in the design of β-sheet peptides has been based in part on the screening of known protein structures for correlation between sequence and secondary structure. 7 Studies of water-soluble peptides that incorporate β-hairpins (loop regions flanked by two strands interlinked via hydrogen bonds) derived from natural proteins have also contributed to our understanding of the folding and stability of β-sheet peptides. 8 Among the most abundant β-hairpins in natural proteins are the two-residue loops, 9 β-turns of types I′ and II′, which appear to impose a twist on adjacent peptide strands. In small de novo designed peptides it was shown that the nonnatural amino acid D-Pro at position i + 1 is effective in driving the formation of β-hairpins in aqueous solution. 10,11 L-Pro was found to be almost absent from two-residue β-hairpins of crystalline proteins; 9b however, in types I and II β-turns L-Pro is the most abundant residue 7b at position i +1. The propensities of L-Pro and D-Pro to promote types I and I′ β-turns, respectively, may be rationalized by the match between the dihedral angles φ i+1 of the turn and the restrained φ angles of L-Pro and D-Pro (∼-60°and ∼+60°, respectively).The 30-residue peptide BS30 was designed to fold into the triplestranded β-sheet depicted schematically in Figure 1. The proposed architecture depends on formation of two reverse turns, and on registry of the hydrophilic and hydrophobic amino acids along the three strands of the sheet. The main axes of the three amphiphilic strands were anticipated to extend parallel to the plane of the interface in an arrangement that is unlikely to occur in globular proteins, where neighboring strands are twisted relative to one another. 13 Accordingly, a type II β-turn (which is nearly planar), 9b