Several surfactant-like peptides undergo self-assembly to form nanotubes and nanovesicles having an average diameter of 30 -50 nm with a helical twist. The peptide monomer contains 7-8 residues and has a hydrophilic head composed of aspartic acid and a tail of hydrophobic amino acids such as alanine, valine, or leucine. The length of each peptide is Ϸ2 nm, similar to that of biological phospholipids. Dynamic light-scattering studies showed structures with very discrete sizes. The distribution becomes broader over time, indicating a very dynamic process of assembly and disassembly. Visualization with transmission electron microscopy of quickfreeze͞deep-etch sample preparation revealed a network of openended nanotubes and some vesicles, with the latter being able to ''fuse'' and ''bud'' out of the former. The structures showed some tail sequence preference. Many three-way junctions that may act as links between the nanotubes have been observed also. Studies of peptide surfactant molecules have significant implications in the design of nonlipid biological surfactants and the understanding of the complexity and dynamics of the self-assembly processes.amino acids ͉ charged and hydrophobic residues ͉ nonlipid surfactants ͉ simplicity to complexity ͉ prebiotic enclosures M olecular self-assembly recently has attracted considerable attention for its use in the design and fabrication of nanostructures leading to the development of advanced materials (1, 2). The self-assembly of biomolecular building blocks plays an increasingly important role in the discovery of new materials and scaffolds (3, 4), with a wide range of applications in nanotechnology and medical technologies such as regenerative medicine and drug delivery systems (5, 6). Recently, Hartgerink et al. (7) reported the design of a chimeric material consisting of a hydrophobic alkyl tail and a hydrophilic peptide containing phosphorylated serine with an RGD motif that facilitates directional alignment of mineralization of hydroxyapatite.We previously described a class of ionic self-complementary peptide that spontaneously self-assemble to form interwoven nanofibers in the presence of monovalent cations (8 -10). These nanofibers further form a hydrogel consisting of greater than 99.5% water. The constituent of the hydrogel scaffold is made of peptides with alternating hydrophilic and hydrophobic amino acids. Such a sequence has a tendency to form an unusually stable ␤-sheet structure in water (8 -10). When the peptides form a ␤-sheet, they exhibit two surfaces, a hydrophilic surface consisting of charged ionic side chains and a hydrophobic surface with hydrophobic side chains. As a result, the self-assembly of these peptides is facilitated by electrostatic interactions on one side and the hydrophobic interaction on the other, in addition to the conventional ␤-sheet hydrogen bond along the backbones. The self-assembling peptide scaffolds have been demonstrated to serve as substrate for tissuecell attachment, extensive neurite outgrowth, and formation of active n...

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The self-assembly of surfactant-like peptides containing 4−10 glycines as the component of the hydrophobic tails and aspartic acids as the hydrophilic heads is described. The peptide monomers form nanotubes and nanovesicles in water at neutral pH. These nanostructures become more polydisperse as the length of the glycine tails increases. These unique structures may serve not only as scaffolds for constructing diverse nanodevices but also as enclosures to encapsulate rudimentary enzymes for studying prebiotic molecular evolution.

A new type of surfactant peptide designed to mimic the properties of cationic lipid systems is described. These cationic surfactant peptides are approximately 2 nm in length with a cationic, hydrophilic head consisting of one to two residues of lysine or histidine followed by a hydrophobic tail of six alanine, valine, or leucine residues. In water, these surfactant peptides form ordered structures with dynamic behaviors. At pH below the pI values of the peptides, dynamic light scattering showed two distinct structural populations with average diameters of 50 nm (>95%) and 100-200 nm (<5%). Transmission electron microscopy visualization of quick-frozen samples revealed these populations to likely represent nanotubes and nanovesicles, respectively, showing great interplay between them. Above the pI, these structures are absent, having further self-assembled into large membranous sheets. These cationic surfactant peptides are distinct from other anionic surfactant peptides and have different applications, possibly being useful as carriers for encapsulation and delivery of a number of small water-insoluble molecules and large biological molecular systems, including negatively charged nucleic acids.