The controlled self-assembly of complex molecules into well defined hierarchical structures is a promising route for fabricating nanostructures. These nanoscale structures can be realized by naturally occurring proteins such as tobacco mosaic virus, capsid proteins, tubulin, actin, etc. Here, we report a simple alternative method based on self-assembling nanotubes formed by a synthetic therapeutic octapeptide, Lanreotide in water. We used a multidisciplinary approach involving optical and electron microscopies, vibrational spectroscopies, and small and wide angle x-ray scattering to elucidate the hierarchy of structures exhibited by this system. The results revealed the hexagonal packing of nanotubes, and high degree of monodispersity in the tube diameter (244 Å) and wall thickness (Ϸ18 Å). Moreover, the diameter is tunable by suitable modifications in the molecular structure. The self-assembly of the nanotubes occurs through the association of ␤-sheets driven by amphiphilicity and a systematic aromatic͞aliphatic side chain segregation. This original and simple system is a unique example for the study of complex self-assembling processes generated by de novo molecules or amyloid peptides. T he ability of simple molecules to spontaneously organize into well defined nanostructures is of fundamental importance and has wide ranging applications in biotechnology and materials sciences (1). In fact, characteristic lengths Ͻ100 nm are not easily accessible at present by lithographic techniques, but can be realized with biological self-assemblies such as tobacco mosaic virus, capsid proteins (2), tubulin (3), or actin (4, 5). These proteins under appropriate conditions possess the unique capability to form long filaments with a well defined diameter. However, the fabrication cost often restricts their potential interest in practical applications. Therefore, a simple alternative route has been emerged based on de novo molecules that self-organize in a programmed way (6-11). The design of such biomimetic systems requires the understanding of the relationship between the molecular structure and the self-assembly process of the nanostructures. This inspiration from natural fibers is difficult to implement when the building blocks themselves are complex, as in the case of proteins. Up to now, no simple synthetic molecule was able to self-assemble into hollow nanotubes with well defined characteristic length in the range of 20-30 nm.Lanreotide is an octapeptide synthesized as a growth hormone inhibitor. Lanreotide forms hydrogels (Autogel), which are already used in acromegaly treatment as s.c. long-acting implants (12). Here we report the molecular and supramolecular organization of self-assembling nanotubes formed by Lanreotide in water (10% wt͞wt, acetate salt). We chose a multidisciplinary approach, by combining polarized light microscopy, electron microscopy, vibrational spectroscopies, small and wide angle x-ray scattering (SAXS and WAXS, respectively) to elucidate the hierarchical structures formed by this system. The ...

Diatoms, shells, bones and teeth are exquisite examples of well-defined structures, arranged from nanometre to macroscopic length scale, produced by natural biomineralization using organic templates to control the growth of the inorganic phase. Although strategies mimicking Nature have partially succeeded in synthesizing human-designed bio-inorganic composite materials, our limited understanding of fundamental mechanisms has so far kept the level of hierarchical complexity found in biological organisms out of the chemists' reach. In this letter, we report on the synthesis of unprecedented double-walled silica nanotubes with monodisperse diameters that self-organize into highly ordered centimetre-sized fibres. A unique synergistic growth mechanism is elucidated by the combination of light and electron microscopy, synchrotron X-ray diffuse scattering and Raman spectroscopy. Following this growth mechanism, macroscopic bundles of nanotubules result from the kinetic cross-coupling of two molecular processes: a dynamical supramolecular self-assembly and a stabilizing silica mineralization. The feedback actions between the template growth and the inorganic deposition are driven by a mutual electrostatic neutralization. This 'dynamical template' concept can be further generalized as a rational preparation scheme for materials with well-defined multiscale architectures and also as a fundamental mechanism for growth processes in biological systems.

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