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 ...

The polymorphism and phase transitions of cocoa butter (CB) have been reexamined separately by differential scanning calorimetry (DSC) and X‐ray diffraction as a function of temperature (XRDT) at scanning rates between 0.1 to 5°C/min and 0.1 to 2°C/min, respectively. A new instrument, which allowed simultaneous DSC and XRDT recordings from the same sample by taking advantage of the high‐energy flux of a synchrotron, was employed for characterization of the intermediate phase transitions. These techniques allowed us to confirm the existence of the six polymorphic forms of CB (called I to VI) by in situ characterization of their formation in the DSC + XRDT sample holder. A detailed study of Form I structure led us to propose a liquid‐crystal organization in which some of the chains displayed sharp long‐spacing lines (d001=52.6±0.5 Å) and a β′ organization (4.19 and 3.77 Å), while the others remained unordered with broad scattering (maxima at about 112 and 36.5 Å). The organization of this liquid crystalline phase is compared to that of fat and oil liquids. This liquid crystalline phase progressively transformed on heating into a more stable phase (Form II, α type, d001=48.5±0.5 Å and short‐spacing at 4.22 Å). Form III was only observed in a sharp temperature domain through its specific short‐spacings. The existence of the six species has been essentially related to the crystallization of monounsaturated triacylglycerols (TAG), while trisaturated species were found partly solid‐soluble in these six polymorphic forms. An insoluble fraction crystallized independently of the polymorphism of the monounsaturated TAG in a separate phase with long‐spacings that were either of the α (49.6±0.5 Å) or β (44.2±0.5 Å) form. In mixture with Form V, this fraction melts and solubilizes in the liquid phase at 37.5°C. Isolation of these high‐melting crystals shows a melting point of about 50°C. High‐performance liquid chromatography analysis of this fraction confirmed an increase from 3.0 to 11.3% of saturated TAG and their association with part of the 1,3‐stearoyl‐2‐oleoylglycerol preferentially to 1‐palmitoyl‐2‐oleoyl‐3‐stearoylglycerol and (1,3‐palmitoyl‐2‐oleoylglycerol).