Franck Artzner

Biomimetic organization: Octapeptide self-assembly into nanotubes of viral capsid-like dimension

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 (≈18 Å). Moreover, the diameter is tunable by suitable modifications in the molecular structure. The self-assembly of the nanotubes occurs through the association of β-sheets driven by amphiphilicity and a systematic aromatic/aliphatic 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.

Clustomesogens: Liquid Crystal Materials Containing Transition-Metal Clusters**

their integration in macro-scopic devices by a bottom-up approach remains a challenge.This task requires systems with self-organization abilities onthe one hand and fluidity on the other hand, to correctautomatically the positioning errors that can occur during theassembly process. Metal-containing liquid crystals (metal-lomesogens) are the typical examples in which the uniquepropertiesofanisotropic fluidsarecombined withthe specificproperties of metals (e.g. geometry of coordination, optic,electronic, magnetic).

Molecular Structure of Self-Assembled Chiral Nanoribbons and Nanotubules Revealed in the Hydrated State

A detailed molecular organization of racemic 16-2-16 tartrate self-assembled multi-bilayer ribbons in the hydrated state is proposed where 16-2-16 amphiphiles, tartrate ions, and water molecules are all accurately positioned by comparing experimental X-ray powder diffraction and diffraction patterns derived from modeling studies. X-ray diffuse scattering studies show that molecular organization is not fundamentally altered when comparing the flat ribbons of the racemate to chirally twisted or helical ribbons of the pure tartrate enantiomer. Essential features of the three-dimensional molecular organizations of these structures include interdigitation of alkyl chains within each bilayer and well-defined networks of ionic and hydrogen bonds between cations, anions, and water molecules between bilayers. The detailed study of diffraction patterns also indicated that the gemini headgroups are oriented parallel to the long edge of the ribbons. The structure thus possesses a high cohesion and good crystallinity, and for the first time, we could relate the packing of the chiral molecules to the expression of the chirality at a mesoscopic scale. The organization of the ribbons at the molecular level sheds light on a number of their macroscopic features. Among these are the reason why enantiomerically pure 16-2-16 tartrate forms ribbons that consist of exactly two bilayers, and a plausible mechanism by which a chirally twisted or helical shape may emerge from the packing of chiral tartrate ions. Importantly, the distinction between commonly observed helical and twisted morphologies could be related to a subtle symmetry breaking. These results demonstrate that accurately solving the molecular structure of self-assembled soft materials--a process rarely achieved--is within reach, that it is a valid approach to correlate molecular parameters to macroscopic properties, and thus that it offers opportunities to modulate properties through molecular design.

Peptide nanotubes: molecular organisations, self-assembly mechanisms and applications

Peptide nanotubes are promising bio-inspired self-assemblies with a wide range of envisioned applications. The present review addresses the recent advances in their fundamental comprehension and mechanistic aspects of their latest downstream uses. Through well-documented examples, including the Lanreotide peptide monodisperse nanotubes, the molecular organisations and interactions underlying such well-defined hierarchical nanoarchitectures are in particular examined. The kinetic and thermodynamic aspects of the corresponding self-assembly processes are also considered, especially the intriguing mechanism of nanotube wall closure. The recently unravelled Lanreotide self-assembly mechanisms have revealed, for instance, the limiting role of electrostatic repulsion in this critical step. Within the numerous applications currently explored, particular attention is given to promising inorganic deposition processes using peptide nanotubes as scaffolds. In exceptional cases, inorganic nanotubes with tunable diameters could be synthesised viapeptide-based template-directed synthesis combined with peptide chemical design. Such examples highlight the importance of advanced molecular and mechanistic understanding of peptide nanotubes, particularly for bottom-up chemical design strategies and downstream applications. Although incomplete, the current fundamental comprehension of peptide nanotubes has already shown its potential by opening up new valuable routes in the field of biomimetic soft matter.

Three-Dimensional Self-Assembling of Gold Nanorods with Controlled Macroscopic Shape and Local Smectic B Order

We describe a method of controlled evaporation on a textured substrate for self-assembling and shaping gold-nanorod-based materials. Tridimensional wall features are formed over areas as large as several square millimeters. Furthermore, analyses by small-angle X-ray scattering and scanning electron microscopy techniques demonstrate that colloids are locally ordered as a smectic B phase. Such crystallization is in fact possible because we could finely adjust the nanoparticle charge, knowledge that additionally enables tuning the lattice parameters. In the future, the type of ordered self-assemblies of gold nanorods we have prepared could be used for amplifying optical signals.

Control of peptide nanotube diameter by chemical modifications of an aromatic residue involved in a single close contact

Supramolecular self-assembly is an attractive pathway for bottom-up synthesis of novel nanomaterials. In particular, this approach allows the spontaneous formation of structures of well-defined shapes and monodisperse characteristic sizes. Because nanotechnology mainly relies on size-dependent physical phenomena, the control of monodispersity is required, but the possibility of tuning the size is also essential. For self-assembling systems, shape, size, and monodispersity are mainly settled by the chemical structure of the building block. Attempts to change the size notably by chemical modification usually end up with the loss of self-assembly. Here, we generated a library of 17 peptides forming nanotubes of monodisperse diameter ranging from 10 to 36 nm. A structural model taking into account close contacts explains how a modification of a few Å of a single aromatic residue induces a fourfold increase in nanotube diameter. The application of such a strategy is demonstrated by the formation of silica nanotubes of various diameters.

Interaction between water-soluble peptidic CdSe/ZnS nanocrystals and membranes: formation of hybrid vesicles and condensed lamellar phases.

Due to their tunable optical properties and their well-defined nanometric size, core/shell nanocrystals (quantum dots, QDs) are extensively used for the design of biomarkers as well as for the preparation of nanostructured hybrid materials. It is thus of great interest to understand their interaction with soft lipidic membranes. Here we present the synthesis of water-soluble peptide CdSe/ZnS QDs and their interaction with the fluid lipidic membrane of vesicles. The use of short peptides results in the formation of small QDs presenting both high fluorescence quantum yield and high colloidal stability as well as a mean hydrodynamical diameter of 10 nm. Their interaction with oppositely charged vesicles of various surface charge and size results in the formation of hybrid giant or large unilamellar vesicles covered with a densely packed layer of QDs without any vesicle rupture, as demonstrated by fluorescence resonance energy transfer experiments, zetametry, and optical microscopy. The adhesion of nanocrystals onto the vesicle membrane appears to be sterically limited and induces the reversion of the surface charge of the vesicles. Therefore, their interaction with small unilamellar vesicles induces the formation of a well-defined lamellar hybrid condensed phase in which the QDs are densely packed in the plane of the layers, as shown by freeze-fracture electron microscopy and small-angle X-ray scattering. In this structure, strong undulations of the bilayer maximize the electrostatic interaction between the QDs and the bilayers, as previously observed in the case of DNA polyelectrolytes interacting with small vesicles.

Elucidation of the self-assembly pathway of lanreotide octapeptide into beta-sheet nanotubes: role of two stable intermediates.

Nanofabrication by molecular self-assembly involves the design of molecules and self-assembly strategies so that shape and chemical complementarities drive the units to organize spontaneously into the desired structures. The power of self-assembly makes it the ubiquitous strategy of living organized matter and provides a powerful tool to chemists. However, a challenging issue in the self-assembly of complex supramolecular structures is to understand how kinetically efficient pathways emerge from the multitude of possible transition states and routes. Unfortunately, very few systems provide an intelligible structure and formation mechanism on which new models can be developed. Here, we elucidate the molecular and supramolecular self-assembly mechanism of synthetic octapeptide into nanotubes in equilibrium conditions. Their complex hierarchical self-assembly has recently been described at the mesoscopic level, and we show now that this system uniquely exhibits three assembly stages and three intermediates: (i) a peptide dimer is evidenced by both analytical centrifugation and NMR translational diffusion experiments; (ii) an open ribbon and (iii) an unstable helical ribbon are both visualized by transmission electron microscopy and characterized by small angle X-ray scattering. Interestingly, the structural features of two stable intermediates are related to the final nanotube organization as they set, respectively, the nanotube wall thickness and the final wall curvature radius. We propose that a specific self-assembly pathway is selected by the existence of such preorganized and stable intermediates so that a unique final molecular organization is kinetically favored. Our findings suggests that the rational design of oligopeptides can encode both molecular- and macro-scale morphological characteristics of their higher-order assemblies, thus opening the way to ultrahigh resolution peptide scaffold engineering.

Self-Association Process of a Peptide in Solution: From β-Sheet Filaments to Large Embedded Nanotubes

Lanreotide is a synthetic octapeptide used in the therapy against acromegaly. When mixed with pure water at 10% (w/w), Lanreotide (acetate salt) forms liquid crystalline and monodisperse nanotubes with a radius of 120 A. The molecular and supramolecular organization of these structures has been determined in a previous work as relying on the lateral association of 26 beta-sheet filaments made of peptide noncovalent dimers, the basic building blocks. The work presented here has been devoted to the corresponding self-association mechanisms, through the characterization of the Lanreotide structures formed in water, as a function of peptide (acetate salt) concentration (from 2% to 70% (w/w)) and temperature (from 15 degrees C to 70 degrees C). The corresponding states of water were also identified and quantified from the thermal behavior of water in the Lanreotide mixtures. At room temperature and below 3% (w/w) Lanreotide acetate in water, soluble aggregates were detected. From 3% to 20% (w/w) long individual and monodisperse nanotubes crystallized in a hexagonal lattice were evidenced. Their molecular and supramolecular organizations are identical to the ones characterized for the 10% (w/w) sample. Heating induces the dissolution of the nanotubes into soluble aggregates of the same structural characteristics as the room temperature ones. The solubilization temperature increases from 20 degrees C to 70 degrees C with the peptide concentration and reaches a plateau between 15% and 25% (w/w) in peptide. These aggregates are proposed to be the beta-sheet filaments that self-associate to build the walls of the nanotubes. Above 20% (w/w) of Lanreotide acetate in water, polydisperse embedded nanotubes are formed and the hexagonal lattice is lost. These embedded nanotubes exhibit the same molecular and supramolecular organizations as the individual monodisperse nanotubes formed at lower peptide concentration. The embedded nanotubes do not melt in the range of temperature studied indicating a higher thermodynamic stability than individual nanotubes. In parallel, the thermal behaviors of water in mixtures containing 2-80% (w/w) in peptide have been studied by differential scanning calorimetry, and three different types of water were characterized: 1), bulk water melting at 0 degrees C, 2), nonfreezing water, and 3), interfacial water melting below 0 degrees C. The domains of existence and coexistence of these different water states are related to the different Lanreotide supramolecular structures. All these results were compiled into a binary Lanreotide-water phase diagram and allowed to propose a self-association mechanism of Lanreotide filaments into monodisperse individual nanotubes and embedded nanotubes.

FTIR spectroscopic characterization of a cationic lipid–DNA complex and its components

FTIR spectroscopy is used to study structural aspects of ternary complexes formed by the cationic lipid dimyristoyltrimethylammoniumpropane (DMTAP), the zwitterionic lipid dimyristoylphosphatidylcholine (DMPC), and deoxyribonucleic acid (DNA). Spectra of the single components are compared with those obtained for both equimolar DMPC–DMTAP mixture and lipid–DNA complex. The IR spectra of mixed lipid–DNA phases are strongly dominated by the lipidic absorption bands. This allows one to easily monitor, in particular, the thermotropic phase behaviour of lipid within the complex. The IR spectra of DNA intercalated between cationic lipid bilayers are determined by subtracting corresponding pure lipid spectra from lipid–DNA complex spectra. These difference spectra indicate deviations of lipid–associated DNA from B-form DNA. Furthermore, two additional water bands arise at positions different from those known for lipid- and DNA-bound water which are indicative of two distinct states of hydration in lipid–DNA complexes. The pure lipid DMTAP exhibits unusual spectroscopic features at the temperature of chain melting, Tm, near 53°C, which are attributed to the existence of a crystalline, headgroup-interdigitated phase existing at temperatures below Tm, in accordance with X-ray diffraction and differential scanning calorimetry (DSC) data.