Ultrafine heat-induced structural perturbations of bone mineral at the individual nanocrystal level

International audienc

α-D-mannosyl and β-D-galactozyl derivatives of cylclodextins

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A-amylose single crystals: influence of amylose concentration, crystallization temperature and surface induction on the crystal morphology

International audienceNarrow fractions of short-chain enzymatically-synthesized amylose have been crystallized from 0.05 to 5.0% w/v aqueous solutions by slow diffusion of acetone or ethanol vapors at 50–60 °C or addition of hot liquid acetone. The fractions were selected according to their ability to form a few micrometer-long A-type acicular single crystals with a well-defined facetted habit. The single crystals grew organized into rosettes or fan-like assemblies whose relative fraction depended on the initial amylose concentration. Rosettes became dominant with increasing concentration while the aspect ratio of the constituting crystals increased with crystallization temperature. In rosettes, the density of crystals increased as well but without forming solid spherulites, due to the topological constraint of packing isomorphous platelet crystals growing from a common nucleus inside a spherical volume. A higher density of crystals was achieved by nucleation on the surface defects of inductive glass slides. Due to the chemical polarity of A-type amylose single crystals, rosettes and crystal mats exposed faces concentrating reducing amylose chain ends, available for chemical labelling or grafting

Topological defects in polycrystalline hexosomes from β-cyclodextrin fatty esters

International audienceColloidal nanoparticles were prepared by aqueous self-assembly of amphiphilic β cyclodextrins (βCDs) acylated on their secondary face with C14 chains to a total degree of substitution of 7.0, via a thermolysin-catalyzed transesterification process. The small angle X ray scattering pattern of the nanoparticles was consistent with a reverse hexagonal organization. Cryo transmission electron microscopy images revealed particles with spectacular tortuous shapes and consisting of misoriented domains with a regular columnar hexagonal structure, separated by sharp interfaces. Edge dislocations as well as a variety of stepped tilt grain boundaries (GBs) composed of symmetrical and asymmetrical sections, together with one twist GB, were identified from axial views of the columnar organization. The tilt GB structure was analyzed using the concepts of coincidence site lattice and structural units developed to describe the atomic structure of interfaces in various types of polycrystals. The tilt GBs were described using sequences of βCD–C14 columns that differed by the number of neighboring columns (5, 6 or 7) and exhibiting distinctive contrasts. To our knowledge, this is the first time that these types of topological defects are described at the nanometric scale by direct observation of colloidal polycrystalline hexosomes of self-organized amphiphiles