Grains and grain boundaries in single-layer graphene atomic patchwork quilts

The properties of polycrystalline materials are often dominated by the size of their grains and by the atomic structure of their grain boundaries. These effects should be especially pronounced in two-dimensional materials, where even a line defect can divide and disrupt a crystal. These issues take on practical significance in graphene, which is a hexagonal, two-dimensional crystal of carbon atoms. Single-atom-thick graphene sheets can now be produced by chemical vapour deposition on scales of up to metres, making their polycrystallinity almost unavoidable. Theoretically, graphene grain boundaries are predicted to have distinct electronic, magnetic, chemical and mechanical properties that strongly depend on their atomic arrangement. Yet because of the five-order-of-magnitude size difference between grains and the atoms at grain boundaries, few experiments have fully explored the graphene grain structure. Here we use a combination of old and new transmission electron microscopy techniques to bridge these length scales. Using atomic-resolution imaging, we determine the location and identity of every atom at a grain boundary and find that different grains stitch together predominantly through pentagon-heptagon pairs. Rather than individually imaging the several billion atoms in each grain, we use diffraction-filtered imaging to rapidly map the location, orientation and shape of several hundred grains and boundaries, where only a handful have been previously reported. The resulting images reveal an unexpectedly small and intricate patchwork of grains connected by tilt boundaries. By correlating grain imaging with scanning probe and transport measurements, we show that these grain boundaries severely weaken the mechanical strength of graphene membranes but do not as drastically alter their electrical properties. These techniques open a new window for studies on the structure, properties and control of grains and grain boundaries in graphene and other two-dimensional materials.     

Recombinant G protein-coupled receptors from expression to renaturation: a challenge towards structure

G protein-coupled receptors (GPCRS) represent a class of integral membrane proteins involved in many biological processes and pathologies. Fifty percent of all modern drugs and almost 25% of the top 200 bestselling drugs are estimated to target GPCRs. Despite these crucial biological implications, very little is known, at atomic resolution, about the detailed molecular mechanisms by which these membrane proteins are able to recognize their extra-cellular stimuli and transmit the associated messages. Obviously, our understanding of GPCR functioning would be greatly facilitated by the availability of high-resolution three-dimensional (3D) structural data. However, expression, solubilization and purification of these membrane proteins are not easy to achieve, and at present, only one 3D structure has been determined, that of bovine rhodopsin. This review presents and compares the different successful strategies which have been applied to solubilize and purify recombinant GPCRs in the perspective of structural biology experiments. Received 21 November 2005; received after revision 20 January 2006; accepted 2 February 2006 An erratum to this article is available at .     

The adrenocorticotropic action of a new synthetic pentacosapeptide

Résumé L'action adrénocorticotrope d'un polypeptide à 25 acides aminés, comprenant 3 modifications de structure par rapport à la séquence 1–25 de l'ACTH naturelle est étudiée et démontrée. La destruction enzymatique de ce pentacosapeptide paraît être plus lente dans le sang que dans les tissus musculaire et sous-cutané. L'augmentation de la dose injectée produit un allongement de la durée de stimulation de la cortico-surrénale.     

Cisplatin-induced genes as potential markers for thyroid cancer

Despite the uncontested role of p53 in cycle arrest/cell death after cisplatin treatment, to date the question whether wild-type p53 confers a resistant or sensitive status on the cell is still a matter of debate. Isogenic and isophenotypic human thyroid papillary carcinoma cell line variants for p53 differently expressed cycle genes after cisplatin treatment. Seven genes (CDC6-related protein, CCNC, GAS1, TFDP2, MAPK10/JNK3, WEE1, RPA1) selected after expression on an Atlas human cell cycle array were analyzed by quantitative real-time PCR. While cisplatin treatment increased their expression in p53 wild-type cells it decreased it in cells with inactivated p53 and had no or less effect on cells with mutated p53. These results show that in a well-defined system, different alterations of p53 can lead to a different regulation of genes and hence to either resistance or sensitivity to cisplatin. Moreover for the first time, MAPK10/JNK3 was identified in human thyroid cells and tissue. Four of the genes (CDC6-related protein, CCNC, GAS1 and TFDP2) were decreased in human papillary carcinoma tissues. Relevance of these genes (especially a decrease in GAS1 in thyroid papillary carcinoma) in various malignant pathologies has already been shown. These genes may be explored as new markers in advanced thyroid cancer such as metastatic and anaplastic forms displaying p53 alterations.Received 26 July 2004; received after revision 14 September 2004; accepted 26 October 2004