Effect of the tube diameter distribution on the high-temperature structural modification of bundled single-walled carbon nanotubes

We present results of a systematic high-resolution transmission electron microscopy study of the thermal evolution of bundled single-walled carbon nanotubes (SWNTs) subjected to approximately 4-h high-temperature heat treatment (HTT) in a vacuum at successively higher temperatures up to 2200 degrees C. We have examined purified SWNT material derived from the HiPCO and ARC processes. These samples were found to thermally evolve along very different pathways that we propose depend on three factors: (1) initial diameter distribution, (2) concomitant tightness of the packing of the tubes in a bundle, and (3) the bundle size. Graphitic nanoribbons (GNR) were found to be the dominant high-temperature filament in ARC material after HTT = 2000 degrees C; they were not observed in any heat-treated HiPCO material. The first two major steps in the thermal evolution of HiPCO and ARC material agree with the literature, i.e., coalescence followed by the formation of multiwall carbon nanotubes (MWNTs). However, ARC material evolves to bundled MWNTs, while HiPCO evolves to isolated MWNTs. In ARC material, we find that the MWNTs collapse into multishell GNRs. The thermal evolution of these carbon systems is discussed in terms of the diameter distribution, nanotube coalescence pathways, C-C bond rearrangement, diffusion of carbon and subsequent island formation, as well as the nanotube collapse driven by van der Waals forces.     

Synthesis of (-)-matairesinol, (-)-enterolactone,and (-)-enterodiol from the natural lignan hydroxymatairesinol

[reaction: see text] We describe here a four-step semisynthetic method for the preparation of enantiomerically pure (-)-enterolactone starting from the readily available lignan hydroxymatairesinol from Norway spruce (Picea abies). Hydroxymatairesinol was first hydrogenated to matairesinol. Matairesinol was esterified to afford the matairesinyl 4,4'-bistriflate, which was deoxygenated by palladium-catalyzed reduction to 3,3'-dimethylenterolactone. Demethylation of 3,3'-dimethylenterolactone and reduction with LiAlH(4) yielded (-)-enterolactone and (-)-enterodiol, respectively.     

Tobacco chemistry. 65. Two new 7,8-epoxycembranoids from tobacco

Two new diterpenoids have been isolated from tobacco. They have been identified as the (1S,2E,4S,6R,7R,8R,11E)- and (1S,2E,4S,6R,7S,8S,11E)-7,8-epoxy-2,11-cembradiene-4,6-diols 1 and 2 by synthesis and X-ray analysis. The conformation about the 5,6 bond in some 7,8-epoxycembranoids is discussed, as is the biogenesis of the two new compounds.     

Site‐Specific Labeling of Affimers for DNA‐PAINT Microscopy

Optical super‐resolution techniques allow fluorescence imaging below the classical diffraction limit of light. From a technology standpoint, recent methods are approaching molecular‐scale spatial resolution. However, this remarkable achievement is not easily translated to imaging of cellular components, since current labeling approaches are limited by either large label sizes (antibodies) or the sparse availability of small and efficient binders (nanobodies, aptamers, genetically‐encoded tags). In this work, we combined recently developed Affimer reagents with site‐specific DNA modification for high‐efficiency labeling and imaging using DNA‐PAINT. We assayed our approach using an actin Affimer. The small DNA‐conjugated affinity binders could provide a solution for efficient multitarget super‐resolution imaging in the future.