Practical asymmetric access to carboxy-differentiated aspartate derivatives via 1,3-dipolar cycloaddition of a nitrone with (R)-4-ethyl-N-vinyloxazolidin-2-one

A new practical approach to enantioenriched carboxy-differentiated aspartate derivatives was achieved in three steps via the 1,3-dipolar cycloaddition of N-benzyl-α-carbonyloxyethylnitrone with (R)-4-ethyl-N-vinyloxazolidin-2-one and chemoselective nucleophilic displacement of aspartimide under appropriate conditions (racemization less than 3%).     

Hot nanotubes: stable heating of individual multiwall carbon nanotubes to 2000 k induced by the field-emission current

Field emission (FE) electron spectroscopy from an individual multiwalled carbon nanotube (MWNT) is used to measure quantitatively stable temperatures at the apex, T(A), of up to 2000 K induced by FE currents approximately 1 microA. The high T(A) is due to Joule heating along the length of the MWNT. These measurements also give directly the resistance of the individual MWNT which is shown to decrease with temperature, and explain the phenomenon of FE-induced light emission which was observed simultaneously. The heating permits thermal desorption of the MWNT and, hence, excellent current stability.     

Band-edge photoluminescence in nanocrystalline ZnO:In films prepared by electrostatic spray deposition

ZnO:In films are successfully prepared by using the electrostatic spray deposition technique. X-ray diffraction indicates that the ZnO:In films have a polycrystalline hexagonal wurtzite structure with lattice parameters a=3.267 Å and c=5.209 Å. Photoluminescence properties of the films are investigated in the temperature range of 11.6-300 K, showing strong luminescence in the whole range of temperature. The temperature dependence of the photoluminescence are carried out with full profile fitting of spectra, which clearly shows that the ultraviolet (UV) emission in In-doped ZnO films at low temperature are attributed to emission of a neutral donor-bound exciton (D^°X) and recombination of donor-acceptor pairs (DAP), while the UV emission at room temperature originates from radiative transition of an electron bound on a donor to the valence band.     

Regioselective synthesis of the tricyclic core of lateriflorone

An efficient synthetic approach to the tricyclic core 8 of lateriflorone is described. Essential to the synthesis was the implementation of a biomimetic tandem Claisen/Diels-Alder reaction that produced the desired tricyclic scaffold as a single isomer. A rationalization of the excellent regio and stereoselectivity of this transformation is also proposed. [reaction: see text]