microwave irradiation is used in the synthesis of four tricyclic chromanones 11-14. the chromanone 14 and 12 are selectively formed thermally and under microwave in the presence of polyphosphoric acid (ppa) from the same dicarboxylic acid 9, respectively. the crystal structures of the two diacids are also reported. the corresponding ortho and meta isomers of diacids crystallize in the space gro...

The capsid shell of infectious hepatitis B virus (HBV) is composed of 240 copies of a single protein called HBV core antigen (HBc). An atomic model of a core assembled from truncated HBc was determined previously by X-ray crystallography. In an attempt to obtain atomic structural information of HBV core in a near native, non-crystalline environment, we reconstructed a 3.5Å-resolution structure ...

Crystal-structure determination using X-ray diffraction from single crystals is a well-developed technique (1). A single crystal structure provides full structural characterization of the form at the atomic scale. The main drawback to single crystal diffraction is the need to grow a sufficiently large and defect-free crystal for analysis, which is not practical for all crystal forms. Furthermor...

Cadmium selenide (CdSe) nanoplatelets of a few atomic layers thick exhibit extremely sharp photoluminescence peaks and are synthesized in the zinc blende crystal structure, whereas the most stable bulk polymorph of CdSe is the wurtzite structure. These platelets can be synthesized very monodispersely in thickness, and are covered with acetate ligands. Here, we show by means of density functiona...

Three-dimensional photonic-crystal grains were found in the scales of the longhorn beetle Prosopocera lactator (Cerambycidae). The local geometric structure can be described as a face-centered-cubic array of spheres, connected by short rods, reminiscent of the "ball-and-stick" models used by solid-state chemists to visualize atomic structures. Based on scanning electron microscopy, x-ray nanoto...

Atomic defects in crystalline structures have pronounced affects on their bulk properties. Aberration-corrected transmission electron microscopy has proved to be a powerful characterization tool for understanding the bonding structure of defects in materials. In this article, recent results on the characterization of defect structures in two dimensional materials are discussed. The dynamic beha...

A new computational approach to modeling crystal structures based on the bond valence method is presented. The Monte Carlo technique is used to determine the atomic structure of perfect and defective crystals in accordance with crystal chemical valence sum and bond network rules. Using this method, the calculated MgO (001) surface relaxation was less than 1% of the interlayer spacing, a value t...

We present a solution to the multiple-scattering inverse problem for low-energy electron diffraction that enables the determination of the three-dimensional atomic structure of an entire surface unit cell directly from measured data. The solution requires a knowledge of the structure of the underlying bulk crystal and is implemented by a maximum entropy algorithm.