Isolation and Structural Elucidation of New Xanthone from Rot Bark of Cratoxylum sumatranum
Sumatranaxanthone A (1), a new xanthone, was isolated from the rot bark of Cratoxylum sumatranum. The structures were established based on spectroscopic studies, notably of the 1D and 2D NMR spectra. Preliminary results showed that 1 has antioxidative activity with inhibition 81% to fit with ascorbat acid standard.
Naturally-occurring xanthones: recent developments.
A literature survey covering the report of naturally occurring xanthones from January 2000 to December 2004, with 219 references, is presented in this review. Among 515 xanthones reported in this period, 278 were new natural xanthones. These xanthones have been identified from 20 families of higher plants (122 species in 44 genera), fungi (19 species) and lichens (3 species). The structural formulas of 368 identified xanthones, their distribution and a brief mention of their biological properties are also included.
HRTEM study of orthorhombic zirconia in MgO-PSZ
High-resolution transmission electron microscopy (HRTEM) was used to study the phase of orthorhombic ZrO2 formed in magnesia partially stabilized zirconia (MgO-PSZ) during HRTEM specimen preparation. Based on the three reported crystal structures of orthorhombic ZrO2, with the space groups Pbcm, Pbc21 and Pbca, here it is shown that orthorhombic ZrO2 formed in MgO-PSZ has the Pbcm structure.