Effect of the Ca/P ratio on the dielectric properties of nanoscaled substoichiometric hydroxyapatite.

Nanoscaled hydroxyapatite (n-HAp) was prepared by a wet chemical precipitation method, pressed to pellets and sintered at various temperatures between 900 and 1200 degrees C. With input stoichiometries of Ca/P ratios between 1.4 and 2.0, compositions in the substoichiometric range of Ca/P between 1.45(1) and 1.62(3) were determined after preparation. After sintering, final values of the Ca/P ratio between 1.45(8) and 1.66(4) were found. Capacitances and dielectric losses were determined in the frequency range between 20 Hz and 1 MHz and dielectric constants calculated from the capacitances. Dependencies of the dielectric properties on the composition, as well as on sintering temperature and frequencies were investigated. The dielectric constants generally tend to increase with increasing Ca-content. Different behaviour was observed for low frequencies (below 10(3) Hz) and for compositions far from the stoichiometric point of hydroxyapatite (Ca/P: 1.67). Comparable results were found for dielectric losses.

Biologically active metabolites from fungi, 17. 8-alpha-acetoxyverrol, a new member of the trichothecene sesquiterpenes.

8-alpha-Acetoxyverrol (4), the first open chain example of the trichothecenes with oxygenation at C-8, was isolated from cultures of Aphanocladium spectabile. The compound doses the biosynthetic gap to the macrocyclic verrucarins.

Isolation and synthesis of chalcones with different degrees of saturation.

Crotaoprostrin, a chalcone not yet known as a plant constituent, was isolated from the aerial parts of the Indian medicinal plant Crotalaria prostrata. The structures of the chalcone polyarvin and the partially hydrogenated naturally occurring derivatives crotaramin, crotaramosmin, and crotin were confirmed by chemical synthesis.