Effect of Thermal Treatment on the Structure and Properties of Hydroxyapatite

X-ray diffraction analysis and transmission electron microscopy were used to demonstrate that hydroxyapatite produced by the precipitation method is a powder composed of anisometric particles with longitudinal size of 70–100 nm and transverse size of 7–9 nm. The particles are constituted by crystallites with longitudinal sizes of 22–24 nm and transverse sizes of 8–10 nm. At a temperature of 600°C, the crystallite sizes grow, and the volume porosity and specific surface area decrease. Synthetic hydroxyapatite has a low thermal stability as compared with hydroxyapatite of biological origin.     

Highly selective substitutions in 2,3-dichloropyrazine. A novel general approach to aloisines

A highly efficient synthesis of the potent CDKs (cyclin-dependent kinases) inhibitors, aloisines (substituted 5H-pyrrolo[2,3-b]pyrazines) is presented. The method is based on highly selective monosubstitution of a single chlorine atom in 2,3-dichloropyrazine with lithiated ketones, esters, and nitriles followed by co-cyclization of the resulting intermediates with primary amines or hydrazines.     

Polymeric waveguides based on photopolymerizing methacrylate compositions

Contact photolithography was used to fabricate three-layer polymeric waveguide structures with transverse dimensions of 50 × 90 μm on the basis of two photopolymerizing methacrylate compositions with different refractive indices. The optical loss on the wavelength of 632.8 nm was 0.37 ± 0.14 dB cm^?1. This loss is mostly due to the light scattering by the material of the waveguide layer produced by bulk polymerization.