Luminescence peculiarities and optical properties of MgMoO<Subscript>4</Subscript> and MgMoO<Subscript>4</Subscript>:Yb crystals

Magnesium molybdate is considered as a promising material for cryogenic scintillation bolometers. The luminescence properties of MgMoO⁴ have been investigated on single crystals grown from melts of stoichiometric and nonstoichiometric compositions and on crystals doped with Yb³⁺ ions. Their optical properties are interpreted taking into account the anisotropy of the MgMoO⁴ crystal structure.     

Structure of the homodimer of uridine phosphorylase from <Emphasis Type="Italic">Salmonella typhimurium</Emphasis> in the native state at 1.9 Å resolution

Uridine phosphorylase (UPh) belongs to pyrimidine nucleoside phosphorylases. This enzyme catalyzes cleavage of the C-N glycoside bond in uridine to form uracil and ribose-1’-phosphate. Uridine phosphorylase supplies cells with nucleotide precursors by catalyzing the phosphorolysis of purine and pyrimidine nucleosides. This is an alternative to de novo nucleotide synthesis. The three-dimensional structure of native uridine phosphorylase from Salmonella typhimurium (StUPh) in a new crystal form was solved and refined at 1.90 Å resolution (R _st = 20.37%; R _free = 24.69%; the rmsd of bond lengths and bond angles are 0.009 Å and 1.223°, respectively). A homodimer containing two asynchronously functioning active sites was demonstrated to be the minimum structural unit necessary for function of the hexameric StUPh molecule (L ₃3L ₂). Each active site is formed by amino acid residues of both subunits.     

Structural features and isomorphous substitutions in chromium- and magnesium-containing beryls and chromium-containing beryllian indialite grown by the flux method

Beryls and beryllian indialite {the general formula M ^VI ₂ T(2)^IV ₃ T(1)^IV ₆O₁₈} synthesized in magnesium-containing flux systems saturated with chromium are investigated using X-ray diffraction. The isovalent schemes of the isomorphous incorporation of chromium into Moctahedra of these compounds and the simultaneously realized heterovalent schemes with the participation of other components are revealed from the occupancies of the positions. It is demonstrated that an increase in the average bond lengths in the M positions leads predominantly to an increase in the parameter α. In the beryllian indialites, the T(1) tetrahedra are substantially closer to perfect tetrahedra, the T(2) tetrahedra are distorted to a lesser extent, and the M octahedra are distorted to a greater extent than those in beryls. The structural indications of the ability of compounds with a beryl structure to congruently melt are distinguished.     

Crystallization of beryllian indialite from its own melt under oxidizing conditions

It is established that beryllian indialite (ideal formula Mg₂BeAl₂Si₆O₁₈) is formed spontaneously under oxidizing conditions in a wide range of relatively high cooling rates at small overheatings of its own melt and short overheating times. The significant difference in the growth rates of the prism and pinacoid faces of beryllian indialite from its own melt (0.08 and 0.40 mm/h, respectively) obtained by the Steber method is explained by the fact that the prism grows according to the tangential mechanism, while the pinacoid grows in the normal way. The face effect in these crystals manifests itself in the enrichment of the prism with beryllium and silicon as opposed to pinacoid.