New rare earth-rich aluminides and indides with cubic Gd4RhIn-type structure

Abstract  

The series of rare earth metal (RE)-rich intermetallics RE ₄ TAl and RE ₄ TIn (T = Ru, Rh, Ir) were synthesized by induction melting of the elements in sealed tantalum tubes. These compounds crystallize with the cubic Gd₄RhIn-type structure, space group F[`4]3mF\bar{4}3m. The structures of eight crystals (including the isotypic compounds Ce₄RuMg and Ce₄RuCd) have been refined from X-ray single-crystal diffractometer data. The structures are composed of condensed RE ₆ T trigonal prisms which form a rigid network with adamantane-like topology. Large cavities within these networks are filled with empty RE ₆ octahedra and Al₄, In₄, Mg₄, or Cd₄ tetrahedra, respectively. Some of the RE ₄ TAl and RE ₄ TIn show small homogeneity ranges that result from small degrees of Al/T and In/T mixing on the 16e sites. All cerium compounds show small anomalies in the plots of the cell volumes. This is confirmed by temperature-dependent magnetic susceptibility measurements. Ce₄RuMg, Ce₄RuCd, Ce₄RuAl, and Ce₄RuIn show intermediate cerium valence and no magnetic ordering down to 3 K. Ce₄RhAl shows essentially trivalent cerium.     

Vinylcarbonates and vinylcarbamates: Biocompatible monomers for radical photopolymerization

The last decade has seen a remarkable interest in the use of biocompatible and biodegradable polymers as scaffolds for tissue engineering. The fabrication of 3D scaffolds by lithography‐based additive manufacturing technology (AMT) represents an appealing approach. As poly(lactic acid), the state of the art biocompatible and biodegradable material, cannot be processed by these photopolymerization‐based techniques, it has so far been necessary to use selected (meth)acrylates. By developing new photopolymers based on vinyl carbonates and vinyl carbamates as a reactive group we have been able to avoid most of the disadvantages of classical (meth)acrylate‐based photopolymers. The new generation of biocompatible monomers show low cytotoxicity, have good storage stability, and are sufficiently photoreactive to be structured by lithography based AMT. The mechanical properties and rates of degradation of the polymers can be easily tuned over a broad range. Degradation results in the formation of nonacidic and nontoxic degradation products of low molecular weight that can be easily transported within the human body. Initial in vivo tests showed significant osseointegration of the 3D cellular scaffolds and no signs of implant rejection. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A facile and effective synthesis of lamivudine 5′-diphosphate

We report on the first solution synthesis of lamivudine 5′-diphosphate in both high yield and purity. Efficient synthesis of lamivudine 5′-monophosphate was obtained through lamivudine H-phosphonate oxidation by (−)-(8,8-dichlorocamphorylsulfonyl)oxaziridine.Diphosphorylation was performed by nucleophilic substitution of the phosphorimidazolate derivative of lamivudine. HPLC coupled with UV or MS detection was found to be an invaluable tool for the follow-up of phosphorylation reactions.     

Oriented Mixed Area and Discrete Minimal Surfaces

Recently a curvature theory for polyhedral surfaces has been established, which associates with each face a mean curvature value computed from areas and mixed areas of that face and its corresponding Gauss image face. Therefore a study of minimal surfaces requires studying pairs of polygons with vanishing mixed area. We show that the mixed area of two edgewise parallel polygons equals the mixed area of a derived polygon pair which has only the half number of vertices. Thus we are able to recursively characterize vanishing mixed area for hexagons and other n-gons in an incidence-geometric way. We use these geometric results for the construction of discrete minimal surfaces and a study of equilibrium forces in their edges, especially those with the combinatorics of a hexagonal mesh.