The luminescence of α- and β-LaNb3O9

The luminescence of undoped and rare-earth-doped LaNb₃O₉ is reported. The two modifications (α and β) show striking differences. Whereas undoped β-LaNb₃O₉ does not luminesce at all (down to 4.2 K), α-LaNb₃O₉ emits efficiently with a quenching temperature of 250 K. Energy transfer from niobate to rare-earth dopants is observed for the α, but not for the β modification. The rare-earth dopant emission consists of sharp lines for the α modification, but is considerably broadened for the β modification. The luminescence properties are discussed in terms of the crystal structure. In addition results for α-NbPO₅ will be given.     

NMR imaging of white button mushroom (Agaricus bisporis) at various magnetic fields

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) have been applied to visualize physiological phenomena in plants and agricultural crops. Imaging sequences that result in contrast of a combination of parameters (e.g., proton density, ) cannot be used for a correct and unique interpretation of the results. In this study multiecho imaging together with monoexponential T₂ decay fitting was applied to determine reliable proton density and T₂ distributions over a mushroom. This was done at three magnetic field strengths (9.4, 4.7, and 0.47 T) because susceptibility inhomogeneities were suspected to influence the T₂ relaxation times negatively, and because the inflences of susceptibility inhomogeneities increase with a rise in magnetic field strength. Electron microscopy was used to understand the different T₂'s for the various tissue types in mushrooms. Large influences of the tissue ultrastructure on the observed T₂ relaxation times were found and explained. Based on the results, it is concluded that imaging mushrooms at low fields (around or below 0.47T) and short echo times has strong advantages over its high-field counterpart, especially with respect to quantitative imaging of the water balance of mushrooms. These conclusions indicate general validity whenever NMR imaging contrast is influenced by susceptibility inhomogeneities.     

Quantum theory as a description of robust experiments: Derivation of the Pauli equation

It is shown that the Pauli equation and the concept of spin naturally emerge from logical inference applied to experiments on a charged particle under the conditions that (i) space is homogeneous (ii) the observed events are logically independent, and (iii) the observed frequency distributions are robust with respect to small changes in the conditions under which the experiment is carried out. The derivation does not take recourse to concepts of quantum theory and is based on the same principles which have already been shown to lead to e.g. the Schrödinger equation and the probability distributions of pairs of particles in the singlet or triplet state. Application to Stern–Gerlach experiments with chargeless, magnetic particles, provides additional support for the thesis that quantum theory follows from logical inference applied to a well-defined class of experiments.     

Development of adamantan-1-yl-methoxy-functionalized 1-deoxynojirimycin derivatives as selective inhibitors of glucosylceramide metabolism in man

In this article, we present a straightforward synthesis of adamantan-1-yl-methoxy-functionalized 1-deoxynojirimycin derivatives. The used synthetic routes are flexible and can be used to create a wide variety of lipophilic mono- and difunctionalized 1-deoxynojirimycin derivatives. The compounds reported here are lipophilic iminosugar based on lead compound 4, a potent inhibitor of the three enzymes involved in the metabolism of the glycosphingolipid glucosylceramide. Iminosugar-based inhibitors of glucosylceramide synthase, one of these three enzymes, have attracted increasing interest over the past decade due to the crucial role of this enzyme in glycosphingolipid biosynthesis. Combined with the fact that an increasing number of pathological processes are being linked to excessive glycosphingolipid levels, glucosylceramide synthase becomes a very attractive therapeutic and research target. Our results presented here demonstrate that relocating the lipophilic moiety from the nitrogen atom to other positions on the 1-deoxynojirimycin ring system does not lead to a more potent or selective inhibitor of glucosylceramide synthase. The beta-aza-C-glycoside analogue (17) retained the best inhibitory potency for glucosylceramide synthase and is a more potent inhibitor than the therapeutic agent N-butyl-1-deoxynojirimycin (3), marketed as treatment for Gaucher disease under the commercial name Zavesca.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

1,2,4-Triazole complexes,part X. Complexes of transition metal(II) cyanates and thiocyanates with 1-phenyl-1,2,4-triazole

Summary Complex formation of transition metal(II) cyanates and thiocyanates (Z) with 1-phenyl-I,2,4-triazole (1-PhTr) is described. An assignment of the i.r. spectra of free and coordinated 1-phenyl-1,2,4-triazole is given. The products are mononuclear M(1-PhTr)₄Z₁ and polvnuclear M(1-PhTr)₂Z₂ compounds. The former occur ascis andtrans isomers; the latter include bridging (thio)cvanates. A tetrahedral coordination is found for zinc complexes.Part IX, D. W. Engelfriet, G. C. Verschoor and W. den Brinker, to be published.