Fine Spectral Analysis of Isotropic Partly Elastic Neutron Transport Operators

This paper deals with spectral theory of a new class of neutron transport operators involving collision operators of the form \(K=K_{i}+K_{e}\) where \(K_{i}\) (resp. \(K_{e}\)) describes the inelastic (resp. elastic) collisions of neutrons with the host material. We give a fine analysis of their asymptotic point spectra for isotropic space homogeneous cross sections in bounded geometries. We provide a new formalism relying on spectral analysis of some non compact symmetrizable operators arising in transport theory. Additional results on essential spectra are also given.     

Glass transition (Tg) and dielectric loss in Na3PO4–Pb3(PO4)2–BiPO4 phosphate glasses

Thermal and dielectric loss properties of Na₃PO₄-Pb₃(PO₄BiPO₄ (Na₂O-PbO-Bi₂O₃-P₂O₅) phosphate glasses, have been studied by the differential scanning calorimetry (DSC) and electrical factor loss (tgδ) measurements. Experiments have been carried out from ambient temperature to 500°C and show a strong influence of sodium ions on T_g and tgδ.     

Hibernation impact on the catalytic activities of the mitochondrial D-3-hydroxybutyrate dehydrogenase in liver and brain tissues of jerboa (<Emphasis Type="Italic">Jaculus orientalis</Emphasis>)

Background

Jerboa (Jaculus orientalis) is a deep hibernating rodent native to subdesert highlands. During hibernation, a high level of ketone bodies i.e. acetoacetate (AcAc) and D-3-hydroxybutyrate (BOH) are produced in liver, which are used in brain as energetic fuel. These compounds are bioconverted by mitochondrial D-3-hydroxybutyrate dehydrogenase (BDH) E.C. 1.1.1.30. Here we report, the function and the expression of BDH in terms of catalytic activities, kinetic parameters, levels of protein and mRNA in both tissues i.e brain and liver, in relation to the hibernating process.

Results

We found that: 1/ In euthemic jerboa the specific activity in liver is 2.4- and 6.4- fold higher than in brain, respectively for AcAc reduction and for BOH oxidation. The same differences were found in the hibernation state. 2/ In euthermic jerboa, the Michaelis constants, K_M BOH and K_M NAD⁺ are different in liver and in brain while K_M AcAc, K_M NADH and the dissociation constants, K_D NAD⁺and K_D NADH are similar. 3/ During prehibernating state, as compared to euthermic state, the liver BDH activity is reduced by half, while kinetic constants are strongly increased except K_D NAD⁺. 4/ During hibernating state, BDH activity is significantly enhanced, moreover, kinetic constants (K_M and K_D) are strongly modified as compared to the euthermic state; i.e. K_D NAD⁺ in liver and K_M AcAc in brain decrease 5 and 3 times respectively, while K_D NADH in brain strongly increases up to 5.6 fold. 5/ Both protein content and mRNA level of BDH remain unchanged during the cold adaptation process.

Conclusions

These results cumulatively explained and are consistent with the existence of two BDH enzymatic forms in the liver and the brain. The apoenzyme would be subjected to differential conformational folding depending on the hibernation state. This regulation could be a result of either post-translational modifications and/or a modification of the mitochondrial membrane state, taking into account that BDH activity is phospholipid-dependent.

     

The synthesis of two diastereomeric seco-rhazinilams with opposite atropomeric chiralities

(−)-Tabersonine 4 was submitted to quaternization and Emde degradation to yield the 3,4-seco derivative 5, which was hydrolyzed and decarboxylated to the diastereomeric indolenines 8 and 9. Oxidative rearrangement of 8 and 9 yielded the two diastereomeric seco-rhazinilams (−)-10 and (+)-11, differing in the atropomeric conformations of their biarylic system. The results are discussed in the realm of oxidation and rearrangements in the aspidosperma series of indole alkaloids.     

Nouveaux polyéthers et polyesters à base d'isosorbide: synthèse et caractérisation

A new family of multifunctional polyethers was synthesized with acceptable yields by condensation of isosorbide with aliphatic and aromatic dihalides in solid-liquid heterogeneous medium (solid KOH in DMSO). Molecular weights evaluated by GPC are rather low (polydispersed oligomers with n = 2–9). On the other hand, polycondensation with aliphatic or aromatic acid dichlorides in mass or in solution allowed the elaboration of polyethers with appreciable weights (4000–8000) in good yields.     

Equilibrium phase diagram of polystyrene and 8CB

The experimental equilibrium phase diagram of a mixture of linear polystyrene of molecular weight M_w = 44,000 g/mol and 4‐cyano‐4′‐n‐octyl‐biphenyl (8CB) is established. The three transitions smectic A‐nematic, nematic‐isotropic, and isotropic‐isotropic are observed. The first two are observed both by optical microscopy and differential scanning calorimetry (DSC) while the isotropic‐isotropic transition could be seen only via optical microscopy. Two series of samples with the same compositions were independently prepared and yielded consistent results both by microscopy and DSC. Measurements of sample compositions with less than 50 weight % of 8CB were influenced by the vicinity of the glass transition temperature (T_g) of the polymer in the mixture. This quantity is also determined by DSC as a function of composition. A single T_g is observed, which decreases with composition of the LC. Other thermodynamic quantities such as the enthalpy variations of LC in the nematic‐isotropic transition and the fraction of LC contained in the droplets are also considered. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1841–1848, 1999     

Stereoselective synthesis of (2E) 3‐amino‐2‐(1H‐benzimidazol‐2‐yl)acrylate and symmetric bisacrylates by transamination reactions

A range of various amines 2(a–i) was tested in transamination reactions using ethyl 2‐(1H‐benzimidazol‐2‐yl)‐3‐dimethylamino‐acrylate 1a. The (E)‐s‐cis/trans conformation of some representative products 4 was analyzed by ¹H and ¹³C NMR spectra. The C‐2/C‐3 bond of the compounds 3(a–i) is strongly polarized by a push‐pull effect. In the same manner, reactions of ethyl 2‐(benzoxazol‐2‐yl)‐3‐dimethylamino‐acrylate 1c with 1,4‐diaminobenzene 2i, ethylenediamine 2i, and 1,5‐diaminomaphthalene 2k have been investigated and gave directly the corresponding symmetric bis‐acrylates 4(a–c) in good yields. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 446–454, 1999