Synthèse en monocristaux et structure du monouranate de sodium β-Na2UO4

β-Na₂UO₄ single crystals were synthesized from a melt with U, Nb, and Na ions. They are orthorhombic Fmmm with a = 5.802(2), B = 5.969(2), and c = 11.699(3) Å, and Z = 4. The structure was refined to R = 0.075 and R_w = 0.096 for 603 independent reflexions with I ≥ 3σ(I). The study shows that Na and O atoms are delocalized and that the structure results from the juxtaposition of four P2₁/b domains.     

Synthesis and properties of fluorine-containing heterocyclic compounds. V. Trifluoromethyl-1,8- and 1,10-phenanthrolines

The condensation of ethyl trifluoroacetoacetate with various heterocyclic amines yielded 2-(trifluoromethyl)phenanthrolin-4-ones. The structures of these compounds were established from a study of their infrared and ultraviolet spectra. Substituted phenanthrolines were prepared by nucleophilic attack on a chlorophenanthroline. The oxidation of 5-methoxy-2-trifluoromethyl-1,10-phenanthroline yielded an o-quinone which was treated with typical quinone reagents. A molecular orbital calculation was carried out in an attempt to explain the ease of reduction of the 1,10-phenanthroline system and the colors of the reduced compounds.     

Affinement de la structure de TiNb2O7 et répartition des cations

TiNb₂O₇ is monoclinic $\text{C2}\text{m}$ with a = 20.351(3), b = 3.801(2), c = 11.882(2) Å, β = 120.19°, Z = 6. The structure, determined by Wadsley in 1961 from visual estimation of intensities, has been refined to R = 0.065 for 915 reflexions with I ≥ 3σI. This study shows that Ti and Nb are not randomly distributed: like several niobo or tantalotitanates with edge-sharing octahedra, this one shows preferential occupation of one type of site by the titanium atoms.     

The first structural and spectroscopic characterization of a neptunyl polyoxometalate complex

The reaction between PW9O349- and NpO2+ has yielded the first structurally characterized neptunyl(V) polyoxometalate complex, [Na2(NpO2)2(A-PW9O34)2]14-. This complex is isostructural with the uranyl(VI) analogue, and there is also spectroscopic evidence for its existence in solution. The complex is readily extracted into toluene, and this may have significance in the sequestering and/or separation of the neptunyl ion in terms of nuclear waste management.     

The π N → e +e−N reaction close to the vector-meson production threshold

The π^? p→e ⁺ e ^? n and π⁺ n→e ⁺ e ^? p reaction cross sections are calculated below and in the vicinity of the vector-meson (?⁰,ω) production threshold. These processes are largely responsible for the emission of e ⁺e^? pairs in pion-nucleus reactions and contribute to the dilepton spectra observed in relativistic heavy ion collisions. They are dominated by the decay of low-lying baryon resonances into vector-meson-nucleon channels. The vector mesons materialize subsequently into e ⁺ e^? pairs. Using πN→?⁰ N and πN→ωN, amplitudes calculated in the center of mass energy interval 1.4 < √s<1.8 GeV, we compute the π^? p→e ⁺ e ^? n and π⁺ n→e ⁺ e ^? p reaction cross sections in these kinematics. Below the vector-meson production threshold, the π⁰?ω interference in the e ⁺ e^? channel appears largely destructive for the π^? p→e ⁺ e ^? n cross section and constructive for the π⁺ n→e ⁺ e ^? p cross section. The pion beam and the HADES detector at GSI offer a unique possibility to measure these effects. Such data would provide strong constraints on the coupling of vector-meson-nucleon channels to low-lying baryon resonances.     

Cubane,Bicyclo[1.1.1]pentane and Bicyclo[2.2.2]octane: Impact and Thermal Sensitiveness of Carboxyl-, Hydroxymethyl- and Iodo-substituents

With the burgeoning interest in cage motifs for bioactive molecule discovery, and the recent disclosure of 1,4-cubane-dicarboxylic acid impact sensitivity, more research into the safety profiles of cage scaffolds is required. Therefore, the impact sensitivity and thermal decomposition behavior of judiciously selected starting materials and synthetic intermediates of cubane, bicyclo[1.1.1]pentane (BCP), and bicyclo[2.2.2]octane (BCO) were evaluated via hammer test and sealed cell differential scanning calorimetry, respectively. Iodo-substituted systems were found to be more impact sensitive, whereas hydroxymethyl substitution led to more rapid thermodecomposition. Cubane was more likely to be impact sensitive with these substituents, followed by BCP, whereas all BCOs were unresponsive. The majority of derivatives were placed substantially above Yoshida thresholds—a computational indicator of sensitivity.     

Conformational arm-wrestling: battles for stereochemical control in benzamides bearing matched and mismatched chiral 2- and 6-substituents

The orientation of a tertiary amide group adjacent to an aromatic ring may be governed by the stereochemistry of an adjacent chiral substituent. With a chiral substituent in both ortho positions, matched/mismatched pairs of isomers result. Evidence for matched stereochemistry is provided by the clean NMR spectra of single conformers, while mismatching gives poor or unexpected selectivities in the formation of chiral substituents, or mixtures of amide conformers. Attempts to use the match-mismatch effect to select for racemic pairs of enantiomeric substituents, and hence develop a "racemate-sequestering" reagent, are described, along with the use of "matching" to scavenge a single enantiomer of a diamine from material of incomplete enantiomeric purity.     

Opening Enediyne Scissors Wider: pH‐Dependent DNA Photocleavage by meta‐Diyne Lysine Conjugates

Photochemical activation of meta‐diynes incapable of Bergman and C1–C5 cyclizations still leads to efficient double‐strand DNA cleavage. Spatial proximity of the two arylethynyl groups is not required for efficient DNA photocleavage by the enediyne‐lysine conjugates. Efficiency of the cleavage is a function of the external pH and DNA damage is strongly enhanced at pH < 7. The pH‐dependence of the DNA photocleavage activity stems from the protonation states of lysine amino groups, the internal electron donors responsible for intramolecular PET quenching and deactivation of the photoreactive excited states. DNA‐binding analysis suggests intercalative DNA binding for phenyl substituted conjugate and groove binding for TFP‐substituted conjugate. Additional insights in the possible mechanism for DNA damage from the ROS (Reactive Oxygen Species) scavenger experiments found that generation of singlet oxygen is partially involved in the DNA damage.     

Stereoselective synthesis of N-aryl proline amides by biotransformation-Ugi-Smiles sequence

An efficient combination of MAO-N-catalyzed desymmetrization of cyclic meso-amines with Ugi-Smiles multicomponent chemistry produced optically pure N-aryl proline amides. This method represents the first report of a fully asymmetric Ugi-Smiles process.     

Does a high UV environment ensure adequate vitamin D status?

This study assesses the Vitamin D status of 126 healthy free-living adults aged 18-87 years, in southeast Queensland, Australia (27 degrees S) at the end of the 2006 winter. Participants provided blood samples for analysis of 25(OH)D (the measure of an individual's Vitamin D status), PTH, Calcium, Phosphate, and Albumin, completed a questionnaire on sun-protective/sun-exposure behaviours, and were assessed for phenotypic characteristics such as skin/hair/eye colour and BMI. We found that 10.2% of the participants had serum 25(OH)D levels below 25 nmol/l (considered deficient) and a further 32.3% had levels between 25 nmol/l and 50 nmol/l (considered insufficient). Our results show that low levels of 25(OH)D can occur in a substantial proportion of the population at the end of winter, even in a sunny climate. 25(OH)D levels were higher amongst those who spent more time in the sun and lower among obese participants (BMI>30) than those who were not obese (BMI<30). 25(OH)D levels were also lower in participants who had black hair, dark/olive skin, or brown eyes, when compared with participants who had brown or fair hair, fair skin, or blue/green eyes. No associations were found between 25(OH)D status and age, gender, smoking status, or the use of sunscreen.