X-ray diffraction/Calorimetry coupling

Polymorphism of trilaurin mixed with 4% of cholesterol was studied with a setup coupling calorimetry and phase characterisation by in-situ X-ray diffraction (Microcalix). Four polymorphic forms were identified. Monotropic and enantiotropic transitions were identified from the reconstruction of Gibbs free energy diagram which allows the control of trilaurin polymorphism. This revised version was published online in July 2006 with corrections to the Cover Date.     

Condensation of 3-methylbenzoxazolinone with α,β-unsaturated acids

The reaction between 3-methylbenzoxazolinone and some unsaturated acids in PPA leads to mixtures of compounds, depending on the acid: 6-crotonyl- (or cinnamoyl)-3-methylbenzoxazolinones, 2,3-dihydro-2,5-(or 2,7)dioxo-3-methylcyclopenta[f]benzoxazoles and 6-(3-oxo-indanyl)-3-methylbenzoxazolinones. The structure of the products was established by ¹³C and ¹H nmr spectroscopy and (or) by independent synthesis. Possible mechanisms of the reaction are discussed; when competition is possible as in the last step of the cyclization, the benzene ring shows a higher reactivity than the aromatic nucleus of the benzoxazolinone; the contrary is observed when the benzene ring is p-chloro-substituted.     

Synthesis and anti-tubulin evaluation of chromone-based analogues of combretastatins

Twenty new hybrid compounds with both combretastatin and flavone moieties were synthesized. These derivatives are classified according to the position of the trimethoxyphenyl ring at C-2 or C-3 of the chromone and presence or absence of a carbonyl as a linker between C-3 and the aryl ring. Most of these compounds were prepared from hesperidin or naringin, two natural and abundant Citrus flavonoids. Seven of these combretastatin analogues revealed anti-tubulin activity but in a medium range.     

Sodium Taurocholate-Induced Lamellar-Micellar Phase Transitions of DPPC

The thermotropic transitions of 1,2-dipalmitoylphosphatidylcholine (DPPC) and the structural changes of its lamellar phases have been studied between 0 and 50°C by both DSC and synchrotron small angle X-ray diffraction/scattering as a function of temperature (XRDT) and sodium taurocholate concentration [TC] in the 0–40 mM range ([DPPC]=50 mM) at pH 7.4. The existence of multiple phase transitions (up to 5 peaks within a 5°C interval) in a narrow domain of temperature between 25 and 42°C depending on the [TC]/[lipid] ratio was observed in the DSC curves. XRDT showed that at low ratios they might correspond to transitions between lamellar phases, the structural characteristics of which are given. At higher ratios a lamellar to micellar transition was observed, and the temperature at which it was observed decreased as a function of the TC content. The relationships with DPPC vesicle bilayer permeabilization and solubilization are discussed.     

Action of α-cyclodextrin on phospholipid assemblies

Interactions of α-cyclodextrin (α-CD) with dimyristoylphosphatidylcholine (DMPC) and Egg phosphatidylcholine (Egg-PC) were studied (i) by analyzing surface pressure-area isotherms and surface tension of phospholipid monolayers formed at the interface between air and α-CD aqueous solutions and (ii) by X-ray diffraction performed on fully hydrated α-CD/phospholipid binary mixtures. The cyclodextrin molecules strongly interact with the two-dimension phospholipid assembly. Their addition into the aqueous sub-phase leads to the removal of part of the phospholipids from the air-water interface: the higher the α-CD concentration, the higher the phospholipid depletion. This should preferentially involve interactions between cyclodextrin and the phosphatidylcholine head group as α-CD is water-soluble and not surface-active. At the three-dimension level, the bilayer packing of the phospholipid lamellar phase appears not affected by the presence of cyclodextrin as shown by X-ray scattering at small angles whereas wide-angle diffraction patterns reveal the formation of a crystalline phase organized in a pseudo-hexagonal lattice usually characteristic of α-CD dimers. These results point out that α-CD should interact with bilayer-forming phospholipid molecules but likely according to a process that would preserve intact at least a part of the multilamellar assembly.     

Metathetical reactions of carbonylate anions with dichlororuthenium complexes: Preparation and characterization of ruthenium—molybdenum and ruthenium—manganese complexes

The possibility of making metal—metal bonded heterobimetallic species by metathesis of ruthenium dichlorides with anionic carbonylates is demonstrated by the isolation of MoRu(μ-Cl)(μ-CO)(CO)₂(PPh₃)₂(η-C₅H₅) (1) and MnRuCl(μ-CO)₂(CO)₃(μ-dppm)₂ (2), obtained by action of [Mo(CO)₃(η-C₅H₅]^? on RuCl₂(PPh₃)₃ and of Mn(CO)₅^? on RuCl₂(dppm)₂, respectively. In contrast, reaction of Mn(CO)₅^? with RuCl₂(PMe₃)₄ yielded an ionic species 3 containing the diruthenium cation Ru₂Cl₃(PMe₃)₆⁺. More interestingly, the action of Mn(CO)₅^? on RuCl₂(PPh₃)₃ resulted in the formation of the unexpected complex MnRu(μ-PPh₂)(CO)₆(PPh₃)₂ (4) in which the phosphido group PPh₂ bridges the two metals; this process is shown to involve a hydride intermediate, and elimination of a molecule of benzene, both identified in the reaction mixture.     

Synthesis of 3-methyl-7-[2-(dimethylaminoethyl)oximino]-5-arylcyclopenta [F] Benzoxazolinones,Potential Ligands of the 5HT1D Receptors

The synthesis of 3-methyl-7-[2-(dimethylaminoethyl)oximino]-5-arylcyclopenta [f] benzoxa-zolinones, potential ligands of the 5HT_1D receptors is described through a 4 steps reaction strategy from 3-methyl-6-acetyl benzoxazolinone.     

Combined cation-exchange and extraction chromatography for the concomitant separation of Zr, Hf, Th, and the Lanthanides from geological materials

A new method was developed, aiming to overcome the iron and titanium interferences which severely limit the applications of a recently introduced extraction chromatography material, referred to as RE resin (formerly, RE Spec), to the analysis of geological samples. The separation scheme is based on the combined use, in tandem columns, of the conventional AG50WX4 cation-exchange resin and the RE extraction chromatography material, without any intervening evaporation step. The Lanthanides are recovered quantitatively, while recoveries for Zr, Hf and Th range from 94 to 98%. These three elements are determined using the isotope dilution method, thereby alleviating the need for a yield correction. Compared with conventional methods based on cation-exchange, this combined scheme offers a greater multi-element capability, significant miniaturisation, acid wastes reduction, and a higher degree of purity of the separated analytes with regard to unwanted elements such as Ba and residual Ca and Al. This concomitant isolation of 17 trace elements of great interest in the Earth and Environmental Sciences, achieved with excellent recoveries and satisfactory blank levels, can be used prior to high precision analysis of ultra-trace elements in geological samples by ICP-Mass Spectrometry.     

Bridging the gap between homogeneous and heterogeneous catalysis: ortho/para H(2) conversion, hydrogen isotope scrambling, and hydrogenation of olefins by Ir(CO)Cl(PPh(3))(2)

Some transition metal complexes are known to catalyze ortho/para hydrogen conversion, hydrogen isotope scrambling, and hydrogenation reactions in liquid solution. Using the example of Vaska's complex, we present here evidence by NMR that the solvent is not necessary for these reactions to occur. Thus, solid frozen solutions or polycrystalline powdered samples of homogeneous catalysts may become heterogeneous catalysts. Comparative liquid- and solid-state studies provide novel insight into the reaction mechanisms.     

An Improved Synthesis of α,β Methylenic Cyclic Ketones

This communication describes a convenient two steps procedure for the preparation of α,β methylenic cyclic ketones from arylmethyl ketones involving a preformed Mannich reagent.