Enantiomeric Distribution Studies of Linalool and Linalyl Acetate. A Powerful Tool for Authenticity Control of Essential Oils

The enantiomeric distributions of linalool and linalyl acetate in various natural products are measured by enantioselective gas chromatography on alkyl-substituted cyclodextrins. Different plant cultivars were investigated by four extraction processes: steam distillation, solvent extraction, supercritical fluid extraction, and headspace analysis. Careful attention must be paid to linalool which undergoes partial racemization under certain processing conditions. In most cases, enantiomeric distribution is a powerful tool for authenticity testing.     

Mechanism of thermal polymerization of cyanate ester systems: Chromatographic and spectroscopic studies

The mechanisms and kinetics of polymerization of mono- and difunctional cyanate esters are investigated using chromatographic (HPLC) and spectroscopic methods (UV, liquid and solid-state NMR, and FTIR). The results obtained after chromatographic separation and identification of the chemical species present in the reaction medium have enabled us to propose a reaction path and a kinetic model for these thermally polymerized systems. Finally, the polymerization of cyanate ester was studied in the presence of different catalysts (imidazole, AcAcCu and AcAcCr) added directly, without solvent, and showed their influence on mechanisms. © 1996 John Wiley & Sons, Inc.     

Investigating the role of c-Jun N-terminal kinases in the proliferation of Werner syndrome fibroblasts using diaminopyridine inhibitors

To develop more potent small molecules with enhanced free radical scavenger properties, a series of N-substituted isatin derivatives was synthesized, and the cytoprotective effect on the apoptosis of PC12 cells induced by H₂O₂ was screened. All these compounds were found to be active, and N-ethyl isatin was found with the most potent activity of 69.7% protective effect on PC12 cells. Structure-activity relationship analyses showed the bioactivity of N-alkyl isatins decline as the increasing of the chain of the alkyl group, furthermore odd-even effect was found in the activity, which is interesting for further investigation.     

Electrochemical properties of perovskite and A<Subscript>2</Subscript>MO<Subscript>4</Subscript>-type oxides used as cathodes in protonic ceramic half cells

Three selected materials have been prepared and shaped as cathode of half cells using the proton-conducting electrolyte BaCe_0.9Y_0.1O_3 − δ (BCY10): two perovskite compounds, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ (BSCF) and La_0.6Sr_0.4Fe_0.8Co_0.2O_3 − δ (LSFC), and the praseodymium nickelate Pr₂NiO_4 + δ (PRN) having the K₂NiF₄-type structure. The electrochemical properties of these compounds have been studied under zero current conditions (two-electrode cell) and under polarization (three-electrode cell). Their measured area-specific resistances were about 1–2 Ω cm² at 600 °C. Under direct current polarization, it appears that the three compounds show almost similar values of current densities at 625 °C; however, at lower temperatures, BSCF appears to be the most efficient cathode material.     

Ca3−xLaxCo4O9+δ (x=0, 0.3): New cobaltite materials as cathodes for proton conducting solid oxide fuel cell

Misfit-type Ca_3−xLa_xCo₄O_9+δ (x=0, 0.3) oxides were synthesised to be evaluated as possible cathode materials for proton conducting fuel cells (PCFCs) based on BaCe_0.9Y_0.1O_3−δ (BCY10) dense ceramic electrolyte. The electrical conductivity value of Ca_2.7La_0.3Co₄O_9+δ (σ≈53 S cm^-1 at 600 °C) is in the range of usually required value for a cathode application (about 50-100 S cm^-1). In order to test the performance of each compound as cathode material, impedance measurements were carried out on Ca_3−xLa_xCo₄O_9+δ/BaCe_0.9Y_0.1O_3−δ/Ca_3−xLa_xCo₄O_9+δ symmetrical half cells over the temperature range 400-800 °C under wet air. A promising electrocatalytic activity has been observed with both compounds Ca₃Co₄O_9+δ and Ca_2.7La_0.3Co₄O_9+δ. Factually, the area specific resistance obtained was about 2.2 Ω cm² at 600 °C.     

Highly Stable and Inert Complexation of Indium(III) by Reinforced Cyclam Dipicolinate and a Bifunctional Derivative for Bead Encoding in Mass Cytometry

H₂cb-te2pa, a cross-bridged cyclam functionalized by two picolinate arms, was used for the formation of an incredible inert In^III chelate. The inertness of the complex was evaluated by UV/Vis experiments in several competitive media and was highlighted by the comparison with [In(dota)]⁻ and [In(dtpa)]²⁻ (H₄dota = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, H₅dtpa = diethylenetriamine pentaacetic acid), which are currently used in biological applications. For the first time, a bifunctional analogue of H₂cb-te2pa was prepared by C-functionalization to keep its coordination properties intact. However, this strategy leads to the formation of two diastereoisomers as evidenced and studied by NMR experiments and DFT calculations. Kinetic studies proved nevertheless that both isomers of the complex are equally inert. They were therefore used without distinction for their covalent grafting on polystyrene beads. The so-called metal-encoded beads were tested for imaging mass cytometry. The detection of ¹¹⁵In allows the generation of images with high quality, proving the great potential of the bifunctional [In(cb-te2pa)]⁺ derivatives for single-cell analysis by mass cytometry.     

H-transfer rates in ion-neutral complexes versus those in intact aliphatic ions

The relative rates of H-transfer between partners in ion-neutral complexes were compared with those in intramolecular rearrangements using results of first differential photoionization mass spectrometry measurements. Complex-mediated H-transfers are inferred to have rates of the same order as those for intramolecular hydrogen rearrangements, suggesting a similar range of motion of the reactive sites in both types of reactions. It is also concluded that at their fastest H-transfers take place between the partners in ion-neutral complexes within at most the time of several rotations of the partners in the complexes. Copyright 1999 John Wiley & Sons, Ltd.