Conformational flexibility in hydrated sugars: the glycolaldehyde-water complex

Conformational flexibility in the smallest hydrated sugar, the glycolaldehyde-water complex, has been investigated in the gas phase by means of a combination of a microwave Fourier transform spectroscopy experiment in a supersonic molecular beam and ab initio quantum chemistry calculations. The water molecule inserts into glycolaldehyde using H-bonding selectivity: the two lowest energy conformations are stabilized by two intermolecular hydrogen bonds, and the next two by one intra- plus one intermolecular hydrogen bond. A dynamical flexibility associated with the two lowest energy conformations has been experimentally observed and accurately modeled with a two-dimensional potential energy surface involving the hydroxyl group and the free OH water group coordinates. The conclusions drawn from the role played in the conformational flexibility by the hydroxyl and carbonyl groups are extended to other carbohydrates and biomolecules.     

Methyl transfer reaction from monomethyltin reagent under palladium(0) catalysis: a versatile method for labelling with carbon-11

The 11C-monomethylstannate prepared from [11C]-methyl iodide and Lappert's stannylene, was subject to a palladium-mediated cross-coupling reaction with an aryl halide under ligand-free conditions, to afford easily purified 11C-methyl(hetero)arenes in high radiochemical yields.     

Nonaqueous capillary electrophoretic behavior of 2-aryl propionic acids in the presence of an achiral ionic liquid. A chemometric approach

Ionic liquids (ILs) appear really attractive as electrolyte additives in nonaqueous capillary electrophoresis (NACE). These salts may offer new possibilities of interactions to modulate analyte effective mobilities. The presence of 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIM NTf2) in acetonitrile/alcohol background electrolytes (BGEs) was investigated in this work. The aim of this study was to elucidate the influence of the IL concentration on the electrophoretic behavior of four arylpropionic acids and to identify the interactions between the analytes and the IL cation. The influence on mobility of the IL concentration, the nature and the proportion of the organic solvents, and the concentration of the ionic components of the BGE was first studied by a univariate approach. A four-factor D-optimal experimental design was then applied to provide a deeper insight into analyte interaction with IL cation present both free in BGE and adsorbed onto the capillary wall.     

Evolving to the optoelectronic mouse for phycotoxin analysis in shellfish

Despite ethical and technical concerns, the in vivo method, or more commonly referred to mouse bioassay (MBA), is employed globally as a reference method for phycotoxin analysis in shellfish. This is particularly the case for paralytic shellfish poisoning (PSP) and emerging toxin monitoring. A high-performance liquid chromatography method (HPLC-FLD) has been developed for PSP toxin analysis, but due to difficulties and limitations in the method, this procedure has not been fully implemented as a replacement. Detection of the diarrhetic shellfish poisoning (DSP) toxins has moved towards LC-mass spectrometry (MS) analysis, whereas the analysis of the amnesic shellfish poisoning (ASP) toxin domoic acid is performed by HPLC. Although alternative methods of detection to the MBA have been described, each procedure is specific for a particular toxin and its analogues, with each group of toxins requiring separate analysis utilising different extraction procedures and analytical equipment. In addition, consideration towards the detection of unregulated and emerging toxins on the replacement of the MBA must be given. The ideal scenario for the monitoring of phycotoxins in shellfish and seafood would be to evolve to multiple toxin detection on a single bioanalytical sensing platform, i.e. ‘an artificial mouse’. Immunologically based techniques and in particular surface plasmon resonance technology have been shown as a highly promising bioanalytical tool offering rapid, real-time detection requiring minimal quantities of toxin standards. A Biacore Q and a prototype multiplex SPR biosensor have been evaluated for their ability to be fit for purpose for the simultaneous detection of key regulated phycotoxin groups and the emerging toxin palytoxin. Deemed more applicable due to the separate flow channels, the prototype performance for domoic acid, okadaic acid, saxitoxin, and palytoxin calibration curves in shellfish achieved detection limits (IC₂₀) of 4,000, 36, 144 and 46 μg/kg of mussel, respectively. A one-step extraction procedure demonstrated recoveries greater than 80 % for all toxins. For validation of the method at the 95 % confidence limit, the decision limits (CCα) determined from an extracted matrix curve were calculated to be 450, 36 and 24 μg/kg, and the detection capability (CCβ) as a screening method is ≤10 mg/kg, ≤160 μg/kg and ≤400 μg/kg for domoic acid, okadaic acid and saxitoxin, respectively.     

A short stereoselective preparation of dienamides from cyclobutene compounds. Application in the synthesis of a new cyclohexene nucleoside.

A short stereoselective synthesis of N-acylamino-1,3-dienes was developed starting from the cyclobutene lactam 8, which was obtained from 2-hydroxypyridine by a photochemical electrocyclic reaction. The tert-butoxycarbonyl derivative 17 was prepared to facilitate nucleophilic attacks to the carbonyl group, and the subsequent thermal ring opening provided dienes 18-21. One of these (20) was used in the synthesis of the cyclohexene nucleoside 30. A Diels-Alder reaction between diene 20 and maleic anhydride provided the endo-cycloadduct 22a. Three additional steps yielded amine 26. Construction of the uracil moiety afforded intermediate 29. Cyclization and removal of the protecting groups occurred in one step in the presence of ammonia, giving the target molecule 30. Diene 20 also underwent [4 + 2] cycloaddition with methyl acrylate to provide predominantly the endo-product 23a, regioselectively.     

Facteurs de lande des niveaux des configurations 5s5p et 5s5d de cd I

A plane Fabry-Pérot is used to measure, with a precision of about 10^-4, the Landé factor of the levels issued from the 5s5p and 5s5d configurations of cadmium I. Calculations taking into account intermediate coupling effects and the anomalous gyromagnetic ratio of the free electron are insufficient to explain some experimental data; in such cases it is necessary to perform a more detailed analysis of the corrections due to the relativistic effects.     

Structure hyperfine du niveau 6s6d3D1 de l'isotope 199 du mercure par interferometrie fabry-perot

The h.f.s of the 6s6d³D₁ state of ¹⁹⁹Hg has been measured by Fabry-Perot interferometry, using the 6³P₀-6³D₁ transition and taking into account the “forbidden” transition 6³P₀-6¹D₂. Two independent results are obtained: 383,67 ± 0,61 mK and 383,38 ± 0,25 mK, which agree with the theoretical value.     

Phase separation as a strategy toward controlling dilution effects in macrocyclic Glaser-Hay couplings

Macrocycles are abundant in numerous chemical applications, however the traditional strategy for the preparation of these compounds remains cumbersome and environmentally damaging; involving tedious reaction set-ups and extremely dilute reaction media. The development of a macrocyclization strategy conducted at high concentrations is described which exploits phase separation of the catalyst and substrate, as a strategy to control dilution effects. Sequestering a copper catalyst in a highly polar and/or hydrophilic phase can be achieved using a hydrophilic ligand, T-PEG(1900), a PEGylated TMEDA derivative. Similarly, phase separation is possible when suitable copper complexes are soluble in PEG(400), a green and efficient solvent which can be utilized in biphasic mixtures for promoting macrocyclization at high concentrations. The latter phase separation technique can be exploited for the synthesis of a wide range of industrially relevant macrocycles with varying ring sizes and functional groups.