Oxidative decarboxylation of arylacetic acids by means of tetrabutylammonium periodate

Tetrabutylammonium periodate (TBAPI) in refluxing dioxane is able to convert arylacetic acids into the corresponding nor-aldehydes in good yields.     

Sommes directes de sous-modules co-irréductibles d'un module

Sans résuméCette étude est le développement d'une note présentée à l'Académie des Sciences de Paris le 16 Mai 1966 (cf. [13]), et d'un exposé donné au Séminaire d'AlgèbreDubreil-Pisot le 28 Novembre 1966 (cf. [14]).     

Doppler-free two-color spectroscopy of the 62 S 1/2–82 S 1/2 cesium transition using semiconductor diode lasers

We report an experimental investigation of the 6S–8S transition of cesium atoms by using Doppler-free two-color spectroscopy. We consider the case in which one of the laser frequencies is nearly resonant with the 6S _1/2–6P _3/2 transition while a second one is swept around the 6P _3/2–8S _1/2 transition. The lineshapes of two-photon absorption spectra are analyzed taking into account the effects of saturation and collisions. Both counterpropagating and copropagating laser-beam schemes are studied. Although for the linewidths are broader copropagating beams, such a scheme has proved advantageous to fully resolve the hyperfine structure of the final state 8S _1/2 and, hence, to measure the dipole magnetic constantA of this state.     

Selective lithiation of 4-(1H-1-pyrrolyl)pyridine. access to new electron-releasing ligands

The first lithiation of 4-(1H-1-pyrrolyl)pyridine has been realized. The use of BuLi-containing lithium aggregates induced the selective pyridine ring functionalization by taking advantage of the electron-donor effect of the pyrrole nucleus. Opportune substituents were introduced alpha to the pyridine nitrogen leading to new electron-enriched pyridylphosphine, bipyridine, and terpyridine ligands.     

Comparison of methods for the determination of ochratoxin A in wine

Different analytical methods for the determination of ochratoxin A (OTA) in wine have been compared. Sample clean-up was based on solid-phase extraction (SPE) with (i) immunoaffinity or (ii) RP-18 sorbent materials applying different experimental protocols. The detection of OTA was accomplished with high-performance liquid chromatography (HPLC) combined either with electrospray ionisation (ESI) tandem mass spectrometry (MS-MS) or fluorescence detection (FL). Comparative method evaluation was based on the investigation of 18 naturally contaminated red wine samples originating from different European countries. The analytical results are discussed in view of the respective method validation data and the corresponding experimental protocols. In general, analytical data obtained with RP-18 SPE combined with LC-MS-MS detection and immunoaffinity extraction combined with FL offered comparable good results in the sub-ppb concentration level indicating that high selectivity of either the sample clean-up or, alternatively the detection system are equally well-suited to guarantee an accurate OTA analysis in wine.     

Hiyama cross-coupling of chloro-, fluoro-, and methoxypyridyltrimethylsilanes: room-temperature novel access to functional bi(het)aryl

The incorporation of chloro, fluoro, or methoxy substituents on the pyridine ring of pyridyltrimethylsilanes allowed us to perform efficient Hiyama cross-coupling with various (het)aryl halides. The reactions proceeded smoothly at room temperature leading to the corresponding functional bis(het)aryl in fair to excellent yields. The presence of pyridine nitrogen alpha to the trimethylsilyl group was requisite to achieve the cross-coupling. [Reaction: see text]     

Optical double-resonance spectroscopy of trapped Cs atoms: hyperfine structure of the 8s and 6d excited states

Transitions between excited states of Cs atoms prepared in a magneto-optical trap are investigated with a two-step excitation process. The first step is provided by the trapping laser radiation, the second step to higher excited states is done with an additional laser. We measure the hyperfine structure of the 8s and 6d states and investigate the effect of the relevant trap parameters on the accuracy of the data.     

The surface chemistry of a nanocellulose drug carrier unravelled by MAS-DNP

Cellulose nanofibrils (CNF) are renewable bio-based materials with high specific area, which makes them ideal candidates for multiple emerging applications including for instance on-demand drug release. However, in-depth chemical and structural characterization of the CNF surface chemistry is still an open challenge, especially for low weight percentage of functionalization. This currently prevents the development of efficient, cost-effective and reproducible green synthetic routes and thus the widespread development of targeted and responsive drug-delivery CNF carriers. We show in this work how we use dynamic nuclear polarization (DNP) to overcome the sensitivity limitation of conventional solid-state NMR and gain insight into the surface chemistry of drug-functionalized TEMPO-oxidized cellulose nanofibrils. The DNP enhanced-NMR data can report unambiguously on the presence of trace amounts of TEMPO moieties and depolymerized cellulosic units in the starting material, as well as coupling agents on the CNFs surface (used in the heterogeneous reaction). This enables a precise estimation of the drug loading while differentiating adsorption from covalent bonding (∼1 wt% in our case) as opposed to other analytical techniques such as elemental analysis and conductometric titration that can neither detect the presence of coupling agents, nor differentiate unambiguously between adsorption and grafting. The approach, which does not rely on the use of ¹³C/¹⁵N enriched compounds, will be key to further develop efficient surface chemistry routes and has direct implication for the development of drug delivery applications both in terms of safety and dosage.

DNP-enhanced solid-state NMR unravels the surface chemistry of functionalized nanocellulose.     

Hyperfine structure and isotope shift of the 3s-3p transitions of atomic oxygen

Using high-resolution saturation spectroscopy, by means of both double heterostructure and multiple quantum-well AlGaAs diode lasers, we investigate the isotope shifts and the hyperfine structure in the 3s-3p transitions of the triplet and quintet systems of atomic oxygen. From the analysis of the signals from¹⁷O we can deduce precise values for the hyperfine structure magnetic dipole constants. A theoretical analysis allows us to bring into evidence core polarization effects in the hyperfine structure. By heterodyning two frequency locked lasers, we perform a direct frequency measurement of the isotope effect on the³ S ₁→³ P _1,2,0 transitions. From the comparison with similar accuracy data on the corresponding quintet transitions, an upper bound to the size of the nuclear volume effect is given, and precise values for the specific mass contributions are consequently obtained.