Séverine Tisse

(l)- or (d)-Valine tert-butylamide grafted on permethylated β-cyclodextrin derivatives as new mixed binary chiral selectors: Versatile tools for capillary gas chromatographic enantioseparation

This work deals with the synthesis of two mixed binary chiral selectors prepared by grafting (L)- or (D)-valine tert-butylamide on permethylated cyclodextrin macrocycle. The enantioselective properties of the new chiral selectors diluted in OV11 polysiloxane (35% phenyl- and 65% methylsiloxane) were investigated by means of injections of 117 racemic mixtures. The mixed chiral selectors with (L)-valine and, to a lesser extent with (D)-valine, were found to have an improved enantioselectivity toward amino acid derivatives by comparison to permethylated cyclodextrin. The enantioseparation capability of these new chiral selectors has proven to be slightly less efficient than Chirasil-L-Val (Alltech) for amino acid derivatives, but it has been extended to include terpenes, lactones, esters, aliphatic compounds and aryl alcohols.

Selective access and full characterization of mono-acidic permethylated β-cyclodextrin derivatives and their methyl esters

Abstract Three acidic derivatives of permethylated β-cyclodextrin, 2 I - O -carboxymethyl-2 II-VII ,3 I-VII ,6 I-VII -eicosa- O -methyl-cyclomaltoheptaose, 6 I - O -carboxymethyl-2 I-VII ,3 I-VII ,6 II-VII -eicosa- O -methyl-cyclomaltoheptaose, 6 I -desoxy-6 I -carboxy-2 I-VII ,3 I-VII ,6 II-VII -eicosa- O- methyl-cyclomaltoheptaose and the corresponding methyl esters have been synthesized with good yields starting from mono-hydroxy permethylated β-CD prepared via tert -butyldimethylsilyl protection in 6-position and p -methoxybenzyl protection at the 2-position. All of these compounds were fully characterized by high field 1 H and 13 C NMR and HPLC/MS.

An alternative scheme for the multiplexed acquisition of 1D and 2D NMR spectra.

Spin system selective 1D (1)H, 2D DQF-COSY and 2D HSQC NMR spectra were recorded in order to fully assign the (1)H and (13)C 1D NMR spectra of an asymmetrical beta-cyclodextrin derivative. Instead of individually accessing the seven sugar anomeric protons by means of long multiplet selective pulses, only short region selective pulses were used. The simultaneously selected anomeric protons were differentiated by allowing their magnetization to evolve under the sole effect of the chemical shift interaction. In each experiment, the seven recorded spectra were linear combinations of the seven desired ones. The combination coefficients were measured and used to obtain almost perfectly separated sugar unit sub-spectra. This multiplexed acquisition scheme resulted in a time gain factor of about 2.

Combining zone melting and preparative chromatography to purify Phenanthrene

The impacts of zone melting and preparative chromatography on Phenanthrene purity were established by GC and DSC experiments. On the one hand, phase diagrams investigations between Phenanthrene and its major impurities (Dibenzothiophene, Fluorene, Carbazole, and Anthracene) have revealed inadequate heterogeneous equilibria for an efficient purification by zone melting, especially for Fluorene. Nevertheless, a clear purification effect has been noticed by applying this thermal process. On the other hand, preparative chromatography has shown a propensity to separate Phenanthrene from Fluorene. This uncommon case demonstrates the advantages of combining purification techniques to reach a sufficient purity level. Moreover, this study highlights the limitations of analytical tools to quantify such high level of purity.

New and old NMR experiments for the resonance assignment of complex oligosaccharides—application to a cyclodextrin derivative

The complete assignment of the 1H and 13C sugar resonances in mono‐3,6‐anhydro‐heptakis(2,3‐O‐methyl)‐hexakis(6‐O‐methyl)‐β‐cyclodextrin, an asymmetrically functionalized β‐cyclodextrin, was carried out by means of 2D NMR experiments. The TOCSY and the homonuclear multiple relay COSY spectra provided most of the 1H assignments. The multiplicity edited HSQC and a set of F1 selective HSQC‐TOCSY and multiple relay HSQC‐COSY spectra gave access to most of the 13C chemical shifts. The latter were fully and accurately determined by means of a pair of complementary, highly folded HSQC‐TOCSY spectra. The TOCSY‐ROESY and ROESY‐TOCSY spectra yielded the sequential assignment of the sugar units. A high resolution F1 selective F1 decoupled version of the TOCSY‐ROESY experiment was recorded. Copyright

Retention modeling and retention time prediction in gas chromatography and flow-modulation comprehensive two-dimensional gas chromatography: The contribution of pressure on solute partition ☆

This study aims at modelling and predicting solute retention in capillary Gas Chromatography (GC) and Flow Modulation comprehensive GC (FM-GCxGC). A new thermodynamic model, taking into account the effects of temperature and pressure, is proposed to describe the variation of the equilibrium partition constant of a solute during its elution. This retention model was challenged with the classical one, and both were applied to: (i) stationary phase film thickness indirect estimation; (ii) retention time (RT) prediction of a set of 11 model polycyclic aromatic hydrocarbons (PAHs) on the SLB-IL60 and DB-35MS columns, in temperature-programmed mode. Film thickness determination led to values about 2 times lower than those indicated by column nominal dimensions, whatever the employed model. Prediction of retention times in GC led to 0.84 and 0.26% mean errors using the classical and the extended models, respectively. Prediction in GCxGC gave 5.5 and 0.44% mean errors in 1st dimension RTs, and 7.3 and 2.2% mean errors in 2nd dimension RTs, using the classical and the extended models, respectively.