Effects of variation in modulator temperature during cryogenic modulation in comprehensive two‐dimensional gas chromatography

Many modulation systems in comprehensive 2D GC (GC×GC) are based on cryogenic methods. High trapping temperatures in these systems can result in ineffective trapping of the more volatile compounds, whilst temperatures that are too low can prevent efficient remobilisation of some compounds. To better understand the trapping and release of compounds over a wide range of volatilities, we have investigated a number of different constant temperature modulator settings, and have also examined a constant temperature differential between the cryo‐trap and the chromatographic oven. These investigations have led us to modify the temperature regulation capabilities of the longitudinally modulated cryogenic system (LMCS). In contrast to the current system, where the user sets a constant temperature for the cooling chamber, the user now sets the temperature difference between the cryo‐trap and the chromatographic oven. In this configuration, the cooling chamber temperature increases during the chromatographic run, tracking the oven temperature ramp. This produces more efficient, volatility‐dependent modulation, and increases the range of volatile compounds that can be analysed under optimal trap‐and‐release conditions within a single analytical run. This system also reduces cryogenic fluid consumption.     

Semi‐Covalent Surface Molecular Imprinting of Polymers by One‐Stage Mini‐emulsion Polymerization: Glucopyranoside as a Model Analyte

This paper describes a new type of surface imprinting technique that combines the advantages of both the semi‐covalent approach and one‐stage miniemulsion polymerization. This process has been successfully applied for the preparation of glucose surface‐imprinted nanoparticles. The selective artificial receptors for glucopyranoside were fully characterized by IR, TEM and BET analyses, and their molecular recognition abilities by binding experiments carried out in batch processes. The molecular affinity and selectivity of the glucose molecularly imprinted polymers were accurately quantified. These characteristics are essential for verification of the efficiency of the developed surface imprinting process. The imprinting effect was clearly demonstrated using the batch rebinding method. We have found that the glucose imprinted polymers produced using the optimized one‐stage mini‐emulsion exhibited quite fast kinetics of binding and equilibration with glucopyranoside templates, compared to polymers prepared by bulk polymerization technique, as well as extremely low levels of unspecific bindings. We also demonstrated that glucose molecular imprinted polymer (MIP) exhibited very good selectivity for its original template compared to other glycopyranoside derivatives, such as galactose. Finally, the extraction of the binding properties from isotherms of binding by fitting to the bi‐Langmuir and Freundlich models allowed the determination of the affinity constant distribution of the binding sites. This imprinting protocol allowed the determination of an affinity constant (K_D), involving exclusively H‐bonding interactions, for the glucose MIP ( P2C ) with the best template 1 , in CH₃CN as the solvent system.

     

Preparation of 7-modified docetaxel analogs using electrochemistry

The electrochemical reduction of 7-iodo docetaxel at E-1.3V vs. SCE in methanol in the presence of lithium chloride and hydrochloric acid leads predominantly to 7-deoxy-docetaxel 9. When the electroreduction is conducted at E-1.7V vs. SCE in the presence of sodium acetate and acetic acid, the cyclopropanol-containing taxoid 10 is formed in good yield. Electrochemical reduction of 7-deoxy-docetaxel at C-10 is also reported. All these docetaxel analogs retain biological activity.     

Synthesis and structures of substituted triphenyl(phenylimino)phosphoranes

Three substituted triphenyl(phenylimino)phosphoranes, namely (4‐cyanophenylimino)triphenylphosphorane, C₂₅H₁₉N₂P, (I), (4‐nitrophenylimino)triphenylphosphorane, C₂₄H₁₉N₂O₂P, (II), and (3‐nitrophenylimino)triphenylphosphorane, C₂₄H₁₉N₂O₂P, (III), were synthesized as precursors for the preparation of substituted diphenylcarbodiimides. All three compounds display a supramolecular arrangement in which the substituted benzene rings are organized in an antiparallel fashion. The nitro group on the ring participates in C—H...O and O...π interactions, forming intermolecular dimers. Compound (III) shows disorder which involves the rotation of one of the phenyl rings of the triphenylphosphine group.     

Geobacter sulfurreducens can protect 304L stainless steel against pitting in conditions of low electron acceptor concentrations

The effect of Geobacter sulfurreducens cells was studied on the electrochemical behaviour of 304L stainless steel, emphasizing the role of the soluble electron acceptor (fumarate). In fumarate-lacking media, the presence of G. sulfurreducens induced free potential ennoblement in a few hours. This ennoblement has already been observed in standard media that contained fumarate. Our previous studies have shown that G. sulfurreducens shifted the pitting potential toward the positive values. The pits induced by the presence of the bacteria were wider and deeper than in the absence of bacteria. Here, in fumarate-lacking media, similar shift in pitting potential was observed, but the repassivation phase was strongly improved. AFM analysis showed that pits were identical with those observed in the absence of bacteria at lower potential. In contrast with all the previous work where G. sulfurreducens enhanced corrosion, here at a low concentration of electron acceptor, the presence of the bacteria protected the steel against pitting.     

DFT study of electronic and magnetic structure of perovskite and post-perovskite CaRhO3

Within density functional theory the equations of state for perovskite (PV) and post-perovskite (PPV) forms of CaRhO₃ are obtained with equilibrium values of volume in agreement with experiment. Energy magnitudes point to a stabilization of PPV versus PV. This is interpreted by analyses of the charge density and the chemical bonding plots, showing that the Rh–O interactions within two oxygen sublattices are selectively differentiated and reinforced for one of the two oxygen sublattices within PPV variety with respect to PV one. Investigation of the magnetic properties shows no magnetic order and a metallic character for PV while ferromagnetism occurs in PPV with a tendency to insulating behavior. This long range order is favored by direct t_2g–t_2g interactions through edge sharing octahedra in PPV CaRhO₃, stronger than indirect t_2g–p_π–t_2g ones in PV variety.     

Chiral separation of basic drugs by capillary electrophoresis with carboxymethylcyclodextrins

Capillary electrophoresis (CE) with carboxymethylated beta- or gamma-cyclodextrins was used to achieve the rapid enantiomeric separation of a set of basic drugs. The enantiomers of 12 chiral amino-containing pharmaceutical compounds belonging to various therapeutic categories were analyzed by CE using an uncoated 60 cm x 75 microm I.D. silica capillary. Several experimental parameters such as the nature, concentration and pH of the buffer, nature and concentration of the anionic cyclodextrin and temperature were studied in order to optimize the enantiomeric separation. The variation of the solute partition coefficient for the chiral selector, the enantioselectivity and resolution factors are used to assess the quality of the chiral separation. It is shown that the solute affinity for the chiral selector is not related to its enantioresolution factor. None of the two cyclodextrin selectors used was able to separate the whole set of basic drugs.     

A spin transition molecular material with a wide bistability domain

[Fe(hyptrz)3](4-chloro-3-nitrophenylsulfonate)22 H2O (1; hyptrz=4-(3-hydroxypropyl)-1,2,4-triazole) has been synthesized and its physical properties have been investigated by several physical techniques including magnetic susceptibility measurements, calorimetry, and M?ssbauer, optical, and EXAFS spectroscopy. Compound 1 exhibits a spin transition below room temperature, together with a very wide thermal hysteresis of about 50 K. This represents the widest hysteresis loop ever observed for an FeII-1,2,4-triazole spin transition material. The cooperativity is discussed on the basis of temperature-dependent EXAFS studies and of the structural features of a CuII analogue. The EXAFS structural model of (1) in both spin states is compared to that obtained for a related material whose spin transition occurs above room temperature. EXAFS spectroscopy suggests that 1,2,4-triazole chain compounds retain a linear character whatever the spin state of the iron(II).