Characterization of semi-packed columns with different cross section in high-pressure gas chromatography.

Hydrodynamics, efficiency, and loading capacity of two semi-packed columns with different cross sections (NANO 315 µm x 18 µm; CAP 1000 µm x 28 µm) and similar pillar diameter and pillar-pillar distance (respectively 5 µm and 2.5 µm) have been compared in high-pressure gas chromatography. A flow prediction tool has been first designed to determine pressure variations and hold-up time across the chromatographic system taking into account the rectangular geometry of the ducts into the semi-packed columns. Intrinsic values of Height Equivalent to Theoretical Plate were determined for NANO and CAP columns using helium as carrier gas and similar values have been obtained (30 µm) for the two columns. Loading capacity of semi-packed columns were determined for decane at 70 °C using helium, and the highest value was obtained from CAP column (larger cross section and stationary phase content). Finally, significant HETP improvement (down to 15 µm) and peak shape were observed when carbon dioxide was used as carrier gas, suggesting mobile phase adsorption on stationary phase in high pressure conditions.

Three-dimensional hydrogen bonding between Landers and planar molecules facilitated by electrostatic interactions with Ni adatoms.

Using a combination of UHV-STM and molecular mechanics calculations, we investigate the surface self-assembly of a complex multi-component metal-molecule system with synergistic non-covalent interactions. Hydrogen bonding between three-dimensional Lander-DAT molecules and planar PTCDI molecules, adsorbed closer to the surface, is found to be facilitated by electrostatic interactions between co-adsorbed Ni adatoms and the flexible molecular DAT groups.

Review on Micro-Gas Analyzer Systems: Feasibility, Separations and Applications.

Over 30 years, portable systems for fast and reliable gas analysis are at the core of both academic and industrial research. Miniaturized systems can be helpful in several domains. The way to make it possible is to miniaturize the whole gas chromatograph. Micro-system conception by etching silicon channel is well known. The main objective is to obtain similar or superior efficiencies to those obtained from laboratory chromatographs. However, stationary phase coatings on silicon surface and micro-detector conception with a low limit of detection remain a challenge. Developments are still in progress to offer a large range of stationary phases and detectors to meet the needs of analytical scientists. This review covers the recent development of micro-gas analyzers. It focuses on injectors, stationary phases, column designs and detectors reported in the literature during the last three decades. A list of commercially available micro-systems and their performances will also be presented.

Chemical modifications of atomic force microscopy tips.

Atomic force microscopy (AFM) works by scanning a very tiny tip over a surface with great precision. The microscope tips can be chemically functionalized to improve the images obtained. Well-defined chemical functionalization of AFM tips is especially important for experiments, such as chemical force microscopy and single molecule recognition force microscopy, to examine specific interactions at the single molecular level. In this chapter, we present an overview of chemical modifications of tips that have been reported to date with regards to the proper fixation of probe molecules, focusing particularly on chemical procedures developed to anchor biological molecules on AFM tips.

Iodination of verapamil for a stronger induction of death, through GSH efflux, of cancer cells overexpressing MRP1.

The multidrug resistance protein 1 (MRP1), involved in multidrug resistance (MDR) of cancer cells, was found to be modulated by verapamil, through stimulation of GSH transport, leading to apoptosis of MRP1-overexpressing cells. In this study, various iodinated derivatives of verapamil were synthesized, including iodination on the B ring, known to be involved in verapamil cardiotoxicity, and assayed for the stimulation of GSH efflux by MRP1. The iodination, for nearly all compounds, led to a higher stimulation of GSH efflux. However, determination of concomitant cytotoxicity is also important for selecting the best compound, which was found to be 10-fold more potent than verapamil. This will then allow us to design original anti-cancer compounds which could specifically kill the resistant cancer cells.

Iodination increases the activity of verapamil derivatives in reversing PGP multidrug resistance.

Iodinated derivatives of verapamil were synthesized and tested as P-glycoprotein (Pgp)-mediated multidrug resistance (MDR) reversal agents. The ability of these compounds to revert MDR was evaluated on daunorubicin-resistant K562 cells, by measuring the intracellular accumulation of rhodamine 123, a fluorescent probe of Pgp transport activity. One of the investigated compounds (16c) was found to be a more potent MDR reversal agent than verapamil and cyclosporin A, used as reference molecules. Further in vitro studies showed that compound 16c restored daunorubicin activity and, when used alone, did not induce cell death, cell cycle perturbation and modification of calcium channel activity in comparison with verapamil.

Self-assembly of hydrogen-bonded chains of molecular landers.

One-dimensional chains of a specially designed lander molecule with di-carboxyl imide functional moieties, enabling complementary intermolecular hydrogen bonding, have been self-assembled under ultra high vacuum conditions on a Au(111) surface and characterized by scanning tunneling microscopy.

Supramolecular architectures on surfaces formed through hydrogen bonding optimized in three dimensions.

Supramolecular self-assembly on surfaces, guided by hydrogen bonding interactions, has been widely studied, most often involving planar compounds confined directly onto surfaces in a planar two-dimensional (2-D) geometry and equipped with structurally rigid chemical functionalities to direct the self-assembly. In contrast, so-called molecular Landers are a class of compounds that exhibit a pronounced three-dimensional (3-D) structure once adsorbed on surfaces, arising from a molecular backboard equipped with bulky groups which act as spacer legs. Here we demonstrate the first examples of extended, hydrogen-bonded surface architectures formed from molecular Landers. Using high-resolution scanning tunnelling microscopy (STM) under well controlled ultrahigh vacuum conditions we characterize both one-dimensional (1-D) chains as well as five distinct long-range ordered 2-D supramolecular networks formed on a Au(111) surface from a specially designed Lander molecule equipped with dual diamino-triazine (DAT) functional moieties, enabling complementary NH...N hydrogen bonding. Most interestingly, comparison of experimental results to STM image calculations and molecular mechanics structural modeling demonstrates that the observed molecular Lander-DAT structures can be rationalized through characteristic intermolecular hydrogen bonding coupling motifs which would not have been possible in purely planar 2-D surface assembly because they involve pronounced 3-D optimization of the bonding configurations. The described 1-D and 2-D patterns of Lander-DAT molecules may potentially be used as extended molecular molds for the nucleation and growth of complex metallic nanostructures.

Chemical modifications of AFM tips for the study of molecular recognition events.

The use of AFM to study molecular recognition events at an incredible level of sensitivity is currently a very active field of research. In order to get information at the single molecule level, it is mandatory to modify in a precise manner the AFM tip to anchor either ligand or receptor molecules. In the following lines, we review the achievements in tip modifications and illustrate the scope and limitations of the different strategies that have been reported.

Verapamil and its derivative trigger apoptosis through glutathione extrusion by multidrug resistance protein MRP1.

This study demonstrates that verapamil and a newly synthesized verapamil derivative, NMeOHI(2), behave as apoptogens in multidrug resistance protein 1 (MRP1)-expressing cells. When treated with either verapamil or NMeOHI(2), surprisingly, baby hamster kidney-21 (BHK) cells transfected with human MRP1 were killed. Because parental BHK cells were not, as well as cells expressing an inactive (K1333L) MRP1 mutant, this indicated that cell death involved functional MRP1 transporter. Cell death was identified as apoptosis by using annexin V-fluorescein labeling and was no longer observed in the presence of the caspase inhibitor Z-Val-Ala-Asp(OMe)-CH(2)F (Z-VAD-FMK). In vitro, both verapamil and its derivative inhibited leukotriene C4 transport by MRP1-enriched membrane vesicles in a competitive manner, with a K(i) of 48.6 microm for verapamil and 5.5 microm for NMeOHI(2,) and stimulated reduced glutathione (GSH) transport 3-fold and 9-fold, respectively. Treatment of MRP1-expressing cells with either verapamil or the derivative quickly depleted intracellular GSH content with a strong decrease occurring in the first hour of treatment, which preceded cell death beginning at 8-16 h. Furthermore, addition of GSH to the media efficiently prevented cell death. Therefore, verapamil and its derivative trigger apoptosis through stimulation of GSH extrusion mediated by MRP1. This new information on the mechanism of induced apoptosis of MDR cells may represent a novel approach in the selective treatment of MRP1-positive tumors.