Melting curves of Bi,Pb and Al using microdifferential thermal analysis up to 1.4 GPa

Abstract

The slopes dΘ/dP relative to the melting points of the elements Bi, Pb and Al have been determined under isostatic pressures up to 1.4 GPa. A μDTA device, which can operate from 300 K to 1050 K, has been wyked out for these investigations. The crucible volume is 2 mm. A differential amplitude signal of 1K can be detected, corresponding, for instance, to a thermal effect of 0.2 J for Pb. The temperature accuracy is about ± 3 K at high pressure. We describe the μDTA device and, briefly, a complementary electrical resistivity set-up. In both cases, data acquisition and processing are computer-controlled.     

Synthesis,characterization, and ion‐complexing properties of polymers displaying densely packed arrays of crown‐ethers as lateral substituents

We report the synthesis and ion‐binding properties of four poly(crown‐ethers) displaying either one or two crown‐ethers (15‐crown‐5 or 18‐crown‐6) on every third carbon alongside the backbone. The polymers were synthesized by living anionic ring‐opening polymerization of disubstituted cyclopropane‐1,1‐dicarboxylates monomers. Cation binding of the polychelating polymers and corresponding monomers to Na⁺ and K⁺ was evaluated by picrate extraction and isothermal calorimetry titration. This novel family of poly(crown‐ethers) demonstrated excellent initial binding of the alkali ions to the polymers, with a higher selectivity for potassium. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2337–2345     

Investigation of space charge effects and ion trapping capacity on direct introduction ultra‐high‐resolution mass spectrometry workflows for metabolomics

Ultra‐high‐resolution mass spectrometry, in the absence of chromatography, is finding its place for direct analyses of highly complex mixtures, such as those encountered during untargeted metabolomics screening. Advances, however, have been tempered by difficulties such as uneven signal suppression experienced during electrospray ionization. Moreover, ultra‐high‐resolution mass spectrometers that use Orbitrap and ICR analyzers both suffer from limited ion trapping capacities, owing principally to space‐charge effects. This study has evaluated and contrasted the above two types of Fourier transform mass spectrometers for their abilities to detect and identify by accurate mass measurement, small molecule metabolites present in complex mixtures. For these direct introduction studies, the Orbitrap Fusion showed a major advantage in terms of speed of analysis, enabling detection of 218 of 440 molecules (<2 ppm error, 500 000 resolution at m/z 200) present in a complex mixture in 5 min. This approach is the most viable for high‐throughput workflows, such as those used in investigations involving very large cohorts of metabolomics samples. From the same mixture, 183 unique molecules were observed by FT‐ICR in the broadband mode, but this number was raised to 235 when “selected ion monitoring‐stitching” (SIM‐stitching) was employed (<0.1 ppm error, 7 T magnet with dynamic harmonization cell, 1.8 million resolution at m/z 200, both cases). SIM‐stitching FT‐ICR thus offered the most complete detection, which may be of paramount importance in situations where it is essential to obtain the most complete metabolic profile possible. This added completeness, however, came at the cost of a more lengthy analysis time (120 min including manual treatment). Compared to the data presented here, future automation of processing, plus the use of absorption mode detection, segmented ion detection (stepwise detection of smaller width m/z sections), and higher magnetic field strengths, can substantially reduce FT‐ICR acquisition times.     

Syntheses of Tetrahydrolipstatin and Absolute Configuration of Tetrahydrolipstatin and Lipstatin

Lipstatin ( 1 ), a natural product, and tetrahydrolipstatin ( 2 ) are pancreatic lipase inhibitors. Non-stereoselective and partially stereoselective syntheses of 2 are used to establish the absolute configuration of tetrahydrolipstatin and lipstatin.     

Photochemistry of Biliverdin IX δ as a model for the study of the photoproducts from natural biliverdin IXγ (pterobilin)

The configurations of biliverdin-IX_γ and -IX_δ dimethyl esters 1 and 2 in solutions, have been studied using Nuclear-Overhauser-Effect (NOE) experiments. Irradiation (500-700 nm) of biliverdin IXδ gave syn-Z → anti-E isomerization of the central methine bridge and in aerated polar solutions, four new cyclized pigments were isolated for which structures 3, 4, 5 and 6 are proposed. Neobiliverdin IXδ 3 is also formed in degassed solution (Φ=4.10^?5) but pigments 4, 5 and 6 arise from photo-oxidation with O₂. Biliverdin IXδ appears to be a good model for the study of photo-reactions occurring on the vinyl groups of the natural biliverdin IXγ (pterobilin).     

Nouvelle synthese simple de deoxtribonucledside-3′-aryl-β-cyanoethyl-phosphates

The deoxyribonucleoside-3′-aryl-β-cyanoethyl-phosphates, very used in the synthesis of oligodeoxynucleotides, were synthesized in high yields in a single step from the nucleoside derivatives with a monofunctional phosphorylating agent : cyclohexylammonium p-chlorophenyl-β-cyanoethyl-phosphate.     

Chirality and Spectroscopic Changes Induced by the Recognition of Ethyl 5-Amino-2-methyl-1,2-dihydro-3-phenylpyrido[3,4-b]pyrazin-7-yl Carbamate Analogs by Tubulin

The two chiral isomers of ethyl 5-amino-2-methyl-l,2-di-hydro-3-phenylpyrido[3,4-b]pyrazin-7-yl carbamate, NSC 613863 (R-isomer)-(+) and NSC 613862 (S-isomer)-(-) (CI980) and the three achiral analogs NSC 330770 (2-de-methylated analog A), NSC 337238 and C179 are potent microtubule inhibitors. These ligands interact with tubulin overlapping the colchicine binding site. This study addresses the effects of recognition by tubulin on the conformational properties of the ligands. The near-UV CD (circular dichroism) band of the R-isomer was suppressed, while that of the S-isomer displayed a more intense negative band when these compounds were bound to tubulin. Interestingly, the three other initially achiral compounds became optically active upon binding to tubulin; particularly, analog A exhibited a negative CD band on the order of magnitude of chiral compounds. The CD changes are reversible, highly specific and actually permit measuring the binding of the ligands by tubulin. These CD changes are compatible with the deformation of the bound ligands. Fluorescence emission is strongly enhanced and blue shifted upon binding to tubulin. Water among a solvent series had a specific solvent effect, except on the 1,2-dehydro analogs NSC 337238 and C179, suggesting hydrogen bonding to Nl. The emission of tubulin-bound R-isomer, S-isomer and analog A could be mimicked by solvent viscosity, supporting the notion that the intramolecular rotation between the pyridopyrazine and phenyl rings is frozen upon binding.     

Calculations of first- and second-order nonlinear molecular hyperpolarizabilities by perturbation methods: I. An efficient method for evaluating time-independent hyperpolarizabilities

From a suitable reorganisation of the sum-over-states (SOS) equations of the usual time-independent perturbation theory, recurrent expressions for static polarizability (α) and second- (beta;) and third-(γ) order hyperpolarizabilities are obtained. These expressions are given in a well-adapted way for computer implementation and lead to an efficient algorithm reducing the computing time by a factor of 50 with respect to a “brute-force” translation of the standard SOS equations.