Comparative analysis of the gas-phase reactions of cylindrospermopsin and the difference in the alkali metal cation mobility

Cylindrospermopsin (CYN) belongs to a group of toxins produced by several strains of freshwater cyanobacteria. It is a compact zwitterionic molecule composed of a uracil section and a tricyclic guanidinium portion with a primarily hepatotoxic effect. Using low multi-stage and high-resolution mass spectrometry, the gas-phase reactions of this toxin have been investigated. Our data show that collision-induced dissociation (CID) spectra of CYN are dominated by neutral losses, and three major initial fragmentation pathways are clearly distinguishable. Interestingly, comparative analysis of protonated and cationizated molecules showed a significant difference in the balance of the SO3 and terminal ring elimination. These data indicate that the differential ion mobility of H+, Li+, Na+ and K+ leads to different fragmentation pathways, giving rise to mass spectra with different profiles.     

Analysis of selected carbonyl oxidation products in wine by liquid chromatography with diode array detection

A high performance liquid chromatography (HPLC) method for the detection and quantitation of acetaldehyde, glyceraldehyde, pyruvic acid, 2-ketoglutaric acid, and formaldehyde in wine, based on the formation of the 2,4-dinitrophenylhydrazones, is presented. These carbonyl compounds often result from the chemical oxidation of major wine components, and are known to affect flavor and color stability. Their analysis in wine is complicated due to their instability and their tendency to react reversibly with bisulfite to form α-hydroxysulfonates. Published methods that break down the sulfonates for the quantitation of total carbonyls in wine involve alkaline hydrolysis of sulfite-bound carbonyls, but we show, for the first time, that this alkaline treatment step significantly increases the concentration of carbonyls during analysis. A solution based on oxygen exclusion is described. The technique offers good specificity, reproducibility (%RSD 0.45-10.6), and limits of detection (1.29-7.53 μg L⁻¹). The method was successfully used to monitor concentration changes of these compounds in both white and red wines.     

Two-dimensional hybrid germanium zeotype formed by selective coordination of the trans-1,2-diaminocyclohexane isomer to the ge atom: heterogeneous acid-base bifunctional catalyst

[C 6H 10(NH 2) 2Ge 3O 6] ICMM9 is a two-dimensional germanate in which the metallic atoms are covalently bonded to chelating diamines. Its layered structure having some similitude with that of the pyroxene mineral, presents a totally new topology with two 4-c nodes. The solvothermal synthesis reaction allows the separation in situ of the two 1,2-diaminocyclohexane isomers by selective coordination of the trans isomer to octahedral Ge atoms of the ICMM9 framework. This material behaves as an active and selective heterogeneous acid-base bifunctional catalyst.     

Self-assembly of ligands designed for the building of a new type of [2 x 2] metallic grid. anion encapsulation and diffusion NMR spectroscopy

The ligands 4,6-bis(pyrazol-1-yl)pyrimidine (bpzpm), 4,6-bis(3,5-dimethylpyrazol-1-yl)pyrimidine (bpz(*)pm), 4,6-bis(4-methylpyrazol-1-yl)pyrimidine (Mebpzpm), and 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine (ppdMe) were synthesized and were made to react with Cu(I) centers in the presence of different counteranions. Different [2 x 2] metallic grids were obtained. With ligands bpzpm, bpz*pm, and Mebpzpm, a new type of grid was obtained where the facing ligands were divergent and two counteranions (BF(4-) or PF(6-)) were hosted in the resulting cavities and exhibit C-H...F and anion...pi interactions in the solid state. The presence of methyl groups on the pyrazolyl rings induced several distortions in the structure. In complexes with the ligand ppdMe, there were found two groups of parallel ligands in the grid, and the cavities generated were smaller. The counteranions were situated outside the grid, and the facing ligands exhibited aromatic pi-pi stacking interactions. Anion-pi interactions involving the pyridazine ring were found. The behavior in solution of the new derivatives with a special emphasis on the cation-anion interactions was studied by UV-vis and NMR spectroscopy. Diffusion NMR experiments performed for some complexes allowed us to conclude that weak cation-anion interactions exist in solution, with the counteranions undergoing fast exchange on the diffusion time scale between the free and ion-paired states.     

Low rank approximation in G0W0 calculations

The single particle energies obtained in a Kohn-Sham density functional theory (DFT) calculation are generally known to be poor approximations to electron excitation energies that are measured in transport, tunneling and spectroscopic experiments such as photo-emission spectroscopy. The correction to these energies can be obtained from the poles of a single particle Green’s function derived from a many-body perturbation theory. From a computational perspective, the accuracy and efficiency of such an approach depends on how a self energy term that properly accounts for dynamic screening of electrons is approximated. The G₀W₀ approximation is a widely used technique in which the self energy is expressed as the convolution of a noninteracting Green’s function (G₀) and a screened Coulomb interaction (W₀) in the frequency domain. The computational cost associated with such a convolution is high due to the high complexity of evaluating W₀ at multiple frequencies. In this paper, we discuss how the cost of G₀W₀ calculation can be reduced by constructing a low rank approximation to the frequency dependent part of W₀. In particular, we examine the effect of such a low rank approximation on the accuracy of the G₀W₀ approximation. We also discuss how the numerical convolution of G₀ and W₀ can be evaluated efficiently and accurately by using a contour deformation technique with an appropriate choice of the contour.     

Fabric phase sorptive extraction: An innovative sample preparation approach applied to the analysis of specific migration from food packaging

Additives added to food packaging materials can migrate to food in contact with them during storage and shelf life. A novel simple, fast and sensitive analyte extraction method based on fabric phase sorptive extraction (FPSE), followed by analysis using ultra-high performance liquid chromatography and mass spectrometry detection (UPLC-MS) was applied to the analysis of 18 common non-volatile plastic additives. Three FPSE media coated with different sol-gel sorbents characterized with different polarities including sol-gel poly(dimethylsiloxane), sol-gel poly(ethylene glycol) and sol-gel poly(tetrahydrofuran) were studied. All three FPSE media showed very satisfactory results. In general, compounds with low logP values seemed to have higher enrichment factors (EFs), especially with poly(tetrahydrofuran) and poly(ethylene glycol) media. For compounds with high logP values, the use of sol-gel poly(dimethylsiloxane) improved the enrichment capacity. Sample preparation time was optimized at 20 min for sample extraction and 10 min for solvent desorption. Acetonitrile was selected as desorption solvent since recoveries were over 70% for 13 out of 18 selected compounds in all FPSE media. The best extraction recovery values were obtained when compounds were dissolved in aqueous acetic acid solution (3%), where 17 out of 18 compounds showed improvement in their signal intensity after FPSE extraction and 10 obtained enrichment factors above 3 for all the tested FPSE media. When FPSE extracts were concentrated under nitrogen, 11 out of 18 compounds reached EFs values above 100.     

Chemiexcitation Efficiency of Intermolecular Electron‐transfer Catalyzed Peroxide Decomposition Shows Low Sensitivity to Solvent‐cavity Effects

Intermolecular chemically initiated electron exchange luminescence (CIEEL) systems are known to possess low chemiluminescence efficiency; whereas, the corresponding intramolecular transformations are highly efficient. As the reasons for this discrepancy are not known, we report in this work our studies of the solvent‐cavity effect on the efficiency of two intermolecular CIEEL systems, the catalyzed decomposition of diphenoyl peroxide and of a relatively stable 1,2‐dioxetanone derivative, spiro‐adamantyl‐1,2‐dioxetanone. The results indicate a very low medium viscosity effect on the quantum yields of these systems, a priori not compatible with these bimolecular transformations, showing also that their low efficiency cannot be due to solvent‐cavity escape of intermediate radical ion pairs. In addition, the solvent‐cage effect on the CIEEL efficiency, after the occurrence of the initial electron transfer, proved also to be very low, indicating the intrinsic low viscosity effect on the chemiexcitation step. Therefore, it is concluded that the low efficiency of these systems is intrinsic to the chemiexcitation step and cannot be improved by medium viscosity effects, being possibly due to sterical hindrance on charge‐transfer complex formation in the initial step of the CIEEL.     

Synthesis and characterization of polyesters derived from sebacic acid,hexanediol, and hydroquinone

Oils and fats derived from animals and plants provide a good renewable source for polymer precursors. In this investigation, fatty acids derived from plant oils and diols were used as monomers to produce polyesters by melt polycondensation. Sebacic acid, hexanediol, and hydroquinone were used as precursors in the polymer synthesis. The polymers were characterized by gel permeation chromatography, Fourier transform infrared spectroscopy, three-bending point flexural test, X-ray diffraction, tensile testing, and contact angle. The resulting polyesters were blended with epoxies to create materials with an increased elongation at break without affecting other mechanical properties.     

Voltammetric sensor based on magnetic particles modified composite electrode for determination of triamterene in biological sample

Some diuretic substances are controlled and monitored by the World Anti-Doping Agency as prohibited substances for use by athletes, such as triamterene (TRT). Thus, this work describes a voltammetric method based on graphite-epoxy composite electrode modified by tosyl-functionalized magnetic particles (GECE/MPs-To) for determination of TRT diuretic in urine sample. The TRT presented an oxidation peak at +1.24 V at GECE/MPs-To with irreversible behavior. Controlled potential electrolysis of the TRT at +1.26 V indicated the two electrons are transferred during amine group oxidation and the main product was identified by LC-MS/MS. The anodic peak current is 25 % higher at the modified electrode, suggesting that TRT is adsorbed on the magnetic particles. Using optimized conditions by using multivariate optimization of the parameters inherent of the square wave voltammetry, a calibration curve was constructed with a linear relationship for TRT from 0.500 to 99.8 μmol L^?1. The limits of detection and quantification were 1.47 and 4.91?×?10^?7 mol L^?1, respectively. The proposed method was applied to urine sample and validated by LC-MS/MS technique where the values found and compared between the two techniques showed no significant difference at 95 % confidence.     

Iron Oxide Nanoparticles Labeled with an Excited‐State Intramolecular Proton Transfer Dye

Excited‐state intramolecular proton transfer (ESIPT) is a particularly well known reaction that has been very little studied in magnetic environments. In this work, we report on the photophysical behavior of a known ESIPT dye of the benzothiazole class, when in solution with uncoated superparamagnetic iron oxide nanoparticles, and when grafted to silica‐coated iron oxide nanoparticles. Uncoated iron oxide nanoparticles promoted the fluorescence quenching of the ESIPT dye, resulting from collisions during the lifetime of the excited state. The assembly of iron oxide nanoparticles with a shell of silica provided recovery of the ESIPT emission, due to the isolation promoted by the silica shell. The silica network gives protection against the fluorescence quenching of the dye, allowing the nanoparticles to act as a bimodal (optical and magnetic) imaging contrast agent with a large Stokes shift.