Comparative analysis of ceramide structural modification found in fungal cerebrosides by electrospray tandem mass spectrometry with low energy collision-induced dissociation of Li+ adduct ions

Fungal cerebrosides (monohexosylceramides, or CMHs) exhibit a number of ceramide structural modifications not found in mammalian glycosphingolipids, which present additional challenges for their complete characterization. The use of Li+ cationization, in conjunction with electrospray ionization mass spectrometry and low energy collision-induced dissociation tandem mass spectrometry (ESI-MS/CID-MS), was found to be particularly effective for detailed structural analysis of complex fungal CMHs, especially minor components present in mixtures at extremely low abundance. A substantial increase in both sensitivity and fragmentation was observed on collision-induced dissociation of [M + Li]+ versus [M + Na]+ of the same CMH components analyzed under similar conditions. The effects of particular modifications on fragmentation were first systematically evaluated by analysis of a wide variety of standard CMHs expressing progressively more functionalized ceramides. These included bovine brain galactocerebrosides with non-hydroxy and 2-hydroxy fatty N-acylation; a plant glucocerebroside having (E/Z)-delta8 in addition to (E)-delta4 unsaturation of the sphingoid base; and a pair of fungal cerebrosides known to be further modified by a branching 9-methyl group on the sphingoid moiety, and to have a 2-hydroxy fatty N-acyl moiety either fully saturated or (E)-delta3 unsaturated. The method was then applied to characterization of both major and minor components in CMH fractions from a non-pathogenic mycelial fungus, Aspergillus niger; and from pathogenic strains of Candida albicans (yeast form); three Cryptococcus spp. (all yeast forms); and Paracoccidioides brasiliensis (both yeast and mycelium forms). The major components of all species examined differed primarily (and widely) in the level of 2-hydroxy fatty N-acyl delta3 unsaturation, but among the minor components a significant degree of additional structural diversity was observed, based on differences in sphingoid or N-acyl chain length, as well as on the presence or absence of the sphingoid delta8 unsaturation or 9-methyl group. Some variants were isobaric, and were not uniformly present in all species, affirming the need for MS/CID-MS analysis for full characterization of all components in a fungal CMH fraction. The diversity in ceramide distribution observed may reflect significant species-specific differences among fungi with respect to cerebroside biosynthesis and function.     

Asymmetric reductive amination of boron-containing aryl-ketones using ω-transaminases

The asymmetric reductive amination of aryl-ketones bearing various boron-functionalities (acid, ester or potassium trifluoroborates) was investigated employing enantiocomplementary ω-transaminases as catalysts. Under the optimized conditions, high conversions (up to 94%) and excellent ee’s (up to >99%) were obtained providing access to both (R)- and (S)-configured amino-aryl boronates under mild reaction conditions.     

Determination of CO2 capture during accelerated carbonation of engineered cementitious composite pastes by thermogravimetry

Journal of Thermal Analysis and Calorimetry - The present study has evaluated the rheological behavior of an oil-based (5W50) hybrid nanofluid [magnesium oxide (65%)–multi-walled carbon...     

The local electrochemical behavior of the AA2098-T351 and surface preparation effects investigated by scanning electrochemical microscopy

In this work, scanning electrochemical microscopy (SECM) measurements were employed to characterize the electrochemical activities on polished and as-received surfaces of the 2098-T351 aluminum alloy (AA2098-T351). The effects of the near surface deformed layer (NSDL) and its removal by polishing on the electrochemical activities of the alloy surface were evaluated and compared by the use of different modes of SECM. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were also employed to characterize the morphology of the surfaces. The surface chemistry was analyzed by X-ray photoelectron spectroscopy (XPS). The surface generation/tip collection (SG/TC) and competition modes of the SECM were used to study hydrogen gas (H₂) evolution and oxygen reduction reactions, respectively. H₂ evolution and oxygen reduction were more pronounced on the polished surfaces. The feedback mode of SECM was adopted to characterize the electrochemical activity of the polished surface that was previously corroded by immersion in a chloride-containing solution, in order to investigate the influence of the products formed on the active/passive domains. The precorroded surface and as-received surfaces revealed lower electrochemical activities compared with the polished surface showing that either the NSDL or corrosion products largely decreased the local electrochemical activities at the AA2098-T351 surfaces.     

Synthesis of Dibromo-Vinyl Chalcogenides

β-Bromovinyl chalcogenides were conveniently prepared in good yields by reacting alkynyl chalcogenides with bromine or by addition of organochalcogenyl bromide to bromoacetylenes in the presence of zinc bromide.     

Pulsed voltammetric/amperometric detection of polycyclic aromatic sulfur heterocycles (PASHs) at the gold disc electrode for studies in petroleum asphalts

This work describes the voltammetric and amperometric behavior of a high number of PASHs (sulfides, thiophenes, benzothiophenes, dibenzothiophenes, indenothiophenes, naphtothiophenes, thienothiophenes, phenanthrothiophenes, and acenaphtothiophenes) at gold disc electrodes aiming at their identification and determination in petroleum asphalts. The adsorption/redox processes expected for sulfur compounds at gold electrodes could be observed in all the studied PASHs in DMSO and hydromethanolic medium. Differential pulse (DP) voltammetry in non-aqueous solutions (0.1 mol L⁻¹ NaClO₄ in DMSO) was approached for determining non-volatile PASHs in asphalts submitted to different aging processes. It was found herein that the DP voltammetric monitoring of PASH oxidation at + 0.7 V (vs. Ag/AgCl/LiCl 3 mol L⁻¹) for virgin/aged asphalts can be used for the comparative study of asphalts based on the consumption of PASHs. Additionally, pulsed amperometric detection (PAD) in hydroalcoholic solution (10 mmol L⁻¹ acetate buffer in 65% methanol) coupled with a chromatographic separation was approached for determining volatile PASHs in asphalts submitted to thermal decomposition processes. A detection cycle of 2 s involving oxidative (0.4 s at + 0.4 V) and reductive (1.2 s at − 1.0 V) cleaning pulses after a detection pulse of − 0.8 V (0.4 s) applied successively to the gold electrode (vs. Pd/PdO) was found to be optimal for regenerating the gold surface during successive chromatographic runs of PASHs. Thus, reversed-phase liquid chromatography (LC)–coupled PAD was found useful to separate a complex mixture of PASHs. The optimized PAD and LC separation was further applied to investigate the presence of electroactive PASHs as volatile compounds in asphalt fumes generated at 260 °C.

     

Self-assembling of phenothiazine compounds investigated by small-angle X-ray scattering and electron paramagnetic resonance spectroscopy

Small-angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) have been carried out to investigate the structure of the self-aggregates of two phenothiazine drugs, chlorpromazine (CPZ) and trifluoperazine (TFP), in aqueous solution. In the SAXS studies, drug solutions of 20 and 60 mM, at pH 4.0 and 7.0, were investigated and the best data fittings were achieved assuming several different particle form factors with a homogeneous electron density distribution in respect to the water environment. Because of the limitation of scattering intensity in the q range above 0.15 A(-1), precise determination of the aggregate shape was not possible and all of the tested models for ellipsoids, cylinders, or parallelepipeds fitted the experimental data equally well. The SAXS data allows inferring, however, that CPZ molecules might self-assemble in a basis set of an orthorhombic cell, remaining as nanocrystallites in solution. Such nanocrystals are composed of a small number of unit cells (up to 10, in c-direction), with CPZ aggregation numbers of 60-80. EPR spectra of 5- and 16-doxyl stearic acids bound to the aggregates were analyzed through simulation, and the dynamic and magnetic parameters were obtained. The phenothiazine concentration in EPR experiments was in the range of 5-60 mM. Critical aggregation concentration of TFP is lower than that for CPZ, consistent with a higher hydrophobicity of TFP. At acidic pH 4.0 a significant residual motion of the nitroxide relative to the aggregate is observed, and the EPR spectra and corresponding parameters are similar to those reported for aqueous surfactant micelles. However, at pH 6.5 a significant motional restriction is observed, and the nitroxide rotational correlation times correlate very well with those estimated for the whole aggregated particle from SAXS data. This implies that the aggregate is densely packed at this pH and that the nitroxide is tightly bound to it producing a strongly immobilized EPR spectrum. Besides that, at pH 6.5 the differences in motional restriction observed between 5- and 16-DSA are small, which is different from that observed for aqueous surfactant micelles.     

Numerical simulation of the liquid phase in SnO<Subscript>2</Subscript> thin film deposition by sol-gel-dip-coating

The fluid flow of the liquid phase in the sol-gel-dip-coating process for SnO₂ thin film deposition is numerically simulated. This calculation yields useful information on the velocity distribution close to the substrate, where the film is deposited. The fluid modeling is done by assuming Newtonian behavior, since the linear relation between shear stress and velocity gradient is observed. Besides, very low viscosities are used. The fluid governing equations are the Navier–Stokes in the two dimensional form, discretized by the finite difference technique. Results of optical transmittance and X-ray diffraction on films obtained from colloidal suspensions with regular viscosity, confirm the substrate base as the thickest part of the film, as inferred from the numerical simulation. In addition, as the viscosity increases, the fluid acquires more uniform velocity distribution close to the substrate, leading to more homogenous and uniform films.