Formation and characterization of gaseous adducts of carbon dioxide to magnesium, (CO2)MgX- (X=OH, Cl, Br)

A good fix: the structure and chemical reactivity of a reduced form of CO(2) bonded to magnesium, XMg(η(2)-O(2)C)(-), is reported. Upon reaction with water it loses CO, while it adds CH(3) upon reaction with alkyl halides, thereby signifying nucleophilicity of the carbon atom in XMg(η(2)-O(2)C)(-) in S(N)2 reactions.     

Hetero diels-alder reaction of vinyl allenes and aldehydes. An experimental and computational study

The hetero Diels-Alder reaction of vinyl allenes and aldehydes in the presence of a Lewis acid has been studied both experimentally and theoretically. Differently substituted vinyl allenes and aldehydes were used to obtain information on the structural requirements of the reaction. Theoretical calculations using the density functional theory indicate that the reaction proceeds through a highly asynchronous polar transition state.     

Rapid analysis of lubricants by atmospheric solid analysis probe–ion mobility mass spectrometry

Formulated lubricants are complex mixtures composed of base oil(s) and additives with various functions (detergents, corrosion inhibiter, antioxidant, viscosity modifiers, etc.). Because of the aliphatic nature of base oil and the chemical diversity of additives, the characterization of lubricant is currently a long and complex process. The comprehensive analysis of lubricant samples involves several techniques such as nuclear magnetic resonance, mass spectrometry, chromatography and infrared spectroscopy. The coupling of atmospheric solid analysis probe (ASAP) with ion mobility‐mass spectrometry (IM‐MS) has been shown to be an efficient tool for the characterization of complex mixture containing vaporizable polar to non‐polar compounds. This approach affords the coupling of a direct ionization technique that does not require sample preparation, with a bi‐dimensional separation method with high peak capacity. In this work, we show that ASAP‐IM‐MS is a suitable method for rapid and direct characterization of lubricant samples. Indeed, base oil and additives yielded, by ASAP, ions series which could be separated by IM‐MS. Molecular additives such as Zn‐dithiocarbamate, phosphite, thiophosphate and Alkyl diphenylamine were ionized as molecular ions [M]^+? or protonated molecules [M + H]⁺, depending of their polarity. In some cases, fragment ions were observed, confirming the additive identification. In addition, high molecular weight polymeric additives such as poly(alkyl methacrylate) (PAM) were pyrolized in the ASAP source leading to characteristic fragment ions. ASAP‐IM‐MS is shown to be a powerful tool for studying complex mixtures, allowing the first comprehensive analysis of lubricants in just a few minutes. Copyright © 2014 John Wiley & Sons, Ltd.     

Shear-induced lamellar phase of an ionic liquid crystal at room temperature

The phase behaviour of a number of N-alkylimidazolium salts was studied using polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. Two of these compounds exhibit lamellar mesophases at temperatures above 50°C. In these systems, the liquid crystalline behaviour may be induced at room temperature by shear. Sheared films of these materials, observed between crossed polarisers, have a morphology that is typical of (wet) liquid foams: they partition into dark domains separated by brighter (birefringent) walls, which are approximately arcs of circle and meet at “Plateau borders” with three or more sides. Where walls meet three at a time, they do so at approximately 120° angles. These patterns coarsen with time and both T1 and T2 processes have been observed, as in foams. The time evolution of domains is also consistent with von Neumann's law. We conjecture that the bright walls are regions of high concentration of defects produced by shear, and that the system is dominated by the interfacial tension between these walls and the uniform domains. The control of self-organised monodomains, as observed in these systems, is expected to play an important role in potential applications.     

Synthesis of substituted pyrrolidines by sequential radical cyclization and N-acyliminium ion reactions

Readily available N-acyl-2-pyrrolines are converted into functionalized -alkoxy-β-iodopyrrolidines by N-iodosuccinimide promoted alcohol addition to the enamine group. These compounds are readily cyclized using a sodium cyanoborohydride-catalytic tributylstannane system affording functionalized pyrrolidines in good yields. The cyclized products undergo N-acyliminium ion reactions, such as BF₃·OEt₂ mediated addition of allyltrimethylsilane.     

Role of Cationization and Multimers Formation for Diastereomers Differentiation by Ion Mobility-Mass Spectrometry

Stereochemistry plays an important role in biochemistry, particularly in therapeutic applications. Indeed, enantiomers have different biological activities, which can have important consequences. Many analytical techniques have been developed in order to allow the identification and the separation of stereoisomers. Here, we focused our work on the study of small diastereomers using the coupling of traveling wave ion mobility and mass spectrometry (TWIMS-MS) as a new alternative for stereochemistry study. In order to optimize the separation, the formation of adducts between diastereomers (M) and different alkali cations (X) was carried out. Thus, monomers [M + X]⁺ and multimers [2M + X]⁺ and [3M + X]⁺ ions have been studied from both experimental and theoretical viewpoints. Moreover, it has been shown that the study of the multimer [2Y + M + Li]⁺ ion, in which Y is an auxiliary diastereomeric ligand, allows the diastereomers separation. The combination of cationization, multimers ions formation, and IM-MS is a novel and powerful approach for the diastereomers identification. Thus, by this technique, diastereomers can be identified although they present very close conformations in gaseous phase. This work presents the first TWIMS-MS separation of diastereomers, which present very close collision cross section thanks to the formation of multimers and the use of an auxiliary diastereomeric ligand.

Shear-induced lamellar ionic liquid-crystal foam

In a recent paper we reported an experimental study of two N-alkylimidazolium salts. These ionic compounds exhibit liquid crystalline behaviour with melting points above 50°C in bulk. However, if they are sheared, a (possibly non-equilibrium) lamellar phase forms at room temperature. Upon shearing a thin film of the material between microscope slides, textures were observed that are strikingly similar to liquid (wet) foams. The images obtained from polarising optical microscopy (POM) were found to share many of the known quantitative properties of a two-dimensional foam coarsening process. Here we report an experimental study of this foam using a shearing system coupled with POM. The structure and evolution of the foam are investigated through the image analysis of time sequences of micrographs obtained for well-controlled sets of physical parameters (sample thickness, shear rate and temperature). In particular, we find that there is a threshold shear rate below which no foam can form. Above this threshold, a steady-state foam pattern is obtained where the mean cell area generally decreases with increasing shear rate. Furthermore, the steady-state internal cell angles and distribution of the cell number of sides deviate from their equilibrium (i.e. zero-shear) values.     

Thermal compatibility studies of nitroimidazoles and excipients

Nitroimidazoles are heterocycle imidazoles with a nitrogen group incorporated in its structure. The objective of this study was to develop a model to characterize possible interactions between active substances and excipients using: Thermogravimetry, Differential Thermal Analysis, Differential Scanning Calorimetry, and DSC coupled to photovisual system. It was used three nitroimidazoles (metronidazole, secnidazole, and tinidazole) and two types of microcrystalline cellulose with different particle size (Microcel and Avicel). The binary mixtures were prepared in proportion (w/w) 1:1 (nitroimidazole:excipient). Thermogravimetric data demonstrated that the tinidazole was the nitroimidazole with better uniformity. The nitroimidazoles obeyed the zero order kinetic reaction, evidencing its vaporization processes. Differential thermal analysis data showed nitroimidazoles compatibility with the different microcrystalline celluloses studied, showing that microcrystalline celluloses stabilized the active substances. Calorimetric data of secnidazole showed two melting points, characteristic of the polymorphs presented in raw material. The vaporization constants values of nitroimidazoles studied were secnidazole > metronidazole > tinidazole and for the binary mixtures these values followed the order tinidazole > metronidazole ≥ secnidazole.     

Prediction of the concentration polarization in the nanofiltration/reverse osmosis of dilute multi-ionic solutions

The aim of this work was to develop a simple and accurate model for predicting the concentration polarization index in the nanofiltration (NF)/reverse osmosis (RO) of dilute multi-ionic solutions. On the grounds of this model, the total flux of the ion i at the feed-solution/membrane interface consists of the sum of the diffusion, convection and migration fluxes, the former of which is determined by conventional mass-transfer correlations duly corrected to take into account the permeation through the membrane (suction effect). The coupling of the ionic fluxes is enforced by the electroneutrality requirement at the feed-solution/membrane interface. The model developed dispenses with the arbitrary assumption of the thickness of a film layer in the vicinity of the membrane surface.

Assessing the accuracy/validity of this model with multi-ionic solutions would be rather harsh, thus the model accuracy and ranges of validity were ascertained for a benchmark case: NF/RO of single salt solutions. The model predicts approximate concentration polarization indexes of the salts A⁺B⁻, A⁺₂B²⁻ and A⁺₃B³⁻ (or A²B⁻₂ and A³⁺B⁻₃) with positive deviations lower than 10% with respect to the benchmark concentration polarization index, for ions diffusivities ratios, D₁/D₂ (or D₂/D₁), in the range 0.16–5.5 and ≡J_v/k_c<3, where J_v is the permeation flux and k_c is the mass-transfer coefficient of the salt for vanishing mass-transfer rates at impermeable walls. The main assumption of the model – the individual mass-transfer coefficients of the ions are independent of each other – appears to hold in a broad range of conditions, for single salt solutions.

The model developed was expeditely applied to predict the concentration polarization in the nanofiltration of solutions containing Na⁺, Cl⁻ and a dye³⁻ (experimental data of Bowen and Mohammad [AIChE J. 44 (8) (1998) 1799–1812]), and its predictions are in fair agreement with the predictions of the extended Nernst–Planck equations in the film layer of the “slowest” ion.