Ices of CO2/H2O mixtures. Reflection-absorption IR spectroscopy and theoretical calculations

Ice mixtures of CO2 and H2O are studied using Fourier transform reflection-absorption infrared (RAIR) spectroscopy. Mixtures are prepared by sequential deposition or co-deposition of the two components from the gas phase onto an Al plate kept at 87 K inside a low-pressure chamber. Two CO2 structures are found in most experiments: a crystalline form similar to pure CO2, which evaporates when warming at 105 K, and a noncrystalline species which remains embedded in amorphous water ice after warming. Significant spectral variations are found depending on the deposition method and the thickness of the solid. Features characteristic of the RAIR technique appear in the spectral regions of the normal modes of the bending and asymmetric stretching CO2 vibrations. Simulations using Fresnel theory and Mie scattering are carried out with acceptable agreement with the experimental spectra of solids of variable thickness, from approximately 1 microm to the limit of nanoparticles. Theoretical calculations of a pure CO2 crystal are performed. The relaxed geometry of the solid and its vibrational spectrum are determined and compared to the experimental results.     

Intramolecular Nicholas reaction: stereoselective synthesis of 5-alkynylproline derivatives

The intramolecular Nicholas reaction of propargylic alcohols derived from N, N-acyl-diprotected omega-semialdehydes obtained from glutamic acid provided stereoselectively 5-alkynylproline derivatives. The suitable choice of the N-protecting group (tosyl or benzoyl derivative) permitted control of the stereochemistry during the ring formation. Semiempirical calculations of the species involved in the cyclization support the observed stereochemistry.     

Covalent and ionic Cu(II) complexes with cyclam and substituted benzoato ligands: structural,thermal, redox and mesomorphic properties

A covalent mononuclear complex, [Cu(p–HOC₆H₄COO)₂(cyclam)] (1), and two ionic mononuclear complexes, [Cu(cyclam)(H₂O)₂](p–CH₃OC₆H₄COO)₂ (2) and [Cu(cyclam)(H₂O)₂](p–CH₃(CH₂)₁₅OC₆H₄COO)₂·H₂O (3), were formed from reaction of cyclam with [Cu₂(p–HOC₆H₄COO)₄(H₂O)₂], [Cu₂(p–CH₃OC₆H₄COO)₄(H₂O)₂] and [Cu₂(p-CH₃(CH₂)₁₅OC₆H₄COO)₄(H₂O)₂], respectively. These complexes were isolated as purple crystals with molecular structures showing distorted octahedral N₄O₂ geometry. Complexes 1 and 2 were irreversibly reduced to Cu(I) and oxidized to Cu(III), while 3 was redox inactive. Complex 2 reacted with N-(hexadecyl)isonicotinamide (L) to form [Cu(cyclam)(L)₂](p–CH₃OC₆H₄COO)₂ (4). These complexes were thermally stable (T_dec > 200 °C for 1–3 and 174 °C for 4). Complexes 3 and 4 behaved as ionic liquids (melting temperatures lower than 100 °C) and exhibited mesomorphism.     

Hydrophilic interaction chromatography with Fourier transform mass spectrometry of monosaccharide anhydrides

A fast, selective, and sensitive method for the determination of three monosaccharide anhydrides (galactosan, mannosan, levoglucosan), based on hydrophilic interaction chromatography and Fourier transform mass spectrometry, was successfully developed. The simple experimental stationary phase and mass spectrometry performance screening allowed the selection of the best available chromatographic and mass spectrometry conditions. Thus, the chromatographic separation was performed on a highly selective stationary phase containing a zwitterionic phosphorylcholine group and the monosaccharide anhydrides were detected as [M+HCOO]^? adduct in the negative mode. The method showed accuracy in the range of 84–111 and 89–102% with interbatch precision expressed as relative standard deviations of 5.6–15.4 and 5.0–9.0% for the aerosol extract and snow samples, respectively. The limit of quantification in absolute values ranged from 10 to 30 pg, the limit of quantification, expressed as concentration, ranged was 0.3–0.9 ng/m³ for aerosol and 10–20 ng/mL for snow samples. The method was successfully applied for the determination of monosaccharide anhydrides in aerosol and snow samples.     

Flow-through solid-phase reflectometric method for simultaneous multiresidue determination of nitrophenol derivatives

In this paper, a flow-through optosensor based on diffuse reflectance spectroscopy and multivariate regression modelling is proposed for simultaneous multiresidue determination of trace level concentrations of nitro-substituted phenols. The optrode integrates on-line anion-exchange sorptive preconcentration and matrix removal with direct detection of sorbed species onto the sensing layer and chemometric deconvolution of overlapped spectra. After recording of the reflectometric spectrum, fast chemosensor regeneration is accomplished with an acidic methanolic eluent followed by a metered volume of alkaline solution. The full automation of the analytical procedure is ensured by flow-programming as executed via a software-controlled multisyringe pump and a set of multiposition and solenoid valves.

Under the optimized chemical and physical variables, the 3σ_blank detection limits for 2-, and 4-nitrophenol and 2,4-dinitrophenol were 0.69, 0.42 and 0.37 μg L⁻¹, respectively, for a sample loading volume of 4.0 mL with enrichment factors of 73, 74 and 81, respectively, and repeatability better than 3.0%. The analytical applicability of the optosensing system was asserted by the satisfactory results attained in its application to monitoring of nitrophenol derivatives in spiked environmental waters including highly saline matrices via the standard additions method.     

The insertion reaction of acetonitrile on aryl nickel complexes stabilized by bidentate N,N'-chelating ligands

Organometallic complexes to be used as single component precursors in the catalytic dimerization/polymerization of olefins usually must contain a labile ligand that can easily be displaced by the olefin. This is the first step in the activation of the precursor. One commonly used labile ligand is a nitrile. Here we report an example of incompatibility between the nickel or palladium aryl bond and acetonitrile. Neutral [MBr(Mes)NN] complexes in which Mes=2,4,6-Me3C6H2, NN=diazabutadiene (DAD), pyridinylimine (PIM), 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen) gave the expected [M(Mes)(3,5-lut)(NN)][BF4] compounds and the unexpected [Ni(Mes){NH=C(Me)(2,4,6-Me3C6H2)}(NN)][BF4] complexes in the presence of TlBF4 and 3,5-lutidine or acetonitrile. The sequence of reactions that leads to the imine ligand must include an initial insertion of the nitrile on the sigma(Ni-Mes) bond. These ionic complexes remain stable under 20 bar of ethylene.     

New alkaloids from Phoebe scortechinii

The leaves of the Phoebe scortechinii (Gamb.) Kochummen Comb. Nov. (Lauraceae), afforded one new proaporphine-tryptamine dimer; (-)-phoebescortechiniine (1), along with two known ones; phoebegrandine A and phoebegrandine B. The proaporphine, tetrahydropronuciferine (2), was isolated for the first time as a natural product. The alkaloids were elucidated primarily by means of high field NMR and HRMS.     

Classical Amphiphilic Behavior of Nonclassical Amphiphiles: A Comparison of Metallacarborane Self‐Assembly with SDS Micellization

The self‐assembly of metallacarboranes, a peculiar family of compounds exhibiting surface activity and resembling molecular‐scale Pickering stabilizers, has been investigated by comparison to the micellization of sodium dodecylsulfate (SDS). These studies have shown that molecules without classical amphiphilic topology but with an inherent amphiphilic nature can behave similarly to classical surfactants. As shown by NMR techniques, the self‐assembly of both metallacarboranes and SDS obey a closed association model. However, the aggregation of metallacarboranes is found to be enthalpy‐driven, which is very unusual for classical surfactants. Possible explanations of this fact are outlined.     

Gas chromatography with mass spectrometry analysis of phosphoserine,phosphoethanolamine, phosphoglycerol,and phosphate

A new, rapid, sensitive, robust, and reliable method has been developed for the qualitative analysis of phosphoserine, phosphoethanolamine, phosphoglycerol, and phosphate using gas chromatography with mass spectrometry and two‐step trimethylsilylation. The method employs hexamethyldisilazane for silylation of the phosphate and hydroxyl groups in the first phase and bis(trimethylsilyl)trifluoroacetamide for silylation of the less‐reactive amino groups in the second phase. This order is of key importance for the method because of the different reactivities of the two reagents and the mechanism of derivatization of the active groups of the analytes. Trimethylsilylated derivatives of the analytes were identified on the basis of their retention times and mass spectra. The probable structures of the major fragments were identified in the spectra of the trimethylsilylated derivatives and characteristic m/z fragments were selected for each analyte. Fragments with m/z 73 and 299 occurred in the spectra of all the analytes. The characteristic retention data were employed to calculate the retention indices of the individual silylated phosphorylated substances in the hydrocarbon range C₁₂–C₁₉ for the DB‐5ms column. The method was employed to measure the polar fraction of the hydrolysate of the cytoplasmic membrane of Bacillus subtilis. The detection limits vary between 5 μg/mL (trimethylsilylated phosphate) and 72 μg/mL (trimethylsilylated phosphoethanolamine).     

Design of experiments in 241Am alpha source preparation by electrodeposition: an approach to process optimization

This work describes a procedure to improve the quality of an ²⁴¹Am alpha source obtained by means of electrodeposition. The technique of design of experiments (DoE) was applied in order to perform a multivariate analysis of the experimental variable effects taking into consideration the following: i—amperage, d—cathode–anode distance, t—time and PP—polishing process. A 3⁴⁻² fractional design was employed using four experimental factors, three levels per factor, and three response variables were studied: H_area = electrodeposited active area, %R = activity recovery percentage, and Δ_1/2 = width at half-height. Thanks to this simple design, 9 experiments were enough, done in triplicate, to discern how Δ_1/2 and %R are modified when experimental factors change. Additionally, this work provides tools to perform effect statistical analysis of experimental factors, and to pose linear models applying significant terms. The models obtained were validated by analysis of variance and they were of help to verify the choice of significant factors by means of DoE and to approximate to the optimization of the preparation method of a ²⁴¹Am alpha source by means of contour plots of Δ_1/2 and %R.