Using Partial Least-Squares Regression in Multivariate UV Spectroscopic Analysis of Mixtures of Imidazolium-Based Ionic Liquids and 1-Methylimidazole for Measurements of Liquid–Liquid Equilibria

Recent interest in the use of room-temperature ionic liquids in various industrial applications sets requirements for analytical techniques that could lead to an efficient determination of concentrations of ionic liquids and/or possible impurities contained in them. Catalytic processes are particularly sensitive to the amount of impurities in the reaction media. Finding suitable and efficient techniques of determining compositions of liquid mixtures appears to be of importance not only for the design and optimization of such catalytic processes but also in measurements of phase equilibria. Imidazolium-based ionic liquids are often contaminated by their precursors 1-chlorobutane and 1-methylimidazole. Therefore, in this work a calibration technique is proposed that makes use of partial least-squares regression in UV spectroscopic determination of concentrations of 1-butyl-3-methylimidazolium hexafluorophosphate and 1-methylimidazole. Spectra of these compounds show significant overlaps making their simultaneous quantitative analysis difficult. Partial least-squares regression using the PLS2 algorithm provides an effective resolution, decomposing complicated spectra and coping with component interferences, nonlinearities and collinearity. The calibration method for the chosen compounds was validated using test samples of known composition and by measuring liquid?Cliquid equilibria at 298.15?K in the ternary system 1-butyl-3-methylimidazolium hexafluorophosphate?+?1-methylimidazole?+?1-chlorobutane.     

Electronegativity equalization method: parameterization and validation for organic molecules using the Merz-Kollman-Singh charge distribution scheme

The electronegativity equalization method (EEM) was developed by Mortier et al. as a semiempirical method based on the density-functional theory. After parameterization, in which EEM parameters A(i), B(i), and adjusting factor kappa are obtained, this approach can be used for calculation of average electronegativity and charge distribution in a molecule. The aim of this work is to perform the EEM parameterization using the Merz-Kollman-Singh (MK) charge distribution scheme obtained from B3LYP/6-31G* and HF/6-31G* calculations. To achieve this goal, we selected a set of 380 organic molecules from the Cambridge Structural Database (CSD) and used the methodology, which was recently successfully applied to EEM parameterization to calculate the HF/STO-3G Mulliken charges on large sets of molecules. In the case of B3LYP/6-31G* MK charges, we have improved the EEM parameters for already parameterized elements, specifically C, H, N, O, and F. Moreover, EEM parameters for S, Br, Cl, and Zn, which have not as yet been parameterized for this level of theory and basis set, we also developed. In the case of HF/6-31G* MK charges, we have developed the EEM parameters for C, H, N, O, S, Br, Cl, F, and Zn that have not been parameterized for this level of theory and basis set so far. The obtained EEM parameters were verified by a previously developed validation procedure and used for the charge calculation on a different set of 116 organic molecules from the CSD. The calculated EEM charges are in a very good agreement with the quantum mechanically obtained ab initio charges.     

Methacrylate monolithic columns of 320 microm I.D. for capillary liquid chromatography

Monolithic capillary columns (320 microm I.D.) were prepared for capillary liquid chromatography (CLC) by radical polymerization of butylmethacrylate (BMA) and ethylenedimethacrylate (EDMA) in the presence of a porogen solvent containing propan-1-ol, butane-1,4-diol and water. The influence of the contents of the porogen solvent and EDMA in the polymerization mixture on the monolith porosity and column efficiency was investigated. The composition of the polymerization mixture was optimized to attain a minimum HETP of the order of tens of microm for test compounds with various polarities. The separation performance and selectivity of the most efficient monolithic column prepared was characterized by van Deemter curves, peak asymmetry factors and Walters hydrophobicity and silanol indices. It was demonstrated that the 320-microm I.D. monolithic column exhibited CLC separation performance similar to that observed for 100- and 150-microm I.D. monolithic columns reported in the literature; moreover, the 320-microm I.D. column was easier to operate in CLC and exhibited a higher sample loadability.     

Selectivity assessment of an arsenic sequential extraction procedure for evaluating mobility in mine wastes

An optimized sequential extraction (SE) scheme for mine waste materials has been developed and tested for As partitioning over a range of pure As-bearing mineral phases, their model mixtures, and natural mine waste materials. This optimized SE procedure employs five extraction steps: (1) nitrogen-purged deionized water, 10 h; (2) 0.01 M NH₄H₂PO₄, 16 h; (3) 0.2 M NH₄-oxalate in the dark, pH3, 2 h; (4) 0.2 M NH₄-oxalate, pH3/80 °C, 4 h; (5) KClO₃/HCl/HNO₃ digestion. Selectivity and specificity tests on natural mine wastes and major pure As-bearing mineral phases showed that these As fractions appear to be primarily associated with: (1) readily soluble; (2) adsorbed; (3) amorphous and poorly-crystalline arsenates, oxides and hydroxosulfates of Fe; (4) well-crystalline arsenates, oxides, and hydroxosulfates of Fe; as well as (5) sulfides and arsenides. The specificity and selectivity of extractants, and the reproducibility of the optimized SE procedure were further verified by artificial model mineral mixtures and different natural mine waste materials. Partitioning data for extraction steps 3, 4, and 5 showed good agreement with those calculated in the model mineral mixtures (<15% difference), as well as that expected in different natural mine waste materials. The sum of the As recovered in the different extractant pools was not significantly different (89–112%) than the results for acid digestion. This suggests that the optimized SE scheme can reliably be employed for As partitioning in mine waste materials.     

Competitive Transfer Hydrogenation of Unsaturated Alcohol-Alkene-Diene Systems

The paper describes hydrogenation of unsaturated alcohols, alkenes and dienes in individual and binary systems of substrates by use of catalytic hydrogen transfer from ammonium formate in methanol on a palladium catalyst. A significant structural effect of hydrogenated alcohols upon their reactivity and adsorptivity was observed. Following comparison to the data acquired from typical hydrogenation by use of molecular hydrogen, it was inferred that the components of the CTH system increase the selectivity of competitive transfer hydrogenation to a significant extent in systems of unsaturated alcohol — unsaturated hydrocarbon with regard to the relative increase of reactivity of unsaturated alcohols. This occurs primarily due to affecting the relative adsorptivity.     

Self-Assembled Hydrogen-Bonding Chains of Copper(II) 2-Nitrobenzoate with Nicotinamide

Abstract  

The synthesis, spectral characterization and crystal structure of two new nitrobenzoatocopper(II) complexes, namely, [Cu₂(2-O₂Nbz)₄(nia)₂]·ACN (1) and [Cu₂(2-O₂Nbz)₄(ACN)₂] (2) (where 2-O₂Nbz = 2-nitrobenzoate, nia = nicotinamide and ACN = acetonitrile) are reported. The complexes 1 and 2 form dinuclear units of the paddle-wheel type around the crystallographic inversion centers. The copper ions are bridged by four 2-nitrobenzoate anions and the neutral N-donor ligands, viz. nicotinamide in 1 and acetonitrile in 2, are coordinated at apical positions. Selected geometric parameters of both complexes are compared with values for related tetra-2-nitrobenzoate complexes of copper(II) as well as the other dimeric copper(II) carboxylates with apical nicotinamide and acetonitrile ligands. The molecules of 1 are linked with N–H···O and C–H···O hydrogen bonds. The π–π stacking interactions in 1 are observed between benzene rings of 2-nitrobenzoate anions and pyridine rings of nicotinamide and also between acetonitrile molecules and benzene rings of 2-nitrobenzoate anions. The C–H···O hydrogen-bonds and CH/π interactions are observed in crystal structure of 2.     

Investigating the spectrum of biological activity of ring-substituted salicylanilides and carbamoylphenylcarbamates

In this study, a series of twelve ring-substituted salicylanilides and carbamoylphenylcarbamates were prepared and characterized. The compounds were analyzed using RP-HPLC to determine lipophilicity. They were tested for their activity related to the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. Moreover, their site of action in the photosynthetic apparatus was determined. Primary in vitro screening of the synthesized compounds was also performed against mycobacterial, bacterial and fungal strains. Several compounds showed biological activity comparable with or higher than the standards 3-(3,4-dichlorophenyl)-1,1-dimethylurea, isoniazid, penicillin G, ciprofloxacin or fluconazole. The most active compounds showed minimal anti-proliferative activity against human cells in culture, indicating they would have low cytotoxicity. For all compounds, the relationships between lipophilicity and the chemical structure are discussed.     

Asymptotic formulas for nonoscillatory solutions of conditionally oscillatory half-linear equations

We establish asymptotic formulas for nonoscillatory solutions of a special conditionally oscillatory half-linear second order differential equation, which is seen as a perturbation of a general nonoscillatory half-linear differential equation

Distortion Varieties

The distortion varieties of a given projective variety are parametrized by duplicating coordinates and multiplying them with monomials. We study their degrees and defining equations. Exact formulas are obtained for the case of one-parameter distortions. These are based on Chow polytopes and Gröbner bases. Multi-parameter distortions are studied using tropical geometry. The motivation for distortion varieties comes from multi-view geometry in computer vision. Our theory furnishes a new framework for formulating and solving minimal problems for camera models with image distortion.