Volumes of mixing 2,4-dimethylpyridine withn-alkanes

In continuation of our work on excess thermodynamic properties of non-electrolyte solutions containing pyridine bases withn-alkanes, we have determined excess molar volumesV ^E for 2,4-dimethylpyridine + C₆ to C₁₀ n-alkanes at 25°C. For the investigated systems noV ^E values were available in the literature for comparison with our data. The experimentalV ^E was used to test the Prigogine-Flory-Patterson theory (PFP), Extended Real Associated Solutions model (ERAS) and the Treszczanowicz-Benson method (TB).     

Synthesis and selectivity of sym-hydroxydibenzo-14crown-4 ionophores for protons,alkali metal cations,and alkaline earth cations in polymeric membranes

Six derivatives of sym-hydroxydibenzo-14-crown-4 have been prepared and incorporated into solvent-polymeric membranes. Responses of the membranes to protons, alkali metal cations, and alkaline earth cations have been determined. The preferred uptake of protons is attributed to proton complexation by stable crown ether alcohol and diol monohydrate species.     

Influence of the Synthetic Conditions on the Structural and Electrochemical Properties of Carbon Nano‐Onions

Thermal annealing of nanodiamonds with diameters of a few nanometers (in an inert atmosphere and at temperatures in the range: 1500–1800 °C) leads to the formation of carbon nano‐onions (CNOs) with diameters between 5 and 6 nm, which correspond to nanostructures with six to eight graphitic layers. The resulting spherical CNO structures were thermally modified under different atmospheres and characterized by SEM, TEM, thermogravimetric analysis and spectroscopic (Raman and diffuse reflectance infrared Fourier transform/FTIR) spectroscopy. The electrochemical properties of the CNOs prepared under different conditions were determined and compared. The results reveal that the CNOs show different structures with predominant spherical “small” carbon nano‐onions. The aim of this article is to investigate the impact of the CNO′s synthesis conditions on the resulting structures and study the effect of further thermal modifications on the sizes, shapes and homogeneity of these carbon nanostructures.     

Formaldehyde activity on historical glass objects in museum microclimate

Degradation of some cultural heritage monuments has been caused by interaction with the closest environment (micro-climate). Amount of separate compounds is very small and because of it, this fact becomes neglected. Time and temperature can induce their activity finally causing deterioration. In this category organic compounds can be interpreted as one of museum show - case element. This statement has been improved by testing glass objects and their suitable sensors (model glasses). Destructive activity of formaldehyde on historical glasses belonging to the XVIII-th c. objects with totally different compositions has been confirmed by carried out experiments. For historical material which is very limited, sensor glass method has been applied. Sensors are prepared on the base of results of chemical analyses of original glass chemical analyses and melted on laboratory scale (according to historical data). Induced corrosion for sensor supports knowledge about deterioration process in real micro-environmental conditions. The following testing methods were used: scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), optical interferometer (OI), inductively couple plasma (ICP).     

Macrocyclic polyfunctional Lewis bases. XIII: Structure of the trichlorocuprate of benzo-15-crown-5 complexed potassium

The structure of the trichlorocuprate of benzo-15-crown-5 complexed potassium was determined from diffractometer data by direct and refined by least squares toR(F)=0.049. The complex of the formula [(C₁₄H₂₀O₅)₂K]₂Cu₂Cl₆ is triclinic. It consists of two sandwich-like crown-ether-complexed potassium cations and the Cu₂Cl ₆ ^2– anion lying in the corner of the unit cell. The sandwich complexes do not exhibit any elements of symmetry. The anion has a flatter structure in comparison to dimers of chlorocuprates of crown-complexed sodium and large organic cations.     

Potentiometric, spectroscopic, electrochemical and DFT characterization of oxovanadium(IV) complexes formed by citrate and tartrates in aqueous solution at high ligand to metal molar ratios: the effects of the trigonal bipyramidal distortion in bis-chelated species and biological implications

The complexation of VO(iv) ion with citrate (L(3-)), d-, l- and dl-tartrate (L(2-)) at high ligand to metal molar ratios was studied in aqueous solution through the combined application of potentiometric, spectroscopic (UV-vis and EPR) and electrochemical (cyclic voltammetry) techniques. Unlike in equimolar solution, mononuclear and not dinuclear species are formed with the binding of carboxylate-COO(-) and alcoholate-O(-) donors yielding mono- and bis-chelated species with VOLH, VOL, VOLH(-1) and VOL(2)H(-2) composition; for tartrates also the "sugar-like" (O(-), O(-)) coordination is involved in the vanadium binding at basic pH values giving rise to the formation of VOL(2)H(-3) and VOL(2)H(-4) complexes. Among the species formed, VOL(2)H(-2) is characterised by a strong distortion towards the trigonal bipyramid with the two V-O(alcoholate) bonds in the equatorial and the two V-O(carboxylate) bonds in the axial positions. The geometry and electronic absorption spectra of such complexes were simulated by DFT methods and it was found that in aqueous solution the distortion follows the steric hindrance of the substituents on the alpha-carbon atom and the hydrophobicity of the ligands. The results were compared with those displayed by simple alpha-hydroxycarboxylates (glycolate, 2-hydroxyisobutyrate, 2-ethyl-2-hydroxybutyrate and benzilate). The trigonal bipyramidal distortion was correlated with the values of: i) Deltalambda = lambda(2) - lambda(3), where lambda(2) and lambda(3) are the central bands in the electronic absorption spectrum; ii) |A(x) - A(y)|, where A(x) and A(y) are the (51)V hyperfine coupling constants along the x and y axes in the anisotropic EPR spectrum; iii) the half-wave potential E(1/2) of oxidation of VO(iv) to the corresponding VO(2)(v) species in the cyclic voltammogram. Finally, a discussion on the possible form of VO(iv)-citrate complexes in blood serum is presented, where it is found that the most relevant species under physiological conditions should be [VO(citrH(-1))](2-).     

NMR and molecular modeling study, as complementary techniques to capillary electrophoresis method to elucidate the separation mechanism of linezolid enantiomers

NMR study and molecular modeling were performed to improve the level of understanding of the chiral recognition process occurring between linezolid and anionic single-isomer cyclodextrin-heptakis-(2,3-diacetyl-6-sulfato)-beta-cyclodextrin (HDAS-beta-CD). NMR spectrometry allowed to estimate the stoichiometry of the complexes between HDAS-beta-CD and S- or R-linezolid and to determine the binding constants. The 1:1 complex stoichiometry was detected in millimolar concentrations and the mode of binding was proposed. The binding constants Ka of the complexes were of the order of 30-80 M(-1). Molecular dynamic simulations of 40ns for four complexes and calculations of binding free energies were performed. These calculations allowed determining the mode of binding of linezolid to HDAS-beta-CD and explaining the binding enantioselectivity.