Qualitative Identification of Metal Ions in Honey by Two-Dimensional Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC - Two-dimensional thin-layer chromatography (2D TLC) has been used as a screening method for detection of the metal ions Al3+, Cr3+,...     

Binding sites on the outside of metallo-supramolecular architectures; engineering coordination polymers from discrete architectures

Aggregation of metallo-supramolecular architectures through additional coordination is explored by introducing metal-binding units onto the outside of the supramolecular architectures. This is achieved within the framework of our imine-based approach to supramolecular architecture, by replacing the pyridylimine units with pyrazylketimine units. An advantage of the design is that it retains the ease-of-synthesis which characterises our imine-based approach. Silver(I) complexes of three pyrazylketimine ligand systems are described. The complexes demonstrate that introducing pyrazine donor units does indeed allow higher-order assembly of the distinct supramolecular architectures into engineered coordination polymers. Two distinct types of aggregation are observed. In the first, the donors on the outside of one architecture bind to the metals of another to link the units into a polymeric array. In the second type, the donors on the outside of the architectures bind to separate metal centres which are themselves not part of the architectures, and these separate metal centres link the units to form the macromolecular array. The weaker donor nature of the pyrazine nitrogens (compared to pyridine) also introduces an additional element into the design; higher coordination numbers are favoured and this can lead to arrays with higher connectivity than those observed in the discrete pyridylimine architectures.     

Simple and fast spectrophotometric determination of H(2)O(2) in photo-Fenton reactions using metavanadate

This work proposes a spectrophotometric method for the determination of hydrogen peroxide during photodegradation reactions. The method is based on the reaction of H₂O₂ with amonium metavanadate in acidic medium, which results in the formation of a red-orange color peroxovanadium cation, with maximum absorbance at 450 nm. The method was optimized using the multivariate analysis providing the minimum concentration of vanadate (6.2 mmol L⁻¹) for the maximum absorbance signal. Under these conditions, the detection limit is 143 μmol L⁻¹. The reaction product showed to be very stable for samples of peroxide concentrations up to 3 mmol L⁻¹ at room temperature during 180 h. For higher concentrations however, samples must be kept refrigerated (4 °C) or diluted. The method showed no interference of Cl⁻ (0.2-1.3 mmol L⁻¹), NO₃⁻ (0.3-1.0 mmol L⁻¹), Fe³⁺ (0.2-1.2 mmol L⁻¹) and 2,4-dichlorophenol (DCP) (0.2-1.0 mmol L⁻¹). When compared to iodometric titration, the vanadate method showed a good agreament. The method was applied for the evaluation of peroxide consumption during photo-Fenton degradation of 2,4-dichlorophenol using blacklight irradiation.     

Raman, FTIR, photoacoustic-FTIR and inelastic neutron scattering spectra of alkaline earth and lanthanide salts of hexahydridoruthenate(II), A2RuH6, (A = Ca, Sr, Eu) and their deuterides

The vibrational spectra (Raman, photoacoustic and Fourier transform infrared and inelastic neutron scattering) of the calcium, strontium and europium salts of hexahydrido- and hexadeuteridoruthenate(II) have been analyzed. All observed fundamental modes and overtone and combination bands are assigned. Density functional theory calculations of the vibrational frequencies assist in the analysis.     

An efficient, metal-free, room temperature aromatization of Hantzsch-1,4-dihydropyridines with urea-hydrogen peroxide adduct, catalyzed by molecular iodine

A mild, highly efficient and metal-free synthetic method for aromatization of 1,4-dihydropyridines employing urea-hydrogen peroxide adduct as oxidant catalyzed by 20 mol % of molecular iodine was developed. The reaction was carried out in ethyl acetate at room temperature and the products were isolated in high to excellent yields. A plausible free-radical mechanism is proposed based on results obtained with derivatives having alkyl and aryl substituents in the 1,4-dihydropyridine ring.     

Slow Magnetic Relaxation in {[CoCxAPy)] 2.15 H2O}n MOF Built from Ladder-Structured 2D Layers with Dimeric SMM Rungs

We present the magnetic properties of the metal-organic framework {[CoCxAPy]·2.15 H₂O}_n (Cx = bis(carboxypropyl)tetramethyldisiloxane; APy = 4,4′-azopyridine) (1) that builds up from the stacking of 2D coordination polymers. The 2D-coordination polymer in the bc plane is formed by the adjacent bonding of [CoCxAPy] 1D two-leg ladders with Co dimer rungs, running parallel to the c-axis. The crystal packing of 2D layers shows the presence of infinite channels running along the c crystallographic axis, which accommodate the disordered solvate molecules. The Co(II) is six-coordinated in a distorted octahedral geometry, where the equatorial plane is occupied by four carboxylate oxygen atoms. Two nitrogen atoms from APy ligands are coordinated in apical positions. The single-ion magnetic anisotropy has been determined by low temperature EPR and magnetization measurements on an isostructural compound {[Zn_0.8Co_0.2CxAPy]·1.5 CH₃OH}_n (2). The results show that the Co(II) ion has orthorhombic anisotropy with the hard-axis direction in the C_2V main axis, lying the easy axis in the distorted octahedron equatorial plane, as predicted by the ab initio calculations of the g-tensor. Magnetic and heat capacity properties at very low temperatures are rationalized within a S* = 1/2 magnetic dimer model with anisotropic antiferromagnetic interaction. The magnetic dimer exhibits slow relaxation of the magnetization (SMM) below 6 K in applied field, with a τ_lf ≈ 2 s direct process at low frequencies, and an Orbach process at higher frequencies with U/k_B = 6.7 ± 0.5 K. This compound represents a singular SMM MOF built-up of Co-dimers with an anisotropic exchange interaction.     

Apple Fibers as Carriers of Blackberry Juice Polyphenols: Development of Natural Functional Food Additives

Blackberry polyphenols possess various health-promoting properties. Since they are very sensitive to environmental conditions such as the presence of light, oxygen and high temperatures, the application of such compounds is restricted. Fibers are recognized as efficient carriers of polyphenols and are often used in polyphenols encapsulation. In the present study, the ability of apple fiber to adsorb blackberry juice polyphenols was examined. Freeze-dried apple fiber/blackberry juice complexes were prepared with different amounts of fibers (1%, 2%, 4%, 6%, 8% and 10%) and a constant amount of blackberry juice. Polyphenol profile, antioxidant activity, inhibition of the α-amylase, color parameters, as well as the IR spectra, of the obtained complexes were assessed. The results showed a negative effect of higher amounts of fiber (more than 2%) on the adsorption of polyphenols and the antioxidant activity of complexes. With the proper formulation, apple fibers can serve as polyphenol carriers, and thus the application as novel food additives can be considered.     

Aroma Profile and Chemical Composition of Reverse Osmosis and Nanofiltration Concentrates of Red Wine Cabernet Sauvignon

Wine aroma represents one of the main properties that determines the consumer acceptance of the wine. It is different for each wine variety and depends on a large number of various chemical compounds. The aim of this study was to prepare red wine concentrates with enriched aroma compounds and chemical composition. For that purpose, Cabernet Sauvignon red wine variety was concentrated by reverse osmosis (RO) and nanofiltration (NF) processes under different operating conditions. Different pressures (2.5, 3.5, 4.5 and 5.5 MPa) and temperature regimes (with and without cooling) were applied on Alfa Laval LabUnit M20 equipped with six composite polyamide RO98pHt M20 or NF M20 membranes. Higher pressure increased the retention of sugars, SO₂, total and volatile acids and ethanol, but the temperature increment had opposite effect. Both membranes were permeable for water, ethanol, acetic acid, 4-ethylphenol and 4-ethylguaiacol and their concentration decreased after wine filtration. RO98pHt membranes retained higher concentrations of total aroma compounds than NF membranes, but both processes, reverse osmosis and nanofiltration, resulted in retentates with different aroma profiles comparing to the initial wine. The retention of individual compounds depended on several factors (chemical structure, stability, polarity, applied processing parameters, etc.).     

Manufacturing and Assessing the New Orally Disintegrating Tablets,Containing Nimodipine-hydroxypropyl-β-cyclodextrin and Nimodipine-methyl-β-cyclodextrin Inclusion Complexes

The aim of the present study was to manufacture new orally disintegrating tablets containing nimodipine–hydroxypropyl-β-cyclodextrin and nimodipine–methyl-β-cyclodextrin inclusion complexes. For obtaining a better quality of the manufactured tablets, three methods of the preparation of inclusion complexes, in a 1:1 molar ratio, were used comparatively; namely, a solid-state kneading method and two liquid state coprecipitation and lyophilization techniques. The physical and chemical properties of the obtained inclusion complexes, as well as their physical mixtures, were investigated using Fourier transformed infrared spectroscopy, scanning electron microscopy, X-ray diffraction analyses, and differential scanning calorimetry. The results showed that the lyophilization method can be successfully used for a better complexation. Finally, the formulation and precompression studies for tablets for oral dispersion, containing Nim–HP-β-CD and Nim–Me-β-CD inclusion complexes, were successfully assessed.