Application of Densitometry and Spectrophotometry for Determination of Gallic Acid in Tea after Chromatographic Separation

JPC – Journal of Planar Chromatography – Modern TLC - Tea is one of the most popular beverages in the world. The exact composition of tea depends on the manufacturing process. Our goal...     

Über die magnetische Untersuchung der Zersetzungsprodukte des Kobalt(II)-hexacyano-ferrates

Zusammenfassung Kobalt(II)-hexacyanoferrat wird in der Luft zersetzt und die Zersetzungsprodukte werden analytisch, durch Röntgenaufnahmen und magnetische Messungen identifiziert.Die Rückstände, deren Zusammensetzung von der Zersetzungstemperatur abhängt, bestehen hauptsächlich aus Co, Co₃O₄, -Fe₂O₃, -Fe₂O₃, CoFe₂O₄ und CoO.     

Adsorption of reactive dye on chitosan in air-lift reactor

This study was undertaken to identify factors exerting the strongest influence on the adsorption of dye. The maximum adsorption capacity (at the adopted operating conditions) was the main parameter used to evaluate the process. In addition, the feasible adsorption capacity of chitosan was evaluated. Breakthrough experiments were carried out in a circulating air-lift reactor at a constant concentration of reactive dye Black 8 (100 mg/dm³). The tests studied different chitosan concentrations in the reactor and a range of flow intensities. The results of the breakthrough tests were compared by means of apparent mass transfer coefficients, determined by slopes at C/C ₀=1/2. The adsorption capacity of chitosan was affected to the greatest extent by the flow rate of the medium to the reactor. In turn, the utilization of the maximum adsorption capacity of chitosan, at the assumed efficiency of dye removal, was determined by chitosan concentration in the reactor.     

Thin-layer chromatography-densitometric measurements for determination of N-(hydroxymethyl)nicotinamide in tablets and stability evaluation in solutions

A thin-layer chromatography (TLC)-densitometric method was developed to determine N-(hydroxymethyl)nicotinamide in tablets and basic solutions along with nicotinic acid. Analysis was performed on silica gel F254 plates using chloroform-ethanol (2 + 3, v/v) mobile phase. The densitometric observations were made at 260 nm. The results showed good precision and accuracy; relative standard deviation was 2.37%, and recovery ranged from 97.60 to 100.82%. The limit of detection was 0.1 microg/spot, while the linearity range was from 0.2 to 1.75 microg/spot. Applicability of the newly developed method was tested for determination of N-(hydroxymethyl)nicotinamide in the preparation Cholamid. Densitometric measurements were used to evaluate stability of N-(hydroxymethyl)nicotinamide in basic solutions. It was found that decomposition corresponded to first-order reaction kinetics. The computed kinetic and thermodynamic parameters at 30 degrees C were as follows: k = 0.00675/min, t0,5 = 1.71 h, t0,1 = 0.26 h, and Ea = 44.75 kJ/mol.     

Dynamic mechanical properties of epoxy/novolac system modified with reactive liquid rubber and carbon filler

This paper reports on the work carried out to evaluate the frequency dependent viscoelastic properties of epoxy/novolac compositons modified with a liquid reactive rubber and carbon filler. For epoxy systems modified with elastomer, three typical transitions were observed: the α-relaxation deeply related to the glass transition of epoxy, the β-transition of epoxy, and the glass transition of rubber appeared near to the β-relaxation of epoxy resin. Considering an Arrhenius equation, the activation energies of β-relaxation were estimated. In the region of glass transition and rubbery state the temperature dependence of the shift factor (α_T) was determined through Williams-Landel-Ferry (WLF) equation.     

Coordination behaviour and two‐dimensional‐network formation in poly[[μ‐aqua‐diaqua(μ5‐propane‐1,3‐diyldinitrilotetraacetato)dilithium(I)cobalt(II)] dihydrate]: the first example of an MII–1,3‐pdta complex with a monovalent metal counter‐ion

The title compound, {[CoLi₂(C₁₁H₁₄N₂O₈)(H₂O)₃]·2H₂O}_n, constitutes the first example of a salt of the [M^II(1,3‐pdta)]²⁻ complex (1,3‐pdta is propane‐1,3‐diyldinitrilotetraacetate) with a monopositive cation as counter‐ion. Insertion of the Li⁺ cation could only be achieved through application of the ion‐exchange column technique which, however, appeared unsuccessful with other alkali metals and the ammonium cation. The structure contains two tetrahedrally coordinated Li⁺ cations, an octahedral [Co(1,3‐pdta)]²⁻ anion and five water molecules, two of which are uncoordinated, and is built of two‐dimensional layers extending parallel to the (010) lattice plane, the constituents of which are connected by the coordinate bonds. O—H_water...O hydrogen bonds operate both within and between these layers. The crystal investigated belongs to the enantiomeric space group P2₁ with only one (Λ) of two possible optical isomers of the [Co(1,3‐pdta)]²⁻ complex. A possible cause of enantiomer separation during crystallization might be the rigidification and polarization of the [M(1,3‐pdta)]²⁻ core, resulting from direct coordination of Li⁺ cations to three out of four carboxylate groups constituting the 1,3‐pdta ligand. The structure of (I) differs considerably from those of the other [M^II(1,3‐pdta)]²⁻ complexes, in which the charge compensation is realized by means of divalent hexaaqua complex cations. This finding demonstrates a significant structure‐determining role of the counter‐ions.     

Chiral macrocyclic aliphatic oligoimines derived from trans-1,2-diaminocyclohexane

Aliphatic dialdehydes of rigid structures having a cyclohexane, a bicyclo[2.2.2]octane or a [7]triangulane skeleton, have been condensed with enantiomerically pure trans-1,2-diaminocyclohexane to give [3+3] or [2+2] macrocyclization products. Unlike acyclic aliphatic imines, these macrocyclic oligoimines show enhanced stabilities and their structures in the crystals could be determined by X-ray diffraction analyses. The enantiomerically pure [7]triangulane dialdehyde showed remarkable diastereoselectivity in the condensation with the two enantiomers of trans-1,2-diaminocyclohexane: only one of the enantiomers gave a [2+2] macrocyclization product. Circular dichroism measurements combined with computational analysis show that the lowest energy electronic transition in these cyclic oligoimines is of n-pi* type.     

Selected β2-, β3- and β2,3-Amino Acid Heterocyclic Derivatives and Their Biological Perspective

Heterocyclic moieties, especially five and six-membered rings containing nitrogen, oxygen or sulfur atoms, are broadly distributed in nature. Among them, synthetic and natural alike are pharmacologically active compounds and have always been at the forefront of attention due to their pharmacological properties. Heterocycles can be divided into different groups based on the presence of characteristic structural motifs. The presence of β-amino acid and heterocyclic core in one compound is very interesting; additionally, it very often plays a vital role in their biological activity. Usually, such compounds are not considered to be chemicals containing a β-amino acid motif; however, considering them as this class of compounds may open new routes of their preparation and application as new drug precursors or even drugs. The possibility of their application as nonproteinogenic amino acid residues in peptide or peptide derivatives synthesis to prepare a new class of compounds is also promising. This review highlights the actual state of knowledge about β-amino acid moiety-containing heterocycles presenting antiviral, anti-inflammatory, antibacterial compounds, anaplastic lymphoma kinase (ALK) inhibitors, as well as agonist and antagonists of the receptors.     

Surface studies of magnesium oxide‐based catalysts modified with X2 or MgX2 (X = Br,I)

The introduction of a halide (Br, I) onto MgO leads to obtaining catalysts whose catalytic activity in transfer hydrogenation of acrolein with ethanol is significantly higher than that of unmodified MgO. In data found in literature, there is no concise view on how the modification of the surface of MgO with a halide affects its surface properties. Although most of the literature studies indicate a dependence of activity on the initial halide‐containing compound and type of halide, no study comprising both these aspects has been performed. The aim of the present study was to conduct measurements of MgO modified with two halides and with two types of initial halide‐containing compounds with surface‐sensitive techniques to determine how each of these factors influences the surface properties of the catalyst. Titration experiments showed that all of the modified catalysts have a smaller diversity of basic site strengths than unmodified MgO. They also revealed that for all studied systems, the modification of the surface leads to the formation of Brønsted acidic sites, which MgO does not possess. XPS spectra indicate that bromine‐modified catalysts give a broader range of surface species than the appropriate iodine‐modified ones. Moreover, they showed that in the case of both iodine‐modified and bromine‐modified catalysts, the one that exhibited the higher concentration of the appropriate halogen on the surface showed a lower activity in catalytic transfer hydrogenation of acrolein with ethanol. Copyright © 2015 John Wiley & Sons, Ltd.     

Photodegradation assessment of amisulpride,doxepin, haloperidol,risperidone, venlafaxine,and zopiclone in bulk drug and in the presence of excipients

Monatshefte für Chemie - Chemical Monthly - Photostability of amisulpride, doxepin, haloperidol, risperidone, venlafaxine, and zopiclone in APIs and powdered tablets during exposure to UVA...