Application of Internal Standard for Micro Extraction– Spectrophotometric Determination of Bismuth in Pharmaceutical Formulations

 A micro extraction – spectrophotometric procedure is developed for the determination of bismuth in pharmaceutical formulations. The procedure is based on the extraction of tetraiodobismuthate(III) ion paired with benzyltributylammonium cation into chloroform. The application of Nile Blue as internal standard (IS) enabled good analytical performance for micro-scale analysis. The ratio between the absorbances measured at 491 nm (bismuth complex) and at 632 nm (IS) was taken as the analytical signal. The procedure was carried out in Eppendorf tubes, lowering significantly the use of reagents and the volume of organic solvent. In the calibration range up to 60 mgċl⁻¹, the linear regression coefficient was 0.9999, the CV for 15 mgċl⁻¹ and for 50 mgċl⁻¹ Bi were 1.6% and 0.7% respectively. The results obtained in the analysis of pharmaceutical formulations were in good agreement with the results of EDTA titration method. Received November 25, 1999. Revision February 14, 2000.     

Hydrotalcite-derived Co-containing mixed metal oxide catalysts for methanol incineration

The Co–Mg–Al mixed metal oxides were prepared by calcination of co-precipitated hydrotalcite-like precursors at various temperatures (600–800 °C), characterised with respect to chemical (AAS) and phase (XRD) composition, textural parameters (BET), form and aggregation of cobalt species (UV–vis-DRS) and their redox properties (H₂-TPR, cyclic voltammetry). Moreover, the process of thermal decomposition of hydrotalcite-like materials to mixed metal oxide systems was studied by thermogravimetric method combined with the analysis of gaseous decomposition products by mass spectrometry. Calcined hydrotalcite-like materials were tested as catalysts for methanol incineration. Catalytic performance of the oxides depended on cobalt content, Mg/Al ratio and calcination temperature. The catalysts with lower cobalt content, higher Mg/Al ratio and calcined at lower temperatures (600 or 700 °C) were less effective in the process of methanol incineration. In a series of the studied catalysts, the best results, with respect to high catalytic activity and selectivity to CO₂, were obtained for the mixed oxide with Co:Mg:Al molar ratio of 10:57:33 calcined at 800 °C. High activity of this catalyst was likely connected with the presence of a Co–Mg–Al spinel-type phases, containing easy reducible Co³⁺ cations, formed during high-temperature treatment of the hydrotalcite-like precursor.     

Determination of aluminium and chromium in serum by atomic absorption spectrometry

Summary The optimal conditions for the determination of aluminium and chromium in blood serum are proposed. Several sample pretreatment procedures for the purpose are compared. The best results are obtained by sample dilution with nitric acid (0.1 mol/l) and addition of Mg(NO₃)₂ as modifier with a magnesium concentration of 0.2 mg/ml. This procedure has been used for studying the intestinal intake of aluminium by patients after oral administration of aluminium compounds.     

A 1:1 cocrystal of baicalein with nicotinamide

Cocrystallization of baicalein with nicotinamide yields a 1:1 cocrystal [systematic name: pyridine‐3‐carboxamide–5,6,7‐trihydroxy‐2‐phenyl‐4H‐chromen‐4‐one (1/1)], C₆H₆N₂O·C₁₅H₁₀O₅. The asymmetric unit contains one baicalein and one nicotinamide molecule, both in neutral forms. Molecules in the cocrystal form column motifs stabilized by an array of intermolecular hydrogen bonds.     

Potassium salts of hypodiphosphoric acid

The synthesis and crystal structures of a series of six crystalline potassium salts of hypodiphosphoric acid, H₄P₂O₆, are reported, namely potassium hydrogen phosphonophosphonate, K⁺·H₃P₂O₆⁻, (I), dipotassium dihydrogen hypodiphosphate monohydrate, 2K⁺·H₂P₂O₆²⁻·H₂O, (II), dipotassium dihydrogen hypodiphosphate dihydrate, 2K⁺·H₂P₂O₆²⁻·2H₂O, (III), pentapotassium hydrogen hypodiphosphate dihydrogen hypodiphosphate dihydrate, 5K⁺·HP₂O₆³⁻·H₂P₂O₆²⁻·2H₂O, (IV), tripotassium hydrogen hypodiphosphate tetrahydrate, 3K⁺·HP₂O₆³⁻·4H₂O, (V), and tetrapotassium hypodiphosphate tetrahydrate, 4K⁺·P₂O₆⁴⁻·4H₂O, (VI). All the hypodiphosphate anions, viz. H₃P₂O₆⁻, H₂P₂O₆²⁻, HP₂O₆³⁻ and P₂O₆⁴⁻, adopt a staggered conformation. The P—P bond lengths [2.1722 (7)–2.1892 (10) Å] do not depend on the basicity of the anion. The compounds are organized into different types of one‐, two‐ or three‐dimensional polymeric hydrogen‐bonded networks, or simply exist in the form of isolated or dimeric units. The coordination numbers of the K⁺ cations range from 6 to 9, and the cationic sublattices are polymeric one‐, two‐ or three‐dimensional networks, or isolated [KO₆] or dimeric [K₂O₁₂] polyhedra.     

Conformational isomers of the [(5‐methyl‐2‐pyridinio)aminomethylene]diphosphonate dianion and [(5‐methyl‐2‐pyridyl)aminomethylene]diphosphonate trianion in salts with 4‐aminopyridine and ammonia

The crystal structures of two salts, products of the reactions between [(5‐methyl‐2‐pyridyl)aminomethylene]bis(phosphonic acid) and 4‐aminopyridine or ammonia, namely bis(4‐aminopyridinium) hydrogen [(5‐methyl‐2‐pyridinio)aminomethylene]diphosphonate 2.4‐hydrate, 2C₅H₇N₂⁺·C₇H₁₀N₂O₆P₂²⁻·2.4H₂O, (I), and triammonium hydrogen [(5‐methyl‐2‐pyridyl)aminomethylene]diphosphonate monohydrate, 3NH₄⁺·C₇H₉N₂O₆P₂³⁻·H₂O, (II), have been determined. In (I), the Z configuration of the ring N—C and amino N—H bonds of the bisphosphonate dianion with respect to the C_ring—N_amino bond is consistent with that of the parent zwitterion. Removing the H atom from the pyridyl N atom results in the opposite E configuration of the bisphosphonate trianion in (II). Compound (I) exhibits a three‐dimensional hydrogen‐bonded network, in which 4‐aminopyridinium cations and water molecules are joined to ribbons composed of anionic dimers linked by O—H...O and N—H...O hydrogen bonds. The supramolecular motif resulting from a combination of these three interactions is a common phenomenon in crystals of all of the Z‐isomeric zwitterions of 4‐ and 5‐substituted (2‐pyridylaminomethylene)bis(phosphonic acid)s studied to date. In (II), ammonium cations and water molecules are linked to chains of trianions, resulting in the formation of double layers.     

Synthesis and photophysical properties of a new amino acid possessing a BODIPY moiety

The synthesis of a new amino acid possessing a BODIPY fluorophore, which is of use in peptide synthesis, is described. The influence of the amino acid as well as of benzoxazole moieties on the BODIPY spectral and photophysical properties is discussed. The photophysical properties of this fluorophore were modified only to a small extent compared to those of the parent compound.     

Fluorescent chemosensors for metal ions based on 3-(2-benzoxazol-5-yl)alanine skeleton

The ability of new chelate ligands, benzoxazol-5-yl-alanine derivatives substituted in position 2 by heteroaromatic substituent, to form complexes with selected metal ions in acetonitrile are studied by means of absorption and steady-state and time-resolved fluorescence spectroscopy. Among the ligands studied, only azaaromatic derivatives form stable complexes with transition metal ions in the ground state. Their absorption bands are bathochromically shifted enabling to use those ligands as ratiometric sensors. The fluorescence of each ligand is quenched by metal ions, however, in the presence of Cd(II) and Zn(II) ions a new red shifted emission band is observed.