Multicommuted flow-through fluorescence optosensor for determination of furosemide and triamterene

Multicommutation implemented with flow-through optosensors is a very promising area of research. This recent approach benefits from the advantages of both methods and results in high sensitivity, selectivity, and speed, and little waste generation. This paper reports the simultaneous determination of furosemide and triamterene, two widely used diuretics, by measurement of their native fluorescence. The system has been proved to be useful for determination of both analytes in pharmaceutical preparations and for determination of triamterene in human urine and serum. A minicolumn filled with Sephadex SPC-25 microbeads was used to achieve separation of both analytes before detection in a flow-through cell filled with the same resin. The sensor is linear in the range 50–1200 and 0.4–8 ng mL⁻¹ with detection limits of 15 and 0.1 ng mL⁻¹ for furosemide and triamterene, respectively.     

Regiospecific synthesis of mono-N-substituted indolopyrrolocarbazoles

[reactions: see text] Two complementary and efficient strategies have been developed for the regiospecific synthesis of unsymmetrical indolopyrrolocarbazoles (IPCs) mono-N-substituted with a pentacycle. A halogen in position 2 of the intermediate bisindolylmaleimides 3a-e allows a selective Mitsunobu coupling by exploiting the increased acidity of the 2-chloro-substituted indole nitrogen. It also promotes an easier cyclization of bisindolylmaleimides 4a-e and 7b-e to IPCs. Alkylation of the 2-unsubstituted indole-3-carboxamides 2a,b and further processing to the corresponding IPCs gives access to the opposite regioisomers.     

Stereocontrolled synthesis of iminocyclitols with an ether bridge

Nor-tropane related bicyclic (6+5) iminocyclitols with an ether bridge and different substituents (hydroxymethyl, aminomethyl, and aminoethyl) on C-1 are prepared starting from a β-d-psicofuranosyl cyanide. The method involves an internal nucleophilic attack of a stabilized amide ion on a 5-mesyloxy derivative. The intermediate N-acetyl O-protected iminocyclitols present atropoisomerism due to restricted rotation of the N-CO amido bond. Conformational aspects of the prepared compounds are discussed.     

Simulation of a crossover from the precipitation wave to moving Liesegang pattern formation

Model simulations to investigate the precipitation wave phenomenon and a crossover from the precipitation wave to moving Liesegang patterns were performed. The chemical scheme contains four chemical species via the interaction of precipitation and redissolution (complex formation), in which the precipitation reaction term was based on Ostwald's supersaturation theory. In this article, for the first time, all the features and behaviors of the heterogeneous traveling waves are reproduced, which were observed experimentally in the work of Zrínyi et al. (Zrínyi, et al. J. Phys. Chem. 1991, 95, 1618.). The detailed investigation of the pattern formation showed three possible states of the system, which depend on the initial concentration of the inner and outer electrolytes, respectively. These are the precipitation wave (single moving precipitation band), the moving Liesegang pattern (moving precipitation bands), and the state where these two patterns coexist.     

Heavy metal analysis of rainwaters: A comparison of TXRF and ASV analytical capabilities

The aim of this work consisted on the implementation of sufficiently accurate and sensitive analytical procedure for the analysis of metal concentration in rainwater. Different sample preparation procedures were tested to achieve the required concentration prior to direct total reflection X-ray fluorescence (TXRF) analysis. TXRF and anodic stripping voltammetry (ASV) were compared in regard to achieved detection limits, precision and accuracy.     

Insoluble eggshell matrix proteins--their peptide mapping and partial characterization by capillary electrophoresis and high-performance liquid chromatography

Avian eggshell matrix proteins were studied by two analytical approaches. Peptide mapping was done by trypsin and pepsin followed by collagenase cleavage; analyses were carried out by capillary electrophoresis and reversed-phase high-performance liquid chromatography (HPLC). Comparison of peptide maps obtained by both methods revealed a complex mixture of peptides in the insoluble layers of the eggshell; it was concluded that there are at least three different insoluble protein/peptide layers in the avian eggshell (cuticle, palisade, and mammillary layer). Partial characterization of peptides in each layer was made by HPLC-mass spectrometry analysis. There is an evidence that the eggshell insoluble proteins contain species susceptible to collagenase cleavage, however, the sequences split by this enzyme probably are not those typical for the main triple-helical core of collagenous proteins. It is proposed that the action of collagenase upon eggshell proteins is caused by the side effect of collagenase described previously with synthetic peptides. Some of the proteins present are probably glycosylated. Fatty acid content in the insoluble eggshell layers (after decalcification) was in the range of 2-4% (which reflected both lipid and lipoproteins bound fatty acids). Porphyrin pigments are dominant in the cuticle layer.     

Structural study of pyrimidine nucleoside analogues. I: Molecular mechanics and semiempirical calculations of 2′-deoxy-2′-fluoroarabinofuranosyluracils

Molecular mechanics (MM) calculations have been performed on the title compounds. For the MM minimum energy conformation obtained by conformational analysis, molecular orbital (MO) calculations (MNDO and AM1) have also been performed. The geometries obtained have been compared with the experimental ones extracted from the Cambridge Structural Database (CSD). A qualitative structure-activity relationship has been pointed out based on the electrostatic potentials calculated at different positions on the electronic surface.     

Phase Equilibria in the Ni–Al–W System at 900°C

Multicomponent Ni-base alloys exhibit good mechanical properties even at elevated temperatures and they are widely used for industrial production of exertion-resistive parts of engines. These properties are mainly determined by the coexistence of a disordered γ matrix with a face centred cubic lattice and cuboidal domains of its ordered γ′ structure. Therefore it is useful to study phase equilibria in Ni-base systems, namely in the regions involving both mentioned phases. One of the conclusions of our recent work on Ni–Al–Cr–W system was a necessity of modification of selected thermodynamic parameters of the ternary Ni–Al–W subsystem in order to achieve a better agreement of our experimental observations with theoretical modelling. This involves new measurements of the microstructure of selected samples of the Ni–Al–W system at 900°C and the comparison of the results with existing literature data in order to confirm our conclusions on higher order system investigated before. It is a first step on the way to an assessment of the Ni–Al–W system, which has not been done before.     

Application of Task-specific Ionic Liquids for Intensified Separations

Summary. Ionic liquids offer tremendous opportunities to intensify reactions and separations in process technologies by tuning their physical and chemical properties. Several ionic liquids are suitable for the separation of aromatic and aliphatic hydrocarbons. CO₂ absorption behavior was influenced by the functionalized chains appended to the room temperature ionic liquid (RTIL) cation. Ionic liquids seem able to combine the chemical features of amine solutions with the characteristic advantages of the physical solvents used for CO₂ absorption.     

Cyclodextrin effects on physical–chemical properties of novocaine

The UV-vis absorption and the fluorescence emission spectra of novocaine were analysed in aqueous cyclodextrin (CD) solutions. Either the absorbance read at λ_max 290 nm or the fluorescence emission intensity at λ_ems 346 nm increase in the presence of both α- and β-CD due to the formation of 1:1 inclusion complexes. The lower polarity of the CD-cavity sensed by the included drug enhances the emitted fluorescence; in fact, the same effect was observed in aqueous mixtures of acetonitrile, dioxane, or dimethylsulfoxide. The inclusion complex formation between the monocation of novocaine and CDs diminishes the electrical conductance of aqueous solutions of novocaine hydrochloride (NoHCl). Both the nitrosation reaction in aqueous acid medium and the ester hydrolysis in alkaline medium are retarded in the presence of CDs. The strongest effect was observed with β-CD as a consequence of the higher stability inclusion complex.