Flow-injection determination of phenylephrine hydrochloride in pharmaceutical dosage forms with on-line solid-phase extraction and spectrophotometric detection

A flow injection method is proposed for the determination of phenylephrine hydrochloride in pharmaceutical dosage forms. The method involves the use of on-line solid-phase extraction by means of a microcolumn containing Dowex 50W X8 ion-exchange resin for the separation of the analyte prior to colour development and spectrophotometric detection in the visible region.

The influence of preconcentration flow, preconcentration pH and elution volume was studied.

The method exhibits appropriate linearity (r² = 0.9999) which was proved statistically by means of the “F”-test. When applied to commercial samples containing several active ingredients and excipients, a significant reduction of interferences was found. Accuracy, evaluated by means of the spike recovery method was in the range 99.7–100.8%, with precision (R.S.D., %) better than 1%.

In order to achieve the automation the system was controlled from a notebook computer by means of a program written in QuickBASIC language. Under these conditions, a sampling frequency of 40 samples per hour could be attained.     

Characterization of hierarchical porosity in novel composite monoliths with adsorption studies

Two different and novel composite monolithic materials with multimodal hierarchical porosity were prepared. The composites were prepared by immobilizing porous clay hetrostructure (PCH) and aluminum pillared clay (PILC), individually, into highly porous framework of a foam like monolith zeolite (MZ). The MZ was prepared hydrothermally, by following a polyurethane foam (PUF) based induced-template procedure and, consists of ZSM-5 framework. The MZ was fabricated into different composite materials through a simple dip coating method. Characterization of these materials with X-ray, SEM, and low temperature nitrogen adsorption techniques shows that composites materials are the morphological mixture (hybrid) of constituting materials. It also show that PCH based composites are meso and microporous, where as PILC based composites are essentially microporous in nature. The materials were further characterized for their hierarchical porosities by adsorption of two VOCs, which were toluene and n-hexane, under ambient conditions. The difference in adsorption of various sized (small to large) molecules was considered to work out the hierarchy of pores in these materials. With help of adsorption data, the hierarchical porosity was established into three size ranges, based on pore volumes of certain pore size ranges (>0.36 nm–<0.49 nm, >0.49 nm–<0.66 nm, and ≥0.66 nm). Water adsorption studies on these materials confirm that the coating of zeolite monolith with clay based adsorbents can also modify the hydrophobicity of original zeolite structure.     

Influence of the preparation method on the morphology of templated NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel

The synthesis of NiCo₂O₄ spinel by several nanocasting strategies (i.e., multi-step nanocasting, one-step nanocasting and soft-templating), in which nickel and cobalt nitrates are used as precursors and Pluronic P123 as surfactant, is explored. First, in the multi-step nanocasting, the effect of the impregnation method (evaporation, solid–liquid and two-solvent) of the SBA-15 silica template on the morphology of NiCo₂O₄ replica is investigated. The evaporation method seems to be the best choice to obtain mesoporous NiCo₂O₄ powder which, after calcination at 375 °C and subsequent template removal, displays the highest surface area (93.1 m²/g). We have also checked the feasibility of the one-step nanoscating approach for the synthesis of ordered NiCo₂O₄ arrays, though this methodology entails severe difficulties, mainly related to the different decomposition temperature of the nitrate precursors and the P123 surfactant. Finally, randomly oriented, aggregated NiCo₂O₄ nanoparticles are obtained by means of P123 surfactant-assisted soft-templating approach.     

Spectrofluorimetric Determination of Second Critical Micellar Concentration of SDS and SDS/Brij 30 Systems

Potentially useful stead-state fluorimetric technique was used to determine the critical micellar concentrations (CMC(1) and CMC(2)) for two micellar media, one formed by SDS and the other by SDS/Brij 30. A comparative study based on conductimetric and surfacial tension measurements suggests that the CMC(1) estimated by the fluorimetric method is lower than the value estimated by these other techniques. Equivalent values were observed for SDS micelles without Brij 30 neutral co-surfactant. The use of acridine orange as fluorescent probe permitted to determine both CMC(1) and CMC(2). Based on it an explanation on aspects of micelle formation mechanism is presented, particularly based on a spherical and a rod like structures.     

Palladium-catalyzed [3 + 2] intramolecular cycloaddition of alk-5-enylidenecyclopropanes

Readily accessible alk-5-enylidenecyclopropanes undergo [3 + 2] intramolecular cycloaddition reactions upon treatment with appropriate palladium complexes. The method allows the rapid and efficient assembly of a variety of bicyclo[3.3.0]octane systems with up to three stereocenters. Preliminary theoretical calculations uncovered previously unsuspected mechanistic possibilities based on either a concerted pallada-ene-like rearrangement or a stepwise process involving zwitterionic intermediates.     

End-performance evaluation of thiourea-modified bituminous binders through viscous flow and linear viscoelasticy testing

Straight-run bitumens are no longer suitable in new asphalt mixtures. Consequently, the use of modified bitumens has become more important. In order to both improve binders’ mechanical properties and prevent it from phase separation whilst stored at high temperature, the paving industry is currently developing new modification routes based on reactive agents. This work studies the use of thiourea, which has proven to efficiently broaden the temperature interval over which the binder demonstrates an adequate performance. On the one hand, viscous flow and dynamic shear tests indicate an enhancement in the high in-service temperature strength, along with a reduced thermal susceptibility. On the other hand, results of dynamic flexural tests reveal a significant decrease in the binder glass transition temperature. Finally, the use of master curves and a further frequency/temperature conversion are proposed, in order to attain a suitable viscoelastic characterisation of bituminous binders at low temperatures.     

Solvatochromic behavior of dyes with dimethylamino electron‐donor and nitro electron‐acceptor groups in their molecular structure

Six dyes with N,N‐dimethylaminophenyl and 4‐nitrophenyl or 2,4‐dinitrophenyl groups in their molecular structures were prepared and characterized. These compounds have different conjugated bridges (C?C, C?N, and N?N) connecting the electron‐donor and the electron‐acceptor groups. All compounds are solvatochromic, with reverse solvatochromism occurring. The solvatochromic band observed in each spectrum for the dyes is due to a π ? π* transition, of an intramolecular charge transfer nature, which occurs from the electron‐donor N,N‐dimethylaminophenyl group to the electron‐acceptor group in the molecules, which is reinforced by the structures of the compounds optimized by applying density functional theory, which exhibit high planarity. The reverse solvatochromism was explained considering two resonance structures. The benzenoid form is better stabilized in less polar solvents and characterizes the region displaying positive solvatochromism, while the dipolar form is better stabilized in more polar solvents, in the region of negative solvatochromism. The Catalán multiparametric approach was used to study the contribution of solvent acidity, basicity, dipolarity, and polarizability to the solvatochromism exhibited by the compounds. These compounds are good candidates for the investigation of the polarizability and, to a lesser extent, the dipolarity of the medium, with very little interference from specific interactions of the solvent through hydrogen bonding. Copyright © 2014 John Wiley & Sons, Ltd.     

Effective recognition of H2PO4- by a new series of dendrimers functionalized with ferrocenyl-urea termini

A new series of dendrimers with poly(propylene imine) backbones and 4, 8, 16, or 32 peripheral ferrocenyl-urea groups were prepared and characterized; their voltammetric behavior in DMSO solution was very sensitive to the presence of hydrogenphosphate anions at submillimolar concentration levels.     

Synthesis of fused oxabicyclic systems by metal-catalyzed intramolecular addition of 1,3-cycloalkyldiones to alkynes

[reaction: see text] Readily available 4-propargyl-1,3-cyclohexanediones and cyclopentanediones can be chemo- and regioselectively cycloisomerized to synthetically appealing fused oxabicyclic systems by simply stirring at room temperature with catalytic amounts of an appropriate metal complex.