Spontaneous vesicle formation and phase behavior in mixtures of an anionic surfactant with imidazoline compounds

Unexpected colloidal assemblies form in aqueous mixtures of sodium dodecylbenzenesulfonate (SDBS) with the following imidazoline compounds: 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (V-44, which is a commonly used free-radical initiator), 2,2'-tetramethylenedi-2-imidazoline (TMI), and the main recombination product (RP) from the decomposition of V-44. All of these imidazoline compounds act as hydrotropes. As the molar ratio of imidazoline to SDBS increases, a gradual transition from micelles to vesicles to bilayers to precipitate is observed. V-44 decomposes slowly at 25 degrees C, and the phase diagrams of V-44/SDBS and RP/SDBS are similar. The vesicular region observed in mixtures of TMI/SDBS is larger in composition than that of V-44/SDBS and RP/SDBS mixtures. At equimolar compositions of SDBS and RP, a novel colloidal structure with multiple closely packed bilayers is observed. In these mixtures, small unilamellar vesicles (<80 nm in diameter) form spontaneously, although with time they coexist with a small amount of precipitate and their size increases steadily. The self-assembly of vesicles occurs over a wide range of compositions when the solution pH is lower than the pK(a) of the imidazoline moiety. Quasi-elastic light scattering, cryogenic transmission electron microscopy, nuclear magnetic resonance, and small-angle neutron scattering were used to determine the characteristic length scales and properties of the assemblies.     

Beitrag zur Auswertung von Gas-Chromatogrammen mit Hilfe chemischer Kennzahlen (S?urezahl, Jodzahl usw.)

Zusammenfassung Bei der Analyse gleichartiger Verbindungen, die verschiedenen homologen Reihen angehören, können sich die gas-chromatographischen Banden überdecken und zu Trugschlüssen bei der Auswertung führen. Es wird gezeigt, wie sich das durch eine kritische Prüfung des Chromatogramms durch Aufstellung von Bilanzen der Kennzahlen vermeiden läßt. Als Beispiel wird die Analyse von Fettsäuren und Estern beschrieben, wobei Säure-, Verseifungs-, Hydroxyl-, Ester-, Jod- und Hexabromidzahl verwendet werden.

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Contribution to the evaluation of gas chromatograms

In the analysis of homogeneous compounds belonging to different homologous series, the gas-chromatographic bands may overlap and lead to fallacies in the evaluation. It is shown how this can be avoided by a critical analysis of the chromatogram using a balance sheet of the parameters. The analysis of fatty acids and esters is described as example, employing the acid, saponification, hydroxyl, ester, iodine, and hexabromide numbers.

     

Within the cell: analytical techniques for subcellular analysis

This review covers recent developments in the preparation, manipulation, and analyses of subcellular environments. In particular, it highlights approaches for (1) separation and detection of individual organelles, (2) preparation of ultra-pure organelle fractions, and (3) utilization of novel labeling strategies. These approaches, based on innovative technologies such as microfluidics, immunoisolation, mass spectrometry and electrophoresis, suggest that subcellular analyses will soon become as commonplace as single cell and bulk cellular assays.     

Determination of Gatifloxacin in Semen by HPLC with Diode-Array and Fluorescence Detection

The objective of this work was to develop an analytical HPLC method, using DAD and fluorescence detection, for determination of gatifloxacin in semen. A reversed-phase column was used with 90:10 water-acetonitrile, containing 10 mM TBA and 25 mM citric acid, as mobile phase. Semen was deproteinized with acetonitrile. Recovery was 95 ± 10%. The limits of quantification by DAD and fluorescence were 2.3 and 0.03 μg.mL^?1 respectively, with RSD of 3.4% for DAD and 2.8% for fluorescence. The method with fluorescence detection was used for quantification of gatifloxacin in the semen of patients under treatment.     

Direct Electrochemical Sensing and Detection of Natural Antioxidants and Antioxidant Capacity in Vitro Systems

This review highlights the role of electrochemical approaches in the sensing of antioxidants and their antioxidant capacity with especial attention to the analytical possibilities of electrochemistry in the direct evaluation of antioxidant capacity exhibited by food and biological samples due to the termed dietary, natural or biological antioxidants (mainly polyphenols, and vitamins C and E). The analytical potency of the electrochemistry is comprehensively stated and the selected results found in the literature are summarized and discussed critically. The main electrochemical approaches used have been cyclic voltammetry (CV) and flow injection analysis with amperometric detection (FIA‐ED). In addition, miniaturization is going to break new frontiers in the evaluation of antioxidant activity.     

A fast radical chain mechanism in the polyfluoroalkoxylation of aromatics through NO2 group displacement. Mechanistic and theoretical studies

Introduction of polyfluoroalkoxy and polyfluoroalkylthio substituents in aromatic rings can be achieved with mild conditions and short times thorough reaction of concentrated solutions of dinitrobenzenes in DMF with polyfluoro alcohols and polyfluoro thiols in moderate excess, in the presence of excess tetrabutylammonium fluoride as a base. Mechanistic studies suggest that under these conditions a fast radical chain mechanism operates. This mechanism is elicited by oxidation of a Meisenheimer complex and proceeds through a radical aromatic substitution with the polyfluoroalkoxy or the polyfluoroalkylthio radicals as key intermediates. At low concentrations, entrainment can be achieved with superoxide anion. A rationale for this effect is discussed. Answers to particular questions about the proposed mechanism are achieved through a theoretical study at the B3LYP/6-31+G(d,p) level. Specifically, the competition between the radical mechanism and the corresponding polar one (classical S(N)Ar reaction) is studied in that way, with the conclusion that the key steps of the radical mechanism in our reaction conditions (polar aprotic solvent) are at least as efficient as the ones of the polar one, thus justifying the observed kinetic advantage for the chain reaction in the conditions where an efficient initiation occurs.     

Transition from the layered Sr2RhO4 to the monodimensional Sr4RhO6 phase

Study of the structural changes occurring during the reduction process of the Sr2RhO4+delta, (214), n=1 term of the Ruddlesden and Popper series, shows that for delta <0.02 values, this material dissociates into the Sr4RhO6 (416) monodimensional phase, alpha = infinity, beta = 0 compound of the (A3B2O6)alpha-(A3B3O9)beta family, and Rh metal. During the first stage, this process occurs by the formation of an intergrowth between the (214) and (416) materials which can be only detected by high resolution electron microscopy and is easily interpreted on the basis of the structural relationship established between them. Further reduction allows the segregation of both phases as separated entities, which coexist with Rh metal. The dissociation process is reversible and, under oxidizing conditions, a layered material with anionic composition delta =0.06 is always obtained. This behaviour seems to be a general way of accommodating the compositional changes in layered A2BO4 phases where the B cation is always in a octahedral environment. The structural mechanism of this transformation is proposed, and the structural relationship between these two low-dimensional oxides is established.     

Effect of the addition of sulfur compounds on the hydroformylation of 1-hexene catalyzed by rhodium systems

The effect of the addition of triphenylphosphine sulfide, thiophene, benzo[b]thiophene and dibenzo[b,d]thiophene on the hydroformylation of 1-hexene catalyzed by rhodium complexes RhH(CO)₄, RhH(CO)₂(PPh₃)₂ and RhH(CO)₂(diphos) was studied. The addition of these sulfur compounds did not affect the activity of non modified rhodium precatalysts, decreased the activity of the PPh₃-modified one and increased the activity of the diphos-modified ones, which is indicative of the sulfur tolerance of these precatalysts. The linear to branched ratio (l/b) varied from 0.5 to 3.4 for the non-modified precatalyst, and from 1.7 to 3.3 for the phosphine-modified ones.     

Chiral relaxation reagents (CRR) in 13C NMR spectroscopy

Enantiomers and chiral relaxation reagents (CRR) afford diastereomeric complexes, which differ clearly in their ¹³C spin-lattice relaxation times.     

Solid-phase microextraction coupled with high-performance liquid chromatography for the analysis of heterocyclic aromatic amines

Solid-phase microextraction (SPME) coupled with high-performance liquid chromatography (HPLC) with UV diode array detection (DAD) for the analysis of heterocyclic aromatic amines (HAs) is described. Four kinds of fiber coatings: Carbowax-templated resin (CW-TPR), Carbowax-divinylbenzene (CW-DVB), poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) and polyacrylate (PA) were evaluated for extraction of nine most biologically active heterocyclic aromatic amines. Different parameters affecting to the microextraction and determination of HAs were studied, such as absorption and desorption time, desorption mode, composition of the solvent for desorption, pH, ionic strength, and percentage of methanol in the sample. To determine these amines in food samples a new simplified procedure is proposed, consisting of treatment of the sample with methanolic NaOH prior microextraction by CW-TPR fiber coating and HPLC-DAD determination. The advantages of this new method are the reduced amounts of time and organic solvents required.