Silver/silver bromide/polypyrrole nanoparticles obtained by microemulsion photopolymerization in the presence of a cationic surfactant

Conductive silver/silver bromide/polypyrrole nanoparticles were obtained by photopolymerization in o/w microemulsions of pyrrole monomer in the presence of silver nitrate as electron acceptor and dopant under UV light irradiation. The microemulsions were prepared using cetyltrimethylammonium bromide (CTAB) as cationic surfactant. The particles were analyzed by scanning electron microscopy (SEM), UV/Vis, Fourier transform infrared spectroscopy, cyclic voltammetry, and X-ray diffraction (XRD). It was observed from SEM analysis that spherical particles can be obtained by this procedure with relatively narrow particles sizes distributions and average particle diameters of the silver cores (Dp) between 39 and 46 nm, which decreases as the surfactant concentration is increased. The conductivities of the resulting materials were between 0.12 and 0.40 S/m. Formation of cores of Ag and AgBr were observed from the XRD analysis, which was ascribed to the reduction of Ag⁺ to Ag⁰ and to reaction of Ag⁺ with the counterion of CTAB surfactant, respectively.     

On the Evaluation of the Number of Binding Sites in Proteins From Steady State Fluorescence Measurements

The number of binding sites for a given solute in a protein is a most relevant parameter. This number can be derived from fluorescence quenching data which provides the fraction of sites occupied at a given free solute concentration. Data are generally treated according to Scatchard′s or Ward′s equations. Lately, a double logarithmic plot of the data has been extensively used with this purpose. The present communication discus the validity of this procedure. It is concluded that this type of plot provides an evaluation of the stoichiometry (molecularity) of the binding process but not the number of equivalent binding sites per protein.     

Magnetic nanoparticles--templated assembly of protein subunits: a new platform for carbohydrate-based MRI nanoprobes

A new approach for the preparation of carbohydrate-coated magnetic nanoparticles is reported. In a first step, we show that the pH-driven assembly-disassembly natural process that occurs in apoferritin protein is effective for the encapsulation of maghemite nanoparticles of different sizes: 4 and 6 nm. In a second step, we demonstrate that the presence of functional amine groups in the outer shell of apoferritin allows functionalization with two carbohydrates, N-acetyl-D-glucosamine and d-mannose. High-resolution electron microscopy (HREM), high angle annular dark field scanning electron microscopy (HAADF-STEM), electron energy loss spectroscopy (EELS), X-ray diffraction (XRD), and SQUID technique have been used to characterize the magnetic samples, termed herein Apomaghemites. The in vivo magnetic resonance imaging (MRI) studies showed the efficiency in contrasting images for these samples; that is, the r(2) NMR relaxivities are comparable with Endorem (a commercial superparamagnetic MRI contrast agent). The r(2) relaxivity values as well as the pre-contrast and post-contrast T(2)*-weighted images suggested that our systems could be used as perspective superparamagnetic contrast agents for magnetic resonance imaging (MRI). The carbohydrate-functionalized Apomaghemite nanoparticles retained their recognition abilities, as demonstrated by the strong affinity with their corresponding carbohydrate-binding lectins.     

Long‐Lived Circularly Polarized Phosphorescence in Helicene‐NHC Rhenium(I) Complexes: The Influence of Helicene,Halogen, and Stereochemistry on Emission Properties

The first enantiopure chiral‐at‐rhenium complexes of the form fac‐ReX(CO)₃(:C^N) have been prepared, where :C^N is a helicene‐N‐heterocyclic carbene (NHC) ligand and X=Cl or I. These have complexes show strong changes in the emission characteristics, notably strongly enhanced phosphorescence lifetimes (reaching 0.7 ms) and increased circularly polarized emission (CPL) activity, as compared to their parent chiral models lacking the helicene unit. The halogen along with its position within the dissymmetric stereochemical environment strongly affect the photophysics of the complexes, particularly the phosphorescence quantum yield and lifetime. These results give fresh insight into fine tuning of photophysical and chiroptical properties of Re‐NHC systems.     

Cyclic Voltammetric Study of Some Anti‐Chagas‐Active 1,4‐Dioxidoquinoxalin‐2‐yl Ketone Derivatives

The electrochemical properties of 24 1,4‐dioxidoquinoxalin‐2‐yl ketone derivatives with varying degrees of anti‐Chagas activity were investigated in the aprotic solvent dimethylformamide (DMF) by cyclic voltammetry and first‐derivative cyclic voltammetry. For this group of compounds, the first reduction in DMF was either reversible or quasireversible and consistent with reduction of the N‐oxide functionality to form the radical anion. The second reduction process for these compounds was irreversible under the conditions used. The reduction potentials correlated well with molecular structure. Substitution in the 3‐, 6‐, and 7‐ positions of the quinoxaline ring by electron‐withdrawing substituents directly affected the ease of reduction and improved the biological activities of these compounds, whereas substitution by electron‐donating groups had the opposite effect. The electrochemical results, when combined with previous work on their mechanism of action against Chagas disease and their measured anti‐Chagas activities, indicated that the quinoxaline 1,4‐dioxide system serves as a promising starting point for chemical modifications aimed at improving the T. cruzi activity via a possible bioreduction mechanism.     

Valorization of Phenolic and Carotenoid Compounds of Sechium edule (Jacq. Swartz) Leaves: Comparison between Conventional,Ultrasound- and Microwave-Assisted Extraction Approaches

Chayote leaves are known for culinary and traditional medicine applications. This work intended to recover carotenoids and phenolic compounds from chayote leaves using the ultrasound-assisted extraction (UAE). A Box–Behnken design was employed to investigate the impact of extraction time, temperature, and ultrasonic power on the recovery of total carotenoids, total phenolic compounds, and antioxidant activities. For comparative purposes, chayote leaf extracts were prepared by maceration (ME) and microwave-assisted extraction (MAE), using the same time and temperature conditions optimized by UAE. Extraction at 50 °C and 170 Watts for 30 min provided the optimal UAE conditions. UAE showed better extraction efficacy than ME and MAE. The HPLC analysis of the extracts showed that the xanthophyll class was the main class of carotenoids, which constituted 42–85% of the total carotenoid content, followed by β-carotene and tocopherol. Moreover, 26 compounds, classified as phenolic acids, flavonols, flavonoids and other polar compounds, were identified in the chayote leaf extracts. Flavonols accounted for 55% of the total compounds quantified (the major compound was myricetin) and phenolic acids represented around 35%, mostly represented by ferulic acid, chlorogenic acid and (+)-catechin. This study revealed the potential of UAE as an effective green extraction technique to recover bioactive compounds from chayote leaves, for food, and for pharmaceutical and cosmetic applications.     

Untersuchung von Butter, Margarine, Tran und anderen Fetten

Ohne Zusammenfassung     

Temperature-promoted large-volume solute enrichment in column-switching miniaturized liquid chromatography: determination of an antioxidant

A two-valve sub-ambient temperature-promoted reversed-phase packed-capillary liquid-chromatography column-switching system has been tailored for sensitive determination of hydrophobic compounds. Such compounds are not easily dissolved in solvent mixtures of non-eluting properties that traditionally are used for solute enrichment in reversed-phase liquid chromatography. Enrichment-column solute focusing of large sample volumes was promoted by use of sub-ambient temperatures only, allowing the use of sample solvents that were stronger or equal to the mobile phase solvent strength. Subsequent column switching and enrichment-column temperature increment provided efficient low-dispersion back-flushed enrichment-column solute desorption onto the analytical column, where the solute was subjected to temperature-programmed gradient action. The antioxidant, Irganox 1076 (octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) extracted from low density polyethylene with 100% acetonitrile served as a hydrophobic model compound. The mobile phase consisted of acetonitrile containing 10 mM triethylamine and formic acid, and the 0.25 mm id enrichment-column and analytical column in lengths of 27 and 250 mm, respectively, were packed with 3.5 microm Kromasil C18 particles. Sample volumes of up to 500 microL were successfully focused on the enrichment column at 5 degrees C using loading flow rates of up to 40 microL min(-1) prior to temperature programming to 90 degrees C. The concentration limit of detection of Irganox 1076 was 6 ng mL(-1) when using an injection volume of 500 microL. The within-assay precision was in the range 3.5-6.8% (n = 6) while the between-day precision was 7.5% (n = 3) relative standard deviation. The method was linear within the investigated mass range 3-100 ng (R2 = 0.9993).     

Short communication controlling LC-SPE-NMR systems

There are several stages of the LC-SPE-NMR process that should be monitored closely to ensure an efficient isolation and concentration of the target analyte, for instance analyte break-through and compound transfer from the LC-SPE to the NMR probe. In this study, analyte break-through monitoring was performed with a UV detector and a mass spectrometer placed after the SPE unit. Easy break-through was a problem when attempting multiple trapping of various compounds using C18 SPE cartridges with the original commercial system. However, on lowering the flow rate over the SPE system and using SPE cartridges packed with porous carbon, the number of trappings possible increased five-fold. To increase control over the on-line SPE-NMR transfer, a gradient pump-UV system was used to elute compounds trapped on an SPE to an NMR probe. The analyte band was placed in the active volume of the probe by a stop-flow mechanism. The modified LC-SPE system was also coupled with off-line NMR analysis for determination of a degradation product of the insecticide monuron, present in the low ppm range.