A General Catalyst Based on Cobalt Core–Shell Nanoparticles for the Hydrogenation of N-Heteroarenes Including Pyridines

Herein, we report the synthesis of specific silica-supported Co/Co₃O₄ core–shell based nanoparticles prepared by template synthesis of cobalt-pyromellitic acid on silica and subsequent pyrolysis. The optimal catalyst material allows for general and selective hydrogenation of pyridines, quinolines, and other heteroarenes including acridine, phenanthroline, naphthyridine, quinoxaline, imidazo[1,2-a]pyridine, and indole under comparably mild reaction conditions. In addition, recycling of these Co nanoparticles and their ability for dehydrogenation catalysis are showcased.     

Strong,large distance impurity dipole interaction in KNbO3 single crystals

It is found that the unrelaxed impurity dipoles can arrange themselves linearly in the structure joining each other end-to-end in pseudocubic [110] direction at the tetragonal to the orthorhombic phase transition. It is shown that this alignment precedes the domain formation at the phase transition, which implies quick movements of the dipoles in the structure, and a strong dipolar interaction. The experiments with the application of dc fields to the crystals showed that the dipolar interaction becomes stronger with the field. The dipoles can see each other across the existing domain walls implying the large distance nature of the interaction. The observation of impurity clusters arranged in pseudocubic [110] direction confirmed the large distance nature of the interaction. It is concluded that this strong, large distance interaction is very interesting in as much as such an interaction of dipoles forms the basis of ferroelectricity.     

Automated standard addition for fluorimetric steady-state and reaction-rate measurements

Instrumentation and methodology are described in which fluorescence measurements are made on a sample before and after a microcomputer-controlled injection of a standard-addition aliquot. From the two measurements an dother information, the analyte concentration in the sample is calculated and reported. The automated standard-addition procedure is shown to reduce measurement errors of 25–40% due to the presence of matrix quenchers or absorbers to less than 2% for fluorimetric steady-state measurements of quinine sulfate and in a fluorimetric reaction-rate method for determination of aluminum.     

Application of an intensified diode array system to diagnosis of matrix effects and the rapid sequential determination of thiamine and riboflavin with fluorescence detection

The unique capabilities of a multiple wavelength spectrofluorometer based on an intensified diode array detector are used for diagnosis of matrix effects and for rapid sequential determination of two analytes. This system is used to investigate problems due to background fluorescence, blank reactions, and scattering for the determination of thiamine in cereal and urine samples by a fluorometric kinetic procedure. A novel determination of thiamine and riboflavin in vitamin pills is based on monitoring the native fluorescence of riboflavin over one wavelength region, and the rate of formation of fluorescent thiochrome from thiamine over another wavelength region, after a computer-controlled change in the pH of the reaction mixture.     

Using molecular dynamics simulations to identify the key factors responsible for chiral recognition by an amino acid-based molecular micelle

Molecular dynamics (MD) simulations were used to investigate the binding of six chiral compounds to the amino acid-based molecular micelle (MM) poly-(sodium undecyl-(L)-leucine-leucine) or poly(SULL). The MM investigated is used as a chiral selector in capillary electrophoresis. The project goal was to characterize the chiral recognition mechanism in these separations and to move toward predictive models to identify the best amino acid-based MM for a given separation. Poly(SULL) was found to contain six binding sites into which chiral compounds could insert. Four sites had similar sizes, shapes, and electrostatic properties. Enantiomers of alprenolol, propranolol, 1,1′-bi-2-naphthyl-2,2′-diyl hydrogen phosphate, 1,1′-bi-2-naphthol, chlorthalidone, or lorazepam were separately docked into each binding pocket and MD simulations with the resulting intermolecular complexes were performed. Solvent-accessible surface area calculations showed the compounds preferentially associated with binding sites where they penetrated into the MM core and shielded their non-polar atoms from solvent. Furthermore, with five of the six compounds the enantiomer with the most favorable free energy of MM association also experienced the most favorable intermolecular hydrogen bonding interactions with the MM. This result suggests that stereoselective intermolecular hydrogen bonds play an important role in chiral discrimination in separations using amino acid-based MMs.GRAPHICAL ABSTRACT     

Determination of humic acid by chemiluminescence

The analytical utility of the chemiluminescence resulting from the reaction of humic acid with permanganate is investigated. The chemiluminescence response curve rises sharply to a peak value at about 0.5 s after mixing and decays somewhat more slowly. The peak signal for a fixed humic acid concentration is shown to pass through a maximum near a permanganate concentration of 17 μmol l^-1 and to increase continuously with potassium hydroxide concentration up to 2.0 mol l^-1. Calibration plots of peak signal vs. humic acid concentration exhibit complex behaviour, being approximately linear up to about 20 mg l^-1, curving slightly toward the concentration axis up to about 40 mg l^-1, and then curving away from the concentration axis above 40 mg l^-1. The detection limit for humic acid is about 0.7 mg l^-1. No interference is observed for thirteen common inorganic species at typical levels in water samples. Substantial differences are observed for humic acid in selected samples determined by the chemiluminescence and visible absorption procedures.     

Determination of cobalt by pyrogallol chemiluminescence

The chemiluminescence reaction involving pyrogallol in alkaline hydrogen peroxide solution is described. With reaction conditions selected for the determination of Co(II), the detection limit for Co(II) was at least two orders of magnitude below the detection limit of all other species tested. The results suggest that Ca, Mg, Mn, and Fe are the most likely interferents for environmental and biological samples. The log-log calibration graph for Co(II) is linear from a detection limit of 0.5 ng/ml up to 10 microg/ml.     

Ultraviolet photochemistry of ethane: implications for the atmospheric chemistry of the gas giants

Chemical processing in the stratospheres of the gas giants is driven by incident vacuum ultraviolet (VUV) light. Ethane is an important constituent in the atmospheres of the gas giants in our solar system. The present work describes translational spectroscopy studies of the VUV photochemistry of ethane using tuneable radiation in the wavelength range 112 ≤ λ ≤ 126 nm from a free electron laser and event-triggered, fast-framing, multi-mass imaging detection methods. Contributions from at least five primary photofragmentation pathways yielding CH₂, CH₃ and/or H atom products are demonstrated and interpreted in terms of unimolecular decay following rapid non-adiabatic coupling to the ground state potential energy surface. These data serve to highlight parallels with methane photochemistry and limitations in contemporary models of the photoinduced stratospheric chemistry of the gas giants. The work identifies additional photochemical reactions that require incorporation into next generation extraterrestrial atmospheric chemistry models which should help rationalise hitherto unexplained aspects of the atmospheric ethane/acetylene ratios revealed by the Cassini–Huygens fly-by of Jupiter.

The vacuum ultraviolet photodissociation dynamics of ethane provide clues for modelling the atmospheric chemistry of the gas giants.     

Kinetic fluorometric FIA determination of total ascorbic acid, based on use of two serial injection valves

The kinetic determination of total ascorbic acid with a flow-injection analysis system is described. The sample is loaded into two serial sample injection valves and injected into a carrier system containing mercuric chloride and o-phenylenediamine. The formation of a fluorescent product is monitored. The single-point and double-point kinetic methods are compared by using both peak height and peak area as the analytical signal. A detection limit of 0.1 mu/ml for vitamin C was achieved with a sample throughput rate of 30 per hour.