In-situ FT-IR studies on cyclic voltammetry of polythiophene

In-situ FT-IR spectra were taken during a cyclic voltammetric study of polythiophene in 1M LiClO₄ in propylene carbonate. The external reflection technique was used in the spectroscopic measurements. A broad band extending from 1500 cm^–1 to higher wave numbers appeared during oxidation of polythiophene with a potential scan from 2.8 V to 4.2 V. Bands due to doping of the polymer at 1330 and 1020 cm^–1 were also found to increase during the same potential scan. The appearance of spectral changes above 3.3 V supports the model of two types of doping processes occurring in the polymer. The observed changes almost disappeared during the reverse scan.     

Voltammetric on-line analysis for some sulphur-containing drugs

Some 2-thiobarbituric acid and thioamide drugs are determined voltammetrically in a flow-through cell. Both direct oxidation in the d.c. mode and cathodic stripping on a mercury-coated glassy carbon electrode are examined for the determination of these drugs. The thiobarbiturie acids can be determined by both methods; the linear range covers 1–2 orders of magnitude with a detection limit in the range 10^-3–10^-6 M depending on the method used and the compound. The thioamides do not plate satisfactorily on the mercury film when operated in the on-line mode and can only be determined by the d.c. anodic oxidation method; the linear range covers at least two orders of magnitude with a detection limit of 5×10^-8–5×10^-7 M depending on the compound.     

Application of an amperometric sensor to in-line monitoring of pulp bleaching with chlorine dioxide

Chlorine dioxide is replacing chlorine as the active compound in pulp bleaching in order to reduce the amount of chlorine used in the process and hence also in the waste waters. In bleaching with chlorine dioxide part of the effective bleaching chemical is usually chlorite. The electrochemistry of chlorine dioxide and chlorite at solid electrodes was studied by cyclic voltammetry at different pH values. The observed voltammograms indicated that reduction of chlorine dioxide gives chlorite and oxidation of chlorite gives chlorine dioxide. Both voltammograms were well developed, indicating a reversible process. Both platinum and glassy carbon were used as the working electrode. The dependence of the limiting current of chlorine dioxide and chlorite on pH was studied at both electrodes. The method was tested in the chlorine dioxide bleaching stage D1 in a typical bleaching process. A good correlation was found between the concentrations of chlorine dioxide and chlorite measured by the in-line amperometric method and a standard titrimetric method.     

Evaluation of surface composition of surface active water-alcohol type mixtures: a comparison of semiempirical models

We study adsorption at planar liquid-vapor interface of surface active binary mixtures and test three well-known models for the composition of surface phase. The models were originally presented by Guggenheim. These are compared to results for model fluids from density functional theory (DFT). The model of Laaksonen and Kulmala is in best agreement with DFT calculations. Surface mole fraction of the solute component from the Guggenheim model exceeds one for a mixture with high surface activity. The failure of the Guggenheim model is also evident in our calculations for water-methanol, water-ethanol, and water-n-propanol mixtures.     

Raman based pH measurements with polyaniline

The reversible acid–base equilibrium between the emeraldine salt (ES) and the emeraldine base (EB) form of thin electropolymerized films of polyaniline (PANI) has been studied between pH 2 and 9 with in situ Raman spectroscopy using the 514, 633 and 780 nm laser excitation wavelengths. The electropolymerization of PANI was done with cyclic voltammetry in a flow cell from a solution consisting of 50 mM aniline and 1.0 M HCl. It is shown that the Raman signal of the CN stretching vibration at 1439 cm⁻¹, originating from the quinoid units of the EB form, can be used for pH measurements between pH 3 and 6 with the 633 nm laser. This vibration is strongly resonance enhanced by the 633 nm laser and its intensity grows therefore considerably in the pH interval where the ES–EB transition mainly takes place (pH 3–6). The influence of the film conditioning pH was also studied as well as the reproducibility of the Raman spectra when pH was changed several times from pH 6 to 3.     

Novel and convenient synthesis of 4(1H)quinolones

A rapid two-step synthesis of 4(1H)quinolones is described. The first step involves condensation of o-nitroacetophenone with N,N-dimethylformamide dimethylacetal yielding highly crystalline enamines. In the second step a reductive cyclization is achieved under catalytic transfer hydrogenation (CTH) conditions. In all cases, the total time of this process was less than 3 h.     

Comparison of voltammetric detection assisted by multivariate curve resolution with amperometric detection in liquid chromatographic analysis of cysteine-containing compounds

A voltammetric detection mode (VD) in conjunction with multivariate curve resolution with alternating least squares (MCR-ALS) method is applied to the analysis of cysteine-containing compounds and compared with a well established amperometric detection (AD) mode in a thin-layer dual Hg/Au cell. VD-MCR-ALS provides an increase in selectivity for cases where satisfactory separation of electroactive compounds is not allowed. However, concentrations needed for a good quantification in VD are higher than in AD due to much large contribution of background in VD.     

Asymmetry induction by cooperative intermolecular hydrogen bonds in surface-anchored layers of achiral molecules.

The mesoscale induction of two-dimensional supramolecular chirality (formation of 2D organic domains with a single handedness) was achieved by self-assembly of 1,2,4-benzenetricarboxylic (trimellitic) acid on a Cu(100) surface at elevated temperatures. The combination of spectroscopic [X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS)], real-space-probe [scanning tunneling microscopy (STM)], and computational [density functional theory (DFT)] methods allows a comprehensive characterization of the obtained organic adlayers, where details of molecular adsorption geometry, intermolecular coupling, and surface chemical bonding are elucidated. The trimellitic acid species, comprising three functional carboxylic groups, form distinct stable mirror-symmetric hydrogen-bonded domains. The chiral ordering is associated with conformational restriction in the domains: molecules anchor to the substrate with an ortho carboxylate group, providing two para carboxylic acid moieties for collective lateral interweaving through H bonding, which induces a specific tilt of the molecular plane. The ease of molecular symmetry switching in domain formation makes homochiral-signature propagation solely limited by the terrace width. The molecular layer modifies the morphology of the underlying copper substrate and induces mum-sized strictly homochiral terraces.     

Polyketide stereotetrads in natural products

Natural products (or secondary metabolites) remain as the most important source for discovery of new and potential drug molecules. With high resolution data of their structures, and the advancement of synthesis possibilities, analysis of the natural products based on their specific structural features is valuable to those entering the field. In this tutorial review we attempt such an analysis indicating the salient features of the structural classes with examples of the synthesis of each one of them. As the particular class of natural products, we have chosen polyketides.     

Validation of three rapid screening methods for detection of verotoxin-producing Escherichia coli in foods: interlaboratory study

An interlaboratory study was conducted for the validation of 3 methods for the detection of all verotoxin-producing Escherichia coli (VTEC) in foods. The methods were a multi-analyte 1-step lateral flow immunoassay (LFIA) for detection of E. coli O157 and verotoxin (VT); an enzyme-linked immunosorbent assay targeted against VT1, VT2, and VT2c (VT-ELISA); and a polymerase chain reaction (PCR) method for detection of VT genes (VT-PCR). Aliquots (25 g or 25 mL) of 4 food types (raw minced [ground] beef, unpasteurized milk, unpasteurized apple juice [cider], and salami) were individually inoculated with low numbers (<9 to 375 cells/25 g) of 6 test strains of E. coli (serogroups O26, O103, O111, O145, and O157) with differing VT-producing capabilities. Five replicates for each test strain and 5 uninoculated samples were prepared for each food type. Fourteen participating laboratories analyzed samples using the LFIA, 9 analyzed the samples by ELISA, and 9 by PCR. The LFIA for O157 and VT had a specificity (correct identification of negative samples) of 92 and 94%, respectively, and a sensitivity (correct identification of positive samples) of 94 and 55%, respectively. The VT-ELISA and VT-PCR had a specificity of 98 and 99%, respectively, and a sensitivity of 89 and 72%, respectively.