Determination of bromate in sea water using multi-dimensional matrix-elimination ion chromatography

A multi-dimensional matrix-elimination ion chromatography approach has been applied to the determination of bromate in seawater samples. Two-dimensional and three-dimensional configurations were evaluated for their efficacy to eliminate the interference caused by the high concentration of ubiquitous ions present in seawater, such as chloride and sulfate. A two-dimensional approach utilising a high capacity second dimension separation comprising two Dionex AS24 columns connected in series was applied successfully and permitted the determination of bromate in undiluted seawater samples injected directly onto the ion chromatography system. Using this approach the limit of detection (LOD) for bromate based on a signal to noise ratio of 3 was 1050 μg/L using a 500 μL injection loop. Good linearity was obtained for bromate with correlation coefficients for the calibration curves of 0.9981 and 0.9996 based on peak height and area, respectively. A three-dimensional method utilising two 10-port switching valves to allow sharing of the second suppressor and detector between the second and third dimension separations showed better resolution and detection for bromate and reduced the LOD to 60 μg/L for spiked seawater samples. Good linearity was maintained with correlation coefficients of 0.9991 for both peak height and area. Ozonated seawater samples were also analysed and exhibited a non-linear increase in bromate level on increasing ozonation time. A bromate concentration in excess of 1770 μg/L was observed following ozonation of the seawater sample for 120 min. Recoveries for the three-dimensional system were 92% and 89% based on peak height and area, respectively, taken over 5 ozonated samples with 3 replicates per sample.     

Lattice Vibrations of Imidazole Crystals

Abstract

Polarized low-frequency Raman spectra of imidazole single crystals were measured with a He-Ne laser source. A new band at 172 cm^?1 (Bg) was observed. An assignment for the lattice vibrations of imidazole crystals is proposed on the bases of this Raman data and far-infrared spectral data of Perchard and Novak, as well as the preliminary results calculated from Harada's and Williams' potentials.     

Synthesis and characterization of miniemulsion copolymers of methyl methacrylate (or styrene) and stearyl methacrylate

The copolymers of methyl methacrylate (MMA) (or styrene (ST))/stearyl methacrylate (SMA) obtained from miniemulsion polymerization were prepared and characterized. All the miniemulsions showed satisfactory colloidal stability upon aging due to the effectively retarded Ostwald ripening by the reactive costabilizer SMA. In subsequent miniemulsion copolymerizations, monomer droplet nucleation predominated in the particle formation process, but homogeneous nucleation could not be ruled out even at such high levels of SMA (20–50 wt.%). The contact angle first increased rapidly and then leveled off when the SMA content increased from 20 to 50 wt.% for both the copolymers of MMA/SMA and ST/SMA. At constant level of SMA, the copolymer of MMA/SMA with a less hydrophobic composition showed a larger contact angle compared to the ST/SMA counterpart. The contact angle (103 ± 1°) of the copolymer MMA/SMA (50/50 w/w) was comparable to that (104°) of PSMA. A schematic model was proposed to explain the experimental results.     

A solid-phase approach to mouse melanocortin receptor agonists derived from a novel thioether cyclized peptidomimetic scaffold

The solid-phase synthesis of a novel thioether cyclized peptidomimetic scaffold, displaying functionality at the i to i + 3 positions, is reported. The thioether bridge is formed on-bead by an intramolecular reaction between a chloroacetylated reduced peptide bond and the free thiol from a cysteine. The crude products were obtained in moderate to very high purity. A series of 19 compounds were prepared and tested for agonist activity at the mouse melanocortin receptors 1, 3, 4, and 5 (mMC1-5R). From these results, several compounds were identified as having low micromolar agonist activity at the mMC1R and mMC4R. The former is involved in skin pigmentation and animal coat coloration. The latter is involved in the regulation of appetite and food intake and is currently a drug target for potential treatment of obesity. The most potent compound 1n with the pharmacophore motif "His-DPhe-Arg-Trp" was identified as having an EC(50) value of 165 nM at mMC1R, 7600 nM at mMC3R, 650 nM at mMC4R, and 335 nM at mMC5R. In addition, some of the compounds showed moderate selectivity for the mMC1R.     

Synthesis and isolation of polytrityl cations by utilizing hexaphenylbenzene and tetraphenylmethane scaffolds

The successful isolation of stable (and soluble) hexa- and tetratrityl cations based on hexaphenylbenzene and tetraphenylmethane scaffold has been accomplished by using readily available starting materials. These robust polytrityl cations can be isolated in crystalline form and stored indefinitely at 0 degrees C. Their structures have been established by (1)H/(13)C NMR spectroscopy and by UV-vis spectroscopy. The structures of these polytrityl cations were further confirmed by quantitative transformations to the reduced (poly)triphenylmethyl derivatives by hydride transfer from triethylsilane, cycloheptatriene, or a borane-dimethyl sulfide complex.     

Sequential Cu-catalyzed amidation-base-mediated camps cyclization: a two-step synthesis of 2-Aryl-4-quinolones from o-halophenones

A direct two-step method for the preparation of 2-aryl- and 2-vinyl-4-quinolones that utilizes a copper-catalyzed amidation of o-halophenones followed by a base-promoted Camps cyclization of the resulting N-(2-ketoaryl)amides is described. With CuI, a diamine ligand, and base as the catalyst system, the amidation reactions proceed in good yields for a range of aryl, heteroaryl, and vinyl amides. The subsequent Camps cyclization efficiently provides the desired 4-quinolones with the conditions that are described.     

Strain and phase identification of the U.S. category B agent Coxiella burnetii by matrix assisted laser desorption/ionization time-of-flight mass spectrometry and multivariate pattern recognition

Accurate bacterial identification is important in diagnosing disease and in microbial forensics. Coxiella burnetii, a highly infective microorganism causative of the human disease Q fever, is now considered a U.S. category B potential bioterrorism agent. We report here an approach for the confirmatory identification of C. burnetii at the strain level which involves the combined use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and supervised pattern recognition via Partial Least Squares-Discriminant Analysis (PLS-DA). C. burnetii isolates investigated in this study included the following prototype strains from different geographical and/or historical origins and with different antigenic properties: Nine Mile I, Australian QD, M44, KAV, PAV, Henzerling, and Ohio. After culture and purification following standard protocols, linear MALDI-TOF mass spectra of pure bacterial cultures were acquired in positive ion mode. Mass spectral data were normalized, baseline-corrected, denoised, binarized and modeled by PLS-DA under crossvalidation conditions. Robustness with respect to uncontrolled variations in the sample preparation and MALDI analysis protocol was assessed by repeating the experiment on five different days spanning a period of 6 months. The method was validated by the prediction of unknown C. burnetii samples in an independent test set with 100% sensitivity and specificity for five out of six strain classes.