Determination of biogenic amines by capillary electrophoresis with pulsed amperometric detection

The biogenic amines, putrescine, cadaverine, spermidine and spermine were separated and quantified by capillary electrophoresis with pulsed amperometric detection. Detection potential of the pulsed amperometric detection was optimized as 0.6 V Optimal separation of the biogenic amines was achieved using a separation buffer of 30 mM citrate at pH 3.5, while keeping the buffer in the detection cell as 20 mM NaOH. Using these conditions, the four biogenic amines were baseline separated. Extrapolated limits of detection for putrescine, cadaverime, spermidine and spermine were 400, 200, 100 and 400 nM for the standard mixture (polyamines dissolved in running buffer), respectively. These are lower than ultraviolet detection and comparable or even lower than laser-induced fluorescence detection results as reported in the literature. The number of theoretical plates was maintained at the 105 level, which is absolutely higher than any reported method. When applying capillary electrophoresis-pulsed amperometric detection to milk analysis, only spermidine was found in amounts varying between 0.1 and 0.5 mg/kg.

Correlation analysis of the structures and gas-liquid chromatographic retention indices of amines

Quantitative structure-retention relationship(QSRR) was studied for amines to gas-liquid chromatography on three stationary phases of different polarities with the topological indices A(m) (A(m1), A(m2), A(m3)) and gravitational index GI. The algorithm of "Leaps and Bounds" was performed for selection of the variables. And the multi-regression and the quasi-Newton neural networks were employed for the calculation with better results.

Prediction of C-13-nuclear magnetic resonance chemical shifts for aliphatic amines

Prediction of C-13-nuclear magnetic resonance chemical shifts for aliphatic amines is performed. The topological, geological and electronic descriptors are generated. To reduce the variables, the best subsets of the descriptors are obtained by using leaps-and-bounds regression analysis. The model is achieved using multiple regression with satisfactory results.

Kinetic isotope effects of proton transfer reaction for amines by ultrasonic relaxation methods: Unexpected evidence from the results in ethylamine solutions

Ultrasonic absorption coefficients for ethylamine in heavy water (D2O) and in light water (H2O) have been measured in the frequency range from 0.8 to 220 MHz at 25 degrees C. A single relaxational process has been observed in these two kinds of solutions. From the concentration dependence of the ultrasonic relaxation parameters, and following the reaction mechanism proposed by Eigen et al. for ethylamine in H2O, the causes of the relaxations have been attributed to a perturbation of an equilibrium associated with a deuteron or proton transfer reaction. The rate and equilibrium constants have been estimated from deuterioxide or hydroxide ion concentration dependence of the relaxation frequency, and the kinetic isotope effects have been determined. In addition, the standard volume changes of the reactions have been calculated from the concentration dependence of the maximum absorption per wavelength, and the adiabatic compressibility has also been determined from the density and sound velocity for ethylamine in D2O and in H2O, respectively. These results are compared with those for propylamine and butylamine and are discussed in relation to the different kinetic properties between D2O and H2O, the reaction radii derived by Debye theory, and the structural properties of the reaction intermediate.

End-column electrochemical detection for aromatic amines with high performance capillary electrophoresis

Electrochemical detection of five species of aromatic amines at a carbon fiber microdisk electrode after separation by capillary electrophoresis is described. Under the optimum conditions, the detection limit for 3,4-dihydroxybenzylamine, N,N-dimethylaniline, p-phenylenediamine, p-aminophenol and aniline sulfate was 0.9, 0.03, 0.075, 1.2 and 0.15 mu M (S/N = 3), respectively. The linear response range was 5-1000, 0.1-500, 0.5-500, 5-500 and 1-200 mu M, respectively The effect of the electrode position and buffer pH on the detection was also studied. This method is very simple, sensitive and stable for the detection of these compounds.

Quantitative analysis of pethidine using liquid secondary ion and tandem mass spectrometry

A method for the quantatitive determination of pethidine in human urine by liquid secondary ion and tandem mass spectrometry is presented. Quantification was carried out by using ketamine as internal standard. It was found that the collision-induced dissociation (CID) spectrum of the [M + H](+) ion of pethidine exhibited a prominent daughter ion at mit 220 and ketamine also yielded the same daughter ion at nit 220, For ((quadrupole)) quantitative analysis, the first quadrupole mass filter was set to transmit mit 220 and a narrow-range magnet scan yielded a spectrum of parents, including mit 238 and 248, corresponding to ketamine and pethidine, respectively. Copyright (C) 1999 John Wiley & Sons, Ltd.

Determination of the secondary structure of the king cobra neurotoxin CM-11

The king cobra neuotoxin CM-11 is a small protein with 72 amino acid residues. After its complete assignments of H-1-NMR resonance's were obtained using various 2D-NMR technologies, including of DQF-COSY, clean-TOCSY AND NOESY, the secondary structure was analysed by studying the various NOEs extracted from the NOESY spectra and the distribution of chemical shifts. The secondary structure was finally determined by MCD as follows: a triple-strand antiparallel beta sheet with I20-W36, R37-A43 and V53--S59 as its beta strands, a short alpha helix formed by W30-G35 and four turns formed by P7-K10, C14-G17, K50-V53 and D61-N64.

NEW TOPOLOGICAL INDEX AND PREDICTION OF PHASE-TRANSFER ENERGY FOR PROTONATED AMINES AND TETRAALKYLAMINES IONS

The applications of new topological indices A(x1)-A(x3) suggested in our laboratory for the prediction of Gibbs energy values of phase transfer (water to nitrobenzene) of amine ions are described with satisfactory results. Multiple regression analysis and neural network were employed simultaneously in this study.

STUDIES OF SPINEL LICRXMN2-XO4 FOR SECONDARY LITHIUM BATTERY

X-ray and electrochemical studies of spinel-related manganese chromium oxides, LiCrxMn2-xO4 (0 less-than-or-equal-to x less-than-or-equal-to 1) were carried out in a lithium nonaqueous cell. X-ray diffraction spectra indicated that the substitution of manganese in LiMn2O4 by trivalent transition metals (Cr3+) cause the linear decrease of lattice parameter with the x in the LiCrMn2-xO4. Some discharge-capacity loss was obtained due to the lattice contraction of LiCrMn2-xO4, but it has a better rechargeability than LiMn2O4. Cyclic voltammetry and electrochemical impedance experiments have shown that the excellent rechargeability of LiCrxMn2-xO4 may be attributed to the good reversibility of the change in its crystal structure for the insertion and extraction of lithium ions.

DEVELOPMENT OF CYLINDRICAL SECONDARY LITHIUM POLYANILINE BATTERIES

The cylindrical 'D'-size batteries were fabricated by polyaniline paste cathode and lithium foil anode sandwiched with microporous polypropylene separator. The electrolyte used was LiClO4 dissolved in a mixed solvent of propylene carbonate and dimethoxyethane. The results of charge/discharge curves, charge/discharge cycles, the short-circuit current, the open-circuit voltage storage and the change of discharge capacity with temperature, discharge current are reported.

A WOUND-TYPE LITHIUM POLYANILINE SECONDARY CELL

A wound-type cell with a polyaniline (PAn) positive electrode, a LiClO4-propylene carbonate (PC) electrolyte, and a lithium foil negative electrode has been constructed. The two electrodes are separated by a polypropylene separator. The PAn is deposited on carbon felt from a HClO4 solution containing aniline by galvanostatic or potentiostatic electrolysis. Using cyclic voltammetry charge/discharge cycles and charge/retention tests, the following results have been obtained: (i) reversibility of the charge/discharge reaction of the PAn electrode is very good; (ii) more than 50 charge/discharge cycles at 80% charge/discharge efficiency and 260 W h kg-1 discharge energy density can be achieved at 50 mA between 2 and 4 V; (iii) the open-circuit voltage and the capacity retention of the battery after storage at open-circuit for 60 days are 3.4 V and 33%, respectively.

ASSIGNMENT OF C-13 NMR-SPECTRA OF POLYMER WITH SEMIEMPIRICAL METHOD - SURVEY OF SPECTRUM OF SECONDARY CARBON OF 1,2-PBD

In chain molecules of 1, 2-PBD, there are two kinds of gauche arrangements, which is the cause of making the spectrum of the secondary carbon in main chain of the polymer split. In such a complex system, the gauche arrangements of the secondary carbon and the tertiary carbon occupy an important position. Hence, the contribution of the tertiary carbon to the chemical shifts of the secondary carbon has a decisive effect on the sequence structure distribution. In comparison the contribution of vinyl groups is ...

Comparison of two marine sponge-associated Penicillium strains DQ25 and SC10: differences in secondary metabolites and their bioactivities

Two strains of Penicillium, DQ25 and SC10, isolated from marine sponge Haliclona angulata (Bowerbank) and Hymeniacidon sp. respectively, were subjected to stationary cultivation under GYP medium for 30 days. The fermentation extracts were undergone bioactivities assays against human pathogens, phytopathogenic fungi and brine shrimp (Artemia salina). Bioassays-guided compounds isolation was performed by Silica gel columns and Sephadex LH-20 chromatography. Spectroscopic methods were used to structures elucidation of the compounds. Results showed the activities of secondary metabolites of strain DQ25 were generally stronger than that of strain SC10. Major bioactive molecules isolated from strain DQ25 were a 1,4-naphthoquinone derivative and an unidentified alkaloid. The two components were not isolated from the extract of strain SC10. ITS sequences revealed that these two species have the greatest similarity with Penicillium vinaceum and Penicillium granulatum respectively.

The enhanced immune protection of Zhikong scallop Chlamys farreri on the secondary encounter with Listonella anguillarum

It is well known that invertebrates are devoid of adaptive immune components and rely primarily on innate immunity to defend against pathogens, but recent studies have demonstrated the existence of enhanced secondary immune protection in some invertebrates. in the present study, the cumulative mortality of scallops received two successive Listonella anguillarum stimulations was recorded, and variations of immune parameters including phagocytosis (phagocytic rate and phagocytic index), phenoloxidase-like enzyme, acid phosphatase and superoxide dismutase activities were also examined. The scallops received a previous short-term L anguillarum stimulation were protected against a long-term stimulation of L. anguillarum. Significantly higher level of phagocytic activities and acid phosphatase activity were observed in the scallops received twice stimulations compared with those only received the secondary stimulation. These results indicated that a short-term immersion with L. anguillarum modulated the scallops' immune system and endowed the scallops with enhanced resistance to the secondary bacterial stimulation: phagocytosis and acid phosphatase were suspected to be involved in the protection. (C) 2008 Elsevier Inc. All rights reserved.