Two new eudesmane derivatives from Verbesina virginica

<正>Two new eudesmane derivatives were isolated from the leaves and flowers of Verbesina virginica,along with the known 6-O-β-E -p-coumaroyl-4α-hydroxyeudesmane(1).Their structures were determined as 6-O-β-Z-p-coumaroyl-4α-hydroxyeudesmane(2) and 6-O-α-E-p-coumaroyl-1β-4α-dihydroxyeudesmane(3) by spectroscopic methods.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

PRESSURE-VELOCITY EQUILIBRIUM HYDRODYNAMIC MODELS

This article describes mathematical models for phase separated mixtures of materials that are in pressure and velocity equilibrium but not necessarily temperature equilibrium. General conditions for constitutive models for such mixtures that exhibit a single mixture sound speed are discussed and specific examples are described.     

Simultaneous determination of dimethoate and its metabolite omethoate in curry leaf using LC-MS/MS and risk assessment

This study presents the method development, validation, and simultaneous determination of dimethoate and its metabolite omethoate in curry leaf. Samples were extracted following modified quick, easy, cheap, effective, rugged, and safe extraction protocol and analyzed using liquid chromatography-tandem mass spectrometry. The limit of quantification in the matrix was 0.005 μg g⁻¹ for dimethoate and omethoate. Extraction using acetonitrile recorded the average recoveries in the range of 82.25 to 112.97% for dimethoate and 85.57 to 107.22% for omethoate at 0.005, 0.025 and 0.050 μg g⁻¹ fortification levels and relative standard deviation less than 5%. Similarly, the relative standard deviation values for intraday (Repeatability) and interday (Reproducibility) tests were less than 15%. Dissipation kinetics of dimethoate 30% emulsifiable concentrate at 200 and 400 g a.i h⁻¹ recorded initial deposits of 5.20 and 10.05 μg g⁻¹ and 0.33 and 0.48 μg g⁻¹ for dimethoate and omethoate, respectively, and half-life of 3.07 and 3.34 days. The estimated hazard index value found more than one at a day after dimethoate application. It is not safe for consumer health to use curry leaves in the initial days after application.     

Effect of the methyl-coenzyme-m reductase protein matrix on the hole-size and nonplanar deformations of coenzyme F430

Methyl-coenzyme-M reductase (MCR) is a key enzyme common to all methane-producing pathogens. It catalyses the final step in methane synthesis. Each MCR contains two noncovalently bound molecules of cofactor F430. Normal-coordinate structural decomposition, hole-size analysis, and molecular mechanics calculations were undertaken to examine the effect of MCR on the hole-size and nonplanar deformations of coenzyme F430. In MCR, the protein prevents F430 from undergoing nonplanar deformations, which results in a more rigid tetrahydrocorphinoid cofactor that has a shorter ideal metal-nitrogen distance in the MCR protein matrix than it does in solution. Changing the coordination number of the nickel ion in F430 has a very small effect on the ideal hole size; however, it has a significant effect on the nonplanar deformations the coenzyme undergoes upon contraction and expansion. In all complexes we examined, cofactor F430 undergoes more nonplanar deformations when it contains a four-coordinate metal ion than it does when it contains a six-coordinate metal ion. Clearly, MCR moderates the hole-size and the nonplanar deformations of coenzyme F430, which are known to affect redox potentials and axial ligand affinities. This suggests that the protein environment may be responsible for tuning the chemistry of the active-site nickel ion.     

Internal energy content of n-butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two-photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd.     

New sample preparation technique for the determination of avoparcin in pressurized hot water extracts from kidney samples

A new approach is presented for the determination of avoparcin in tissue. Complete recovery from spiked swine kidney was achieved with hot water modified with 30% ethanol (v/v). The samples were extracted at 75 degrees C and 50 atm by accelerated solvent extraction. In situ sample clean-up was achieved by using matrix solid-phase dispersion utilizing the acrylic polymer XAD-7 HP, and by adding triethylammonium phosphate (TEAP) to the extraction solvent. The aqueous extracts were concentrated by solid-phase extraction (SPE) on the hydrophilic interaction chromatography (HILIC) material polyhydroxyethyl aspartamide. Complete analyte retention was possible during SPE when the kidney extracts were modified with 70% ethanol. A 200 A, 5 microm HILIC column with UV225 detection was used for the separation of avoparcin. The retention time was less than 15 min with 47% aqueous component in acetonitrile and 15 mM TEAP as eluent. The average recovery of avoparcin from kidney samples was 108%.