LC-NMR coupling technology: recent advancements and applications in natural products analysis

An overview of recent advances in nuclear magnetic resonance (NMR) coupled with separation technologies and their application in natural product analysis is given and discussed. The different modes of LC-NMR operation are described, as well as how technical improvements assist in establishing LC-NMR as an important tool in the analysis of plant-derived compounds. On-flow, stopped-flow and loop-storage procedures are mentioned, together with the new LC-SPE-NMR configuration. The implementation of mass spectrometry in LC-NMR is also useful on account of the molecular weight and fragmentation information that it provides, especially when new plant species are studied. Cryogenic technology and capillary LC-NMR are the other important recent developments. Since the plant kingdom is endless in producing potential drug candidates, development and optimization of LC-NMR techniques convert the study of natural products to a less-time-consuming task, speeding up identification.     

A criterion for dewetting initiation from surface disturbances on ultrathin polymer films

Nanoindentation-induced defects on ultrathin (h = 17 nm) polystyrene (PS) films that are spin cast on silicon (Si) substrates, with residual depths of penetration lower than the film thickness (<17 nm), can either grow to initiate dewetting or level, which results in a flat polymer surface, upon heating above the glass-transition temperature (T(g)). The excess surface energy (DeltaF(gamma)) of the system, which is added to the initially flat coating with the formation of an indent, provides a critical value, DeltaF(gamma,crit) = 6.1 x 10(-16) J, which determines indent evolution upon annealing. An indent grows when DeltaF(gamma) > DeltaF(gamma,crit) and levels when DeltaF(gamma) < DeltaF(gamma,crit). This conclusion is in agreement with previous reports, which used DeltaF(gamma) to distinguish the two (dewetting/leveling) opposing processes (1) in the case of indents deeper than the film thickness and (2) in the case of built-in ordered surface disturbances by capillary force lithography.     

A multireference coupled-cluster potential energy surface of diazomethane, CH(2)N(2)

The intrinsically multireference dissociation of the C-N bond in ground-state diazomethane (CH(2)N(2)) at different angles has been studied with the multireference Brillouin-Wigner coupled-cluster singles and doubles (MRBWCCSD) method. The morphology of the calculated potential energy surface (PES) in C(s)() symmetry is similar to a multireference perturbational (CASPT3) PES. The MRBWCCSD/cc-pVTZ H(2)C-N(2) dissociation energy with respect to the asymptotic CH(2)(?(1)A(1)) + N(2)(X(1)Sigma(g)(+)) products is D(e) = 35.9 kcal/mol, or a zero-point corrected D(0) = 21.4 kcal/mol with respect to the ground-state CH(2)(X(3)B(1)) + N(2)(X(1)Sigma(g)(+)) fragments.     

Effects of metal irises on the guided-mode properties in asymmetrical slab waveguides

The diffraction phenomenon caused by metal transverse irises placed into an asymmetrical slab waveguide is examined by using the integral equation method. We concentrate on the possibility of controlling the radiation characteristics of the structure by changing the irises positions and the slab waveguide asymmetry. The aperture electric-field distribution is expressed in terms of a finite series of Chebyshev polynomials. The dominant TE guided-mode reflection and transmission coefficients, the near-field distribution and the far-field radiation pattern are calculated, while numerical results are presented for several cases of asymmetrical slab waveguides and different irises’ positions.     

Pressure anisotropy effects on nonlinear electrostatic excitations in magnetized electron-positron-ion plasmas

The propagation of linear and nonlinear electrostatic waves is investigated in a magnetized anisotropic electron-positron-ion (e-p-i) plasma with superthermal electrons and positrons. A two-dimensional plasma geometry is assumed. The ions are assumed to be warm and anisotropic due to an external magnetic field. The anisotropic ion pressure is defined using the double adiabatic Chew-Golberger-Low (CGL) theory. In the linear regime, two normal modes are predicted, whose characteristics are investigated parametrically, focusing on the effect of superthermality of electrons and positrons, ion pressure anisotropy, positron concentration and magnetic field strength. A Zakharov-Kuznetsov (ZK) type equation is derived for the electrostatic potential (disturbance) via a reductive perturbation method. The parametric role of superthermality, positron content, ion pressure anisotropy and magnetic field strength on the characteristics of solitary wave structures is investigated. Following Allen and Rowlands [J. Plasma Phys. 53, 63 (1995)], we have shown that the pulse soliton solution of the ZK equation is unstable to oblique perturbations, and have analytically traced the dependence of the instability growth rate on superthermality and ion pressure anisotropy.     

Traces and idempotents in group algebras

Let G be a group and E an idempotent matrix with entries in the complex group algebra C G. In this paper, we study arithmetic properties of the coefficients r _E (g), gG, of the Hattori-Stallings rank r _E of E. Bass proved in [2] that the r _E (g)s are algebraic numbers. Following Zaleskii, we proceed by reduction to positive characteristic and give an alternative proof of that assertion, while obtaining at the same time an upper bound for the degree of the minimum polynomial of r _E (g) over Q.     

Phenolic compounds and antioxidant activity of olive leaf extracts

The total phenolic content and antioxidant activities of olive leaf extracts were determined. Plant material was extracted with methanol and fractionated with solvents of increasing polarity, giving certain extracts. The qualitative changes in the composition of the extracts were determined after the storage of leaves for 22?h at 37°C, before the extraction. Total polyphenol contents in extracts were determined by the Folin-Ciocalteu procedure. They were also analysed by liquid chromatography-mass spectrometry. Their antioxidant activities were evaluated using the diphenyl picrylhydrazyl method and the β-carotene linoleate model assay. Moreover, the effects of different crude olive leaf extracts on the oxidative stability of sunflower oil at 40°C and sunflower oil-in-water emulsions (10% o/w) at 37°C, at a final concentration of crude extract 200?mg?kg(-1) oil, were tested and compared with butylated hydroxyl toluene.     

Determination of Herbicides in Natural Waters Using Solid Phase Microextraction (SPME) and Gas Chromatography Coupled with Flame Thermionic and Mass Spectrometric Detection

Abstract

This study develops a method for solid phase microextraction (SPME) of ten widespread herbicides from water. The selected herbicides belong to different chemical groups are EPTC, molinate, propachlor, trifluralin, atrazine, propazine, terbuthylazine, prometryne, alachlor. Their determination was carried out by gas chromatography with flame thermionic and mass spectrometric detection. To perform the SPME, two types of fibre have been assayed: Carbowax-divinylbenzene (CW-DVB) of 65 μm thickness and polydimethylsiloxane-divinylbenzene (PDMS-DVB) of 65 μm thickness. The main factors affecting the SPME process such as pH, ionic strength, methanol content, memory effect, stirring rate and adsorption-time profile were studied. The method was applied to spiked natural waters such as ground water, sea water, lake water and river water in a concentration range of 0.1 to 10 μg/L. Limits of detection with each of the detectors were determined to be 1 – 20 ng/L in PDMS-DVB and 2–20 ng/L CW-DVB fibres. The recoveries of herbicides compared to distilled water were in relatively high levels 78.3–127.3 % and the average r² values of the calibration curves were above 0.99 for all the analytes. The SPME conditions were finally optimized in order to obtain maximum sensitivity and samples were applied for the trace-level determination in river water samples originating from Ioannina region (Greece).     

Photooxidation of aryl alkanes by a decatungstate/triethylsilane system in the presence of molecular oxygen

Decatungstate photocatalyzes the oxidation of aryl alkanes to the corresponding tertiary hydroperoxides and alcohols, in the presence of molecular oxygen. The addition of triethylsilane to the reaction mixture substantially increases the proportion of hydroperoxide formed.     

The effect of aging and natural organic matter on the Th(OH)4 solubility

The solution chemistry of actinides, particularly hydrolysis, is of major importance in the design of nuclear waste repositories and in relation to nuclear fuel reprocessing cycles. In this study the formation and solubility of the Th(OH)₄ solid phase has been investigated as a function of the aging time and the presence of natural organic matter (e.g. humic acid) in 0.1 M NaClO₄, at weak acid pH and under normal atmospheric conditions. Th(OH)₄ has been prepared by alkaline precipitation and characterized by TGA, ATR–FTIR, XRD, and solubility measurements. According to the experimental data Th(OH)₄ is stable and remains the solubility limiting solid phase even in the presence of increased humic acid concentration in solution. Increasing humic acid concentration doesn’t affect the crystallite size and the solubility product of Th(OH)₄. Th(OH)₄ solubility is basically pH depended and governed by the presence of colloidal species. However, solid phase aging, which in absence of humic acid favors crystallinity, affects significantly the Th(OH)₄ solubility.