High‐performance liquid chromatographic method for the quantification of Mitragyna inermis alkaloids in order to perform pharmacokinetic studies

In Africa, Mitragyna inermis (Willd.) O. Kuntze (Rubiaceae) is commonly used in traditional medicine to treat malaria. Antimalarial activity is mostly due to the hydromethanolic extract of M. inermis leaves and especially to the main alkaloids, uncarine D and isorhynchophilline. In the present study, we describe for the first time an HPLC method for the simultaneous quantification of uncarine D and isorhynchophylline in biological matrices. SPE was used to extract the components and the internal standard naphthalene from human and pig plasma samples. Chromatographic separation was performed on a C‐18 reversed column at a flow rate of 1 mL/min, using methanol–phosphate buffer (10:90, pH 7), as a mobile phase. Good linearity was observed over the concentration ranges of 0.0662–3.31 μg/mL for uncarine D and 0.0476–2.38 μg/mL for isorynchophylline. The precision was less than 12% and the accuracy was from 86 to 107% without any discrepancy between the two species. Uncarine D and isorhynchophylline recoveries were over 80%. These results allowed the quantification of both uncarine D and isorhynchophylline in pig plasma after intravenous administration of M. inermis extract.     

Preparation and sorption properties of a β‐cyclodextrin‐linked chitosan derivative

β‐Cyclodextrin (β‐CD) was coupled to chitosan by the intermediate of its monochlorotriazinyl derivative, called βW7MCT, so that a chitosan derivative bearing cyclodextrin was obtained. Because the average degree of substitution of the cyclodextrin derivative was 2.8, the reaction yielded crosslinked insoluble products. The structure of these materials has been investigated by high‐resolution magic‐angle spinning (HRMAS) with gradients. For the first time, HRMAS spectra of chitosan polymers containing β‐CD were obtained. This NMR technique produced one‐ and two‐dimensional well‐resolved solid‐state spectra. These data confirm the proposed structure. Decontamination of waters containing textile dyes were carried out with the crosslinked derivatives. These tests showed that the new chitosan derivatives are characterized by a rate of sorption and a global efficiency superior to that of the parent chitosan polymer and of the well‐known cyclodextrin‐epichlorohydrin gels. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 169–176, 2001     

Rapid-Pulsing Artifact-Free Double-Quantum-Filtered Homonuclear Spectroscopy: The 2D-INADEQUATE Experiment Revisited

Rapid pulsing artifacts are observed in the conventional phase-cycled carbon-13 2D INADEQUATE experiment. By using the product operator formalism, it is shown that they result from the effects of imperfect 90° and 180° excitation pulses on the most abundant molecules containing only one isolated carbon-13 nucleus. The labeled longitudinal magnetization remaining at the end of one scan is recycled by the subsequent acquisition, giving rise to multiple-quantum (p= 0, ±1, ±2, …) artifacts in theF₁dimension. By considering pairs of scans instead of single scans, a new phase cycle is proposed. It is based on a scheme for compensating for imperfections in the excitation cluster by a proper combination of the pulse phases in two consecutive scans. Because the artifacts are 90° out of phase compared to the desired signal, a concomitant rearrangement of the receiver phase achieves suppression of all unwanted signals. Experiments are presented on menthol dissolved in CDCl₃as a test compound. Improvements in spectrum quality as well as increased sensitivity are discussed.     

Photochemical Properties and Activity of Water‐Soluble Polymer/C60 Nanohybrids for Photodynamic Therapy

Water‐soluble star‐like poly(vinyl alcohol)/C₆₀ and poly{[poly(ethylene glycol) acrylate]‐co‐(vinyl acetate)}/C₆₀ nanohybrids are prepared by grafting macroradicals onto C₆₀ and are assessed as photosensitizers for photodynamic therapy. The photophysical and biological properties of both nanohybrids highlight key characteristics influencing their overall efficiency. The macromolecular structure (linear/graft) and nature (presence/absence of hydroxyl groups) of the polymeric arms respectively impact the photodynamic activity and the stealthiness of the nanohybrids. The advantages of both nanohybrids are encountered in a third one, poly[(N‐vinylpyrrolidone)‐co‐(vinyl acetate)]/C₆₀, which has linear grafts without hydroxyl groups, and shows a better photodynamic activity.

     

An adapted Galerkin method for the resolution of Dirichlet and Neumann problems in a polygonal domain

The Neumann problem for Laplace's equation in a polygonal domain is associated with the exterior Dirichlet problem obtained by requiring the continuity of the potential through the boundary. Then the solution is the simple layer potential of the charge q on the boundary. q is the solution of a Fredholm integral equation of the second kind that we solve by the Galerkin method. The charge q has a singular part due to the corners, so the optimal order of convergence is not reached with a uniform mesh. We restore this optimal order by grading the mesh adequately near the corners. The interior Dirichlet problem is solved analogously, by expressing the solution as a double layer potential.     

Synthesis and characterization of novel silica gel supported N-pyrazole ligand for selective elimination of Hg(II)

The polar organic molecule N-(2-hydroxyethyl)-3,5-dimethylpyrazole reacted with a 3-glycidoxypropyltrimethoxysilane silylant agent, previously anchored on a silica surface in a heterogeneous way to yield the product SiPz. The epoxide group was opened yielding chelating pendant group bonded to the inorganic surface. The product was characterized through elemental analysis, infrared spectroscopy, ¹³C NMR, surface area and thermogravimetry. The binding and adsorption abilities of SiPz was investigated for Hg²⁺, Cd²⁺, Pb²⁺, Cu²⁺, Zn²⁺, K⁺, Na⁺ and Li⁺ cations and compared to results of classical liquid-liquid extraction with the unbound N-pyrazole compound. The grafting at the surface of silica does not affect complexing properties of the ligand and the SiPz exhibits a high selectivity toward Hg²⁺ ion with no complexation being observed towards Zinc and alkali metals. The extracted and the complexing cation percentage were determined by atomic absorption measurements.     

Lewis acid- and Bronsted acid-catalyzed stereoselective rearrangement of epoxides derived from himachalenes: access to new chiral polycyclic structures

The acid-catalyzed rearrangement of two enantiomerically pure epoxides derived from sesquiterpernic himachalenes, which are the main components of the essential oil of the Atlas cedar, has been studied using various Lewis and Bronsted acids. Several new polycyclic compounds have been obtained with different selectivities depending upon the catalysts used and the reaction conditions, and were fully characterized by spectroscopic methods. Mechanisms to explain the formation of the different compounds observed in the reaction mixture have also been proposed.     

A computational toy model for shallow landslides: Molecular dynamics approach

The aim of this paper is to propose a 2D computational algorithm for modeling the triggering and propagation of shallow landslides caused by rainfall. We used a molecular dynamics (MD) approach, similar to the discrete element method (DEM), that is suitable to model granular material and to observe the trajectory of a single particle, so to possibly identify its dynamical properties. We consider that the triggering of shallow landslides is caused by the decrease of the static friction along the sliding surface due to water infiltration by rainfall. Thence the triggering is caused by the two following conditions: (a) a threshold speed of the particles and (b) a condition on the static friction, between the particles and the slope surface, based on the Mohr–Coulomb failure criterion. The latter static condition is used in the geotechnical model to estimate the possibility of landslide triggering. The interaction force between particles is modeled, in the absence of experimental data, by means of a potential similar to the Lennard-Jones one. The viscosity is also introduced in the model and for a large range of values of the model’s parameters, we observe a characteristic velocity pattern, with acceleration increments, typical of real landslides. The results of simulations are quite promising: the energy and time triggering distribution of local avalanches show a power law distribution, analogous to the observed Gutenberg–Richter and Omori power law distributions for earthquakes. Finally, it is possible to apply the method of the inverse surface displacement velocity [4] for predicting the failure time.