Optimization and validation of an enantioselective method for a chiral drug with eight stereo-isomers in capillary electrophoresis

Highly selective capillary electrophoresis (CE) screening methods were applied to find a satisfactory separation of a chiral drug with eight stereoisomeric compounds. The initial separation conditions were further optimized using response surface modelling by applying a Box-Behnken experimental design. This approach resulted in a rapid and efficient optimization of the buffer concentration, the concentration of two cyclodextrins, and the run voltage, in order to obtain final separation conditions of the method. Further optimization and validation of the system in terms of sensitivity and robustness resulted in a method that is suitable for quality control release purposes.     

Determination of fluoxetine and norfluoxetine in rat brain microdialysis samples following intraperitoneal fluoxetine administration

Fluoxetine (FLX) and the N-desmethyl metabolite, norfluoxetine (NFLX) in rat brain microdialysis samples were determined by high-performance liquid chromatography (HPLC) with fluorescence detection using pre-column derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F). In vitro experiment showed that the relative recovery of FLX across microdialysis membrane was enhanced by adding β-cyclodextrin (β-CD) or β-CD polymer to microdialysis perfusion fluid. The perfusion fluid containing β-CD polymer, which has polymeric glyceryl linkers attached to the hydroxyl group, gave the better recovery with satisfactory precisions. Using 1% β-CD polymer in Ringer’s solution as the perfusate, in vivo rat brain microdialysis experiment on intraperitoneal administration of FLX (10 mg/kg) to rats was carried out. The fluorescence peaks of FLX and NFLX appeared later than 30 min after the administration of FLX, and then, gradually increased with time. Two hours later, FLX reached a plateau level, but NFLX slowly increased, and at 24-48 h, NFLX levels were higher than FLX levels. These data suggest that long distributions of FLX and the potent metabolite, NFLX, in brain contributed to the long-term drug actions in vivo.     

Reduced rings whose finitely generated modules decompose

This paper proves Hua's Theorem and, from this, the Fundamental Theorem of Projective Geometry for the projective line over a commutative ring with “many units”.     

Synthesis of a 6H-Benzofuro[3,2-c][1]benzopyran-6-one. A New Application of the Hurtley Reaction

A copper(I)bromide promoted substitution of 2-bromobenzofuran-3- carboxylic acid (2b) with dimedone and subsequent lactonization offers a new route to a modified coumestane ring system.     

Thin-Layer Chromatographic Determination of Alpha-Amyrin in the Bark of Mallotus philippensis Lamk

JPC – Journal of Planar Chromatography – Modern TLC - A simple, precise, and accurate high-performance thin-layer chro-matographic method has been established for determination of...     

Resonant Raman scattering in Mn:ZnO dilute magnetic semiconductors

We report on micro-Raman measurements performed under various visible excitations on wurtzite Zn_1−xMn_xO thin films grown by MOCVD, for a wide range of Mn content (0<x<0.22). We observe a shift of the frequency of the E₂ phonon for increasing Mn content, indicating a substitution of the Mn atoms at the tetrahedral Zn sites of the host matrix. All spectra also reveal a dominant feature related to local vibrations of Mn atoms, as well as the A₁ (LO) phonon of the ZnMnO alloy. Both features are resonantly enhanced by the absorption of the incident laser light by internal transitions of the Mn²⁺ ions.     

Shift equations iteration solution to <Emphasis Type="Italic">n</Emphasis>-level close coupled equations,and the two-level nonadiabatic tunneling problem revisited

The shift equations iteration (SEI) solves the n-level quantum scattering problem in one dimension, i.e., the close-coupled equations, free from exponential instability arising from closed channels. SEI provides exponential-instability-free transmission and reflection coefficients, and is well suited to two-sided scattering problems such as conduction in molecular wires. Our most efficient implementation of SEI utilizes an adaptation of the log-derivative symplectic integrator described by Manolopoulos and Gray in (J Chem Phys 102:9214, 1995). The two-level nonadiabatic tunneling system is investigated—in the tunneling regime, above the barrier, and at resonance. Nonadiabatic components in the upper channel wavefunction (and lower channel wavefunction at resonance energies) are found to be non-adiabatic, i.e., not describable by WKB functions. Their behavior is characterized in terms of an empirical model relating these components to adiabatic components in the lower (upper) channel and the potential energy coupling.     

Magneto-optical Faraday and Kerr effect of orthoferrite thin films at high temperatures

Orthoferrites present, as bulk materials, reorientation transitions of their magnetic moment alignment at temperatures depending on the rare-earth (RE) ion. In particular, orthoferrites (REFeO₃) with RE = Sm, Dy, present this transition at T _SRT = 443 K and 36 K, respectively. The spectra of the complex Kerr and Faraday angle have been measured on orthoferrite thin films (RE = Sm, Dy, Y), which were prepared by pulsed laser deposition on amorphous quartz substrates. The obtained spectra exhibit contributions of both surfaces and interfaces. Propagation effects of the polarized light in the magneto-optical medium which is interpreted in terms of a simplified theoretical formalism, is also observed. For selected photon energies, temperature dependent Faraday rotation measurements, , on orthoferrite thin films (RE = Sm, Dy, Y) have been performed. A quite different thermal variation compared to the bulk magnetization has been observed. Curie temperatures are found to be close to the bulk values or slightly larger by 10 K to 20 K as in the case of DyFeO₃ and YFeO₃. For RE = Sm and Dy, increases with increasing temperature contrary to the saturation magnetization, passes through a maximum at about 460 K and vanishes with a T _C of 647±18 K, 695 K for RE = Sm and Dy respectively. Received 28 July 2000     

Synthesis and Properties of Higher Nuclearity Polyazanes

Polyazanes (i.e., higher nuclearity homologues of hydrazines) with increasing numbers of bound nitrogen atoms (from 3 to 5), including the first pentazane ever described, were prepared by the addition of lower-order polyazanes to diazo reagents. A structure was obtained. It was shown that the polynitrogen chains adopt a helical conformation. DFT modeling shows that the arrangement persists in solution. Although the polyazanes are all reducing agents, they become less so as the number of nitrogens increases.     

Completions of commutative topological rings

Let R be a commutative ring and f a filter of ideals of R. We characterize when the Hausdorff completion of R with the f topology is a product of local Hausdorff completions. This generalizes a theorem of E. Matlis dealing with the completions of an integral domain relative to the topology of the classical torsion theory.