Reversed-phase determination of famotidine, potential degradates, and preservatives in pharmaceutical formulations by high-performance liquid chromatography using silica as a stationary phase

An analytical method was developed for the determination of famotidine, potential degradates, and preservatives in several pharmaceutical formulations. The method employs reversed-phase chromatography on a silica column with a methanol-phosphate solution as the mobile phase. The influence of the concentration of phosphate and organic modifier are discussed. Accuracy and precision for this method along with assay data from different formulations of famotidine are presented. Two different commercial silica columns were tested with this method. Chromatographic differences related to the surface area and pore size of the silica are discussed.     

Stereocontrolled synthesis of bicyclic lactone derivatives via tungsten-mediated [3 + 2] cycloaddition of epoxides with a tethered alkynyl group

In the presence of BF3*Et2O, alkynyltungsten complexes underwent [3 + 2] cycloaddition with tethered epoxides to give bicyclic -lactones efficiently. Only one diastereomeric product was formed despite the presence of three stereogenic centers. A mechanism is proposed that involves formation of a tungsten-vinylidenium species via an SN2 attack of the epoxide carbon by an alkynyltungsten group to give a tungsten-enol ether species via counterattack at the central tungsten-vinylidenium carbon by the OBF3- terminus. Most of the tungsten enol ether species were too unstable for isolation and underwent hydrolysis to give only cis-fused -bicyclic lactones. This cyclization works for both cis- and trans-epoxides and tolerates various functional groups. In the case of trans-phenyl epoxide, the reaction led to an addition product via a 6-endo attack of epoxide by the tungsten fragment. This method provides a simple enantiospecific synthesis of complex bicyclic lactones if a chiral epoxide is used in the cyclization. It is also applicable to the one-pot synthesis of bicyclic unsaturated gamma-lactones if a suitable alkynyltungsten functionality is used.     

Laser-based detection of PAHs and BTXE-aromatics in oil polluted soil samples

Time-resolved laser-induced fluorescence spectroscopy and fiber optics are applied for the detection of aromatic hydrocarbons in oil contaminated water and soil samples. Time-integrated data accumulation of fluorescence intensities in an early and in a late time window with respect to the exciting laser pulse simplifies the method in such a way that it becomes very attractive for practical applications. For ultraviolet laser excitation at 337 nm and recording fluorescence signals at 400 nm, typical detection limits of the present set-up are 0.5 mg engine oil/L in water and 5 mg engine oil/kg in soil. A discrimination between BTXE-aromatics and PAHs in oil polluted soil or water samples is possible, when more than one laser wavelength in the ultraviolet is used for the excitation. The possibilities for a thermal discrimination between different aromatics are also discussed.     

Analytical approach to very large benzenoid polymers

We consider rigorous evaluation of conjugated-circuit resonance energies for families of structurally related benzenoid hydrocarbons of increasing size. Local and global aromatic properties of such molecules are investigated with particular interest in modeling high polymers. Using the algebra of large numbers, exact formulas for contributions from individual benzene rings of polymers with up to 25,000 repeating units (close to half a million carbon atoms) were derived. All arithmetic procedures were carried out in terms of whole numbers retaining all digits, of which there were sometimes more than 10⁵. © 1995 by John Wiley & Sons, Inc.     

Room-temperature phosphorescence and fluorescence of nitrogen heterocyclics adsorbed on silica gel chromatoplates

The room-temperature phosphorescence of benzof]quinoline and phenanthridine has been enhanced considerably by spotting HBr-ethanol solutions of the compounds onto silica gel chromatoplates. Acridine showed no room-temperature phosphorescence but gave very strong fluorescence on silica gel chromatoplates. The analytical aspects are discussed, and some evidence is provided for the interactions of the compounds with the substrate.     

Tellurate and periodate solutions as media for paper electrophoresis of carbohydrates

Electrophoretic separations of sugars and other polyhydroxy compounds may be performed in 0.2M telluric acid media adjusted to pH 10 with sodium hydroxide, and in 0.07M sodium metaperiodate at pH 11. Oxidation by periodate appears to be only slight under these conditions. Migration rates of 21 compounds are reported relative to the movement of d-ribose. In both electrolytes the compounds form anionic complexes.     

Processus de photopolymerisation du methacrylate de methyle en presence de chlorure de zinc

The photopolymerization of methylmethacrylate in solution or in bulk, initiated by DMPA (2,2-dimethoxy-2-phenylacetophenone) and BP (benzophenone), has been investigated in the presence of ZnCI₂ as a complexing agent. We have studied the steady state polymerization (measurement of R, and OT) and the behaviour of the excited states by laser spectroscopy. We have shown the following points: R_p and DP increase with [ZnCI₂]; the rate constant for propagation increases with [ZnC12]; the rate of initiation remains constant in presence of BP-ZnCl₂ but increases with DMPA-ZnCl₂. The results are accounted for by the results of laser spectroscopy.     

Polyethylenimine catalysts containing an isolated apolar binding site: Solovolysis of p-nitrophenyl esters

The preparation dodecane-block-poly[ethylenimine-graft-4(5)-methylimidazole] copolymers and related model compounds has been described and such polymers have been described and such polymers have been demonstrated to be efficient catalysts for the hydrolysis of activated phenyl esters in aqueous solutions. Polymeric catalysts that contain isolated apolar blocks exhibited enhanced catalytic activity for the hydrolysis of the p-nitrophenyl esters of acetate and butyrate compared with polymer model compounds. This rate enhancement was atributed to the apolar binding of substrate within the apolar polymer regime. Twenty-to 100-fold increases in the second-order rate constants were observed for the hydrolysis of the longer-chain p-nitrophenyl esters. This is indicative of a significant hydrophobic interaction. The contribution of the apolar block to the hydrophobic interaction was masked in the hydrolysis of the p-nitrophenyl caproate and p-nitrophenyl laurate substrates. In both instances the dominant contribution to the hydrophobic interactions was ascribed to a substrate-imidazole intermediate rather than the apolar block of the catalyst. The pH-rate profiles for the hydrolysis of p-nitrophenyl esters by the various catalysts indicated an absence of any cooperative interactions between imidazole residues or amine groups.