Investigation of LiAlH4-THF formation by direct hydrogenation of catalyzed Al and LiH

The formation of LiAlH(4)-THF by direct hydrogenation of Al and LiH in tetrahydrofuran (THF) was investigated using spectroscopic and computational methods. The molecular structures and free energies of the various possible adducts (THF-AlH(3), THF-LiH and THF-LiAlH(4)) present in a LiAlH(4)/THF solution were calculated and the dominant species were determined to be contact ion pairs where three THF molecules coordinate the lithium. Raman and X-ray absorption spectroscopy were used to investigate the effect of different Ti precursors on the formation of Al-H species and LiAlH(4)-THF and determine the optimal reaction conditions. A unique sample stage was developed from a microfluidic cell to evaluate the catalysts in situ. The effectiveness of two types of catalysts, titanium chloride (TiCl(3)) and titanium butoxide (Ti(C(4)H(9)O)(4)), and the catalyst concentration were evaluated under similar reaction conditions. Both catalysts were effective at facilitating hydrogenation, although TiCl(3) was more effective over the first few cycles with the greatest kinetic enhancement achieved with a low concentration of around 0.15 mol%. These results were qualitatively supported by infrared spectroscopy, which indicated that although a small amount of Ti is necessary for disassociating H(2), excess surface Ti (>0.1 ML) hinders the formation of Al-H species.     

Bromodimethylsulfonium bromide (BDMS)-catalyzed multicomponent synthesis of 3-aminoalkylated indoles

Bromodimethylsulfonium bromide (BDMS)-catalyzed three-component coupling reaction between indoles, aldehydes, and N-alkylanilines is reported to access substituted 3-aminoalkylated indoles at room temperature in high yields (82-96%) within 1.5-3.5 h. The salient features of this protocol are the simplicity of the procedure, the ready accessibility of the catalyst, its cost effectiveness, and higher yields in relatively short reaction times.     

Analysis of Saffron (Crocus sativus L. Stigma) Components by LC–MS–MS

A liquid chromatographic tandem mass spectrometric validated method was developed for the detection of chemicals attributing color, flavor, taste and medicinal properties to saffron (Crocus sativus L. stigma). Ultrasonic extractions of saffron stigmas were followed by LC procedure with Pinnacle II Cyano (5 μm 150 × 2.1 mm) column and acetonitrile: water (70:30, v/v) as mobile phase. Deprotonated ions formed by a turbo ion spray in negative MS mode were used to detect the analytes. MS–MS detection was by monitoring precursors (m/z) fragmentations; of 149 → 113 (safranal), 327 → 283 (crocetin), 329 → 167 (picrocrocin), 355 → 327 (dimethyl crocetin), 489 → 327 (crocin E), 535 → 489 (carotenes), 651 → 327 (crocin C), 813 → 652 (crocin B), 975 → 651 (crocin A) and 1,137 → 813 (crocin F). The method was validated for linearity, precision, repeatability and specificity.     

On the converse of a theorem of Schur

A well known theorem of Schur states that for any group G, if G/Z(G) is finite, then G′ is finite. We give a very short and elementary proof of a further generalization of the converse of Schur’s theorem proved by Niroomand [5] and Sury [7] and also improve the bound for the order of G/Z(G) obtained by Niroomand and Sury.     

Liquid chromatography/electrospray ionization tandem mass spectrometry validated method for the simultaneous quantification of sibutramine and its primary and secondary amine metabolites in human plasma and its application to a bioequivalence study

A high-throughput and sensitive bioanalytical method using liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) has been developed for the estimation of sibutramine and its two metabolites (M1 and M2). The extraction of sibutramine, its metabolites and imipramine (internal standard (IS)) from the plasma involved treatment with phosphoric acid followed by solid-phase extraction (SPE) using a hydrophilic-lipophilic balanced HLB cartridge. The SPE eluate without drying and reconstitution was analyzed by LC/MS/MS, equipped with a with turbo ion spray (TIS) source, operating in the positive and multiple reaction monitoring (MRM) acquisition mode. Sample preparation by this method yielded extremely clean extracts with quantitative and consistent mean recoveries; 95.12% for sibutramine, 92.74% for M1, 95.97% for M2 and 96.60% for the IS. The total chromatographic run time was 3.0 min with retention times of 2.51, 2.13, 2.09 min for sibutramine, M1, M2 and imipramine, respectively. The developed method was validated in human plasma matrix, with a sensitivity of 0.1 ng/mL (coefficient of variance (CV), 2.07%) for sibutramine, 0.1 ng/mL (CV, 3.59%) for M1 and 0.2 ng/mL (CV, 4.93%) for M2. Validation of the method for its accuracy, precision, recovery, matrix effect and stability was carried out especially with regard to real subject sample analysis. The response was linear over the dynamic range 0.1 to 8.0 ng/mL for sibutramine and M1, and 0.2 to 16.0 ng/mL for M2 with correlation coefficients of r > or = 0.9959 (sibutramine), 0.9935 (M1) and 0.9943 (M2). The method was successfully applied for bioequivalence studies in 40 human subjects with 15 mg capsule formulations.     

Pointers toward the occurrence of C-F...F-C interaction: Experimental charge density analysis of 1-(4-fluorophenyl)-3,6,6-trimethyl-2-phenyl-1,5,6,7-tetrahydro-4H-indol-4-one and 1-(4-fluorophenyl)-6-methoxy-2-phenyl-1,2,3,4-tetrahydroisoquinoline

A charge density study of crystalline 1-(4-fluorophenyl)-3,6,6-trimethyl-2-phenyl-1,5,6,7-tetrahydro-4H-indol-4-one (A) and 1-(4-fluorophenyl)-6-methoxy-2-phenyl-1,2,3,4-tetrahydroisoquinoline (B) has been carried out using high-resolution X-ray diffraction data collected at 113(2) K. Weak intermolecular interactions of the type C-H...O, C-H...pi, and pi...pi hold the molecules together in the crystal lattice along with interactions of the type C-H...F and unusual C-F...F-C examined via charge density analysis. The topological features are evaluated in terms of Bader's theory of atoms in molecules through the first four criteria of Koch and Popelier. The C-F...F-C contact is observed to be across the center of symmetry in B and not in A, and further, this interaction appears to possess a certain correlation with the electron density properties at the critical point which suggests that such an interaction fits into the hierarchy of weak interactions.     

Gas chromatography electron ionization mass spectrometric analysis of trimethylsilyl derivatives of bis(2-hydroxyethylthio)alkanes and bis(2-hydroxyethylsulfonyl) alkanes

This communication describes GC-MS analysis of bis(trimethylsilyl) (bis-TMS) derivatives of bis(2-hydroxyethylthio)alkanes (BHETAs) and bis(2-hydroxyethylsulfonyl) alkanes (BHESAs) which are important markers of sulfur mustard class of chemical warfare agents. The study was undertaken with a view to develop spectral database of these compounds for verification analysis of Chemical Weapons Convention (CWC). Based on the obtained mass spectra of bis-TMS derivatives of BHETAs and BHESAs, the fragmentation routes are proposed, which explain most of the characteristic ions.     

Microemulsion mediated in situ derivatization-extraction and gas chromatography-mass spectrometric analysis of alkylphosphonic acids

Detection and identification of environmental signatures of chemical warfare agents is an important aspect of verification program of Chemical Weapons Convention (CWC). Alkylphosphonic acids (APAs) are ultimate and persistent degradation products of nerve agents. Their identification in a sample submitted for off-site analysis infers possible indication of contamination with nerve agents. This paper describes the development of a new sample preparation method which involves 'in situ derivatization and extraction' (INDEX) of acids from water. Derivatization is performed by alkylation of APAs with alkylbromides in surfactant less microemulsion (SLME). The derivatized analytes were analyzed by gas chromatography coupled with mass spectrometry. The developed method involves simultaneous derivatization (alkylation) and extraction of acidic analytes mediated by surfactant less microemulsion. Various derivatization-extraction parameters such as solvent, reaction time and temperature, base and alkyl bromides were optimized. Pentyl bromide in the presence of potassium carbonate and diisopropylamine at 100 degrees C derivatized the selected acids efficiently. Kinetic data for alkylation of methylphosphonic acids and some carboxylic acids were obtained to assess their relative susceptibility for alkylation in microemulsion. Methylphosphonic acid and isopropyl methylphosphonic acid took 140-150 min to reach completion while carboxylic acids took 100 min to complete the reaction. INDEX could be successfully performed even in the presence of interfering Ca(2+) and Mg(2+) ions.