Synthesis of aromatic tetracyclic tin compounds by template and transmetallation reactions: Alkyl vs aryl migration from tin to nitrogen

The syntheses of [bis(3,5-di-tert-butyl-2-hydroxy-2-phenyl)amine]diphenyltin (1) and [bis(3,5-di-tert-butyl-2-hydroxy-2-phenyl)amine]dichloro-phenyl-stannate (2) by template reactions using 3,5-di-tert-butylcatechol, aqueous ammonia and SnPh₂Cl₂ are reported. We also report the syntheses of compounds 2, [bis(3,5-di-tert-butyl-2-hydroxy-2-phenyl)amine]trichloro-stannate (4), [bis(3,5-di-tert-butyl-2-hydroxy-2-phenyl)methylamine]chloro-methyltin (5), and [bis(3,5-di-tert-butyl-2-hydroxy-2-phenyl)-n-butylamine]n-butyl-chlorotin (6) and [bis(3,5-di-tert-butyl-2-hydroxy-2-phenyl)amine]n-butyl-dichloro-stannate (7), performed by transmetallation reactions of the octahedral zinc coordination compound Zn[3,5-di-tert-butyl-1,2-quinone-(3,5-di-tert-butyl-2-hydroxy-1-phenyl)imine]₂ (3) with SnPhCl₃ or SnPh₂Cl₂, SnCl₄, SnMe₂Cl₂, Sn(nBu)₂Cl₂ and Sn(nBu)Cl₃, respectively. The X-ray diffraction structures of compounds 1, 2, 4 and 6 are reported. The transmetallation reactions with Sn(alkyl)₂Cl₂ afforded pentacoordinated tin compounds, where an alkyl group migrated from tin to nitrogen, while similar reactions with Sn-Ph compounds did not present any phenyl group migration.     

Development and validation of a fast isocratic liquid chromatography method for the simultaneous determination of norfloxacin,lomefloxacin and ciprofloxacin in human plasma

A simple and fast liquid chromatographic method coupled with fluorescence detection (LC‐FD) is reported, for the first time, for the simultaneous quantification of norfloxacin (NOR), ciprofloxacin (CIP) and lomefloxacin (LOM) in human plasma, using levofloxacin as internal standard (IS). Sample preparation consists of a single‐step precipitation of plasma proteins followed by vortex‐mixing and centrifugation. Chromatographic separation was achieved within 7 min on a reversed‐phase C₁₈ column with a mobile phase consisting of 0.1% aqueous formic acid (pH = 3.0, triethylamine)–methanol (82:18, v/v) pumped isocratically at 1.2 mL/min. The detector was set at excitation/emission wavelengths of 278/450 nm. Calibration curves were linear (r² ≥ 0.994) in the range of 0.02–5.0 µg/mL, and the limit of quantification was established at 0.02 µg/mL for all analytes (NOR, CIP and LOM). The overall precision did not exceed 8.19% and accuracy was within ±10.91%. NOR, CIP and LOM were extracted from human plasma with an overall mean recovery ranged from 90.1 to 111.5%. No interferences were observed at the retention times of the analytes and IS. This novel LC‐FD method enables the reliable determination of NOR, CIP and LOM in a single chromatographic run, which may be suitable to support human pharmacokinetic‐based studies with those antimicrobial agents. Copyright © 2010 John Wiley & Sons, Ltd.     

Functionalized carbon dots as sensors for gold nanoparticles in spiked samples: Formation of nanohybrids

This paper reports the synthesis, passivation and functionalization of luminescent carbon dots (CDs) possessing surface thiol ending groups. A simple procedure involving amidation of passivated carbon dots (p-CDs) with cysteamine boosts their photoluminescent properties and enables their use as easily controlled fluorescent nanosensors for determining citrate–gold nanoparticles (AuNPs). The mechanism behind the quenching phenomenon was established from fluorescence measurements at high temperatures and lifetime tests, and found to involve static quenching leading to the formation of CD–AuNP nanohybrids. A method for determining AuNPs in complex matrices was developed and validated by application to spiked drinking water and mussel tissues. The limits of detection and quantitation for AuNPs thus obtained were 0.20 and 0.66 nmol L^–1, respectively.     

Comparative properties of Amazonian oils obtained by different extraction methods

Pequi (Caryocar brasiliense Camb.), baba?u (Orbignya phalerata Mart.), buriti (Mauritia flexuosa), and passion fruit (Passiflora edulis) oils were studied to determine their antibacterial, antioxidant and cytotoxic activities, as well as their total phenol and carotenoid contents. The fatty acid contents were determined by GC-MS. The three types of passion fruit oils studied were refined, cold pressed or extracted from seeds in a Soxhlet apparatus. The oils thus obtained showed differences in antioxidant activity and carotenoid content, but were similar in regard to total phenols. Buriti and pequi had the highest carotenoid contents, while refined and cold pressed passion fruit oil displayed the highest antioxidant activity. Pequi oil was the only oil to display antibacterial and cytotoxic activity.     

Identification and characterization of impurities of tetracosactide by capillary electrophoresis and liquid chromatography coupled to time-of-flight mass spectrometry

Tetracosactide is a synthetic peptide analogue of the human adrenocorticotropic hormone that stimulates the production of cortisol in the adrenal cortex. The medical use of the compound is primarily the diagnosis of the adrenal cortex function. In order to characterize impurities of the drug, tetracosactide samples were analysed by both liquid chromatography and capillary electrophoresis coupled to a quadrupole time-of-flight mass spectrometer. The identification of the impurities was carried out based on accurate mass determination and fragment ion spectra. The presence of several peptides of lower and higher masses than tetracosactide could be shown, including N- and C-terminally truncated peptides as well as peptides which still contained protecting groups or additional amino acids. Furthermore, a semi-quantitative estimation of the relative amounts of the impurities in different samples as well as a commercial preparation revealed that the number and the type of the impurities varied between the samples. Comparing the selectivity of liquid chromatography and capillary electrophoresis regarding the separation of tetracosactide impurities, it can be stated that capillary electrophoresis showed a higher suitability for the separation of tetracosactide fragments (smaller peptides) while the larger peptides, i.e. those wearing protecting groups, were separated more efficiently by liquid chromatography.     

The Influence of Nd and Sm on the Structure and Properties of Sol-Gel-Derived TiO2 Powders

TiO₂ nanopowders modified by Nd and Sm were prepared using the sol-gel technique. It was found by XRD analysis that the samples containing Sm are amorphous up to 300 °C, while those with Nd preserve a mixed organic-inorganic amorphous structure at higher temperatures (400 °C). The TiO₂ (rutile) was not detected up to 700 °C in the presence of both modified oxides. TiO₂ (anatase) crystals found at about 400 °C in the Sm-modified sample exhibited an average crystallite size of about 25–30 nm, while doping with Nd resulted in particles of a lower size—5–10 nm. It was established by DTA that organic decomposition is accompanied by significant weight loss occurring in the temperature range 240–350 °C. Photocatalytic tests showed that the samples heated at 500 °C possess photocatalytic activity under UV irradiation toward Malachite green organic dye. Selected compositions exhibited good antimicrobial activity against E. coli K12 and B. subtilis.     

Development of shaping technologies for crystals grown from melts

The development of technologies for growing crystals with a given shape and designing the growth equipment for the Czochralski and conventional and modified Stepanov methods have been considered. The reviewed experimental data lead to the conclusion that it is possible to provide three-dimensional control of the crystal geometry with the aid of a die in the growth process.     

Initial-layer theory and model equations of Volterra type

^** Email: amb16{at}nyu.edu It is demonstrated here that there exist initial layers to singularlyperturbed Volterra equations whose thicknesses are not of theorder of magnitude of O(), 0. It is also shown that the initial-layertheory is extremely useful because it allows one to constructthe approximate solution to an equation, which is almost identicalto the exact solution.     

Remarkable effect of the preparation technique on the state of cobalt ions in BEA zeolites evidenced by FTIR spectroscopy of adsorbed CO and NO, TPR and XRD

The state of cobalt in two BEA zeolites was studied by XRD, TPR, and FTIR spectroscopy using CO and NO as probe molecules. One of the samples, CoAlBEA (0.4 wt % of Co), was prepared by conventional ion exchange and the other, CoSiBEA (0.7 wt % Co), by a two-step postsynthesis method involving dealuminated SiBEA zeolite. The introduction of Co into SiBEA leads to an increase of unit cell parameters of the BEA structure and to the consumption of silanol groups in vacant T-sites of the dealuminated zeolite. In contrast, no structural changes are observed after incorporation of cobalt into AlBEA by ion-exchange. The reduction temperature of cobalt in CoSiBEA zeolite (1130 K), is much higher than for CoAlBEA and indicates a strong interaction of cobalt ions with SiBEA. Low-temperature CO adsorption on CoAlBEA results in (i) H-bonded CO, (ii) Co(3+)-CO adducts (2,208 cm(-1)) and (iii) a small amount of Co(2+)-CO complexes (2,188 cm(-1)). In agreement with these results, NO adsorption leads to the appearance of (i) NO(+) (2,133 cm(-1), formed with the participation of the zeolite acidic hydroxyls), (ii) Co(3+)-NO (1932 cm(-1)), and (iii) a small amount of Co(2+)(NO)(2) dinitrosyls (nu(s) = 1,898 and nu(as) = 1,814 cm(-1)). Low-temperature CO adsorption on CoSiBEA leads to formation of two kinds of Co(2+)-CO adducts (2,185 and 2,178 cm(-1)). No Co(3+) cations are detected. In line with these results, adsorption of NO reveals the existence of two kinds of Co(2+)(NO)(2) dinitrosyls (nu(s) = 1,888 and nu(as) = 1,808 cm(-1) and nu(s) = 1,878 and nu(as) = 1,799 cm(-1), respectively).