Development of a method to determine albendazole and its metabolites in the muscle tissue of yellow perch using high-performance liquid chromatography with fluorescence detection

An HPLC method was developed for the determination of albendazole (ABZ) and its metabolites, a sulfoxide (ABZSO), a sulfone (ABZSO2), and albendazole-2-aminosulfone (ABZ-2-NH2SO2), from yellow perch muscle tissue with adhering skin. The muscle tissue samples were made alkaline with potassium carbonate and extracted with ethyl acetate, followed by a series of liquid-liquid extraction steps. After solvent evaporation, the residue was reconstituted in the initial mobile phase combination of the gradient. The mobile phase consisted of a buffer, 50 mM ammonium acetate (pH = 4.0) in 10% methanol-water, and 100% acetonitrile. The gradient was from 20% acetonitrile to 85% acetonitrile. The analytes were chromatographed on an RP Luna C18(2) column and detected by fluorescence with excitation and emission wavelengths of 290 and 330 nm, respectively. The average recoveries from fortified muscle tissue for ABZ (20-100 ppb), ABZ-SO (20-200 ppb), ABZSO2 (8-100 ppb), and ABZ-2-NH2SO2 (20-100 ppb) were 85, 95, 101, and 86%, respectively, with corresponding CV values of 9, 3, 6, and 4%, respectively. Their LOQ values were 10, 10, 1, and 10 ppb, respectively. The procedure was applied to determine ABZ and its major metabolites in the incurred muscle tissue of yellow perch obtained after orally dosing the fish with ABZ.     

Facile synthesis of unusual glycosyl carbamates and amino acid glycosides from propargyl 1,2-orthoesters as glycosyl donors

Propargyl 1,2-O-orthoesters are exploited for the synthesis of 1,2-trans O-glycosides of protected amino acids. N-Fmoc- and N-Cbz protected serine/threonine - benzyl/methyl esters reacted well with glucosyl-, galactosyl-, mannosyl- and lactosyl- derived propargyl 1,2-orthoesters affording respective 1,2-trans glycosides in good yields under AuBr(3)/4 ? MS Powder/CH(2)Cl(2)/rt. t-Boc serine derivative gave serine 1,2-orthoester and glycosyl carbamate. Optimized conditions enabled preparation of new glycosyl carbamates from N-Boc protected amines in a single step using gold catalysts and propargyl 1,2-orthoesters in excellent yields.     

Simultaneous detection and quantification of parecoxib and valdecoxib in canine plasma by HPLC with spectrofluorimetric detection: development and validation of a new methodology

Parecoxib is the injectable prodrug of valdecoxib, a cicloxygenase-2 selective drug, currently used in human medicine. Recent studies have suggested both its excellent clinical effectiveness and wide safety profile. The aim of the present study was to develop and validate a new high-performance liquid chromatography (HPLC) with spectrofluorimetric detection method to quantify parecoxib and valdecoxib in canine plasma. Several parameters both in the extraction and the detection method were evaluated. The applicability of the method was determined by administering parecoxib to one dog: the protocol provided the expected pharmacokinetic results. The final mobile phase was acetonitrile: AcONH₄ (10 mM; pH 5.0) 55:45, v/v, with a flow rate of 0.4 mL min⁻¹, and excitation and emission wavelengths of 265 and 375 nm, respectively. The analytical column was a reverse-phase C18 ODS2 3-μm particle size. Protein precipitation in acidic medium followed by two successive liquid–liquid steps was carried out. The best extraction solvent was cyclohexane:Et₂O (3:2, v/v) that gave recoveries ranging from 81.1% to 89.1% and from 94.8% to 103.6% for parecoxib and valdecoxib, respectively. The limits of quantification were 25 and 10 ng mL⁻¹ for parecoxib and valdecoxib, respectively. The chromatographic runs were specific with no interfering peaks at the retention times of the analytes, as confirmed by HPLC–mass spectrometry experiments. The other validation parameters were in agreement with the European Medicines Evaluation Agency and International Conference on Harmonisation guidelines. In conclusion, this method (extraction, separation and applied techniques) is simple and effective. This is the first time that use of a HPLC with spectrofluorimetric detection technique to simultaneously detect parecoxib and valdecoxib in plasma has been reported. This technique may have applications for pharmacokinetic studies.     

Redox-rich spin-spin-coupled semiquinoneruthenium dimers with intense near-IR absorption

Using the [RuCl(μ-tppz)ClRu](2+) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine] platform for bridging two o-quinone/catecholate two-step redox systems (unsubstituted, Q(n), or 3,5- di-tert-butyl-substituted, DTBQ(n)), we have obtained the stable complexes [(Q(?-))Ru(II)Cl(μ-tppz)ClRu(II)(Q(?-))] (1) and the structurally characterized [(DTBQ(?-))Ru(II)Cl(μ-tppz)ClRu(II)(DTBQ(?-))] (2). The compounds exhibit mostly quinone-ligand-based redox activity within a narrow potential range, high-intensity near-IR absorptions (λ(max) ≈ 920 nm; ε > 50,000 M(-1) cm(-1)), and variable intra- and intermolecular spin-spin interactions. Density functional theory calculations, electron paramagnetic resonance (EPR), and spectroelectrochemical results (UV-vis-near-IR region) for three one-electron-reduction and two one-electron-oxidation processes were used to probe the electronic structures of the systems in the various accessible valence states. EPR spectroscopy of the singly charged doublet species showed semiquinone-type response for 1(+), 2(+), and 2(-), while 1 exhibits more metal based spin, a consequence of the easier reduction of Q as compared to DTBQ. Comparison with the analogous redox series involving a more basic N-phenyliminoquinone ligand reveals significant differences related to the shifted redox potentials, different space requirements, and different interactions between the metals and the quinone-type ligands. As a result, the tppz bridge is reduced here only after full reduction of the terminal quinone ligands to their catecholate states.     

Platinum-nanogaps for single-molecule electronics: room-temperature stability

We present the formation of single-molecule devices based on nanometre-spaced platinum electrodes. The electrodes are fabricated using a self-breaking electromigration method which yields nanogaps with long-term stability at room temperature [Prins et al., APL, 2009, 94, 123108.]. The stability at room temperature allows for detailed comparison of the device electrical properties before and after deposition of the molecules. In this way, conductance as a result of direct tunneling between the electrodes can be distinguished from conductance through the molecule. After molecule deposition, some devices display transport in the strong coupling regime while others are in the weak-coupling Coulomb blockade regime. Gated transport is observed in the latter case.     

Metal‐based isatin‐bearing sulfonamides: their synthesis,characterization and biological properties

A new series of antibacterial and antifungal isatin bearing sulfonamides and their cobalt (II), copper (II), nickel (II) and zinc (II) metal complexes have been synthesized, characterized and screened for their in vitro antibacterial activity against Bacillus cereus, Corynebacterium diphtheriae, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Salmonella typhi, Shigilla dysentriae and Staphylococcus aureus and for in vitro antifungal activity against Trichophyton schoenleinii, Candid glabrata, Pseudallescheria boydii, Candida albicans, Aspergillus niger, Microsporum canis and Trichophyton mentagrophytes. The results of these studies revealed that all compounds showed moderate to significant antibacterial activity. The brine shrimp bioassay was also carried out to study their in vitro cytotoxic properties. Only three compounds, 2, 11 and 22 displayed potent cytotoxic activity as LD₅₀ = 1.56 × 10^?7, 1.59 × 10^?7 and 1.67 × 10^?7 M /ml respectively, against Artemia salina. Copyright © 2006 John Wiley & Sons, Ltd.     

Measurement of transverse vibrations/visualization of mode shapes in square plate by using digital speckle pattern interferometry and wavelet transform

New filtering scheme is investigated and implemented on digital speckle pattern interferometric fringes to enhance the signal-to-noise ratio (SNR) in the speckle interferograms. To establish the potential of new filtering scheme the experiment was conducted on the vibrating cantilever beam. Experimental results revealed that the new filtering scheme is more powerful than other known filtering schemes (Kumar et al. Opt Laser Eng 2004;41:81–93. Kumar et al. Opt Laser Technol 2001;33:567–571. Shakher et al. Opt Eng 2002;41:176–180. Shakher et al. Proceedings ICICS, Singapore, 9–12 September 1997, p. 953–956. Bowler et al. Proceedings of IEE second international conference on image processing, London, 1986, p. 24–26. Lim. Opt Eng 1981;20:670–678. Devila et al. J Mod Opt 1995;42:1795–1804; Kaufmann et al. Opt Eng 1996;35:9–14). The new scheme reduced the speckle noise and improved SNR in speckle interferograms. Further, the new investigated filtering scheme is implemented to study the mode shapes of square plates under two different boundary conditions. In the first condition all the edges of the square plate were fixed while in the second condition two adjacent edges were fixed and the remaining two edges were free. From the experimental results it is clear that the mode shapes are more distinctly visible with the implementation of the new filtering scheme as compared to other known schemes. Under both the boundary conditions the recorded resonance frequencies were compared with the calculated values of resonance frequencies based on classical theory. The results obtained form DSPI show good agreement with classical theory.     

NaIO4-mediated C-H activation of alkylbenzenes and alkanes with LiBr

NaIO₄ oxidizes lithium bromide efficiently under acidic conditions to functionalize alkylbenzenes and alkanes and produce the corresponding bromo and acetoxy derivatives in excellent yields. The protocol also demonstrates the direct conversion of cyclohexane into trans-1,2-dibromocyclohexane in moderate yield.