Rapid resolution liquid chromatography-mass spectrometry and high-performance liquid chromatography-fluorescence detection for metabolism and pharmacokinetic studies of ergosta-4,6,8(14),22-tetraen-3-one

Ergosta-4,6,8(14),22-tetraen-3-one (ergone) from many medicinal plants has been demonstrated to possess a variety of pharmacological activities in vivo and in vitro, including cytotoxic, diuretic and immunosuppressive activity. Metabolism and pharmacokinetic studies on rat were conducted for ergone. Rapid resolution liquid chromatography with atmospheric pressure chemical ionization tandem multi-stage mass spectrometry (RRLC-APCI-MSⁿ) and high-performance liquid chromatography with fluorescence detection (HPLC-FLD) methods were applied for the identification and quantification of ergone and its metabolite from rat plasma, faeces and urine. A metabolite was identified by RRLC-DAD-APCI-MSⁿ: 22,23-epoxy-ergosta-4,6,8(14)-triaen-3-one (epoxyergone). The concentrations of the analyte with its metabolites were determined by HPLC-FLD at excitation wavelength of 370 nm and emission wavelength of 485 nm. The samples were deproteinized with methanol after addition of camptothecin as internal standard (IS). The analysis was performed on a Diamonsil C18 column (150 mm × 4.6 mm × 5 μm) with a mobile phase gradient consisting of methanol and water at a flow rate of 1 mL min⁻¹. The assay was linear over the concentration range of 42-1500, 36-7500 and 42-1500 ng mL⁻¹ for plasma, faecal homogenate and urine respectively. The absolute recoveries were found to be 97.0 ± 1.2%, 98.1 ± 0.7% and 96.6 ± 1.8% for plasma, faecal homogenate and urine respectively. The intra-day and inter-day relative standard deviations (RSD) were less than 10%. The previous HPLC-MS/MS method is not affordable for most laboratories because of the specialty requirement and high equipment cost. However, the HPLC-FLD method is economic and operating simply for quantitative determination of ergone and its metabolite in rat plasma, faeces and urine. In addition, liquid chromatography coupled with ion trap multi-stage mass spectrometry is becoming a useful technique for ergone metabolite identification.     

Colorimetric and fluorometric sensing of the Lewis acidity of a metal ion by metal-ion complexation of imidazo[1,2-a]pyrazin-3(7H)-ones

Metal-ion complexation of 7-benzylimidazo[1,2-a]pyrazin-3(7H)-one derivative (2) with Li⁺, Mg²⁺, Ca²⁺, Ba²⁺, Sc³⁺, and La³⁺ in acetonitrile resulted in successive modulations of its UV/vis absorption and fluorescence spectroscopic properties. This result indicates that 2 can be used as a colorimetric and fluorometric sensor of the Lewis acidity of a metal ion in aprotic solutions. The hypothesis that the metal-ion complex has a O10(imidazopyrazinone)-metal ion bond was supported by X-ray crystallographic analysis and quantum chemical calculations for a Li⁺ complex of 7-methylimidazo[1,2-a]pyrazin-3(7H)-one derivative (1).     

Synthesis and evaluation of benzothiazolyl and benzimidazolyl asparagines as amino acid based selective fluorimetric chemosensors for Cu

A series of emissive N-tert-butyloxycarbonyl benzyl ester asparagines bearing benzothiazole and benzimidazole units at the side chain, functionalised with electron donor or acceptor groups, were evaluated as novel amino acid based fluorimetric chemosensors for transition metal cations, such as Cu²⁺, Zn²⁺, Co²⁺ and Ni²⁺. Selective removal of the protecting groups at the N- and C-terminals was carried out in order to assess the influence of the presence of blocking groups on the overall coordination ability. The results indicate that there is a strong interaction through the donor N, O and S atoms at the side chain of the various asparagines, with high selectivity towards Cu²⁺ in a 1:1 complex stoichiometry. Association constants and detection limits for Cu²⁺ were calculated. The photophysical and metal ion sensing properties of these asparagines suggest that they can be suitable for incorporation into peptidic chemosensor frameworks.     

Synthesis and photophysical properties of tetrafluorophenyl-modified carbazole oligomers

A series of tetrafluorophenyl-modified oligo(3,6-carbazole ethynylene)s (CfCzCf, CfCz2Cf, CfCz3Cf, (CfCz)2Cf, and Cf2CzCf2) were synthesized by a Pd/Cu-catalyzed Sonogashira coupling reaction and fully characterized. Their photophysical and electronic properties as well as their thermal stabilities were investigated. It is noteworthy that these tetrafluorophenyl modified compounds showed relative thermal stabilities and low-lying HOMO levels ranging from −5.54 to −5.60 eV, which might be the promising candidates for hole-transporting materials in OLEDs.     

Synthesis of reversible fluorescent organogel containing 2-(2′-hydroxyphenyl)benzoxazole: fluorescence enhancement upon gelation and detecting property for nerve gas simulant

A new low molecular mass organogelator 1 containing 2-(2′-hydroxyphenyl)benzoxazole (HPB) group with long alkyl chain was synthesized by the reaction with 5-amino-2-(2′-hydroxy-4′-methylphenyl)benzoxazole and dodecyl isocyanate in THF at room temperature. The reversible gelation ability of 1 was investigated using a heating-cooling method in various organic solvents. The stable organogel was formed from carbon tetrachloride or from cyclohexane at the concentration as low as 0.9%. The self-assembled supramolecular gel structure formed by non-covalent bonding was confirmed with field emission-scanning electron microscope (FE-SEM) exhibiting fibril- or ribbon-shaped structure depending on the solvent used. Regarding the aggregation-induced emission enhancement (AIEE) phenomenon, the optical properties were investigated in its solution and gelled state. The detecting properties of resulting organogel toward nerve gas simulant were monitored by UV-vis and fluorescence spectroscopy. Both color change from colorless to greenish yellow and disruption of gel structure resulting from alteration in intermolecular forces were observed upon the exposure to nerve gas simulant.     

Application of dispersive liquid-liquid microextraction and spectrophotometric detection to the rapid determination of rhodamine 6G in industrial effluents

A rapid and effective preconcentration method for extraction of rhodamine 6G was developed by using a dispersive liquid-liquid microextraction (DLLME) prior to UV-vis spectrophotometry. In this extraction method, a suitable mixture of acetone (disperser solvent) and chloroform (extractant solvent) was injected rapidly into a conical test tube containing aqueous solution of rhodamine 6G. Therefore, a cloudy solution was formed. After centrifugation of the cloudy solution, sedimented phase was evaporated, reconstituted with methanol and measured by UV-vis spectrophotometry. Different operating variables such as type and volume of extractant solvent, type and volume of disperser solvent, pH of the sample solution, salt concentration and extraction time were investigated. The optimized conditions (extractant solvent: 300 μL of chloroform, disperser solvent: 3 mL of acetone, pH: 8 and without salt addition) resulted in a linear calibration graph in the range of 5-900 ng mL⁻¹ of rhodamine 6G in initial solution with R² = 0.9988 (n = 5). The Limits of detection and quantification were 2.39 and 7.97 ng mL⁻¹, respectively. The relative standard deviation for 50 and 250 ng mL⁻¹ of rhodamine 6G in water were 2.88% and 1.47% (n = 5), respectively. Finally, the DLLME method was applied for determination of rhodamine 6G in different industrial waste waters.     

Acridinedione-functionalized gold nanoparticles and model for the binding of 1,3-dithiol linked acridinedione on gold clusters

The design and synthesis of 1,3-dithiol linked acridinedione functionalized gold nanoparticles (ADDDT-GNP) is described. ADDDT-GNP was characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), UV-vis, steady-state and time-resolved fluorescence techniques. Conformational analysis of 1,3-dithiol ligands using density functional theory (DFT) reveals that they can cap on gold clusters through 1,2-capping mode, in which the two sulfur atoms of the dithiol bind covalently with two adjacent gold atoms on the surface of the cluster. The present study shows that three conformers of the ligand can cap in the 1,2-mode of capping. The triexponential fluorescence decay observed in the capped nanogold complex with fluorophore-labeled 1,3-dithiol may originate from the three conformers of the complex in the 1,2-capping mode.     

Effect of carbon nanotubes and their dispersion on thermal curing of polyimide precursors

The process of thermal imidization reaction is significant for temperature and time control in the polyimide industry. Here, we report the effect of carbon nanotubes and their states of dispersion on the thermal imidization of the precursor films of polyimide (poly(amic acid)) for the first time. The curing process was followed by measuring Fourier transform-infrared (FT-IR) spectra, fluorescence spectra, thermogravimetric-differential scanning calorimeter (TG-DSC) properties and the refractive indices of films. It was found that by evenly dispersing 1 wt% of carbon nanotubes assisted by a dispersant in the poly(amic acid),the full imidization temperature of the polyimide can be reduced from 300 °C to 250 °C. Different states of distribution of CNTs were observed by light microscopy and scanning electron microscopy, and proved that a better dispersion of carbon nanotubes dramatically enhanced the speed of imidization. Moreover, the DSC results showed that lower decomposition temperature of poly(amic acid) could be obtained with more uniform distribution of carbon nanotubes, which means the process of cyclodehydration of the poly(amic acid) was accelerated.     

Identification and localization of organic coating degradation onset by impedance imaging

The aim of this work was to demonstrate the potential of a localized impedance measurement technique to identify and spatially localize the onset spots of polymeric coating degradation. The technique, which has not yet been applied in the field of organic coatings, utilizes atomic force microscopy (AFM) in contact mode. During the scan a single-frequency voltage perturbation signal is applied between the AFM tip and the coated metal substrate. A current response signal is registered. As a result an impedance map of the scanned region is created. The method was applied to investigation of acrylic coating degradation during exposure to UV radiation. Localized topography and impedance images revealed formation of micro-cracks in the coating layer, which gradually converted into through-the-coating defects with an increase in the irradiation time. Thus the method allowed early identification and localization of the sites of degradation onset, which was not possible using classical impedance measurement.     

Fluorescence line narrowing spectroscopy of Eu in zinc-thallium-tellurite glass

The environment of Eu³⁺ in zinc-thallium-tellurite glass of the molar composition 60TeO₂-30TlO_0.5-9.9ZnO-0.1Eu₂O₃ was investigated by laser-induced fluorescence line narrowing (FLN) techniques using Eu³⁺ as a local site probe. From the site selective luminescence spectra of Eu³⁺ at 7 K, the energies of the Stark components of the ⁷F₁ and ⁷F₂ states were recorded and then the crystal field parameters B_nm were calculated assuming a C_2v site symmetry. The ratios B₂₂/B₂₀ and B₄₄/B₄₀ for each excitation energy within ⁷F₀-⁵D₀ transition were obtained and compared with the values calculated for Eu³⁺ in other types of glasses.