Selective Cosmetic Mercury Analysis Using a Silver Ink Screen‐Printed Electrode with Potassium Iodide Solution

A new method for selective determination of trace mercury has been demonstrated by linear scan voltammetry using silver ink screen printed electrode (AgSPE) in presence of potassium iodide (KI) dissolved 0.05 M H₂SO₄ solution. At AgSPE, iodide oxidation peak current signal found to be systematically decreased (inhibitory current anodic peak current signal, i ) with increase in the Hg concentrations, [Hg]. This observation is further utilized for construction of new Hg electroanalytical assays in this work. On the AgSPE, Hg inhibitory detection potential found at 0 V vs. Ag/AgCl, which is 720 mV lower than that of unmodified SPE system. Under optimal experimental conditions, i signals were linearly increased against [Hg] in the window of 500–4500 ppb (40 μM KI) with a correlation coefficient (r) of 0.9988. The limit of detection (LOD) and limit of quantification (LOQ) were 98 and 318 ppb, respectively. This approach was further utilized to analyze hidden Hg in the cosmetic samples. Real sample assays were consistent with that of result obtained from ICP‐OES, which confirm the applicability of the proposed method for practical applications.     

Stable second‐order nonlinear optical poly(amide–imide)/inorganic materials via simultaneous sequential self‐repetitive reaction and sol–gel process

A series of thermally stable organic/inorganic second‐order nonlinear optical (NLO) composites via sequential self‐repetitive reaction (SSRR) and sol–gel process has been developed. This SSRR is based on carbodiimide (CDI) chemistry. The difunctional azo chromophores (2,4‐diamino‐4′‐(4‐ nitrophenyl‐diazenyl)azobenzene (DNDA)) was reacted with excessive amount of 4, 4′‐methylene‐ diphenylisocyanate (MDI) to form poly‐CDI, and subsequently trimellitic anhydride (TMA) was added to obtain poly(N‐acylurea). The organic/inorganic composites containing prepolymer of phenyltriethoxysilane (PTEOS) and poly(N‐acylurea) in different weight ratios (10:90, 30:70, 50:50, 70:30, 90:10 wt%) were prepared, respectively. The moderate glass transition temperature (T_g) characteristic of the poly(N‐acylurea) allows the NLO‐active polymer to achieve high poling efficiency. After in situ poling and curing process, the T_gs of the composites were elevated, and higher than that of the pristine poly(amide–imide) sample. Electro‐optical (EO) coefficients (r₃₃) of about 5.5 ～ 18.0 pm/V at 830 nm were obtained. Excellent temporal stability at 100°C, and waveguide characteristics (3.1–4.2 dB/cm at 830 nm) were also obtained for these composites. Copyright © 2008 John Wiley & Sons, Ltd.     

Fabrication and characterization of P(VDF-HFP)/SBA-15 composite membranes for Li-ion batteries

This study reports on the preparation of a composite polymer electrolyte for secondary lithium-ion battery. Poly(vinylidiene fluoride-hexafluoropropylene) (P(VDF-HFP)) was used as the polymer host, and mesoporous SBA-15 (silica) ceramic fillers used as the solid plasticizer were added into the polymer matrix. The SBA-15 fillers with mesoporous structure and high specific surface can trap more liquid electrolytes to enhance the ionic conductivity. The ionic conductivity of P(VDF-HFP)/SBA-15 composite polymer electrolytes was in the order of 10⁻³ S cm⁻¹ at room temperature. The characteristic properties of the composite polymer membranes were examined by using FTIR spectroscopies, scanning electron microscopy (SEM), and an AC impedance method. For comparison, the LiFePO₄/Li composite batteries with a conventional microporous polyethylene (PE) separator and pure P(VDF-HFP) polymer membrane were also prepared and studied. As a result, the LiFePO₄/Li composite battery comprised the P(VDF-HFP)/10 wt.% m-SBA-15 composite polymer electrolyte, which achieves an optimal discharge capacity of 88 mAh g⁻¹ at 20 C rate with a high coulomb efficiency of 95%. It is demonstrated that the P(VDF-HFP)/m-SBA-15 composite membrane exhibits as a good candidate for application to LiFePO₄ polymer batteries.     

Enantiotropic nematics from cross-like 1,2,4,5-tetrakis(4'-alkyl-4-ethynylbiphenyl)benzenes and their biaxiality studies

The theoretically predicted optimum length/breadth/width ratio for maximizing shape biaxiality was investigated experimentally by the facile and successful synthesis of cross-shaped compound 3, which showed enantiomeric nematic phase behavior. This cross-like core structure could alternatively be viewed as two fused V-shaped mesogens, which have recently immerged as a new direction in biaxial nematic research, at the bending tips that can act as a new structure for biaxial investigations. Whilst the thermal analysis data of compound 3 did not meet the expected theoretical values for biaxial nematics, surface-induced biaxiality was evidenced by optical studies. Cluster-size analysis within the nematic phase of compound 3 revealed the formation of meta-cybotactic nematics, which approached the cluster sizes of cybotactic nematics. The split small-angle 2D X-ray diffraction patterns of magnetic-field-aligned samples indicated that the nematic phase was composed of small smectic?C-like clusters with the tilting of molecules within the clusters. The wide-temperature-range enantiomeric nematic phase of cross-like compound 3 enabled the molecular skeleton to serve as an alternative skeleton to bent-rod mesogens, which exhibited nematic phases with the potential competition of transitions to higher-order liquid-crystalline phases and crystallization, for future biaxial investigations.     

Noble Gas in a Ring

We have designed a new type of molecule with a noble gas (Ng = Kr and Xe) atom in a six-membered ring. Their structures and stability have been studied by density functional theory and by correlated electronic structure calculations. The results showed that the six-membered ring is planar with very short Ng–O and Ng–N polar covalent bonds. The calculated energy barriers for all the unimolecular dissociation pathways are higher than 20 and 35 kcal/mol for Ng = Kr and Xe, respectively. The current study suggests that these molecules and their derivatives might be synthesized and observable at cryogenic conditions.     

Simultaneous quantitation of urinary cotinine and acrylonitrile-derived mercapturic acids with ultraperformance liquid chromatography–tandem mass spectrometry

Acrylonitrile (AN), a widely used industrial chemical also found in tobacco smoke, has been classified as a possible human carcinogen (group 2B) by the International Agency for Research on Cancer. AN can be detoxified by glutathione S-transferase (GST) to form glutathione (GSH) conjugates in vivo. It can be metabolically activated by cytochrome P450 2E1 to form 2-cyanoethylene oxide, which can also be detoxified by GST to generate GSH conjugates. The GSH conjugates can be further metabolized to mercapturic acids (MAs), namely, N-acetyl-S-(2-cyanoethyl)cysteine (CEMA), N-acetyl-S-(2-hydroxyethyl)cysteine (HEMA), and N-acetyl-S-(1-cyano-2-hydroxyethyl)cysteine (CHEMA). This study developed an ultraperformance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) method to quantitatively profile the major AN urinary metabolites (CEMA, HEMA, and CHEMA) to assess AN exposure, as well as analyze urinary cotinine (COT) as an indicator for tobacco smoke exposure. The limits of quantitation were 0.1, 0.1, 1.0, and 0.05 μg/L for HEMA, CEMA, CHEMA, and COT, respectively. This method was applied to analyze the three AN-derived MAs in 36 volunteers with no prior occupational AN exposure. Data analysis showed significant correlations between the level of COT and the levels of these MAs, suggesting them as biomarkers for exposure to low levels of AN. The results demonstrate that a highly specific and sensitive UPLC-MS/MS method has been successfully developed to quantitatively profile the major urinary metabolites of AN in humans to assess low AN exposure.     

Bifunctional Ion‐Selective Electrode Based on C60‐Cryptand 22 for Silver and Iodine Ions

Fullerence C60‐cryptand 22 was prepared and successfully applied as the electric carrier in the PVC electrode membrane of a bifunctional ion‐selective electrode for cations, e.g., Ag⁺ ions as well as anions, e.g., I^? ions. The bifunctional ion‐selective electrode based on C60‐cryptand 22 can be applied as a Silver (Ag⁺) ion selective electrode with an internal electrode solution of 10^?3 M AgNO₃ in water (pH = 6.3), or as an Iodide (I^?) ion selective electrode with an acidic internal electrode solution of 10^?4 M KI_(aq) (pH = 2) in which the cryptand 22 is protonated, and the C60‐cryptand 22 is changed to C60‐Cryptand22–H⁺ and becomes an anionic electro‐carrier to absorb the I^? ion. The Ag⁺ ion selective electrode based on C60‐cryptand 22 gave a linear response with a near‐Nernstian slope (59.5 mV decade^?1) within the concentration range 10^?1‐10^?3 M Ag⁺_(aq). The Ag⁺ ion electrode exhibited comparatively good selectivity for silver ions, over other transition‐metal ions, alkali and alkaline earth metal ions. The Ag⁺ ion selective electrode with good stability and reproducibility was successfully used for the titration of Ag⁺_(aq) with Cl^? ions. The Iodide (I^?) Ion selective electrode based on protonated C60–cryptand22‐H⁺ also showed a linear response with a nearly Nernstian slope (58.5 mV decade^?1) within 10^?1 ‐ 10^?3 M I^? _(aq) and exhibited good selectivity for I^? ions and had small selectivity coefficients (10^?2–10^?3) for most of other anions, e.g., F^? , OH^?, CH₃COO^?, SO₄^2?, CO₃^2?, CrO₄^2?, Cr₂O₇^2? and PO₄^3? ions.     

Cytotoxic and anti-inflammatory diterpenoids from the Dongsha Atoll soft coral Sinularia flexibilis

Seven new diterpenoids, namely, flexibilisolides C–G (1–5), flexibilisin C (6), and a novel 11,12-secoflexibillin (7), along with seven known compounds, 8–14, were isolated from the Dongsha Atoll soft coral Sinularia flexibilis. The structures of the new metabolites were elucidated by extensive spectroscopic analysis and comparison of the NMR data with those of known analogues. Compounds 1, 8, and 11 were shown to exhibit moderate cytotoxic activity against HeLa and B16 cancer cell lines, and compound 10 was found to exhibit more potent cytotoxic activity against SK-Hep1 and B16 cancer cell lines. Moreover, compounds 1, 2, 8, 9, and 11–14 could significantly inhibit the accumulation of the pro-inflammatory iNOS protein and 1, 8, 11, and 14 could reduce the accumulation of COX-2 protein in LPS-stimulated RAW264.7 macrophage cells.     

Thermal degradation behaviour and kinetic analysis of unsaturated polyester-based composites and IPNs by conventional and modulated thermogravimetric analysis

The thermal degradation behaviour of epoxy/unsaturated polyester based polymer interpenetrating networks (IPNs), and unsaturated polyester containing various flame-retardants have been investigated by TGA and Py/GC/MS. The kinetic parameters of various polymers were analysed by conventional and modulated thermogravimetric analysis (MTGA) methods. The activation energies of degradation were calculated by the Coats-Redfern and MTGA methods, respectively. The results of both conventional and MTGA analyses reveal that the decomposition of IPNs consists of two non-interfering decomposition processes for epoxy polymer and cured unsaturated polyester, respectively. For the flame-retardant containing unsaturated polyesters, ammonium polyphosphate (APP) played an important role in the second-step of the pyrolysis reaction of APP-containing samples. It is important to note that the possibilities of reaction order for these pyrolysis processes are significantly distinguishable by Coats-Redfern method. Furthermore, the activation energies for various samples calculated by MTGA method are on average larger than those calculated from the Coats-Redfern method. The results also reveal that when either the flame-retardant or the epoxy was added to the unsaturated polyester, the heat resistance of the unsaturated polyester was enhanced.