Application of algebraic method to the high overtones of C6H6 and C6D6

Both the spectra and infrared transition strengths of C₆H₆ and C₆D₆ for the C? H stretching overtones up to as high as v = 10 are described in high precision with few parameters (six for the spectra and four for the transition strengths) by the Iachello–Oss algebraic model. The Hamiltonian model is solved in the symmetry adapted bases, which are constructed by the symmetrized boson representation (SBR) technique. The results show that the combination of the algebraic method and SBR technique is a powerful method for describing vibrations of large molecules and high overtones. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Highly regioselective construction of spirocycles via phosphine-catalyzed [3 + 2]-cycloaddition

A direct entry to spirocycles with low to moderate regioselectivity was achieved by triphenylphosphine-catalyzed [3 + 2]-cycloaddition of active exo-methylenecycles (1) and ethyl 2,3-butadienoate (2). The regioselectivity of the reaction was greatly improved by using the bulky tert-butyl ester of the 2,3-butadienoate (5). The regioselectivity of the reaction was further enhanced by using the tert-butyl 2-butynoate as the substrate. This protocol provided an efficient entry to the skeleton of spirocarbocycles, especially spiro[4.n]alkanes.     

Capillary electrophoresis on-line coupled with hydride generation-atomic fluorescence spectrometry for speciation analysis of selenium

A new method for speciation analysis of two inorganic selenium species was developed by on-line coupling of capillary electrophoresis (CE) with hydride generation-atomic fluorescence spectrometry (HG-AFS) and on-line conversion of Se(VI) to Se(IV). Baseline separation of Se(VI) and Se(IV) was achieved by CE in a 50 cm x 75 microm inside diameter (ID) fused-silica capillary at -20 kV using a mixture of 15 mmol.L(-1) NaH2PO4 and 0.5 mmol.L(-1) cetyltrimethylammonium bromide (pH 7.5) as electrolyte buffer. Se(VI) was on-line reduced to Se(IV) by mixing the CE effluent with concentrated HCl. The precision (relative standard deviation, RSD, n=7) ranged from 0.7 to 1.3% for migration time, 6.4 to 3.7% for peak height response, and 5.9 to 6.1% for peak area for the two selenium species at the 500 microg.L(-1) (as Se) level. The detection limits were 33 and 25 microg.L(-1) (as Se) for Se(VI) and Se(IV), respectively. The recoveries of the two selenium species in five locally collected water samples ranged from 88 to 114%. The developed method was applied to speciation analysis of inorganic selenium species in spiked natural water samples.     

Molecular recognition thermodynamics of bile salts by beta-cyclodextrin dimers: Factors governing the cooperative binding of cyclodextrin dimers

The complex stability constants (K(S)), standard molar enthalpy (DeltaH degrees), and entropy changes (DeltaS degrees) for the inclusion complexation of two families of beta-cyclodextrin (beta-CD) dimers, i.e. beta-CD dimers Se1-Se4 bearing 2,2'-diselenobis(benzoyl) tether (Se-dimers) and beta-CD dimers Py1-Py4 bearing 2,2'-bipyridine-4,4'-dicarboxy tether (Py-dimers), with four bile salt guests, i.e. sodium cholate (CA), sodium deoxycholate (DCA), sodium glycocholate (GCA), and sodium taurocholate (TCA), were determined at 25 degrees C in Tris buffer solution (pH 7.4) at 298.15 K by means of isothermal titration microcalorimetry. The thermodynamic parameters obtained, together with the ROESY spectra of interactions between beta-CD dimers and bile salts, consistently suggest that the length, flexibility, and structure of spacers linking the two beta-CD cavities not only determine the binding modes but also significantly alter the molecular selectivity of beta-CD dimers.     

Factorial design in the optimization of preconcentration procedure for lead determination by FAAS

The present paper proposes a preconcentration procedure for lead determination using flame atomic absorption spectrometry (FAAS). It is based on lead(II) ions extraction as brilliant cresyl blue (BCB) complex and its sorption onto Diaion HP-2MG, a methacrylic ester copolymer. The optimization step was carried out using factorial design and the variables studied were pH, shaking time and reagent concentration. In the established experimental conditions, lead can be determinate with a limit of detection of 3.7 μg L⁻¹ lead (N = 20) and a relative standard deviation of 7% for a lead concentration of 100 μg L⁻¹. The accuracy was confirmed by analysis of a certified reference material, the stream sediment furnished by National Research Centre for Certified Reference Materials (NRCCRM), China (GBW 07310). Effect of other ions in the procedure proposed was also studied. The method was applied for lead determination in real samples of water, tea, soil and dust. Tests of addition/recovery in the experiments for lead determination in water samples revealed that the proposed procedure could be applied satisfactorily for analysis of these samples.     

Chiral separation of amino acids derivatized with fluoresceine-5isothiocyanate by capillary electrophoresis and laser-induced fluorescence detection using mixed selectors of beta-cyclodextrin and sodium taurocholate

Chiral separation of 20 pairs of amino acids derivatized with fluoresceine-5-isothiocyanate (FITC) by capillary electrophoresis and laser-induced fluorescence detection was studied using the mixture of beta-cyclodextrin (beta-CD) and sodium taurocholate (STC) as selector. Resolution was considerably superior to that obtained by using either beta-CD or STC alone. The molar ratio of beta-CD to STC of about 2:3 was found to be critical to achieve maximum separation. At this beta-CD-to-STC ratio, chiral separation occurred at really low total concentration of beta-CD and STC (<0.1 mM). Other impacting factors were investigated including the total concentration of beta-CD and STC, pH, and capillary conditioning procedure between two successive runs. Using a running buffer of 80 mM borate containing 20 mM beta-CD and 30 mM STC at pH 9.3, all of the 20 pairs of FITC-amino acid enantiomers were baseline resolved. The resolutions of the most pairs of the amino acid enantiomers (17 of 20) were higher than 3.0, only three pairs gave a resolution lower than 3.0 but higher than 1.90 (beta-phenylserine, pSer). The highest resolution reached 14.58 (Glu). Two derivatives of beta-CD, 2-hydroxypropyl-beta-CD (HP-beta-CD) and heptakis(2,6-di-O-methyl)-beta-CD (DM-beta-CD) were also explored. HP-beta-CD showed similar cooperative effect with STC, while DM-beta-CD together with STC led to poorer chiral separation.     

Interaction between cucurbit[6]uril and bispyridinecarboxamide

The interaction between cucurbit[6]uril and N,N′-(m-bispyridinecarboxamide)-1,n-alkane (m = 2, 3, 4; n = 4, 6, 8) has been investigated by ¹H-NMR, ESI-MS and single crystal X-ray diffraction method. The results show that cucurbit[6]uril can form pseudorotaxanes with N,N′-(m-bispyridinecarboxamide)-1,6-hexane (m = 2, 3, 4) easily. When the alkyl chain length increases (n = 8), the binding mode is identical, but the binding ability of the host towards guest decreases. In both two cases cucurbit[6]uril shows no selectivity towards positional isomers. However, in the case of n = 4, the binding mode is different, having relations with positional substitution of the guest. Only N,N′-(m-bispyridinecarboxamide)-1,4-butane (m = 2) can form pseudorotaxane with cucurbit[6]uril, while the other two (m = 3, m = 4) form external complex with cucurbit[6]uril. The possible reason for the difference has been discussed.     

A new tetrathiafulvalene–diamide cation salt with [Cu2Br4]2− anions

The title salt, bis[2,3‐bis(aminocarbonyl)‐8,9‐bis(methylsulfanyl)tetrathiafulvalenium] di‐μ‐bromido‐bis[bromidocopper(II)], (C₁₀H₁₀N₂O₂S₆)₂[Cu₂Br₄], contains 2,3‐bis(aminocarbonyl)‐8,9‐bis(methylsulfanyl)tetrathiafulvalenium radical cations, [DMT‐TTF(CONH₂)₂]^·+, and [Cu₂Br₄]²⁻ anions. The cations are associated across centres of inversion in a head‐to‐tail fashion via short face‐to‐face S...S stacking (TTF moiety). These dimers are further assembled into a one‐dimensional chain structure via interdimer double S...S contacts involving the methylsulfanyl groups. The one‐dimensional chains give rise to a two‐dimensional structure through intermolecular double N—H...O hydrogen bonds involving the amide group. The [Cu₂Br₄]²⁻ anions, which straddle centres of inversion, are located between the cation layers. Electron paramagnetic resonance measurements show a radical signal, indicating that the two TTF^·+ radicals are not completely coupled in the dimer.     

Dysfunction of Shh signaling activates autophagy to inhibit trophoblast motility in recurrent miscarriage

In early pregnancy, the placenta anchors the conceptus and supports embryonic development and survival. This study aimed to investigate the underlying functions of Shh signaling in recurrent miscarriage (RM), a serious disorder of pregnancy. In the present study, Shh and Gli2 were mainly observed in cytotrophoblasts (CTBs), Ptch was mainly observed in syncytiotrophoblasts (STBs), and Smo and Gli3 were expressed in both CTBs and STBs. Shh signaling was significantly impaired in human placenta tissue from recurrent miscarriage patients compared to that of gestational age-matched normal controls. VEGF-A and CD31 protein levels were also significantly decreased in recurrent miscarriage patients. Furthermore, inhibition of Shh signaling impaired the motility of JAR cells by regulating the expression of Gli2 and Gli3. Intriguingly, inhibition of Shh signaling also triggered autophagy and autolysosome accumulation. Additionally, knockdown of BECN1 reversed Gant61-induced motility inhibition. In conclusion, our results showed that dysfunction of Shh signaling activated autophagy to inhibit trophoblast motility, which suggests the Shh pathway and autophagy as potential targets for RM therapy.Subject terms: Embryology, Endocrine reproductive disorders, Autophagosomes     

Electrochemical determination of iodide on a vanadium oxide-polypropylene carbonate coated glassy carbon electrode

A vanadium oxide-modified glassy carbon electrode was simply and conveniently fabricated by casting vanadium tri(isoproxide) oxide (VO(OC₃H₇)₃) and poly(propylene carbonate) (PPC) onto the glassy carbon electrode surface. The electrochemical properties of iodide at the VO(OC₃H₇)₃-PPC film-modified glassy carbon electrode were investigated by cyclic voltammetry, and an anodic peak was observed at approximately +0.71 V (vs. SCE). Based on this, a sensitive and convenient electrochemical method was proposed for the determination of iodide. Flow injection amperometry (FIA) exhibited a good linear relationship with the concentration of iodide in the range of 5 × 10⁻⁷ mol L⁻¹ and 1 × 10⁻³ mol L⁻¹, and the detection limit was 1 × 10⁻⁷ mol L⁻¹. Quantitative recovery of iodide in synthetic samples has been obtained and the interferences from different cations and anions have been studied. The method has been successfully applied to the determination of iodide in dry edible seaweed. The concentrations of iodide measured by this method are in good agreement with those obtained by spectrophotometric method.