Colorimetric detection of fluoride in an aqueous solution using Zr(IV)-EDTA complex and a novel hemicyanine dye

A new highly sensitive and selective colorimetric method for fluoride determination in water is described. The novel reagent used is a hemicyanine dye (HC), which forms a stable complex with Zr-EDTA, the fluoride-binding site, through the hydroxyl groups. The hemicyanine-chelating Zr-EDTA complex (HC-Zr-EDTA) is ready to react with fluoride ion to release HC. This result in remarkable color change of the sensing solutions from red (λ_max = 513 nm) to yellow (λ_max = 427 nm) at pH 4.40. When applied to the colorimetric determination of fluoride ions, a linear range from 3.0 × 10⁻⁶ to 5.0 × 10⁻⁵ mol/L and a detection limit of 2.8 × 10⁻⁶ mol/L with a correlation coefficient of 0.9993 can be achieved under the optimized conditions. Because of the specific affinity of fluorides for the [Zr-EDTA], there is little interference by other ions. This method has been successfully applied to the determination of fluorides in toothpaste samples.     

Ferrocene‐based derivative bearing phenol group recognitive sites: efficient H2PO4− receptor

Two artificial receptors, bearing ferrocene and phenol groups, were synthesized and their anion‐binding properties were evaluated for F^?, Cl^?, Br^?, I^?, AcO^? and by UV–vis, ¹H NMR titration and cyclic voltammetry experiments in order to research the effect of different substituents on anion‐recognition properties. Results indicate that the anion binding abilities can be effectively tuned by introducing a nitro group in the ortho position of the phenyl ring of the receptors, and the most obvious effect is for . Copyright © 2007 John Wiley & Sons, Ltd.     

Rational Design of Pt−Pd−Ni Trimetallic Nanocatalysts for Room-Temperature Benzaldehyde and Styrene Hydrogenation

Nanostructures of the multimetallic catalysts offer great scope for fine tuning of heterogeneous catalysis, but clear understanding of the surface chemistry and structures is important to enhance their selectivity and efficiency. Focussing on a typical Pt−Pd−Ni trimetallic system, we comparatively examined the Ni/C, Pt/Ni/C, Pd/Ni/C and Pt−Pd/Ni/C catalysts synthesized by impregnation and galvanic replacement reaction. To clarify surface chemical/structural effect, the Pt−Pd/Ni/C catalyst was thermally treated at X=200, 400 or 600 °C in a H₂ reducing atmosphere, respectively termed as Pt−Pd/Ni/C−X. The as-prepared catalysts were characterized complementarily by XRD, XPS, TEM, HRTEM, HS-LEIS and STEM-EDS elemental mapping and line-scanning. All the catalysts were comparatively evaluated for benzaldehyde and styrene hydrogenation. It is shown that the “PtPd alloy nanoclusters on Ni nanoparticles” (PtPd/Ni) and the synergistic effect of the trimetallic Pt−Pd−Ni, lead to much improved catalytic performance, compared with the mono- or bi- metallic counterparts. However, with the increase of the treatment temperature of the Pt−Pd/Ni/C, the catalytic performance was gradually degraded, which was likely due to that the favourable nanostructure of fine “PtPd/Ni” was gradually transformed to relatively large “PtPdNi alloy on Ni” (PtPdNi/Ni) particles, thus decreasing the number of noble metal (Pt and Pd) active sites on the surface of the catalyst. The optimum trimetallic structure is thus the as synthesised Pt−Pd/Ni/C. This work provides a novel strategy for the design and development of highly efficient and low-cost multimetallic catalysts, e. g. for hydrogenation reactions.     

Ultra-stable and multistimuli-responsive nanoparticles coated with zwitterionic pillar[n]arene for enhanced cellular uptake

Nanoparticle surface property is crucial for circulation stability,cellullar uptake and other biological characteristics.Zwitte rionic pillar[n]arenes(ZPns) we re used to coat gold nanopa rticles(GNPs) via hostguest interaction.The resulting GNPs demonstrated higher stability in blood serum compared to polyethylene glycol(PEG)-coated GNPs.ZPn-coated GNPs were responsive to UV-irradiation,competitive displacement and acidic pH.UV-irradiation or competitive displacement could lead to the removal of ZPn coating to expose GNPs,which enhanced cell uptake efficiency by 5.9-and 7.4-fold,respectively.     

Periodic solutions for neutral coupled oscillators network with feedback and time-varying delay

This paper is considered to be about the existence of periodic solutions for neutral coupled oscillators network with feedback control and time-varying delay (NCONFT). Based on the systematic method which is firstly applied for NCONFT and consisting of coincidence degree theory, graph theory, and Lyapunov method, some sufficient criteria are obtained to verify the existence of periodic solutions for NCONFT. What’s more, how coupling topology, feedback control, and time-varying delay affect the existence of periodic solutions for NCONFT can be shown by these sufficient criteria. Finally, a numerical simulation is offered to illustrate the effectiveness of our results.     

Grouped Functional Time Series Forecasting: An Application to Age-Specific Mortality Rates

Age-specific mortality rates are often disaggregated by different attributes, such as sex, state, and ethnicity. Forecasting age-specific mortality rates at the national and sub-national levels plays an important role in developing social policy. However, independent forecasts at the sub-national levels may not add up to the forecasts at the national level. To address this issue, we consider reconciling forecasts of age-specific mortality rates, extending the methods of Hyndman et al. in 2011 Hyndman, R. J., Ahmed, R. A., Athanasopoulos, G., and Shang, H. L. (2011), “Optimal Combination Forecasts for Hierarchical Time Series,” Computational Statistics and Data Analysis, 55, 2579–2589.[Crossref], [Web of Science ®] , [Google Scholar] to functional time series, where age is considered as a continuum. The grouped functional time series methods are used to produce point forecasts of mortality rates that are aggregated appropriately across different disaggregation factors. For evaluating forecast uncertainty, we propose a bootstrap method for reconciling interval forecasts. Using the regional age-specific mortality rates in Japan, obtained from the Japanese Mortality Database, we investigate the one- to ten-step-ahead point and interval forecast accuracies between the independent and grouped functional time series forecasting methods. The proposed methods are shown to be useful for reconciling forecasts of age-specific mortality rates at the national and sub-national levels. They also enjoy improved forecast accuracy averaged over different disaggregation factors. Supplementary materials for the article are available online.     

Sensitive determination of yohimbine in plasma by micropipette tip-based poly(methacrylic acid-co-ethylene glycol dimethacrylate) monolith SPME coupled with HPLC method

A simple, miniaturized micropipette tip-based poly(MAA-co-EGDMA) monolith was prepared by in situ polymerization for sensitive micro-extraction of yohimbine in aqueous and plasma samples. Several parameters for monolith preparation were systematically optimized to obtain monolith with better permeability and absorption property. Methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) were selected as monomer and crosslinker and the ratio of MAA and EGDMA was 1:6. Methanol containing 30% dimethyl sulfoxide was selected as porogens. The prepared micropipette tip-based poly (MAA-co-EGDMA) monolith could be easily connected with a syringe infusion pump for loading solutions. Several factors such as washing solvents, flow rate of sampling, sample volume, and pH of sample solutions which affect enrichment efficiency of yohimbine were also evaluated in this work. Under optimized conditions, good enrichment capacity and stability of poly(MAA-co-EGDMA) monolith were obtained. Finally, the prepared micropipette tip-based poly(MAA-co-EGDMA) monolith solid phase micro-extraction combined with high-performance liquid chromatography was also used to analyze yohimbine in plasma samples. The developed method exhibited good sensitivity with limit of detection as low as 0.5?ng/mL, and also showed wide linearity in the range of 1.0–2000 ng/mL with R²?≥?0.998, excellent reproducibility with relative standard deviation (RSD) ≤?2.5%, and good recoveries in the range of 97.9–103.8% of yohimbine in human plasma.     

Extracting the time scales of conformational dynamics from single-molecule single-photon fluorescence statistics

The quenching rate of a fluorophore attached to a macromolecule can be rather sensitive to its conformational state. The decay of the corresponding fluorescence lifetime autocorrelation function can therefore provide unique information on the time scales of conformational dynamics. The conventional way of measuring the fluorescence lifetime autocorrelation function involves evaluating it from the distribution of delay times between photoexcitation and photon emission. However, the time resolution of this procedure is limited by the time window required for collecting enough photons in order to establish this distribution with sufficient signal-to-noise ratio. Yang and Xie have recently proposed an approach for improving the time resolution, which is based on the argument that the autocorrelation function of the delay time between photoexcitation and photon emission is proportional to the autocorrelation function of the square of the fluorescence lifetime [Yang, H.; Xie, X. S. J. Chem. Phys. 2002, 117, 10965]. In this paper, we show that the delay-time autocorrelation function is equal to the autocorrelation function of the square of the fluorescence lifetime divided by the autocorrelation function of the fluorescence lifetime. We examine the conditions under which the delay-time autocorrelation function is approximately proportional to the autocorrelation function of the square of the fluorescence lifetime. We also investigate the correlation between the decay of the delay-time autocorrelation function and the time scales of conformational dynamics. The results are demonstrated via applications to a two-state model and an off-lattice model of a polypeptide.     

Global Existence of Solutions for the Kawahara Equation in Sobolev Spaces of Negative Indices

We first prove that the Cauchy problem of the Kawahara equation, δtu ＋ uδxu ＋βδx^3u＋γδx^5u = 0, is locally solvable if the initial data belong to H^r（R） and r〉 r≥-7/5, thus improving the known local well-posedness result of this equation. Next we use this local result and the method of ＂almost conservation law＂ to prove that global solutions exist if the initial data belong to H^r（R） and r〉-1/2.