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.     

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.     

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.     

A resonance light-scattering (RLS) serving for various quantitative events since 1995: A comment proposed towards how to apprehend well the meaning of RLS and its corresponding guiding role

A resonance light-scattering (RLS), which was creatively suggested for the first time by Pasternack et al. in 1993 [R.F. Pasternack, C. Bustamante, P.J. Collings, A. Giannetto, E.J. Gibbs, J. Am. Chem. Soc. 115 (1993) 5393], have been enjoyably practiced by numerous investigators for various quantitative events since 1995, and hitherto many research papers and some review papers have got published on lots of international journals specialized in or related to analytical and/or bioanalytical sciences. As revealed from these published papers of interests, however, it is a pity that the meaning of RLS is often apprehended unsatisfactorily both in theory and in practice. In this comment, as a result, I would like to do my best to propose an apprehension of the meaning of RLS as full and exact as possible and simultaneously I would like to deliver the important guiding role of this proposed apprehension in the course of the applications of RLS for various quantitative purposes.     

Surface-enhanced Raman scattering of 4,4′-bipyridine on silver by density functional theory calculations

Surface-enhanced Raman scattering (SERS) of 4,4′-bipyridine (BPy) on silver foil substrate was measured using the 488, 514.5, and 1064 nm excitation lines. Density functional theory (DFT) methods were used to calculate the structure and vibrational spectra of Ag–BPy, Ag₃–BPy and Ag₄–BPy complexes with B3LYP/6-31++G(d,p)(C,H,N)/Lanl2dz(Ag) basis set. The Raman bands of BPy were assigned on the basis of the calculation of potential energy distribution. The calculated spectra of Ag–BPy and Ag₄–BPy complexes were much closer to the experimental results of BPy adsorbed on silver surface than that of Ag₃–BPy complexes. The vibrational frequencies that are sensitive to the planar or non-planar structure of BPy and to the dihedral angle of two pyridyl rings were discussed. The DFT results showed that the angles between two pyridyl rings for Ag–BPy and Ag₄–BPy were skewed by about 38.44° and 37.1°, respectively. The energy gaps of the HOMO and LUMO from DFT were 415–912 nm for BPy–Ag complexes. The relative intensities of SERS bands changed with different excitation laser lines. Thus, a chemical enhancement mechanism should play an important role in the SERS of BPy on silver substrate.     

A new car-following model with consideration of inter-vehicle communication

In this paper, we construct a new car-following model with inter-vehicle communication (IVC) to study the driving behavior under an accident. The numerical results show that the proposed model can qualitatively describe the effects of IVC on each vehicle’s speed, acceleration, movement trail, and headway under an accident and that the new model can overcome the full velocity difference (FVD) model’s shortcoming that collisions occur under an accident, which illustrates that the new model can better describe the driving behavior under an accident than the FVD model.     

Continuous detrended cross-correlation analysis on generalized Weierstrass function

The paper mainly introduces a continuous detrended cross-correlation analysis method to detect the long-range fractal scaling behaviors of continuous and integrable functions. The effects of such method are tested by the generalized Weierstrass function with various seeds. It presents accurate scaling characterization as desired by comparing with that from the popular detrended cross-correlation analysis method of discrete case.     

Simple optimized Brenner potential for thermodynamic properties of diamond

We have examined the commonly used Brenner potentials in the context of the thermodynamic properties of diamond. A simple optimized Brenner potential is proposed that provides very good predictions of the thermodynamic properties of diamond. It is shown that, compared to the experimental data, the lattice wave theory of molecular dynamics (LWT) with this optimized Brenner potential can accurately predict the temperature dependence of specific heat, lattice constant, Grüneisen parameters and coefficient of thermal expansion (CTE) of diamond.