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.     

Influence of Temperature on the Formation of Silver Nanoparticles by using a Seed‐Free Photochemical Method under Sodium‐Lamp Irradiation

Silver nanoparticles can be prepared by using a seed‐free photo‐assisted citrate reduction method under the irradiation of a sodium lamp. Under the same irradiation intensity, bath temperatures are crucial in influencing the reaction rate, morphologies of final products, and shape evolution of the silver nanostructures. For example, when the bath temperature is 80 °C, the product yields of silver nanoplates, nanorods, and nanodecahedra are 38±6 %, 35±10 %, and 12±8 %, respectively. However, when the bath temperature is 30 °C, the product yields of silver nanoplates, nanorods, and nanodecahedra are 6±3 %, 0 %, and 83±16 %, respectively. Time‐dependent UV/Vis spectra and TEM images show that silver nanoplates were formed at the earlier reaction stage and greatly decreased in amount at the later stage when the bath temperatures are less than or equal to 40 °C. This indicates that the silver nanoplates, which can be regarded as intermediates, are kinetically favored products. They are not thermodynamically favored products at these relatively low bath temperatures. The SERS spectra of crystal violet (CV) show that all the silver colloids synthesized at various temperatures exhibit good enhancement factors and that the colloids prepared at lower bath temperatures have a higher enhancement factor.     

Recent advances of green pretreatment techniques for quality control of natural products

A few advancing technologies for natural product analysis have been widely proposed, which focus on decreasing energy consumption and developing an environmentally sustainable manner. These green sample pretreatment and analysis methods following the green Analytical Chemistry (GAC) criteria have the advantage of improving the strategy of chemical analyses, promoting sustainable development to analytical laboratories, and reducing the negative effects of analysis experiments on the environment. A few minimized extraction methodologies have been proposed for replacing the traditional methods in the quality evaluation of natural products, mainly including solid-phase microextraction (SPME) and liquid phase microextraction (LPME). These procedures not only have no need for large numbers of samples and toxic reagent, but also spend a small amount of extraction and analytical time. This overview aims to list out the main green strategies on the application of quality evaluation and control for natural products in the past 3 years.     

High-Efficiency Oxygen Reduction to Hydrogen Peroxide Catalyzed by Nickel Single-Atom Catalysts with Tetradentate N2O2 Coordination in a Three-Phase Flow Cell

Carbon-supported Ni^II single-atom catalysts with a tetradentate Ni-N₂O₂ coordination formed by a Schiff base ligand-mediated pyrolysis strategy are presented. A Ni^II complex of the Schiff base ligand (R,R)-(−)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine was adsorbed onto a carbon black support, followed by pyrolysis of the modified carbon material at 300 °C in Ar. The Ni-N₂O₂/C catalyst showed excellent performance for the electrocatalytic reduction of O₂ to H₂O₂ through a two-electron transfer process in alkaline conditions, with a H₂O₂ selectivity of 96 %. At a current density of 70 mA cm⁻², a H₂O₂ production rate of 5.9 mol g_cat.⁻¹ h⁻¹ was achieved using a three-phase flow cell, with good catalyst stability maintained over 8 h of testing. The Ni-N₂O₂/C catalyst could electrocatalytically reduce O₂ in air to H₂O₂ at a high current density, still affording a high H₂O₂ selectivity (>90 %). A precise Ni-N₂O₂ coordination was key to the performance.     

A ytterbium polymer incorporating ethyl-4,5-imidazole-dicarboxylate and formate coligand: Structure, luminescent, and magnetic properties

A new lanthanide-organic coordination polymer incorporating both substituted imdazole dicarboxylate and formate auxiliary ligand, namely {[Yb₃(HEimda)₄(μ₂-HCOO) · 4H₂O] · 2H₂O} _n (I) (H₃Eimda = 1H-2-ethyl-4,5-imidazole-dicarboxylic acid), has been prepared and was structurally characterized by elemental analysis, IR and X-ray diffraction. It crystallizes in the monoclinic system, space group of C2/c. The polymer I is built from two dimensional (2D) double decker networks based on the Ln₄HEimda₄ tetranuclear basic carboxylate as secondary building unit. The extensive hydrogen bonds extend the 2D lamellar network into a 3D supramolecular aggregate. The emission spectrum of polymer I exhibits ligand-to-metal charge-transfer luminescence. Variable-temperature magnetic susceptibility measurement reveals that the end to end bridging fashion of formate group results in the depopulation of the stark levels for a single Yb³⁺ ion and/or possible antiferromagntic interactions between Yb³⁺ ions within the carboxylato bridged dinuclear unit.     

Dextran-coated CdSe quantum dots for the optical detection of monosaccharides by resonance light-scattering technique

A resonance light-scattering (RLS) detection method for saccharides was developed using dextran-coated CdSe quantum dots (dextran-CdSe-QDs) optical probes. The dextran-CdSe-QDs can be aggregated with concanavalin A (Con A), and the change in RLS intensity is used to monitor the extent of aggregation. The presence of glucose competitively binds with Con A, dissociating the Con A/dextran-CdSe-QDs complexes, affording the RLS intensity change and hence determining glucose concentrations in the range from a few to about 90 mM. Transmission electron microscopy was used to investigate the competitive interaction between glucose and dextran-CdSe-QDs with Con A. The competitive strategy could also be used to detect similar types of saccharides and the affinities of various monosaccharides for Con A increased in the order galactose?glucose < fructose < mannose. The proposed method was successfully applied to determine glucose in the human serum.

A resonance light-scattering (RLS) detection method for saccharides was developed using dextran-coated CdSe quantum dots (dextran-CdSe-QDs) optical probes. The dextran-CdSe-QDs were coupled to concanavalin A (Con A) to facilitate the aggregation of nanoparticles. The presence of glucose competitively binds with Con A, dissociating the Con A/dextran-CdSe-QDs complexes affording the RLS intensity change and hence determining glucose in the range from a few millimolar to about 90 mM. The proposed method was applied to the determination of glucose in human serum samples with satisfactory results.

     

Carrier ampholyte-free solution isoelectric focusing as a prefractionation method for the proteomic analysis of complex protein mixtures

The field of proteomics requires methods that offer high sensitivity and wide dynamic range. One of the strategies used to improve the dynamic range is sample prefractionation, such as microsolution isoelectric focusing (IEF). We have modified a commercial solution IEF instrument, the Rotofor, to prefractionate protein mixtures by carrier ampholyte-free solution IEF. The focusing chamber of the Rotofor was divided into several compartments by polyacrylamide membranes with imbedded Immobiline mixtures of specific pH values. When an electric field is applied, each protein migrates to the compartment confined by membranes with pH values flanking its isoelectric point. The approach was demonstrated for the focusing of myoglobin into a predicted compartment, as well as the separation of a complex soluble yeast protein mixture into several distinct fractions. The proteins were dissolved in water or 30% isopropanol. The method is applicable to both gel-based and solution-phase protein identification methods, without the need for further sample preparation.     

Synthesis of novel mesoporous carbon nanoparticles and their phytotoxicity to rice (Oryza sativa L.)

Despite the remarkable number of investigations on the potential risks of the engineered nanomaterials (ENMs) to terrestrial plants, there was limited knowledge regarding the effects of mesoporous carbon nanoparticles (MCNs) with different sizes on crops. The objective of our study was to evaluate the toxicity of MCNs to rice (Oryza sativa L.) seedlings. Two novel MCNs with different particle sizes (MCN1: 150 and MCN2: 80?nm) were synthesized using the high-temperature pyrolysis method and characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy, and Raman spectra. Phytotoxicity of two MCNs was then comparatively evaluated using rice as a model plant. The rice seedlings were hydroponically exposed to both MCN suspensions with concentrations of 0, 10, 50, 150?mg/L for 20?days. Exposure to 150?mg/L MCN1 resulted in more than 21% and 29% decrease in root length and in shoot length, respectively. MCN2 significantly reduced the root and shoot lengths by approximately 70% and 57% at the concentration of 150?mg/L. Additionally, the concentrations of three endogenous phytohormones, including brassinolide (BR), indole propionic acid (IPA), and dihydrozeatinriboside (DHZR) in plant shoots were increased significantly compared with the control. Our findings illustrated that size-effects of MCNs contributed greatly in causing phytotoxicity to plants, which should have drawn our attention to the use of these novel ENMs in agriculture given the evidence of their potential risks to crops. More importantly, this is the first study on assessment of the phytotoxicity of MCNs to rice seedlings from the perspective of plant hormones.