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Artificial enzymes with high stability, adjustable catalytic activity, controllable preparation, and good reproducibility have been widely studied. Noble metal nanozymes, particularly gold nanoparticles (Au NPs), exhibit good catalytic activity, but their stability is poor. In this study, zeolitic imidazolate framework-8 (ZIF-8) was used as a carrier for Au NPs, thus improving the utilization efficiency and conservation stability of the nanozymes. A ZIF-8/Au nanocomposite with peroxidase activity and a raspberry-shaped structure was synthesized. In the assay, ZIF-8/Au catalyzed the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to a blue product oxidized TMB (oxTMB). Glutathione (GSH) selectively inhibited this reaction, with a detection limit of 0.28 µM and linear range of 0.5–60 µM. Using the photo and chromaticity analysis functions, we developed a portable analysis method using a smartphone equipped with a camera module as a detection terminal for a wide range of rapid screening techniques for GSH. Preparation of raspberry-shaped ZIF-8/Au improved the catalytic activity of Au NPs and good results were demonstrated in serum, which suggests their promising application under physiological conditions. [ABSTRACT FROM AUTHOR]

The metal—organic frameworks (MOFs) are expected as ideal biomimetic enzymes for colorimetric glucose detection because of their large surface areas, well defined pore structures, tunable chemical composition, and multi-functional sites. However, the intrinsically chemical instability and low mimetic enzyme activity of MOFs hinder the application of them in imitating the enzyme reactions. In this work, we demonstrated a metal-MOF synergistic catalysis strategy, by loading Pt nanoparticles (Pt NPs) on MIL-88B-NH2 (Fe-MOF) to increase peroxidase-like activity for the detection of glucose. The induced electrons transfer from Pt atom to Fe atom accelerated the redox cycling of Fe3+/Fe2+, improved the overall efficiency of the peroxidase-like reaction, and enabled the efficient and robust colorimetric glucose detection, which was proved by both experiments and density functional theory (DFT) calculation. Additionally, the sensitivity and chemical stability of this synergistic effect strategy to detect the glucose are not affected by the complex external factors, which represented a great potential in fast, easy, sensitive, and specific recognition of clinical diabetes. [ABSTRACT FROM AUTHOR]

As a new low-cost photothermal nanoprobe, Prussian blue nanoparticles (PB NPs) have been demonstrated to have more potential in photothermometric-based point-of-care testing (POCT) application. However, most of the existing PB NP-based photothermometric sensors were constructed mainly relying on in situ generation of PB NPs or their combination with antigens and antibodies, therefore usually suffering from the inherent defects like complicated preparation and cumbersome surface process as well as high-cost modification. To break this limitation of PB NP-based photothermometric POCT, we proposed an ingenious redox reaction-controlled nanoprobe conversion strategy and successfully applied to photothermometric detection of ascorbate oxidase (AAO). In this design, the heat of PB NP photothermal system under 808-nm laser irradiation dramatically decreased with the addition of AA, due to a unique AA-induced Prussian blue to Prussian white (PB-to-PW) conversion. Upon AAO addition, the heat of reaction system increased because of the enzymatic catalytic reaction between AAO and AA, which led to a significant reduction of AA and resultantly inhibited PB-to-PW conversion. Such target-mediated nanoprobe conversion resulted in an obvious temperature change that could be easily detected by a common thermometer and exhibited good linear ranges from 0.25 to 14 mU/mL with a detection limit as low as 0.21 mU/mL for POCT analysis of AAO. This facile, convenient, and portable photothermometric sensing platform provides an innovative route for the design of PB NP nanoprobe-based photothermometric detection methods. [ABSTRACT FROM AUTHOR]

A new kind of NiFe2O4-based magnetic covalent organic framework nanocomposites (NiFe2O4@COFs) was fabricated through facile synthesis approach under room temperature. The NiFe2O4@COFs exhibited higher adsorption capacity for brominated flame retardants than carbon nanotube material based on hydrophobic interactions, π-π stacking interaction, and van der Waals forces. In addition, the adsorption isotherm and the kinetic model were more suitable for Langmuir and pseudo-second-order model, respectively. NiFe2O4-based magnetic covalent organic framework nanocomposites combined with HPLC-UV (absorption wavelength: 214 nm) technology has excellent adsorption performance, which exhibited low detection limits (0.03–1.9 μg L−1), wide linear range (0.11–1000 μg L−1), good recoveries (91.5–102%) with a relative standard deviation of less than 2.9%. Finally, the prepared magnetic material was successfully used asadsorbents of magnetic solid-phase extraction and applied to the determination of five BFRs from the real water samples. [ABSTRACT FROM AUTHOR]

In this work, an octahedral magnetic metal organic frameworks composed of Fe3O4@NH2-MIL-101 was synthesized through simple solvothermal reaction for magnetic solid phase extraction (MSPE) of six pesticides with benzene ring in environmental water samples. The Fe3O4@NH2-MIL-101 was characterized by various techniques. The results showed Fe3O4@NH2-MIL-101 exhibits ultra-high surface area (1012.7 m2 g−1), large pore volume (0.64 cm3 g−1) and high magnetic responsivity (30.0 emu g−1), which can be used as an ideal adsorbent for rapid isolation and enrichment of target analytes. A sensitive method was developed by using Fe3O4@NH2-MIL-101-based MSPE coupled with HPLC (High performance liquid chromatography) with UV (Ultraviolate) detector. The linear range extended to 1000 µg L−1 was achieved, low limits of detection (S/N = 3) of 0.13–0.86 µg L−1 and good reproducibility (1.8–3.1%). The applicability of Fe3O4@NH2-MIL-101 was demonstrated for determining six pesticides in water samples with satisfactory recoveries at two spiking levels of 20.0, 80.0 µg L−1 were in the range of 70.5 to 119.8% with the RSDs less than 8.1%. These accurate experimental results by this method indicated that the novel Fe3O4@NH2-MIL-101 as a MSPE adsorbent was an attractive option for efficient extraction and enrichment trace pesticides in future. [ABSTRACT FROM AUTHOR]

Naproxen, a widely used nonsteroidal anti-inflammatory drug, has been detected in many environmental matrixes and is regarded as an emerging pollutant. Sulfate radical (SO4·-) -based advanced oxidation processes have attracted wide attention due to their high efficiency and applicability in the removal of emerging contaminants. In this study, CuFe2O4 was used as an efficient catalyst to activate peroxymonosulfate to oxidize naproxen. The results suggested that 92.3% of naproxen was degraded and 50.3% total organic carbon was removed in 60 min in the presence of 0.3 g·L−1 CuFe2O4 and 2 mM peroxymonosulfate. This degradation system showed strong adaptability in a wide pH range from 4.0 to 10.0. Free radical scavenger experiments and electron spin resonance analysis indicated that 1O2, ·OH, and SO4·- are the main active species. Finally, the potential degradation pathways of naproxen were proposed by detecting and analyzing the degradation products with ultra-high-performance liquid chromatography combined with mass spectrometry. The results of this study suggest that the CuFe2O4-activated peroxymonosulfate system is a promising technology for the removal of naproxen from natural water. [ABSTRACT FROM AUTHOR]

Enzyme-mimicking (nanozyme)-based biosensors are attractive owing to their unique catalytic efficiency, multifunctionality, and tunable activity, but examples of oxidase-like nanozymes are quite rare. Herein, we demonstrated that histidine-capped gold nanoclusters (His@AuNCs) possessed intrinsic oxidase-like activity, which could directly oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to blue colored ox-TMB without H2O2. The assembly of reduced graphene oxide (RGO) with His@AuNCs could further improve its oxidase-like activity and the His@AuNCs/RGO nanocomposites had a lower Michaelis constant (Km) and higher catalytic constant (Kcat) for TMB oxidation. Furthermore, compared to other nanomaterials, the as-prepared His@AuNCs/RGO also exhibited enhanced electrocatalytic activity toward TMB. Interestingly, nitrite inhibited the catalytic (chromogenic) and electrocatalytic processes of His@AuNCs/RGO in the oxidation of TMB. The oxidase-like and electrocatalytic activity of His@AuNCs/RGO was evaluated with nitrite and TMB as substrates, and the results indicated that TMB and nitrite might share the same catalytic active sites. On the basis of these findings, a colorimetric and electrochemical sensor was developed with the His@AuNCs/RGO composite as an oxidase mimic for determination of nitrite with linear ranges of 10–500 μM and 2.5–5700 μM, respectively. The developed method was successfully applied to the detection of nitrites in real samples. The present work suggests that the oxidase-like nanozyme is not only suitable for colorimetric assay but also for development of electrochemical sensors in bioanalysis. Graphical abstract The colorimetric and electrochemical detection of nitrite using His@AuNCs/RGO. [ABSTRACT FROM AUTHOR]

An approach for fabrication of graphene sponge (GS)-based solid-phase extraction (SPE) followed by high-performance liquid chromatography (HPLC) with ultraviolet detection (HPLC-UV) is proposed, which was applied to determine the six benzotriazole UV filters in water and cosmetic samples. Several extraction conditions including type of elution solvent, the volume of elution solvent, and salt effect were optimized. Under the optimum conditions, the GS-SPE-HPLC-UV method shows a low limit of detection (LOD, S/N = 3) of 0.02-0.08 μg L−1 for standard solution, limits of quantification (LOQ, S/N = 10) of 0.07-0.26 μg L−1 for standard solution, wide linear ranges from 20.0 to 1000 μg L−1 for all compounds for standard solution, correlation coefficients (r) of more than 0.999, except for 2-(2′-hydroxy-5′-methylphenyl)benzotriazole (UV-P), and acceptable reproducibility (relative standard deviations, RSDs < 6.5% for intra-day, RSDs < 8.1% for inter-day). The satisfactory recoveries were obtained in the range 89-105% with RSDs lower than 9.8% at the three spiked levels of 20, 50, and 100 μg L−1. Every home-made GS-SPE cartridge can be reused for more than 60 cycles. The method is facile, low-cost, rapid, sensitive, and suitable for the determination of UV filters in water and cosmetics samples.ᅟ [ABSTRACT FROM AUTHOR]

The authors describe a zinc(II) benzenetricarboxylate (Zn-BTC) based metal-organic framework (MOF) with chrysanthemum-like structure, and its application to the adsorption of pesticides from real water samples. The Zn-BTC MOF was characterized by XRD, TGA, SEM, nitrogen adsorption-desorption analysis and FT-IR spectroscopy. The MOF was used in dispersive solid-phase extraction of six aromatic pesticides from various wastewater samples prior to their quantification by HPLC. Extraction times, extraction temperature, amount of adsorbent, and oscillation rate were optimized. Under the optimal conditions, the method has relative standard deviations (RSDs) of 6.1-10.1%, and good linearity (correlation coefficients higher than 0.9974). The LODs and LOQs for seven pesticides are found to be 0.20-1.60 μg·L and 0.66-5.28 μg·L, respectively. The RSDs of within batch extraction are 1.6-9.5% and 3.9-12%. [ABSTRACT FROM AUTHOR]

In this article, we constructed an electrochemical sensor for highly sensitive determination of β-nicotinamide adenine dinucleotide (NADH) using the poly(diallyldimethylammonium chloride)-functionalized reduced graphene oxide nanocomposite modified electrode (PDDA-rGO/GCE). The nanocomposite was characterized by transmission electron microscopy, Fourier transform-infrared spectrometry, ultraviolet-visible absorption spectrometry, cyclic voltammetry, and electrochemical impedance spectroscopy. The experimental results demonstrated that the fabricated sensor exhibited excellent electrocatalytic activity on the oxidation of NADH with a decreased about 200 mV in overpotential and 5.0-fold increment in the oxidation peak current compared to a bare GCE. Applying cyclic voltammetry, a wide linear range from 1.0 × 10 to 2.9 × 10 M with low limit of detection (LOD) of 3.4 × 10 M and high sensitivity of 463.3 μA mM cm were obtained, which was superior to other NADH electrochemical sensors reported previously. Furthermore, the fabricated NADH sensor possessed excellent selectivity, reproducibility, and stability. The oxidation mechanism of NADH at the PDDA-rGO/GCE was also discussed in detail. [ABSTRACT FROM AUTHOR]

The cathodic electrochemiluminescence (ECL) behavior of meso-tetra(4-sulfonatophenyl)porphyrin (TSPP) with potassium peroxydisulfate (KSO) as the coreactant in aqueous solution with strong and stable emission was exploited to determine Cu down to nanomolar concentration. Two possible reaction mechanisms have been proposed to understand the generation of ECL by the TSPP/KSO system. The effects of the concentration of TSPP and KSO, pH of the medium, and scan rate on the ECL intensity were studied in detail. The ECL intensity was efficiently quenched by trace amounts of Cu. This phenomenon was used to develop a new method, which can offer rapid, reliable, and selective detection of Cu. Under the optimum conditions, plots of the ECL of the TSPP/KSO system versus the concentration of Cu are linear in the range of 5 to 160 nM with a detection limit of 1.56 nM (S/N = 3). The proposed ECL sensor was successfully applied for analysis of tap and river water samples. It is anticipated that TSPP could be a new class of promising luminescent agent for ECL sensors. [ABSTRACT FROM AUTHOR]

An electrochemical sensor for simultaneous determination of 5-hydroxytryptamine (5-HT) and dopamine (DA) was developed in this paper based on an ionic liquid functionalized-graphene (IL-graphene) modified glassy carbon electrode. Transmission electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis were used to characterize the formation of the IL-graphene composites. Due to functionalization of the ionic liquid, IL-graphene can not only be dispersed well in aqueous solutions, but also exhibit a strong positive charge. Cyclic voltammetry and differential pulse voltammetry results demonstrated that 5-HT and DA can be detected selectively and sensitively at the constructed electrode with peak-to-peak separation about 164 mV. Under the optimized condition, the linear responses were obtained in the range of 2.0 × 10 to 1.0 × 10 M with a detection limit of 6.7 × 10 M for 5-HT, and in the range of 1.0 × 10 to 1.0 × 10 M with a detection limit of 3.3 × 10 M for DA (S/N = 3), respectively. Moreover, the designed sensor was further applied to the simultaneous determination 5-HT and DA levels in human serum samples with reliable recovery. The excellent performance of this sensor was ascribed to the network-like structure of IL-graphene which provided large surface area to contact 5-HT or DA. [ABSTRACT FROM AUTHOR]

Novel graphene oxide-ordered mesoporous silica materials with two-dimensional mesoporous structure and large surface area were successfully fabricated through sol-gel and self-assembly methods. The synthesized materials were characterized by small-angle X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption. By taking advantage of the excellent properties, the hybrid materials were employed as the adsorbent for removal of heavy metals in environmental waters by adsorption separation-inductively coupled plasma mass spectrometry. The results showed that the materials exhibited superior adsorption capacity, the removal efficiencies for As, Cd, Cr, Hg, and Pb reached 97.7, 96.9, 96.0, 98.5, and 78.7 %, respectively. The facile, low-cost, and environmental friendly synthesis method as well as highly efficient adsorption ability made it become a promising adsorbents for the removal of toxic heavy metals at low or trace concentrations from wastewater. [ABSTRACT FROM AUTHOR]

Two novel mesoporous cellular foams (MCFs) materials with well-defined large and aerogel-like mesostructure were successfully synthesized using tetraethyl orthosilicate as silica source, cyclohexane (CHE) as a swelling agent and triblock copolymer Pluronic P123 and F68 as a template, respectively. The effect of CHE on the expansion of the framework were characterized in detailed by small-angle X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption. The results showed that CHE was an effective swelling agent on the pore size of MCFs. All as-prepared materials were employed as the adsorbent to brominated flame retardants (BFRs) from environmental water samples. The adsorption study indicated the new materials exhibited superior adsorption capacity, the removal efficiencies of MCF-1-1.5 for seven BFRs reached 81.4-95.2 % in industrial wastewater. The recoveries of method were in the range of 86.3-105.7 % for Xiaoqing River sample and 74.6-114.6 % for chemical plant wastewater sample. [ABSTRACT FROM AUTHOR]

A sensitive and selective imprinted electrochemical sensor for the determination of aflatoxin B (AFB) was constructed on a glassy carbon electrode by stepwise modification of functional multiwalled carbon nanotubes (MCNTs), Au/Pt bimetallic nanoparticles (Au/PtNPs), and a thin imprinted film. The fabrication of a homogeneous porous poly o-phenylenediamine (POPD)-grafted Au/Pt bimetallic multiwalled carbon nanotubes nanocomposite film was conducted by controllable electrodepositing technology. The sensitivity of the sensor was improved greatly because of the nanocomposite functional layer; the proposed sensor exhibited excellent selectivity toward AFB owing to the porous molecular imprinted polymer (MIP) film. The surface morphologies of the modified electrodes were characterized using a scanning electron microscope. The performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy in detail. A linear relationship between the sensor response signal and the logarithm of AFB concentrations ranging from 1 × 10 to 1 × 10 mol L was obtained with a detection limit of 0.03 nmol L. It was applied to detect AFB in hogwash oil successfully. [ABSTRACT FROM AUTHOR]

In this article, simultaneous determination of dihydroxybenzene isomers [hydroquinone (HQ), catechol (CC), and resorcinol (RC)] was investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at thionine functionalized multiwalled carbon nanotube (TH-MWCNTs) modified glass carbon electrode. CV and DPV results showed that the TH-MWCNTs modified electrode exhibited excellent recognition ability toward the three isomers of dihydroxybenzene. Their oxidize peak currents were linear over ranges from 9.0 × 10 to 3.6 × 10 M for HQ, from 3.3 × 10 to 8.1 × 10 M for CC and from 4.3 × 10 to 9.0 × 10 M for RC, with the detection limits of 2.7 × 10, 1.0 × 10, and 1.1 × 10 M, respectively. The proposed method would potentially be applied to multi-component analysis in environmental control and chemical industry. [ABSTRACT FROM AUTHOR]

A simple and cost-effective electrochemical method synthesized platinum nanoparticles on graphene nanosheet (PtNPs@GNS) is reported, and the Pt loading of the PtNPs@GNS can be controlled by electrodeposition. The structure and element analysis of the PtNPs@GNS have been investigated by scanning electron microscopy (SEM), Raman spectrum, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The electrochemical measurement including electrochemical active surface area, current density, mass activity, oxidation peak potential,shows the PtNPs@GNS have more performance electrocatalytic properties for methanol oxidation reaction (MOR) compared to Vulcan XC-72 carbon (XC-72) supported PtNPs electrocatalysts. Probably, the cause which may be attributes to no aggregation of PtNPs and the well-dispersion on surface of GNS, so PtNPs@GNS show large electrochemically active surface area, highly electrocatalytic activity and stability in direct methanol fuel cells. [ABSTRACT FROM AUTHOR]

In this study, the new electrocatalyst of platinum support on polypyrrole-functionalized graphene (GNS-PPy/PtNPs) is reported. The polypyrrole-functionalized graphene (GNS-PPy) is constructed first with graphene nanosheets (GNS) and polypyrrole (PPy) particles by constant potential deposition. And then PtNPs are deposited on the surface of GNS-PPy by cyclic voltammetry. The as-prepared GNS-PPy/PtNPs is characterized by scanning electron microscopy, energy-dispersive spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy. The prepared GNS-PPy/PtNPs catalyst is employed for methanol oxidation reactions. Compared with GNS/PtNPs and PPy/PtNPs, the GNS-PPy/PtNPs has higher catalytic activity (508 mA/mg), better stability, and stronger poisoning-tolerance ( I/ I = 4.18) due to high dispersion of PtNPs on large surface of GNS-PPy as well as synergic effect among the GNS, PPy particles, and PtNPs. The experimental results indicate that GNS-PPy/PtNPs may be an ideal candidate catalyst for direct methanol fuel cell. [ABSTRACT FROM AUTHOR]

A sensitive amperometric sensor for norfloxacin (NF) was introduced. The receptor layer was prepared by molecularly imprinted photopolymerization of acrylamide and trimethylolpropane trimethacrylate on the surface of a gold electrode. The binding mechanism of the molecularly imprinted polymer was explored by ultraviolet (UV) and infrared (IR) spectroscopy. The chemosensor was characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance (EI), and scanning electron microscopy (SEM). The electrode prepared by photopolymerization has a better recognition ability to template molecules than that of electropolymerization and NIP. Some parameters affecting sensor response were optimized. Norfloxacin was detected by measurements of an amperometric i- t curve. The linear relationships between current and logarithmic concentration are obtained from 1.0 × 10 to 1.0 × 10 mol L. The detection limit of the sensor was 1.0 × 10 mol L. The proposed method is sensitive, simple, and cheap, and is applied to detect NF in human urine successfully. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The insertion and abstraction reaction mechanisms of singlet and triplet CCl2 with CH3MH (M=O, S) have been studied by using the DFT, NBO and AIM methods. The geometries of reactions, the transition state and products were completely optimized by B3LYP/6–311G(d, p). All the energy of the species was obtained at the CCSD(T)/6–311G(d, p) level. The calculated results indicated that the major pathways of the reaction were obtained on the singlet potential energy surface. The singlet CCl2 can not only trigger the insertion reaction with C-H and M-H in four pathways, by which the products P1 [CH3OCHCl2, reaction I(1)], P3[Cl2HCCH2OH, reaction I(2)], P5[CH3SCHCl2, reaction II(1)] and P7[Cl2HCCH2SH, reaction II(2)] are produced respectively, but also abstract M-H, resulting P4 [CH2O+CH2Cl2, reaction I(3)] and P8[CH2S+CH2Cl2, reaction II(3)]. In addition, the important geometries in domain pathways have been studied by AIM and NBO theories. [ABSTRACT FROM AUTHOR]

The insertion reaction mechanisms of siglet and striglet CCl2 with CH3CHO have been studied by using the OFT, NBO, CCSD(T) and AIM method. The geometries of reactions, transition state and products were completely optimized by B3LYP/6-31G(d). All the energy of the species was obtained at the CCSD(T)/6-31G(d,p) level. The calculated results indicated that all the major pathways of the reaction were obtained on the singlet potential energy surface. The singlet Cd2 can not only insert the CαH (reaction I) but also can react with CβH (reaction II). There are three main existing pathways and the products are P1 (CH3COHCCl2), P2 (CH2COHCHCl2) and P4[CHCl2CHCHOH] respectively. Reaction II happens more easily according to the energy changes and the barrier in rate-controlling step. In addition, the important geometries in domain pathways have been studied by AIM theory. And also, the energy changes of H in the inserted CH bond have been investigated. [ABSTRACT FROM AUTHOR]

The insertion reaction mechanism of CBr2with CH3CHO has been studied by using the B3LYP/6-31G(d) method. The geometries of reactions, transition state and products were completely optimized. All the energy of the species was obtained at the CCSD(T)/6-31 G(d) level. All the transition state is verified by the vibrational analysis and the internal reaction coordinate (IRC) calculations. The results show that the propionaldehyde (HP1) is the main product of CH2 insertion with CH3CHO. The calculated results indicated that all the major pathways of the reaction were obtained on the singlet potential energy surface. The singlet CBr2 not only can insert the Cα-H [reaction 1(1)]) but also can react with CβH [reaction II(1)]. The statistical thermodynamics and Eyring transition state theory with Wigner correction are used to study the thermodynamic and kinetic characters of 1(1) and 11(1) in temperature range from 100 to 2200 K. The results show that the appropriate reaction temperature rang is 250 to 1750 K and 250 to 1600 K at 1.0 atm for 1(1) and 11(1) respectively. The rate constant and equilibrium constant are distinct in the range from 250 to 1000 K so that 1(1) more easily occurs, while the reactions are not selected in the temperature range of 1000-1600 K. [ABSTRACT FROM AUTHOR]

The insertion reaction mechanism of CBr2 with CH3CH2O has been studied by using the B3LYPI6-311G(d) and CCSD(T)/6-311G(d) at single point. The geometries of reactions, transition state and products were completely optimized. All the transition state is verified by the vibrational analysis and the internal reaction coordinate (IRC) calculations. The results show that reaction (1) is the dominant reaction path, which proceeds via two steps: i) two reactants form an intermediate (IM1), which is an exothermal re- action of 8.62 kJ · mol-1 without energy barrier; ii) P1 is obtained via the TS1 and the H-shift, in which the energy barrier is 44.53 kJ · mol-1. The statistical thermodynamics and Eyring transition state theory with Wigner correction are used to study the thermodynamic and kinetic characters of this reaction in temperature range from 100 to 2200 K. The results show that the appropriate reaction temperature ranges from 200 to 1900 K at 1.0 atm, in which the reaction has a bigger spontaneity capability, equilibrium constant (K) and higher rate constant (k). [ABSTRACT FROM AUTHOR]

A sensor is described for determination of superoxide anion (O2˙−). The electrode consists of nitrogen-doped cotton carbon fiber (NCFs) modified with silver nanoparticles (AgNPs) which have excellent catalytic capability. The resulting sensor, best operated at working potentials around −0.5 V (vs. SCE), can detect O2˙− over an extraordinarily wide range that covers 10 orders of magnitude, and the detection limit is 2.32 ± 0.07 fM. The electrode enables the release of O2˙− from living cells under normal or under oxidative stress conditions to be determined. The ability to scavenge the superoxide anions of antioxidants was also investigated. In the authors' perception, the method represents a viable tool for studying diseases related to oxidative stress.Schematic presentation of the construction of an electrochemical sensor based on Nitrogen-doped cotton carbon fiber and silver nanoparticles. It can be used for the direct detection of superoxide anions released from Glioma cells (U87) under normal or under oxidative stress conditions. [ABSTRACT FROM AUTHOR]