Electrochemical determination of picric acid based on platinum nanoparticles–reduced graphene oxide composite

Platinum nanoparticles–reduced graphene oxide composite-modified glassy carbon electrode (PtNPs–rGO/GCE) was developed as a simple, selective and sensitive electrochemical sensor for determination of picric acid (PA). Cyclic voltammogram (CV) of PA showed three well-defined irreversible reduction peaks at the potentials of ?0.43, ?0.57 and ?0.66 V versus Ag/AgCl. In this work, the interference effect of other nitrophenol compounds (NPhCs) was significantly reduced by appropriate adjusting of pH. Square wave voltammetry was used for quantification of PA in the range of 5–500 µM (1.15–115 mg L^?1) with practical detection limit of 1 µM (0.23 mg L^?1). The proposed sensor was successfully applied for the determination of PA in two natural water samples.     

Agar: a natural and environmentally-friendly support composed of copper oxide nanoparticles for the green synthesis of 1,2,3–triazoles

ABSTRACT

A novel, green and cost-effective heterogeneous nanocatalyst was synthesized by supporting copper (I) oxide nanoparticles on magnetic agar (Cu₂O/Agar@Fe₃O₄). Then, it was characterized with multiple techniques, such as scanning electron microscopy and transmission electron microscopy images, energy-dispersive X-ray analysis, Fourier-transform infrared (FT–IR) spectroscopy, thermogravimetric (TG) analysis, X-ray diffraction pattern, vibrating sample magnetometer curve, and inductively coupled plasma analysis. The catalytic activity of the newly designed catalyst was investigated in a one-pot three-component reaction of alkyl halides, sodium azide, and alkynes to obtain 1,4–disubstituted 1,2,3–triazoles in high yields in water–ethanol media. The present catalyst was simply separated from the reaction media by an external magnet and reused at least five subsequent runs without significant activity loss.     

Electrochemical biosensor for amplified detection of Pb2+ based on perfect match of reduced graphene oxide–gold nanoparticles and single-stranded DNAzyme

Analytical and Bioanalytical Chemistry - In this study, a sensitive amplification strategy for Pb2+ detection using reduced graphene oxide (RGO) and gold nanoparticles (AuNPs) was proposed....     

Electrochemical biosensor for simultaneous determination of guanine and adenine based on dopamine-melanin colloidal nanospheres–graphene composites

Dopamine-melanin colloidal nanospheres (Dpa-melanin CNDs)–graphene composites-modified glassy carbon electrode (GCE) was prepared by a simple procedure and then successfully used to simultaneously determine guanine and adenine. Scanning electron microscopy (SEM) images and transmission electron microscopy (TEM) were used to characterize the morphology of the Dpa-melanin CNSs–graphene composite. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the electrode modifying process. Differential pulse voltammetry (DPV) was used to study the electrocatalytic activity toward the electrochemical oxidation of guanine and adenine. The modified electrode exhibited enhanced electrocatalytic behavior and good stability for the simultaneous determination of guanine and adenine compared with bare GCE. The electrochemical biosensor exhibited wide linear range of 0.5 to 150 μM with detection limit of 0.05 and 0.03 μM for guanine and adenine detection (S/N?=?3), respectively. Furthermore, the biosensor showed high sensitivity, good selectivity, good reproducibility, and long-term stability to guanine and adenine detection. At the same time, the fabricated electrode was successfully applied for the determination of guanine and adenine in denatured DNA samples with satisfying results. These results demonstrated that Dpa-melanin CNSs–graphene composite was a promising substrate for the development of high-performance electrochemical biosensor.     

Recent advances on the synthesis and application of tetrahydro-γ-carbolines

Tetrahydro-γ-carbolines(THγ Cs) constitute one of the most important subtypes of indole alkaloids. In addition to being substructures of natural products, these structural motifs and moieties can often be found in pharmaceuticals due to their diverse bioactivities such as antiviral, antibacterial, antifungal,antiparasitic, antitumor, anti-inflammatory, and neuropharmacological activities. Beyond the pharmacological and biological aspects of these scaffolds, they have considerable synthetic appli...     

Electrochemical and photochemical approaches for the synthesis of the C28–C38 fragment of okadaic acid

Okadaic acid, a potent and selective inhibitor of Protein Phosphatases 1 and 2A (PP1 and PP2A), is widely used as a probe for various biochemical processes. We describe herein two innovative methods for the synthesis of the terminal C28–C38 fragment of the natural polyether. Suárez photochemical oxidative cyclization and electrochemical oxidation of malonates to their ketals equivalents have been successfully applied for the assembly of the key spiroketal core.     

Influence of the synthesis conditions on the structure and composition of the titanium–magnesium nanocatalyst and on its activity in isoprene polymerization

Synthesis of titanium–magnesium nanocatalyst in a high-pressure reactor under the conditions modeling the industrial conditions was studied. A laboratory scale plant including the units for the product synthesis, washing, and filtration was developed. The effect of elevated pressure (10–90 atm) on the process course, on the properties of the catalyst formed, and on the isoprene polymerization was studied for the first time. An increase in pressure leads to an increase in titanium incorporation into the catalyst from 1.52 to 2–2.3 wt % and simultaneously to an increase in the trivalent titanium content to 81 wt %. The titanium–magnesium nanocatalyst with such properties exhibits enhanced performance in isoprene polymerization without deteriorating the polymer microstructure. The development of the catalyst synthesis procedure on the laboratory scale plant will allow pilot-scale modeling of this process in the future.     

Preparation and application of novel polymer nanoparticles in the detection of copper ion and cysteineEI北大核心CSCD

A novel amphiphilic copolymer,dipropenoxystyrene anthracene and acrylic acid copolymer（BASA-AA） was designed and synthesized based on divinyl anthracene. The polymer self-assembled rapidly in water to create polymer nanoparticles（BASA-AA NPs）with a uniform size of 45 nm,no dye leakage,and great brightness（Φ= 36%）. Because of the enormous number of carboxyl groups on the surface of the particles,it can disperse extremely well in water,and can be used for the rapid detection of copper ion and cysteine（Cys）in pure water, with the limit of detection of 45 nmol/L. The fluorescent intensity of the nanoparticles will be greatly reduced after the introduction of copper ion,realizing the detection of copper ion with high selectivity and sensitivity. A composite probe made of BASA-AA NPs and copper ion can detect Cys in the range of 0.1-10 µμmol/L,with the detection limit of 84 nmol/L,due to the high binding capacity of the sulfhydryl group and copper ion. The method is simple and rapid in material synthesis and preparation,and shows high selectivity and sensitivity in pure water. © 2023, Youke Publishing Co.,Ltd. All rights reserved.     

Comparison of performances of bioanodes modified with graphene oxide and graphene–platinum hybrid nanoparticles

The performances of graphene oxide (GO) and graphene–platinum hybrid nanoparticles (Gr-Pt hybrid NPs) were compared for biofuel cell (BFC) systems. This is the first study that constitutes these nanomaterials in BFC systems. For this purpose, fabricated bioanodes were combined with laccase modified biocathode in a single cell membraneless BFC. Power and current densities of these systems were calculated as 2.40 μW cm^− 2 and 211.90 μA cm^− 2 for GO based BFC and 4.88 μW cm^− 2 and 246.82 μA cm^− 2, for Gr-Pt hybrid NPs based BFC. As a result, a pioneer study which demonstrates the effective performances of combination of graphene with Pt was conducted.     

Direct electrochemistry of glucose oxidase immobilized on TiO2–graphene/nickel oxide nanocomposite film and its application

A novel electrochemical platform based on nickel oxide (NiO) nanoparticles and TiO₂–graphene (TiO₂–Gr) was developed for the direct electrochemistry of glucose oxidase (GOD). The electrochemical behavior of the sensor was studied using cyclic voltammetry and chronoamperometry. The experimental results demonstrated that the nanocomposite well retained the activity of GOD and the modified electrode GOD/NiO/TiO₂–Gr/GCE exhibited excellent electrocatalytic activity toward the redox of GOD as evidenced by the significant enhancement of redox peak currents in comparison with bare GCE. The biosensor responded linearly to glucose in the range of 1.0–12.0?mM, with a sensitivity of 4.129?μA?mM^?1 and a detection limit of 1.2?×?10^?6?M under optimized conditions. The response time of the biosensor was 3?s. In addition, the developed biosensor possessed good reproducibility and stability, and there was negligible interference from other electroactive components.     

PANI–TiC nanocomposite film for the direct electron transfer of hemoglobin and its application for biosensing

A novel polyaniline and titanium carbide (PANI–TiC) nanocomposite was synthesized by an in situ chemical oxidative polymerization method, and a hydrogen peroxide (H₂O₂) biosensor was fabricated by PANI–TiC with hemoglobin (Hb)-modified glassy carbon electrode (GCE). Scanning electron microscope and energy dispersive X-ray spectroscopy showed the morphology and ingredient of PANI–TiC. Electrochemical investigation of the biosensor showed a pair of well-defined, quasi-reversible redox peaks with E _pa?=??0.318 V and E _pc?=??0.356 V (vs SCE) in 0.1 M, pH 7.0 sodium phosphate-buffered saline at the scan rate of 150 mV s^?1. Transfer rate constant (k _s) was 2.01 s^?1. The Hb/PANI–TiC/GCE showed a good electrochemical catalytic response for the reduction of H₂O₂ with the linear range from 0.5 to 285.5 μM and the detection limit of 0.2 μM (S/N?=?3). The apparent Michaelis–Menten constant (K _m) was estimated to be 1.21 μM. Therefore, the PANI–TiC as a novel matrix opened up a further possibility for study on the design of enzymatic biosensors with potential applications.     

Iron-catalyzed C–H amination and its application in organic synthesis

Transition-metal-catalyzed direct C–H bond amination is an attractive strategy in preparation of nitrogen containing molecules which are common in naturally occurring and pharmaceutically important compounds. Comparing to the precious metals commonly used in this reaction, non-precious metals such as iron are abundant in earth, relatively low toxic, and more biocompatible, which meet the increasing demand for environmentally benign and sustainable chemical processes. In this review, we described the development in iron catalyzed C–H bond amination reactions from historical landmarks to recent achievements, and placed emphasis on their applications in organic synthesis, i.e. natural product synthesis and/or modification.     

Sol–gel synthesis of mesoporous silicas containing albumin and guanidine polymers and its application to the bilirubin adsorption

The organic–inorganic composite materials based on mesoporous silica were synthesized using sol–gel method. The surface area of silicas was modified by bovine serum albumin (BSA) and guanidine polymers: polyacrylate guanidine (PAG) and polymethacrylate guanidine. The mesoporous silicas were characterized by nitrogen adsorption–desorption analysis, Fourier transform infrared spectroscopy, transmission electron microscopy. The obtained materials were used as adsorbents for selective bilirubin removal. It was shown that the structural properties and surface area of modified materials depend on the nature of polymers. Incorporation of polymers in silica gel matrix during sol–gel process leads to the formation of mesoporous structure with high pore diameter and a BET surface area equals to 346 m²/g for SiO₂/BSA and 160 m²/g for SiO₂/PAG. Analysis of adsorption isotherms showed that modification of silica by BSA and guanidine polymers increases its adsorption ability to bilirubin molecules. According to Langmuir model, the maximum bilirubin adsorption capacity was 1.18 mg/g.     

Electrochemical synthesis of stannane–silane and stannane–germane copolymers

Poly(dibutylstannylene-co-dibutylsilylene) and poly(dibutylstannylene-co-dibutylgermylene) were synthesized for the first time, by electrochemical reduction of dibutyldichlorostannane together with dibutyldichlorosilane and dibutyldichlorogermane, respectively, in a one-compartment cell equipped with a platinum cathode and a silver anode, using tetrabutylammonium perchlorate and 1,2-dimethoxyethane as the supporting electrolyte and the solvent, respectively. Most of absorption peaks observed for the copolymers were located between those of polystannylene and polysilylene/polygermylene. A copolymer with relatively high stannane content had a relatively long absorption peak, which is close to that of a homopolymer polydibutylstannylene. A copolymer with a higher stannane content was more sensitive to the moisture in air.     

Electrochemical detection of benzo(a)pyrene and related DNA damage using DNA/hemin/nafion–graphene biosensor

A novel electrochemical biosensor, DNA/hemin/nafion–graphene/GCE, was constructed for the analysis of the benzo(a)pyrene PAH, which can produce DNA damage induced by a benzo(a)pyrene (BaP) enzyme-catalytic product. This biosensor was assembled layer-by-layer, and was characterized with the use of cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and atomic force microscopy. Ultimately, it was demonstrated that the hemin/nafion–graphene/GCE was a viable platform for the immobilization of DNA. This DNA biosensor was treated separately in benzo(a)pyrene, hydrogen peroxide (H₂O₂) and in their mixture, respectively, and differential pulse voltammetry (DPV) analysis showed that an oxidation peak was apparent after the electrode was immersed in H₂O₂. Such experiments indicated that in the presence of H₂O₂, hemin could mimic cytochrome P450 to metabolize benzo(a)pyrene, and a voltammogram of its metabolite was recorded. The DNA damage induced by this metabolite was also detected by electrochemical impedance and ultraviolet spectroscopy. Finally, a novel, indirect DPV analytical method for BaP in aqueous solution was developed based on the linear metabolite versus BaP concentration plot; this method provided a new, indirect, quantitative estimate of DNA damage.     

Microwave assisted non-aqueous sol–gel synthesis of LiNiPO4 and its copper doped analogues

A series of single phase LiNi_(1?x)Cu_xPO₄ (0 < x < 0.99) was successfully synthesized by non-aqueous sol–gel method followed by microwave (MW) annealing. The advantage of MW short span annealing is obvious from the nanometer sized particles compared to reported microparticles. XRD, IR and SEM studies were conducted to investigate the phase purity, crystal structure, lattice parameters and morphology respectively. It was found that 10 min of microwave annealing is a time and cost effective approach to produce single phase compositions at low temperature. X-ray studies confirmed the single phase formation of pure and the doped analogues which were found to be iso-structural with the parent LiNiPO₄ compound. The cell parameters with the addition of copper content were in accord with the Vegards law. Impedance studies pointed toward enhanced electrical properties of doped samples as compared to the undoped one.