Chiral resolution and bioactivity of enantiomeric furofuran lignans from Juglans mandshurica Maxim

Abstract

Enantiomers have generally been reported mostly for racemic mixtures with a 1:1 ratio, as in that case there were weak Cotton effects in the ECD spectrum and negligible optical rotations. A furofuran lignan (sesamin), with a remarkable rotation and significant Cotton effects, was isolated from Juglans mandshurica Maxim. Subsequently, sesamin was resolved by chiral HPLC to afford a pair of enantiomers, (+)-sesamin (a) and (?)-sesamin (b), in a ratio of approximately 1:3. Their absolute configurations were determined by computational analysis of their electronic circular dichroism (ECD) spectrum. In addition, the pair of enantiomers were evaluated for the inhibition of self-induced Aβ aggregation. Interestingly, (+)-sesamin (a) (67.7%) and (?)-sesamin (b) (80.6%) exhibited different degrees of anti-Aβ aggregation activity. The different inhibition profiles were further explained by molecular dynamics and docking simulation study.     

A Novel Enhanced Chemiluminescence System with Ag(III) Complex for the Determination of Ofloxacin and Levofloxacin in Pharmaceutical Preparation and Biological Fluid

A novel chemiluminescence (CL) method is developed for determination of ofloxacin and levofloxacin with Ag(III) complex in H₂SO₄ solution medium. The CL intensity is proportional to drug concentration in a wider range with a correlation coefficient of 0.999. The limit of detection (s/n = 3) for ofloxacin and levofloxacin was 5.3 × 10^?9 g ml^?1 and 8.3 × 10^?9 g ml^?1, respectively, and their recoveries from urine and serum samples were in the range of 90.1–112% with the RSDs of 1.0–2.8%. The proposed method was applied for analysis of real samples with satisfactory result. The possible CL mechanism was discussed.     

Molecular Imprinting-Chemiluminescence Sensor for the Determination of Amoxicillin

The amoxicillin-imprinted polymer was synthesized with methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as a cross-linker. The binding characteristic of the imprinted polymer to amoxicillin was evaluated by equilibrium binding experiments. Using the imprinted polymer as recognition material, 3-(3′-nitrophenyl)-5(2′-sulfonylphenylazo)-rhodanine (4NRASP) was synthesized by the authors and was used as chemiluminescence (CL) reagent. A novel chemiluminescence (CL) sensor for the determination of amoxicillin was developed based on the CL reaction of amoxicillin with potassium permanganate in an acidic medium. The sensor displayed excellent selectivity and high sensitivity. The linear response range of the sensor was from 5.0 × 10^?9 to 1.0 × 10^?6 g · mL^?1 (r = 0.9985) and the detection limit was 1.3 × 10^?9 g · mL^?1. The relative standard deviation for the determination of 1.0 × 10^?7 g · mL^?1 amoxicillin solution was 1.7% (n = 11). The sensor was applied to the determination of amoxicillin in urine samples with satisfactory results.     

Electrocatalysis of Horseradish Peroxidase Immobilized on Cobalt Nanoparticles Modified ITO Electrode

Abstract

It is the first time that Horseradish peroxidase (HRP) was successively immobilized on the magnetic cobalt nanoparticles modified ITO (indium tin oxide) electrode. Morphologies of electrode surface were featured by the field emission‐scanning electron microscope (FSEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the modified process of electrode. Direct electrochemistry and electrocatalysis of HRP immobilized on nano‐Co/ITO were investigated. The biosensor exhibited high sensitivity, good stability, and excellent electrocatalytic activity to the reduction of H₂O₂. Under the optimized experimental conditions, a calibration curve over 2.0×10^?9～2.0×10^?8 mol l^?1 and 2.0×10^?7～2.0×10^?6 mol l^?1, with a limit of detection of 1.9×10^?9 mol l^?1 was obtained. The apparent Michaelis‐Menten constant (K _M ^app ) for HRP/nano‐Co/ITO electrode was calculated to be 0.79 mmol l^?1, indicating a higher affinity of HRP attached on the modified electrode.     

Development and application of a fluorescent sensor for potassium ions based on a calix[6]arene ionophore and a novel cationic dye

A plasticised poly(vinyl chloride) optode membrane incorporated with a calix[6]arene hexaester, a H⁺-selective chromoionophore (3,3′,5,5′-tetramethyl-N,N-dibenzylbenzidine, a novel synthetic cationic dye) and a lipophilic potassium tetrakis(4-chlorophenyl)borate was used as a sensing device for the indirect optical determination of potassium ions. It exhibited a reversible response to the potassium ion in 0.05 mol/l HCl buffer media in the concentration range from 1 × 10^? 6 to 1 × 10^? 2 mol/l. The linear range was from 1.53 × 10^? 5 to 3.20 × 10^? 3 mol/l. The proposed optode sensor exhibited a fast response of less than 1 min, good repeatability (n = 7, RSD = 3.62%) at 5 × 10^? 5 mol/l, and long-term stability with 92% of its initial sensitivity after 1 month of storage. The selectivity of the potassium-selective membrane allows its application for the detection of the potassium concentration in real sample analysis. The result was satisfactory compared with atomic absorption spectrometry.     

Electrochemical Study of Interaction Between Clozapine and DNA and Its Analytical Application

Abstract

The interaction between clozapine (CLZ) as an orally administrated antipsychotic drug with double stranded calf thymus DNA (dsDNA) was investigated at electrode surface using differential pulse voltammetry (DPV). Activated carbon paste electrode (CPE) was modified with dsDNA and used for monitoring the changes of the characteristics peak of CLZ in 0.05 M acetate buffer (pH 4.3). The adsorptive stripping voltammetry on dsDNA‐modified carbon paste electrode (dsDNA‐CPE) was used for determination of very low concentration of CLZ. Under optimal conditions, the oxidation peak current is proportional to CLZ concentration in the range of 7×10^?9?1.2×10^?6 mol l^?1 with a detection limit of 1.5×10^?9 mol l^?1 for 180 s accumulation time by DPV. The proposed dsDNA‐CPE was successfully used for determination of CLZ in human serum samples with recovery of 97.0±2.5%.     

Electrooxidation of trifloxystrobin at the boron-doped diamond electrode: electrochemical mechanism,quantitative determination and degradation studies

The boron-doped diamond (BDD) presents attractive electrochemical sensing characteristics that are useful in analytical applications based on voltammetry and amperometry. It has a wide potential window in aqueous solutions enabling the quantification of the fungicide trifloxystrobin, measured at +1744 mV (versus Ag/AgCl), by square-wave anodic voltammetry in a Britton–Robinson (BR) buffer (0.04 mol L^?1; pH 4.00)/acetonitrile 70/30% v/v. The activation of the electrode was made using galvanostatic chronopotentiometry and cyclic voltammetry (CV). The linear analyte addition curve, I_p (µA) = (1.0 × 10^–1 ± 4.8 × 10^–6) C (mol L^?1) + (8.8 × 10^–2 ± 1.1 × 10^–3); R² = 0.997, was obtained using amplitude of 40 mV, frequency of 30 Hz, step potential of 20 mV. The instrumental limit of detection (LOD) was 1.4 × 10^–7 mol L^?1 (0.058 mg L^?1) and the dynamic linear range covered three decades (up to 1 × 10^–5 mol L^?1 or 4.1 mg L^?1). The samples were analysed with recoveries about 80% in orange juice samples and from 92.4% to 104.0% in water samples. A study to evaluate potential interferences was made in the presence of other fungicides. Diagnostic studies indicated that oxidation of trifloxystrobin in aqueous medium at the surface of the BDD is irreversible, involving two steps, each one with two electrons. The UV degradation of trifloxystrobin was evaluated using the proposed electrochemical method and the kinetics of degradation established with half-life of 1.07 min.     

Micellar‐Enhanced Spectrofluorimetric Determination of Trazodone Hydrochloride in Human Urine and Serum

Abstract

A novel developed spectrofluorimetric method for the determination of trazodone hydrochloride in the presence of sodium dodecyl sulfate (SDS) surfactant micelles was described. Under optimal conditions, there was a good linear relationship between fluorescence intensity and trazodone hydrochloride concentration in the range of 4.0×10^?9 to 8.0×10^?6 mol · l^?1with the detection limit of 1.3×10^?9 mol · l^?1 (S/N=3). This method has been used to determine trazodone hydrochloride in biological fluids.     

Determination of Albumin Using the Chemiluminescence of Tb3+/K2S2O8 System

A new chemiluminescence system of Tb³⁺/K₂S₂O₈ was developed for the determination of albumin. Some experimental conditions were examined and optimized. The linear ranges of the calibration curves are 5.0 × 10^?9–5.0 × 10^?6 mol/L for bovine serum albumin, 5.0 × 10^?8–1.0 × 10^?5 mol/L for human serum albumin and 2.5 × 10^?7–1.0 × 10^?5 mol/L for ovalbumin, and the corresponding detection limits are 1.9 × 10^?9 mol/L, 1.5 × 10^?8 mol/L, and 1.5 × 10^?7 mol/L, respectively. The method was applied to the determination of albumin in human serum samples, and the results were in agreement with those obtained by the bromcresol green method. The relative errors for the analytical results were from ?2.0% to 4.3%.     

Electrochemical detection of ursolic acid from spruce (Picea abies) essential oils using modified amperometric microsensors

Ursolic acid (UA) is a natural pentacyclic triterpenoid carboxylic acid found in some medicinal plant species. In this paper, amperometric microsensors based on a powder which contained graphite (G) and carbon nanoparticles (CN) (G-CN) unmodified and modified with chitosan (CHIT) and tetraphenyl-porphine cobalt(II) (Co(II)TPP) are proposed for the analysis of UA plant source essential oils obtained from spruce (Picea Abies). Differential pulse voltammetry (DPV) was used to optimize the method and for the determination of ursolic acid from different types of botanical samples. The optimum working pH was 5.00 for the G-CN and (Co(II)TPP)/G-CN microsensors and pH 3.00 for CHIT/G-CN in the presence of a 0.1?mol L^?1 KCl supporting electrolyte. The linear concentration ranges for ursolic acid (UA) were between 0.1 and 100 µmol L^?1 for the unmodified microsensor (G-CN), 0.01, 1 µmol L^?1 for the microsensor modified with chitosan (CHIT/G-CN), and 0.01 and 10 µmol L^?1 for the microsensor modified with (Co(II)TPP)/G-CN). It is the first time these amperometric microsensors have been used for the reliable analysis of ursolic acid (UA) in three original botanical samples obtained from different parts of spruce (Picea abies): resin essential oil, cons essential oil, cons and sprouts essential oil, with recovery rate values up to 99.29%.     

Chemiluminescence Determination of Organophosphorus Pesticides Chlorpyrifos in Vegetable

Abstract

A novel chemiluminescence method for the quantitative assay of the organophosphorus pesticide chlorpyrifos in vegetable samples is presented. The determination is based on the reaction of chlorpyrifos with luminol-H₂O₂ in alkaline medium with sodium chloride being enhancer. Under the optimum conditions, the increased CL intensity was proportional with the concentration of chlorpyrifos in the range of 1.0 × 10^?8 g · ml^?1 ? 1.0 × 10^?6 g · ml^?1 and the detection limit was 3.5 × 10^?9 g · ml^?1 (3σ). The relative standard is less than 3.9% for 5.0 × 10^?7g · ml^?1 chlorpyrifos (n = 7). This method has been successfully applied to the determination of chlorpyrifos residue in vegetable sample. Further study was focused on the mechanism of chlorpyrifos and the possible mechanism was proposed.     

Determination of Diammonium Glycyrrhizinate and Its Antioxidant Activity Using a Novel Chemiluminescence System

A novel chemiluminescence (CL) system was established for the determination of diammonium glycyrrhizinate (DG) in pharmaceutical preparations and its ability of scavenging hydroxyl radical. It was shown that a strong CL signal was observed when Eosin Y mixed with Fenton reagent. The CL intensity was decreased significantly when DG was added to the reaction system and partially scavenged the hydroxyl radicals in the solution. The extent of decrease in the CL intensity had a good stoichiometrical relationship with DG concentration. Based on this, we developed a new method for the determination of DG using a flow injection chemiluminescence (FI-CL) technique. Under the optimal conditions, the linear range of DG concentration was 6.0 × 10^?8–5.0 × 10^?6 mol/L (R = 0.9982) with a detection limit of 8.0 × 10^?9 mol/L (SN = 3), and the RSD was 3.8% for 2.0 × 10^?7 mol/L DG (n = 11). This method was successfully used in the determination of DG in tablets and the evaluation of hydroxyl radical scavenging capacity of DG. The possible reaction mechanism of the CL system is discussed.     

Fluorescence Probe Enhanced Spectrofluorimetric Method for the Determination of Prulifloxacin in Pharmaceutical Formulations and Biological Fluids

Abstract

Spectrofluorimetry for the determination of prulifloxacin (PUFX) was developed based on the strong fluorescence of PUFX after adding fluorescence probe yttrium in buffer solution (pH = 6.80), and various factors of influencing fluorescence have been researched. Under the optimum conditions, the liner range was 2.0 × 10^?8 to 9.1 × 10^?6 mol L^?1 and the detection limit was 8.5 × 10^?9 mol L^?1. The relative standard deviation was 2.1% for 11 measurements of 5.0 × 10^?7 mol L^?1 PUFX standard solution. The mechanism of the sensitizing effect of probe was discussed. The method was applied for the determination of PUFX in actual sample; the result obtained was satisfactory.     

Flow‐Injection Spectrophotometric Determination of N‐acetylcysteine in Pharmaceutical Formulations with On‐Line Solid‐Phase Reactor Containing Zn(II) Phosphate Immobilized in a Polyester Resin

Abstract

A flow‐injection spectrophotometric procedure was developed for determining N‐acetylcysteine in pharmaceutical formulations. The sample was dissolved in deionized water and 400 µl of the solution was injected into a carrier stream of 1.0×10^?2 mol l^?1 sodium borate solution. The sample flowed through a column (70 mm length×2.0 mm i.d.) packed with Zn₃(PO₄)₂ immobilized in a polymeric matrix of polyester resin and Zn(II) ions were released from the solid‐phase reactor because of the formation of the Zn(II) (N‐acetylcysteine)₂ complex. The mixture merged with a stream of borate buffer solution (pH 9.0) containing 5.0×10^?4 mol l^?1 Alizarin red S and the Zn(II)Alizarin red complex formed was measured spectrophotometrically at 540 nm. The analytical curve was linear in the N‐acetylcysteine concentration range from 3.0×10^?5 to 1.5×10^?4 mol l^?1 (4.9 to 24.5 µg ml^?1) with a detections limit of 8.0×10^?6 mol l^?1 (1.3 µg ml^?1). The relative standard deviations (RSDs) were smaller than 0.5% (n=10) for solutions containing 5.0×10^?5 mol l^?1 (8.0 µg ml^?1) and 8.0×10^?5 mol l^?1 (13.0 µg ml^?1) of N‐acetylcysteine, and the analytical frequency was 60 determinations per hour. A paired t‐test showed that all results obtained for N‐acetylcysteine in commercial formulations using the proposed flow‐injection procedure and a comparative procedure agreed at the 95% confidence level.     

A consistent model for the thermal decomposition of NCN3 and the singlet– triplet relaxation of NCN

The thermal decomposition of cyanogen azide (NCN₃) and the subsequent collision‐induced intersystem crossing (CIISC) process of cyanonitrene (NCN) have been investigated by monitoring excited electronic state ¹NCN and ground state ³NCN radicals. NCN was generated by the pyrolysis of NCN₃ behind shock waves and by the photolysis of NCN₃ at room temperature. Falloff rate constants of the thermal unimolecular decomposition of NCN₃ in argon have been extracted from ¹NCN concentration–time profiles in the temperature range 617 K <T< 927 K and at two different total densities: k(ρ ≈ 3 × 10^?6 mol/cm³)/s^?1=4.9 × 10⁹ × exp (?71±14 kJ mol^?1/RT) (± 30%); k(ρ ≈ 6 × 10^?6 mol/cm³)/s^?1=7.5 × 10⁹ × exp (‐71±14 kJ mol^?1/RT) (± 30%). In addition, high‐temperature ¹NCN absorption cross sections have been determined in the temperature range 618 K <T< 1231 K and can be expressed by σ /(cm²/mol)= 1.0 × 10⁸ ?6.3 × 10⁴ K^?1 × T (± 50%). Rate constants for the CIISC process have been measured by monitoring ³NCN in the temperature range 701 K <T< 1256 K resulting in k_CIISC (ρ ≈ 1.8 ×10^?6 mol/cm³)/ s^?1=2.6 × 10⁶× exp (‐36±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 3.5×10^?6 mol/cm³)/ s^?1 = 2.0 × 10⁶ × exp (?31±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 7.0×10^?6 mol/cm³)/ s^?1=1.4 × 10⁶ × exp (?25±10 kJ mol^?1/RT) (± 20%). These values are in good agreement with CIISC rate constants extracted from corresponding ¹NCN measurements. The observed nonlinear pressure dependences reveal a pressure saturation effect of the CIISC process. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 30–40, 2013     

Sensitive Chemiluminescence Determination of Three Thiol Compounds Based on Cu(II)-Catalyzing Luminol Reaction in the Absence of an Oxidant

Abstract

A simple and sensitive flow-injection chemiluminescence method was proposed for the determination of three thiol compounds, namely cysteine, acetylcysteine, and glutathione. Weak chemiluminescence was produced directly by the reaction of these mentioned compounds with luminol in an alkaline solution without adding any special oxidants. The chemiluminescence signal could be significantly enhanced by Cu(II). The proposed method allows the determination of 4.0 × 10^?9 to 1.0 × 10^?7 g/mL cysteine, 7.0 × 10^?10 to 1.0 × 10^?7 g/mL acetylcysteine, and 4.0 × 10^?9 to 1.0 × 10^?6 g/mL glutathione with the detection limits of 8 × 10^?10 g/mL, 2 × 10^?11 g/mL, and 7 × 10^?10 g/mL, respectively. The proposed method was applied to the analysis of some commercial formulations containing acetylcysteine.     

Highly Sensitive Flow-Injection Chemiluminescence Detection of Carbonyl Compounds in Wine Samples

A modified Trautz–Schorigin reaction, by using tannic acid-H₂O₂ system for the oxidation and determination of two kinds of carbonyl compounds was developed in this paper. It was found that formaldehyde and acetaldehyde could effectively enhance the chemiluminescence signals of tannic acid–H₂O₂ system in alkaline medium. Under optimized conditions, the proposed method has a linear range of 7 × 10^?9–1 × 10^?4 mol L^?1 for formaldehyde and 1 × 10^?8–1 × 10^?4 mol L^?1 for acetaldehyde with detection limits of 9 × 10^?11 and 3 × 10^?10 mol L^?1, respectively. The relative standard deviations for 15 repeated measurements of 1 × 10^?6 mol L^?1 HCHO and CH₃CHO are 1.13% and 1.65%, respectively. Analysis time per sample is 35 seconds. A comparison of results found by the proposed method with those obtained by a standard reference method provided good agreement. The proposed method is simple, rapid, convenient, and sensitive.     

Simultaneous determination of oleanolic acid,ursolic acid,quercetin and apigenin in Swertia mussotii Franch by capillary zone electrophoresis with running buffer modifier

The method of capillary zone electrophoresis (CZE) with direct UV detection was developed for the determination of oleanolic acid, ursolic acid, quercetin and apigenin. and then for the first time successfully applied to the analysis of four analytes in Swertia mussotii Franch and its preparations. Various factors affecting the CZE procedure were investigated and optimized, and the optimal conditions were: 50 × 10^?3 mol/L borate‐phosphate buffer (pH 9.5) with 5.0 × 10^?3 mol/L β‐cyclodextrin, 15 kV separation voltage, 20 °C column temperature, 250 nm detection wavelength and 5 s electrokinetic injection time (voltage 20 psi). Under the conditions, oleanolic acid, ursolic acid, quercetin and apigenin could be determined within the test ranges with a good correlation coefficient (r² > 0.9991). The limits of detection for conditions, oleanolic acid, ursolic acid, quercetin and apigenin were 0.3415, 0.2003, 0.0062 and 0.2538 µg/mL, respectively, and the intra‐ and inter‐day relative standard deviations were no more than 4.72%. This procedure provided a convenient, sensitive and accurate method for simultaneous determination of oleanolic acid, ursolic acid, quercetin and apigenin in S. mussotii Franch. Copyright © 2014 John Wiley & Sons, Ltd.     

A new sensitive and selective sensor for heavy metal ions based on tannin extracted from the skin of Punica granatum L

This article presents the development of a sensor made from a gold electrode and a receiving polymeric membrane based on tannin extracted from the skin of Punica granatum. L (pomegranate) for real-time detection of heavy metals in a hydrous environment. The basic principle of this device is the complexing (chelating) of metal ions through the adjacent hydroxyl groups contained in the chemical structures of the tannins. The electrochemical characterisation was performed by using electrochemical impedance spectroscopy and square wave voltammetry. Other morphological and structural analyses were performed by using Fourier transform infrared spectroscopy and atomic-force microscopy. The results obtained showed the high sensitivity of the developed device (detection limits of 6.35 × 10^?9 g L^?1 for Cu²⁺, 1.1 × 10^?8 g L^?1 for Cd²⁺ and 2 × 10^?7 g L^?1 for Pb²⁺) and the possibility of simultaneously detecting several heavy metals, each one in a highly selective manner with highly acceptable response time (48s).     

Use of ionic liquid based chitosan as sorbent for preconcentration of fluoroquinolones in milk,egg, fish,bovine, and chicken meat samples by solid phase extraction prior to HPLC determination

The possibility of using ionic liquid based chitosan sorbent for the separation and preconcentration of fluoroquinolone antibiotics (marbofloxacin, enoxacin, ofloxacin, ciprofloxacin, and enrofloxacin) has been studied. For this reason, different ionic liquids were prepared and coated on the chitosan sorbent. The conditions of the preconcentration of fluoroquinolones on a microcolumn have been optimized and the extraction efficiencies of the prepared sorbents have been compared. The compounds were eluted with 5 mL of 20% NH₃ (v/v, MeOH) solution and determined by HPLC with diode array and fluorescence detector. The limits of detection were found as 4.23 µ g L^?1 for marbofloxacin, and 1.09 µg L^?1 for enoxacin; 3.23 × 10^?3 µg L^?1 for ofloxacin; 8.39 × 10^?3 µg L^?1 for ciprofloxacin; and 19.50 × 10^?3 µg L^?1 for enrofloxacin. The developed method was applied for the analysis of fluoroquinolone in milk, egg, fish, bovine, and chicken samples and the recoveries were obtained in the range 70–100%.