Assays for serum cholinesterase activity by capillary electrophoresis and an amperometric flow injection choline biosensor

A capillary electrophoresis method and a durable choline biosensor were developed for measuring serum cholinesterase (EC 3.1.1.8) activity, a useful clinical index for liver function. The former is based on separation of benzoate and benzoylcholine (the artificial substrate of cholinesterase) in an uncoated fused-silica capillary. The migration time of benzoylcholine and benzoate was 1.3 min and 5.5 min, respectively. By the peak areas of A₂₃₃ signals, the linear dynamic ranges for both analytes were 0.01–50.0 mM, and the relative standard deviations of 1.0 mM benzoylcholine and benzoate were less than 4% and 6%, respectively.The FIA-choline sensor was constructed with the working electrode of the flow cell covered with a natural chitinous membrane purified from Taiwanese soldier crab, Mictyris brevidactylus. The biomembrane served as the supporting material for enzyme immobilization (choline oxidase, EC 1.1.3.17), and also prevented protein adsorption on the electrode surface. The calibration curve was linear between 0.05 and 5.0 mM (r = 0.999). The relative standard deviations for 1.0 mM choline (n = 7) were less than 3%, and the activity of the bioactive membrane lasted for about 2 months. The analytical results of both methods correlated well (r = 0.940).     

Determination of sulfate and chloride ions in highly saline oilfield water by capillary electrophoresis using bilayer-coated capillaries and indirect absorption detection

Analysis of highly saline oilfield waters for anions presents challenges. Traditional analytical techniques used for such analysis tend to suffer from both poor sensitivity and selectivity due to the high concentrations of salt present in the samples. A capillary electrophoresis method was developed for the simultaneous determination of chloride and sulfate anions which is relevant to the oilfield analysis industry and of economic value. Due to the extremely high concentrations of chloride in highly saline oilfield waters, it is difficult to achieve baseline electrophoretic separation necessary for accurate quantitation. By using a capillary with a noncovalently bound bilayer coating using Polybrene, a cationic polymer and sodium dodecyl sulfate (SDS), an anionic surfactant and a buffer consisting of 50 mM TRIS, 30 mM SDS, 5% methanol and 26 mM chromium trioxide (CrO₃) at pH 6.7, baseline separation (R_s > 1.5) of chloride and sulfate was achieved. To mimic possible oilfield water samples, model water solutions of 5%, 10%, 15% and 20% chloride containing low ppm sulfate were prepared and successfully analysed using the method developed. In addition, the method was applied to determine chloride and sulfate anions in highly saline oilfield water samples. The accuracy of the method developed was verified by analysing NIST certified standards of chloride and sulfate. The results obtained for chloride and sulfate with the indirect CE-UV method were in close agreement (94–100% accuracy; <2.5% relative standard deviations) with those of the certified standard analysed by ion chromatography.     

Analysis of methotrexate and its eight metabolites in cerebrospinal fluid by solid-phase extraction and triple-stacking capillary electrophoresis

We establish a triple-stacking capillary electrophoresis (CE) separation method to monitor methotrexate (MTX) and its eight metabolites in cerebrospinal fluid (CSF). Three stacking methods with different mechanisms were combined and incorporated into CE separation. Complete stacking and sharp peaks were achieved. Firstly, the optimized buffer (60 mM phosphate containing 15% THF and 100 mM SDS) was filled into the capillary, which was followed by the higher conductivity buffer (100 mM phosphate, 2 psi for 45 s). The analytes extracted from CSF were injected at 2 psi for 99.9 s, which provided long sample zones and pH junction for focusing. Finally, the stacking step was performed by sweeping, and separation was achieved by micellar electrokinetic chromatography. The results of the linear regression equations indicated high linearity (r ≥ 0.9981) over the range of 0.5–7 μM. In intra- and inter-batch results, all data of RSD and RE were below 11%, indicating good precision and accuracy of this method. The LODs (S/N = 3) were 0.1 μM for MTX, 7-hydroxymethotrexate (7-OHMTX) and MTX-polyglutamates (MTX-(Glu) _{n, n = 2–5}), 0.2 μM for MTX-(Glu)₆, and 0.3 μM for 2,4-diamino-N ¹⁰-methylpteroic acid (DAMPA) and MTX-(Glu)₇. Our method was implemented for analysis of MTX and its metabolites in the CSF, and could be used for evaluation of its curative effects of acute lymphoblastic leukemia patients. The data were also confirmed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. The results showed good coincidence.     

Stacking and determination of phenazine-1-carboxylic acid with low p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript> in soil via moving reaction boundaryformed by alkaline and double acidic buffers in capillary electrophoresis

As shown herein, a normal moving reaction boundary (MRB) formed by an alkaline buffer and a single acidic buffer had poor stacking to the new important plant growth promoter of phenazine-1-carboxylic acid (PCA) in soil due to the leak induced by its low pK _a. To stack the PCA with low pK _a efficiently, a novel stacking system of MRB was developed, which was formed by an alkaline buffer and double acidic buffers (viz., acidic sample and blank buffers). With the novel system, the PCA leaking into the blank buffer from the sample buffer could be well stacked by the prolonged MRB formed between the alkaline buffer and blank buffer. The relevant mechanism of stacking was discussed briefly. The stacking system, coupled with sample pretreatment, could achieve a 214-fold increase of PCA sensitivity under the optimal conditions (15 mM (pH 11.5) Gly-NaOH as the alkaline buffer, 15 mM (pH 3.0) Gly-HCl-acetonitrile (20%, v/v) as the acidic sample buffer, 15 mM (pH 3.0) Gly-HCl as the blank buffer, 3 min 13 mbar injection of double acidic buffers, benzoic acid as the internal standard, 75 μm i.d. × 53 cm (44 cm effective length) capillary, 25 kV and 248 nm). The limit of detection of PCA in soil was decreased to 17 ng/g, the intra-day and inter-day precision values (expressed as relative standard deviations) were 3.17–4.24% and 4.17–4.87%, respectively, and the recoveries of PCA at three concentration levels changed from 52.20% to 102.61%. The developed method could be used for the detection of PCA in soil at trace level.     

Application of co-electroosmotic capillary electrophoresis for the determination of inorganic anions and carboxylic acids in soil and plant extract with direct UV detection

Summary Indirect UV detection in capillary zone electrophoresis (CZE) is frequently used for the determination of inorganic anions and carboxylic acids. However, there are few reports on direct UV detection of these solutes in real samples. This paper describes the use of direct UV detection of inorganic anions and organic acids in environmental samples using co-electroosmotic capillary zone electrophoresis (co-CZE) at 185 nm. The best separation and detection of the solutes was achieved using a fused silica capillary with an electrolyte containing 25 mM phosphate, 0.5 mM tetradecyltrimethylammonium bromide (TTAB) and 15% acetonitrile (v/v) at pH 6.0. Four common inorganic anions (Cl⁻, NO₂ ⁻, NO₃ ⁻ and SO₄ ²⁻) and 11 organic acids (oxalic, formic, fumaric, tartaric, malonic, malic, citric, succinic, maleic, acetic, and lactic acid), were determined simultaneously in 15 min. Linear calibration plots for the test solutes were obtained in the range 0.02–0.5 mM with detection limits ranging from 1–9 μM depending on the analyte. The proposed method was successfully used to determine inorganic anions and carboxylic acids in soil and plant tissue extracts with direct injection of the sample.     

Validated method for the determination of ethylglucuronide and ethylsulfate in human urine

Detection of the alcohol metabolites ethylglucuronide (EtG) and ethylsulfate (EtS) has become routine in many forensic laboratories over the last few years. Most previously published methods using liquid chromatography coupled with electrospray tandem mass spectrometry require a post-chromatographic addition of solvent and/or extensive sample preparation prior to analysis. The aim of the study was to develop a simplified method. To 20 μL urine, internal standard containing EtG-d5 and EtS-d ₅ was added and the mixture was treated with elution buffer internal standard. EtG and EtS were separated using a Shimadzu Prominence high performance liquid chromatography (HPLC) system with a C18 separation column (Restek Ultra Aqueous C18, 4.6 × 150 mm, 5 μm), using isocratic elution with a mobile phase consisting of 10 mM ammonium acetate buffer pH 7 (total run time, 6 min). The compounds were detected using an Applied Biosystems API 5000 liquid chromatography tandem mass spectrometry system (atmospheric pressure chemical ionization, multiple-reaction monitoring mode). The method was fully validated according to international guidelines. The assay was found to be selective for the compounds of interest. It was linear from 0.1 to 10 mg/L for all analytes (R ² > 0.99). Matrix effects studies showed the presence of a slight but consistent ion enhancement (n = 10 different urine samples) at low concentrations and no effects at higher concentrations. Accuracy data were between 0.75% and 8.1% bias for EtG and between −5.0% and −11.3% bias for EtS. Precision data were between 4.3% and 6.9% relative standard deviations (RSD) for EtG and between 6.0% and 7.5% RSD for EtS. No instability was observed after repeated freezing and thawing. This fast, reliable, and accurate method enables the detection and quantification of alcohol metabolites in urine. The method is easier to use and more sensitive than previously published methods.     

Ultrasound and surfactant-assisted dispersive liquid–liquid microextraction prior to poly(ethylene oxide)-mediated stacking in CE for highly sensitive determination of barbiturates in human fluids

This study developed a facile, highly sensitive technique for extracting and quantifying barbiturates in serum samples. This method combined ultrasound and surfactant-assisted dispersive liquid–liquid microextraction with poly(ethylene oxide)-mediated stacking in capillary electrophoresis. Factors influencing the extraction and stacking performance, such as the type and volume of extraction solvents, the type and concentration of surfactant, extraction time, salt additives, sample matrix, solution pH, and composition of the background electrolyte, were carefully studied and optimized to achieve the optimal detection sensitivity. Under the optimized extraction (injecting 140 μL C₂H₄Cl₂ into 1 mL of sample with pH 4 (5 mM sodium phosphate containing 0.05 mM Tween 20 and sonication for 1 min) and separation conditions (150 mM tris(hydroxymethyl)aminomethane-borate with pH 8.5 containing 0.5% (m/v) poly(ethylene oxide)), the limits of detection (signal-to-noise ratio = 3) of five barbiturates ranged from 0.20 to 0.33 ng/mL, and the calculated sensitivity improvement ranged from 868- to 1700-fold. The experimental results revealed excellent linearity (R² > 0.99), with relative standard deviations of 2.1%–3.4% for the migration time and 4.3%–5.7% for the peak area. The recoveries of the spiked serum samples were 97.1% –110.3%. Our proposed approach offers a rapid and practical method for quantifying barbiturates in biological fluids.     

In situ emulsification microextraction using a dicationic ionic liquid followed by magnetic assisted physisorption for determination of lead prior to micro-sampling flame atomic absorption spectrometry

For the first time, a simple and efficient in situ emulsification microextraction method using a dicationic ionic liquid followed by magnetic assisted physisorption was presented to determine trace amounts of lead. In this method, 400 μL of 1.0 mol L⁻¹ lithium bis (trifluoromethylsulfonyl) imide aqueous solution, Li[NTf₂], was added into the sample solution containing 100 μL of 1.0 mol L⁻¹ 1,3-(propyl-1,3-diyl) bis (3-methylimidazolium) chloride, [pbmim]Cl₂, to form a water immiscible ionic liquid, [pbmim][NTf₂]₂. This new in situ formed dicationic ionic liquid was applied as the acceptor phase to extract the lead-ammonium pyrrolidinedithiocarbamate (Pb-APDC) complexes from the sample solution. Subsequently, 30 mg of Fe₃O₄ magnetic nanoparticles (MNPs) were added into the sample solution to collect the fine droplets of [pbmim][NTf₂]₂, physisorptively. Finally, MNPs were eluted by acetonitrile, separated by an external magnetic field and the obtained eluent was subjected to micro-sampling flame atomic absorption spectrometry (FAAS) for further analysis. Comparing with other microextraction methods, no special devices and centrifugation step are required. Parameters influencing the extraction efficiency such as extraction time, pH, concentration of chelating agent, amount of MNPs and coexisting interferences were studied. Under the optimized conditions, this method showed high extraction recovery of 93% with low LOD of 0.7 μg L⁻¹. Good linearity was obtained in the range of 2.5–150 μg L⁻¹ with determination coefficient (r²) of 0.9921. Relative standard deviation (RSD%) for seven repeated measurements at the concentration of 10 μg L⁻¹ was 4.1%. Finally, this method was successfully applied for determination of lead in some water and plant samples.     

Preparation and catalytic activity of titanium silicalite-1 zeolite membrane with TPABr as template

The preparation of the supported titanium silicalite-1 (TS-1) zeolite membrane with inexpensive tetrapropylammonium bromide (TPABr)/weak base synthesis system was studied by three methods, and the catalytic activity of the obtained TS-1 zeolite membrane was evaluated with the oxidation of 2-propanol (IPA) under pervaporation condition. It was found that TS-1 zeolite membrane could be successfully prepared with “seeding” or “seeding in situ” method, but could not be achieved with “in situ” method. Adding a little amount of promoter ions of PO₄³⁻ into the synthesis gel was of benefit to the catalytic activity of the prepared TS-1 zeolite membrane, but had no obvious effect on the membrane layer formation on the mullite porous support. For “seeding” method, the membrane prepared with the synthesis gel having molar composition of SiO₂:0.1TPABr:0.9Et₂NH:0.03TiO₂:80H₂O:0.06H₃PO₄ at 150 °C for 48 h showed the highest oxidation conversion of IPA of 72% accompanied by a flux of 0.35 kg/m² h. Further more, much higher IPA oxidation conversion of 76% accompanied by a flux of 0.65 kg/m² h was obtained for the TS-1 zeolite membrane prepared with the same synthesis gel by “seeding in situ” method at 150 °C for 72 h.     

Quantification of eight active ingredients in crude and processed radix polygoni multiflori applying miniaturized matrix solid‐phase dispersion microextraction followed by UHPLC

A rapid, efficient, and green sample preparation method has been developed to extract eight active ingredients (gallic acid, catechins, epicatechin, polydatin, 2,3,5,4′‐tetrahydroxystilbene‐2‐O‐β‐d ‐glucoside, resveratrol, emodin, and physcion) in radix polygoni multiflori by miniaturized matrix solid‐phase dispersion microextraction. Simple and sensitive ultra high performance liquid chromatography combined with ultraviolet detection has been applied to analyze the multiple compounds. The best results were obtained by adding 25 mg sample into 25 mg adsorbent and grinding for 2 min with disorganized silica as adsorbent and 1 mL 150 mM 1‐dodecyl‐3‐methylimidazolium bromide as a green eluting solvent. Good linearity (r² > 0.998) for each analyte was obtained by this method. The intra‐day and inter‐day precision (RSD) were both below 5.31%, and the recoveries of the analytes ranged from 93.3 to 100.0%. This simple miniaturized matrix solid‐phase dispersion microextraction method for analyzing the compounds in radix polygoni multiflori needs a short time and requires little sample and reagent. Thus, this method is far more eco‐friendly and efficient than traditional extraction methods (reflux and ultrasound‐assisted extraction). The present investigation provided a promising method for the fast preparation and discrimination of chemical differences in crude and processed radix polygoni multiflori.     

Preparative and scaled‐up separation of high‐purity α‐linolenic acid from perilla seed oil by conventional and pH‐zone refining counter current chromatography

α‐Linolenic acid is an essential omega‐3 fatty acid needed for human health. However, the isolation of high‐purity α‐linolenic acid from plant resources is challenging. The preparative separation methods of α‐linolenic acid by both conventional and pH‐zone refining counter current chromatography were firstly established in this work. The successful separation of α‐linolenic acid by conventional counter current chromatography was achieved by the optimized solvent system n‐heptane/methanol/ water/acetic acid (10:9:1:0.04, v/v), producing 466 mg of 98.98% α‐linolenic acid from 900 mg free fatty acid sample prepared from perilla seed oil with linoleic acid and oleic acid as by‐products. The scaled‐up separation in 45× is efficient without loss of resolution and extension of separation time. The separation of α‐linolenic acid by pH‐zone refining counter current chromatography was also satisfactory by the solvent system n‐hexane/methanol/water (10:5:5, v/v) and the optimized concentration of trifluoroacetic acid 30 mM and NH₄OH 10 mM. The separation can be scaled up in 180× producing 9676.7 mg of 92.79% α‐linolenic acid from 18 000 mg free fatty acid sample. pH‐zone refining counter current chromatography exhibits a great advantage over conventional counter current chromatography with 20× sample loading capacity on the same column.     

Novel fusion method for direct determination of uranium in ilmenite,rutile, columbite,tantalite, and xenotime minerals by laser induced fluorimetry

A simple, rapid, effective and eco-friendly decomposition method is developed for the determination of uranium (U) by laser induced fluorimetry (LIF). The salts of sodium di-hydrogen phosphate (NaH₂PO₄) and di-sodium hydrogen phosphate (Na₂HPO₄) were used in the ratio of 1:1 (phosphate flux) for the decomposition and dissolution of refractory, non silicate minerals like ilmenite, rutile, columbite, tantalite, and xenotime. The effect of associated matrix elements (Ti, Fe, Nb, Ta, Mn and Y present in the sample) on quenching of uranyl fluorescence was studied. The flux used for the sample decomposition has several advantages. In the reported sample decomposition methods, α-hydroxy acids are used as complexing agents to prevent hydrolysis and to get clear and stable solution. This solution can not be directly used for U determination by LIF as α-hydroxy acids quench uranyl fluorescence, hence separation is required. In the present method no such separation is required. The flux itself acts as fluorescence enhancing reagent and buffer (maintaining the optimum pH of 7.1 ± 0.1). The fused melt of the flux mixture, when disintegrated in water, gives clear and stable solution and has high tolerance for most of inorganic quenchers compared to reported phosphate buffers. Also just by dilution (due to high sensitivity of LIF), the concentration of quenchers could be brought down well within the tolerance limit. The accuracy and precision of the method was evaluated by analyzing Certified Reference Materials (IGS-33 and IGS-34 of Institute of Geological Sciences, UK) and Synthetic Minerals. The accuracy of the data is further evaluated by comparing with standard decomposition methods. The results are well within the experimental error. The RSD of the method is ±10% (n = 6) at 10 ppm level for Ilmenite and for other minerals the RSD of the method is ±5% (n = 6) at 50 ppm level. The method is being routinely applied to various refractory samples received from Rare Metal and Rare Earth Investigations for determination of uranium by laser fluorimetry.     

Determination of Total Radiochemical Purity of [18F]FDG and [18F]FET by High-Performance Liquid Chromatography Avoiding TLC Method

The goal of this work was to present two high-performance liquid chromatography (HPLC) method that could be applied for the determination of the total radioactive purity of 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) and O-(2-[¹⁸F]fluoroethyl)-L-tyrosine ([¹⁸F]FET). The separation of [¹⁸F]fluoride ions, [¹⁸F]FET and [¹⁸F]FET intermediate was accomplished on LiChrosper RP-18, 250?×?4 mm, 5 µm (Merck) analytical column. For mobile phase 10 mM potassium dihydrogen phosphate buffer at pH7 (A) and acetonitrile (B) was used: 0–2 min: 15% B; 2–12 min: 85% B; 12–15 min: 15% B, respectively. Analysis of [¹⁸F]FDG was performed using LiChrosper 100 NH₂, 250?×?4.5 mm, 5 µm (Merck) analytical column. The initial mobile phase composition was 10 mM KH₂PO₄ buffer (pH7) and acetonitrile (15:85, v/v) and the acetonitrile ratio was decreased to 15% at 2 min after the sample injection and held for 5 min. Complete elution of [¹⁸F]fluoride ions from stationary phases could be achieved by adding 10 mg/mL K[¹⁹F]F to radioactive samples in a ratio 1:1 during the sample preparation. Recovery of [¹⁸F]fluoride ions ranged from 99.5 to 100.6%. The validation of the developed methods showed good results for linearity (r²?=?0.9981–0.9996), specificity (R_S?=?3.7–10.2), repeatability (%Area RSD_%?=?1.2–4.3%) and limit of quantitation (LOQ?=?1.6–4.5 kBq). During the cross-validation similar radiochemical purity values were obtained by the novel HPLC methods and thin layer chromatography performed according to the recommendations of the Ph. Eur. monographs.

     

Use of high‐conductivity sample solution with sweeping‐micellar electrokinetic capillary chromatography for trace‐level quantification of paliperidone in human plasma

Paliperidone is a new antipsychotic drug with a relatively low therapeutic concentration of 20–60 ng/mL. We established an accurate and sensitive CE method for the determination of paliperidone concentrations in human plasma in this study. To minimize matrix effect caused by quantification errors, paliperidone was extracted from human plasma using Oasis HLB SPE cartridges with three‐step washing procedure. To achieve sensitive quantification of paliperidone in human plasma, a high‐conductivity sample solution with sweeping‐MEKC method was applied for analysis. The separation is performed in a BGE composed of 75 mM phosphoric acid, 100 mM SDS, 12% acetonitrile, and 15% tetrahydrofuran. Sample solution consisted of 10% methanol in 250 mM phosphoric acid and the conductivity ratio between sample matrix and BGE was 2.0 (γ, sample/BGE). The results showed it able to detect paliperidone in plasma samples at concentration as low as 10 ng/mL (S/N = 3) with a linear range between 20 and 200 ng/mL. Compared to the conventional MEKC method, the sensitivity enhancement factor of the developed sweeping‐MEKC method was 100. Intra‐ and interday precision of peak area ratios were less than 6.03%; the method accuracy was between 93.4 and 97.9%. This method was successfully applied to the analysis of plasma samples of patients undergoing paliperidone treatment.     

Nonaqueous CE for Rapid and Sensitive Determination of Matrine and Oxymatrine in Sophora flavescens and Its Medicinal Preparations

A simple, rapid, and sensitive non-aqueous capillary electrophoresis procedure for the quantitative determination of matrine and oxymatrine is established. Optimum separation conditions were obtained when the sample was injected under pressure for 3 s at 50 mbar and separated with the buffer containing 70 mM ammonium acetate, 7.0% (v/v) acetic acid, and 10% (v/v) acetonitrile in methanol medium at 25 kV applied voltage. The analytes were detected at 205 nm. The two alkaloids can be separated within 12 min and quantified with high sensitivity. The method was validated in terms of reproducibility, linearity, and accuracy when applied to the analysis of matrine and oxymatrine in Sophora flavescens and its medicinal preparations.     

Chiral separation of lansoprazole and rabeprazole by capillary electrophoresis using dual cyclodextrin systems

Novel capillary electrophoresis methods using CDs as chiral selectors were developed and validated for the chiral separation of lansoprazole and rabeprazole, two proton pump inhibitors. Fourteen different neutral and anionic CDs were screened at pH 4 and 7 in the preliminary analysis. Sulfobutyl‐ether‐β‐CD with a degree of substitution of 6.5 and 10 at neutral pH proved to be the most suitable chiral selector for both compounds. Various dual CD systems were also compared, and the possible mechanisms of enantiomer separation were investigated. A dual selector system containing sulfobutyl‐ether‐β‐CD degree of substitution 6.5 and native γ‐CD proved to be the most adequate system for the separations. Method optimization was carried out using an experimental design approach, performing an initial fractional factorial screening design, followed by a central composite design to establish the optimal analytical conditions. The optimized methods (25 mM phosphate buffer, pH 7, 10 mM sulfobutyl‐ether‐β‐CD/20 mM γ‐CD, +20 kV voltage; 17°C temperature; 50 mbar/3 s injection, detection at 210 nm for lansoprazole; 25 mM phosphate buffer, pH 7, 15 mM sulfobutyl‐ether‐β‐CD/30 mM γ‐CD, +20 kV voltage; 18°C temperature; 50 mbar/3 s injection, detection at 210 nm for rabeprazole) provided baseline separation for lansoprazole (R_s = 2.91) and rabeprazole (R_s = 2.53) enantiomers with favorable migration order (in both cases the S‐enantiomers migrates first). The optimized methods were validated according to current guidelines and proved to be reliable, linear, precise, and accurate for the determination of 0.15% distomer as chiral impurity in dexlansoprazole and dexrabeprazole samples.     

Nanoceria Supported Gold Catalysts for CO Oxidation

Two types of CeO₂ nanocubes (average size of 5 and 20 nm, respectively) prepared via the hydrothermal process were selected to load gold species via a deposition‐precipitation (DP) method. Various measurements, including X‐ray diffraction (XRD), Raman spectra, high resolution transmission electron microscopy (HRTEM), in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), and temperature‐programmed reduction by hydrogen (H₂‐TPR), were applied to characterize the catalysts. It is found that the sample with ceria size of 20 nm (Au/CeO₂‐20) was covered by well dispersed both Au³⁺ and Au^δ+ (0 < δ < 1). For the other sample with ceria size of 5 nm (Au/CeO₂‐5), Au³⁺ is the dominant gold species. Au/CeO₂‐20 performed better catalytic activity for CO oxidation because of the strong CO adsorption of Au^δ+ in the catalysts. The catalytic activity of Au/CeO₂‐5 was improved due to the transformation of Au³⁺ to Au^δ+. Based on the CO oxidation and in situ DRIFTS results, Au^δ+ is likely to play a more important role in catalyzing CO oxidation reaction.     

Effect of buffer composition and preparation protocol on the dispersion stability and interfacial behavior of aqueous DPPC dispersions

The effect of the buffer composition and the preparation protocol on the dynamic surface tension (DST) and vesicle sizes of aqueous dipalmitoylphosphatidylcholine (DPPC) dispersions was studied. Four isotonic buffers were used in preparing DPPC dispersions at physiological conditions for possible biological applications: (1) a standard PBS solution; (2) the above PBS with 1 mM CaCl₂; (3) PBS with one tenth the previous standard phosphate salt concentrations and 2.5 mM CaCl₂; and (4) 150 mM NaCl with 2.5 mM CaCl₂ and 10 mM HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid). Two protocols, with a new method and an old method (Bangham method), were used in preparing the DPPC dispersions. The DPPC dispersions prepared with the new method contained mostly vesicles and were quite stable at 25 or 37 °C. Dynamic light scattering (DLS) and spectroturbidimetry (ST) results showed that the DPPC vesicle sizes in buffer (4) were much smaller than those in the other buffers. When the DPPC dispersions were prepared with the new method, the diameter of the DPPC particles was smaller than those with the old method. The DPPC vesicles with the new method were more stable than those with the other method. The DPPC dispersions of 1000 ppm at 37 °C with the new method produced, at pulsating area conditions at 20 cycles per minute, low tension minima (γ_min), lower than 10 mN/m, in buffers (1), (2), and (4). With buffer (4) the DSTs were lower and were achieved faster than with the other buffers. A minimum concentration of 1000 or 250 ppm DPPC was needed to produce DSTs lower than 10 mN/m within 10 min or less, with buffer (2) or (4), respectively. IRRAS results suggest that DPPC in buffer (2) or (4) forms a close-packed monolayer at the interface. These results have implications for designing efficient protocols of lipid dispersion preparation and lung surfactant replacement formulations in treating respiratory disease.     

Synthesis and Ameliorative Effect of Isatin–Mesalamine Conjugates on Acetic Acid‐induced Colitis in Rats

A series of new isatin–mesalamine conjugates ( 9a – g ) were synthesized via conjugation of isatin ( 3a ) and its derivatives ( 3b – 3d , 4 , 5 , and 6 ) with mesalamine ( 7 ) by using chloroacetyl chloride as a bifunctional linker. Compounds 3a – 3d were prepared by employing Sandmeyer reaction. Compounds 4 , 5 , and 6 were obtained from isatin ( 3a ) via previously reported methods. The synthesized compounds were characterized by IR, mass, ¹H NMR, and ¹³C NMR spectral techniques. Synthesized compounds ( 3a – d , 4 , 5 , 6 , and 9a – g ) were evaluated for in vitro antioxidant activity by DPPH assay method using ascorbic acid as standard. Hybrids 9b (IC₅₀ = 368.6 ± 3.5 μM) and 9f (IC₅₀ = 335.1 ± 2.9 μM) showed better antioxidant activity than its parent compounds such as 3a (IC₅₀ = 556.8 ± 2.9 μM), 5 (IC₅₀ = 511.9 ± 3.6 μM), and 7 (IC₅₀ = 768.9 ± 2.7 μM). Acetic acid‐induced ulcerative colitis in rat model was chosen to examine the antioxidant potential of the synthesized hybrids ( 9b and 9f ) in the amelioration of ulcerative colitis. Colonic myeloperoxidase and malondialdehyde enzymes were used as biomarkers of anti‐ulcerative colitis activity. In the present study, hybrids 9b and 9f reduced the levels of colonic myeloperoxidase and malondialdehyde enzymes significantly (p < 0.05) when compared with control (colitic), at a dose (0.03 mM/12.5 mg/kg b.w. p.o.) (50%) less than that of its parent moieties mesalamine (0.16 mM/25 mg/kg) and isatin (0.16 mM/25 mg/kg). Thus, the molecular hybridization was proved to be significant in enhancing the activity of hybrids 9b and 9f by reducing the dose.     

Electrophilic reactivities of 7-L-4-nitrobenzofurazans in σ-complexation processes: Kinetic studies and structure–reactivity relationships

The second-order rate constants (k) for reaction of 7-chloro-4-nitrobenzofurazan 1 and 7-methoxy-4-nitrobenzofurazan 2 with a series of nitroalkyl anions and several of para-substituted phenoxide anions in aqueous solution at 20 °C have been reported. On the basis of the linear novel approach recently designed by Mayr and coworkers, the electrophilicity parameters E at the C-5 position of the two nitrobenzofurazans 1 and 2 have been quantified and ranked on the comprehensive electrophilicity scale. Mayr's approach was found to correctly predict the rate constants for the addition of phenoxide anions at the C-5 position of 1 and 2 witting a factor of <2. Analysis of the kinetic measurements using Brønsted's model shows that β_nuc values remain remarkably constant for changes in the nature of the substituent and that the σ-complexation process is associated with high Marcus intrinsic barriers. In addition, satisfactory correlations between the log k_exp (k_exp values measured in this work for reactions of benzofurazans 1 and 2 with a series of phenoxide anions in aqueous solution at 20 °C) and log k_calcd (k_calcd values calculated from equation 1 using the electrophilicity parameters E of benzofurazans 1 and 2 and the previously published nucleophilicity parameters N and s_N of the phenoxide anions) with a slope very close to unity have been obtained and discussed.