Determination of Organophosphorus Pesticides in Fortified Tomatoes by Fluorescence Quenching of Cadmium Selenium – Zinc Sulfide Quantum Dots

Quantum dots (QDs) have attracted great interest in fluorescence sensing. However, due to the surface passivation of QDs, it is still challenging to develop a sensing method based on the direct use of QD without the involvement of molecular recognition receptors. In this work, a very simple but practical strategy for highly passivated commercial CdSe/ZnS core-shell QDs is proposed to directly determine phosphorothiolate pesticides. This strategy is based on the fact that thiophosphorus hydrolyzates, formed in the alkaline hydrolysis of phosphorothiolates, strongly quench the fluorescence emission of the QDs by an electron transfer mechanism. The design is very easy to implement, requiring only the addition of the analyte into the quantum dot solution at room temperature. The ‘light-off’ response shows a wide linear range from 0.0001 to 160?μg mL^?1 with a detection limit of approximately 0.0967?ng mL^?1 (0.00012?mg kg^?1), which is considerably lower than the maximum residue limit of 0.01?mg kg^?1 allowed by the European Union. More importantly, ethion may be determined directly in fortified tomatoes by this protocol, demonstrating potential broad applications in food quality control.     

Characterization of the Interaction between Bovine Serum Albumin and Lomefloxacin by Capillary Zone Electrophoresis

Three capillary zone electrophoresis (CZE) methods of the frontal analysis (FA), vacancypeak (VP) and simplified Hummel-Dreyer (SHD) were applied to investigate interaction betweenbovine serum albumin (BSA) and lomefloxacin, the experimental condition was established after alarge number of tests. Based on the site-binding model, the binding parameters were measuredaccording to the site model by Scatchard.     

Production of Polyclonal Antibody of Morphine and Determination of Morphine in Urine by Capillary Electrophoresis Immunoassay with Laser-induced Fluorescence Detection

N-Conjugated antigen was synthesized and polyclonal antibody with high specificity was obtained from immunizing animals. With this polyclonal antibody, a rapid and efficient CEIA-LIF method was developed to determine the free morphine in urine of abusers. The detection limit was calculated to be 40 ng/mL. Simulated urine samples were analyzed with good recoveries, which showed the feasibility of its application in specific morphine determination in urine of morphine abusers.     

Carboxymethyl-β-cyclodextrin for Chiral Separation of Amino Acids Derivatized with Fluorescene-5-isothiocyanate by Capillary Electrophoresis and Laser-induced Fluorescence Detection

A method using carboxymethyl-β-cyclodextrin (CM-β-CD) as selector for chiral separation of amino acids by capillary electrophoresis and laser-induced fluorescence detection was studied. Resolution was better than that obtained by β-CD or HP-β-CD.     

Characterization of the Interaction Between Lantibiotics, Nisin and Duramycin, and β-Lactoglobulin by Affinity Capillary Electrophoresis

Affinity capillary electrophoresis was used to study quantitatively the noncovalent interactions between β-lactoglobulin (β-LG), a milk whey protein, and two lantibiotics, nisin (a dairy biopreservative lantibiotic) and duramycin (a bovine mastitis treatment lantibiotic). The study involved measuring the change in effective electrophoretic mobility of the lantibiotic as the concentration of β-LG in the background electrolyte is increased. Nonlinear regression analysis was used to model the dependence of the effective mobility of the lantibiotic on β-LG concentration in the BGE. Using this approach, binding constants were determined to be 3.1 (±0.2) × 10⁸ M^?1 for nisin and 2.2 (±0.1) × 10⁸ M^?1 for duramycin. Both binding constants were comparable indicating the similarity of affinity properties of nisin and duramycin towards β-LG. These results demonstrate that affinity capillary electrophoresis is a suitable method for characterizing the interaction between lantibiotics and β-LG.     

Characterization of the Interaction Between Lantibiotics,Nisin and Duramycin,and β-Lactoglobulin by Affinity Capillary Electrophoresis

Affinity capillary electrophoresis was used to study quantitatively the noncovalent interactions between β-lactoglobulin (β-LG), a milk whey protein, and two lantibiotics, nisin (a dairy biopreservative lantibiotic) and duramycin (a bovine mastitis treatment lantibiotic). The study involved measuring the change in effective electrophoretic mobility of the lantibiotic as the concentration of β-LG in the background electrolyte is increased. Nonlinear regression analysis was used to model the dependence of the effective mobility of the lantibiotic on β-LG concentration in the BGE. Using this approach, binding constants were determined to be 3.1 (±0.2) × 10⁸ M⁻¹ for nisin and 2.2 (±0.1) × 10⁸ M⁻¹ for duramycin. Both binding constants were comparable indicating the similarity of affinity properties of nisin and duramycin towards β-LG. These results demonstrate that affinity capillary electrophoresis is a suitable method for characterizing the interaction between lantibiotics and β-LG.

     

Analysis of Amino Acids in a Single Human Red Blood Cell by Capillary Zone Electrophoresis with Intracellular NDA—derivatization and Electrochemical Detection

A novel method for determination of amino acids in individual red blood cells has been developed. In this method, the derivatization reagents (NDA and CN^-) are introduced into living cells by electroporation. After completion of derivatization,the amino acids in a single cell is determined by capillary zone electrophoresis with end-column amperometric detection.     

Syntheses and Crystal Structures of a Cadmium(Ⅱ) and a Zinc(Ⅱ) Complexes with the Flexible Ligand 1-Acetic Acid-2, 2'-biimidazole

Reactions of NaAcebiim(NaAcebiim = 1-acetic acid-2, 2′-biimidazole monosodium salt) and cadmium or zinc nitrate produce two supramolecular architectures, namely, 1D [Cd(Acebiim)(NO3)(H2O)]n(1) and 0D [Zn(Acebiim)2(H2O)2]·2H2O(2) in acidic aqueous solutions. Single-crystal X-ray diffraction analysis reveals that complex 1 crystallizes in the triclinic system, space group P1, and 2 is of monoclinic system, space group P21/n. In 1, two nitrate groups link two Cd(Ⅱ) ions forming [Cd2(NO3)2(H2O)2] as secondary building units that are interconnected by the Acebiim- ligand into an infinite ladder. In 2, the hydrogen-bonded synthon R22(16) between the N–H moieties and carboxylic acid link [Zn(Acebiim)2(H2O)2], generating a 1D-extended ribbon. Moreover, hydrogen bonds and π-π interactions further stabilize the 3D supramolecular architecture.     

Capillary isoelectric focusing of microorganisms in the pH range 2–5 in a dynamically modified FS capillary with UV detection

The isoelectric points of many microbial cells lie within the pH range spanning from 1.5 to 4.5. In this work, we suggest a CIEF method for the separation of cells according to their isoelectric points in the pH range of 2–5. It includes the segmental injection of the sample pulse composed of the segment of the selected simple ampholytes, the segment of the bioanalytes and the segment of carrier ampholytes into fused silica capillaries dynamically modified by poly(ethylene glycole). This polymer dissolved in the catholyte, in the anolyte and in the injected sample pulse was used for a prevention of the bioanalyte adsorption on the capillary surface and for the reduction of the electroosmotic flow. Between each focusing run, the capillaries were washed with the mixture of acetone/ethanol to achieve the reproducible and efficient CIEF. In order to trace of pH gradients, low-molecular-mass pI markers were used. The mixed cultures of microorganisms, Escherichia coli CCM 3954, Candida albicans CCM 8180, Candida parapsilosis, Candida krusei, Candida glabrata, Candida tropicalis, CCM 8223, Proteus vulgaris, Klebsiela pneumoniae, Staphylococcus aureus CCM 3953, Streptococcus agalactiae CCM 6187, Enterococcus faecalis CCM 4224 and Staphylococcus epidermidis CCM 4418, were focused and separated by the CIEF method suggested here. This CIEF method enables the separation and detection of the microbes from the mixed cultures within several minutes. The minimum detectable number of microbial cells was less than 10³.     

Characterization of the Penetration of the Blood–Brain Barrier by High-Performance Liquid Chromatography (HPLC) Using a Stationary Phase with an Immobilized Artificial Membrane

The biological activity of drugs on organisms is associated with the pharmacokinetic properties, such as the ability to penetrate through environments of varying polarity such as cellular organelles. In this area, particular attention is turned to the physicochemical properties that determine the potential of drugs to pass across the blood–brain barrier and thus to act on the central nervous system. In this study, special effort has been devoted to the simulation of passive diffusion of seven drugs (propranolol, ibuprofen, atenolol, promazine, chlorpromazine, imipramine, and desipramine) through the blood–brain barrier by high-performance liquid chromatography (HPLC) using a column with an immobilized artificial membrane. Gradient reverse elution was used to develop a linear correlation model for the capacity factors k_IAM and the in vivo logarithmic values of brain-to-blood drug concentration ratios (log BB) with R of 0.9851. Eleven additional pharmaceuticals were determined by the same method to predict their potential to penetrate the blood–brain barrier. The reported analytical method represents an alternative tool for rapid and noninvasive assessment of the absorption properties of chemicals, especially for the development of novel drugs. The retention of the studied compounds on the immobilized artificial membrane column was also compared with three other C18-based stationary phases. Herein, the results of the HPLC determination of drugs using an immobilized artificial membrane are briefly discussed with respect to a general application of the method for evaluating a broader spectrum of pharmaceutical compounds.     

Investigation on the thermal decomposition and flame retardancy of wood treated with a series of molybdates by TG–MS

A flame-retardant wood was prepared using a series of insoluble molybdates through the double bath technique. The flame retardancy of the wood samples was studied with the limiting oxygen index (LOI) method. The relationships between the flame-retardant performance and the thermal property of wood were studied by the thermogravimetry (TG), derivative thermogravimetry (DTG), differential thermal analysis (DTA), scanning electron microscopy (SEM), and the thermogravimetry–mass spectrometry (TG–MS) analysis methods. The results showed that the insoluble molybdates, which were precipitated into the wood by the double bath technique, can obviously improve the flame retardancy of wood. Similarly, the transition metal molybdates showed higher flame-retardant efficiency than the main group metal molybdates do, which probably due to the thermal barrier effect that Fe₂(MoO₄)₃ acts during the combustion of the samples. At the same time, Fe₂(MoO₄)₃ catalyzed the dehydration and carbonization reactions of wood, and caused an increase in the amount of char produced, and an improvement of the stability of the char residue. Moreover, the mass spectrometry results indicated that the excess transition metal ions speed up the deep decomposition of the char residue, and resulting in the smoldering of wood.     

Molecular Recognition of Hydrocarbon Guests by a Supramolecular Capsule Formed by the 4:4 Self-Assembly of Tris(Zn2+–Cyclen) and Trithiocyanurate in Aqueous Solution

We have previously reported that the trimeric Zn²⁺–cyclen complex (tris(Zn²⁺–cyclen), [Zn₃L¹]⁶⁺) and the trianion of trithiocyanuric acid (TCA³⁻) assembled in a 4:4 ratio to form a cuboctahedral supramolecular cage, [(Zn₃L¹)₄(TCA³⁻)₄]¹²⁺ (hereafter referred to as a Zn–cage), in neutral aqueous solution (cyclen=1,4,7,10-tetraazacyclododecane). Herein, we examined the molecular recognition of C₁–C₁₂ hydrocarbons (C_nH_(2n+2) (n≈1–12)), cyclopentane, cyclododecane, cis-decalin, and trans-decalin by the Zn–cage under normal atmospheric pressure. This cage complex was also able to encapsulate guest molecules that had larger volumes than that of the inner cavity of the Zn–cage, thereby suggesting that the inner shape of the Zn–cage was flexible. Computational simulations of Zn–cage–guest complexes provided support for this conclusion. Moreover, the solvent-accessible surface areas (SASA) of the Zn–cage host, guest molecules, and the Zn–cage-guest complexes were calculated and the data were used to explain the order of stability determined by the guest-replacement experiments. The storage of volatile molecules in aqueous solution by the Zn–cage is also discussed.     

Characterization of Nucleotides and Nucleotide Sugars in Candida albicans by High Performance Liquid Chromatography–Mass Spectrometry with a Porous Graphite Carbon Column

An optimized high performance liquid chromatography electrospray ionization/tandem mass spectrometry method was developed and optimized for the determination of seven nucleotides and nucleotide sugars in the extract of Candida albicans. The chromatographic separation was performed on a porous graphitic carbon column with gradient elution using acetonitrile and aqueous ammonia acetate containing 0.1% formic acid adjusted to pH 8.8. Negative-ion mode electrospray ionization mass spectrometry was applied to improve the selectivity and sensitivity of the analysis. The calibration curves showed excellent linearity over approximately three orders of magnitude with correlation coefficients exceeding 0.9946. The relative standard deviations of measurements were smaller than 4% (n = 5) and the accuracy of the intra-day and inter-day measurements were between 95.2% and 106.7%. The extraction recovery of each component was within satisfactory ranges. The validated method was applied to characterize the nucleotides metabolic profiles of the biofilm compared to the planktonic mode to evaluate changes of energy states in different growth modes of C. albicans. The levels of nucleotides and nucleotide sugar in the biofilm model treated with 5-fluoropyrimidine, baicalein, and sodium houttuyfonate were determined to investigate their effects on nucleotide metabolism and the mechanisms of antifungal agents.     

One-pot synthesis of ketones and lactones by oxidation of the parent hydrocarbons with KHSO5 catalyzed by manganese(III) porphyrins in a biphasic,solid–liquid,system

The oxidation of alkanes to ketones and lactones by Oxone® (KHSO₄×K₂SO₄×2KHSO₅) catalyzed by manganese porphyrins has been studied in an anhydrous two-phase (solid Oxone®/DCE solution) catalytic system. Under the experimental conditions adopted, i.e., an excess of Oxone® over the organic substrate and catalytic amount of Mn(TDCPP)Cl, almost complete hydrocarbon conversions are obtained. Acyclic alkanes give ketones as main oxygenated product whereas cyclic alkanes give mainly lactones together with minor amounts of alcohols and ketones. The overall process leading to lactones involves two subsequent manganese porphyrin catalyzed oxidative steps and a stoichiometric reaction involving monopersulfate and the intermediate ketone. The lack of a water phase and of strong acids prevents the hydrolysis of the lactones formed. The products are obtained in yields ranging from low to fair depending on the nature of substrate, catalyst, and on phase transfer agent concentration.     

Mineralization and Kinetics of Reactive Brilliant Red X-3B by a Combined Anaerobic–Aerobic Bioprocess Inoculated with the Coculture of Fungus and Bacterium

Mineralization of Reactive Brilliant Red X-3B by a combined anaerobic–aerobic process which was inoculated with the co-culture of Penicillium sp. QQ and Exiguobacterium sp. TL was studied. The optimal conditions of decolorization were investigated by response surface methodology as follows: 132.67 g/L of strain QQ wet spores, 1.09 g/L of strain TL wet cells, 2.25 g/L of glucose, 2.10 g/L of yeast extract, the initial dye concentration of 235.14 mg/L, pH 6.5, and 33 °C. The maximal decolorization rate was about 96 % within 12 h under the above conditions. According to the Haldane kinetic equation, the maximal specific decolorization rate was 89.629 mg/g˙h. It was suggested that in the anaerobic–aerobic combined process, decolorization occurred in the anaerobic unit and chemical oxygen demand (COD) was mainly removed in the aerobic one. Inoculation of fungus QQ in the anaerobic unit was important for mineralization of X-3B. Besides, the divided anaerobic–aerobic process showed better performance of COD removal than the integrated one. It was suggested that the combined anaerobic–aerobic process which was inoculated with co-culture was potentially useful for the field application.     

Comments on the Implementation of a Simple Peak Capacity Optimization Procedure and Comparison of Poly(styrene–divinylbenzene) and RP-18 Silica Monolithic Capillary Columns of 5-cm for the Analysis of Protein Digests

For the analysis of protein digests, the peak capacity in reversed-phase liquid chromatography is of paramount importance. A univariate method to maximize the peak capacity as developed by Wang et al. (Anal Chem 78:3406–3416, 20) has been applied and tested for a monolithic RP-18 silica capillary column. In their method, using model peptides representing a bovine serum albumin digest, the gradient time and temperature are kept constant while the flow rate and eluent strength are varied. Despite our criticism on the fixed starting conditions, a long gradient time leading to an unnecessary long analysis time and a high temperature leading to possible degradation products in the chromatogram, and the peak capacity as the only optimization parameter this fast and simple optimization strategy turns out to be applicable to capillary monolithic columns. Furthermore, the influence of the peak capacity on a second optimization parameter, the MS protein identification score, is examined. The procedure is also used to enhance the performance of two popular types of monolithic capillary LC columns (silica-C18 and poly(styrene–divinylbenzene)) of the same length for the analysis of protein digests. Comparison of both columns show that the calculated chromatographic parameters, like productivity and peak capacity, and identification score for both columns are about the same. For a more complicated nine-protein digest the performance of the silica monolith is slightly better.

     

Comments on the Implementation of a Simple Peak Capacity Optimization Procedure and Comparison of Poly(styrene–divinylbenzene) and RP-18 Silica Monolithic Capillary Columns of 5-cm for the Analysis of Protein Digests

For the analysis of protein digests, the peak capacity in reversed-phase liquid chromatography is of paramount importance. A univariate method to maximize the peak capacity as developed by Wang et al. (Anal Chem 78:3406–3416, 20) has been applied and tested for a monolithic RP-18 silica capillary column. In their method, using model peptides representing a bovine serum albumin digest, the gradient time and temperature are kept constant while the flow rate and eluent strength are varied. Despite our criticism on the fixed starting conditions, a long gradient time leading to an unnecessary long analysis time and a high temperature leading to possible degradation products in the chromatogram, and the peak capacity as the only optimization parameter this fast and simple optimization strategy turns out to be applicable to capillary monolithic columns. Furthermore, the influence of the peak capacity on a second optimization parameter, the MS protein identification score, is examined. The procedure is also used to enhance the performance of two popular types of monolithic capillary LC columns (silica-C18 and poly(styrene–divinylbenzene)) of the same length for the analysis of protein digests. Comparison of both columns show that the calculated chromatographic parameters, like productivity and peak capacity, and identification score for both columns are about the same. For a more complicated nine-protein digest the performance of the silica monolith is slightly better.     

Preparation of chitosan nanoparticles by TPP ionic gelation combined with spray drying,and the antibacterial activity of chitosan nanoparticles and a chitosan nanoparticle–amoxicillin complex

Chitosan nanoparticles were prepared from chitosan with various molecular weights by tripolyphosphate (TPP) ionic gelation combined with a spray drying method. The morphologies and characteristics of chitosan nanoparticles were determined by TEM, FE-SEM and from their mean sizes and zeta potentials. The effect of chitosan molecular weight (130, 276, 760 and 1200 cPs) and size of spray dryer nozzle (4.0, 5.5 and 7.0 µm) on mean size, size distribution and zeta potential values of chitosan nanoparticles was investigated. The results showed that the mean size of chitosan nanoparticles was in the range of 166–1230 nm and the zeta potential value ranged from 34.9 to 59 mV, depending on the molecular weight of chitosan and size of the spray dryer nozzles. The lower the molecular weight of chitosan, the smaller the size of the chitosan nanoparticles and the higher the zeta potential. A test for the antibacterial activity of chitosan nanoparticles (only) and a chitosan nanoparticle–amoxicillin complex against Streptococcus pneumoniae was also conducted. The results indicated that a smaller chitosan nanoparticle and higher zeta potential showed higher antibacterial activity. The chitosan nanoparticle–amoxicillin complex resulted in improved antibacterial activity as compared to amoxicillin and chitosan nanopaticles alone. Using a chitosan nanoparticle–amoxicillin complex could reduce by three times the dosage of amoxicillin while still completely inhibiting S. pneumoniae.     

Mechanistic studies on the N-formylation of amines with CO2 and hydrosilane catalyzed by a Cu–diphosphine complex

The reaction mechanism, reaction intermediates, and catalytically active species of the Cu–diphosphine-catalyzed N-formylation of amines (R¹R²NH) with CO₂ and hydrosilane were investigated. The NMR and kinetic experiments show that the catalytically active species is a Cu-hydride–diphosphine complex, which was generated from the Cu precursor, diphosphine ligand, and hydrosilane. Isotopic experiments using ¹³CO₂ and deuterated hydrosilane revealed the incorporation of the carbonyl group of CO₂ and the H atom of Si–H moiety into the formamide (R¹R²NCHO) product. The formation of a Cu-formate species as an intermediate of the reaction was clarified by in situ ¹H and ¹³C NMR studies.