Mechanism of action of Bacillus thuringiensis toxins

The selectivity of Bacillus thuringiensis toxins is determined both by the toxin structure and by factors inherent to the insect. These toxins contain distinct domains that appear to be functionally important in toxin binding to protein receptors in the midgut of susceptible insects, and the subsequent formation of a pore in the insect midgut epithelium. In this article features necessary for the insecticidal activity of these toxins are discussed. These include toxin structure, toxin processing in the insect midgut, the identification of toxin receptors in susceptible insects, and toxin pore formation in midgut cells. In addition a number of B. thuringiensis toxins act synergistically to exert their full insecticidal activity. This synergistic action is critical not only for expressing the insecticidal activity of these toxins, but could also play a role in delaying the onset of insect resistance.

Separation and Mapping of Chromosomes of Parasitic Protozoa

Many protozoan parasites represent an important group of human pathogens. Pulsed Field Gradient Gel Electrophoresis (PFGE) analysis has been an important tool for fundamental genetic studies of parasites like Trypanosoma, Leishmania, Giardia or the human malaria parasite Plasmodium falciparum. We present PFGE conditions allowing a high resolution separation of chromosomes ranging from 500 to 4000 kb within a two day electrophoresis run. In addition, we present conditions for separating large chromosomes (2000-6000 kb) within 36 hr. We demontrate that the application of two dimentional PFGE (2D-PFGE) technique to parasite karyotypes is a very useful method for the analysis of dispersed gene families and comparative studies of the intrachomosomal genome organization

Evaluation of the role of ATP-binding cassette transporters as a defence mechanism against temephos in populations of Aedes aegypti

The role of ATP-binding cassette (ABC) transporters in the efflux of the insecticide, temephos, was assessed in the larvae of Aedes aegypti. Bioassays were conducted using mosquito populations that were either susceptible or resistant to temephos by exposure to insecticide alone or in combination with sublethal doses of the ABC transporter inhibitor, verapamil (30, 35 and 40 μM). The best result in the series was obtained with the addition of verapamil (40 μM), which led to a 2x increase in the toxicity of temephos, suggesting that ABC transporters may be partially involved in conferring resistance to the populations evaluated.

Ion-selective electrodes: historical, mechanism of response, selectivity and concept review

This paper presents a review of the concepts involved in the working mechanism of the ion-selective electrodes, searching a historical overview, moreover to describe the new advances in the area.

Mechanism of 3,4-dihydroxybenzaldehyde electropolymerization at carbon paste electrodes: catalytic detection of NADH

Cyclic voltammetry was used to study 3,4-dihydroxybenzaldehyde (3,4-DHB) electropolymerization processes on carbon paste electrodes. The characteristics of the electropolymerized films were highly dependent on pH, anodic switching potential, scan rate, 3,4-DHB concentrations and number of cycles. Film stability was determined in citrate/phosphate buffer solutions at the same pH used during the electropolymerization process. The best conditions to prepare carbon paste modified electrodes were pH 7.8; 0.0 <= Eapl <= 0.25 V; 10 mV s-1; 0.25 mmol L-1 3,4-DHB and 10 scans. These carbon paste modified electrodes were used for NADH catalytic detection at 0.23 V in the range 0.015 <= [NADH] <= 0.21 mmol L-1. Experimental data were used to propose a mechanism for the 3,4--DHB electropolymerization processes, which involves initial phenoxyl radical formation.

Ultra-trace monitoring of copper in environmental and biological samples by inductively coupled plasma atomic emission spectrometry after separation and preconcentration by using octadecyl silica membrane disks modified by a new schiff's base

Ultra-trace amounts of Cu(II) were separated and preconcentrated by solid phase extraction on octadecyl-bonded silica membrane disks modified with a new Schiff,s base (Bis- (2-Hydroxyacetophenone) -2,2-dimethyl-1,3-propanediimine) (SBTD) followed by elution and inductively coupled plasma atomic emission spectrometric detection. The method was applied as a separation and detection method for copper(II) in environmental and biological samples. Extraction efficiency and the influence of sample matrix, flow rate, pH, and type and minimum amount of stripping acid were investigated. The concentration factor and detection limit of the proposed method are 500 and 12.5 pg mL-1, respectively.

Flow analysis by using solenoid valves for As(III) determination in natural waters by an on-line separation and pre-concentration system coupled to a tungsten coil atomizer

A flow system coupled to a tungsten coil atomizer in an atomic absorption spectrometer (TCA-AAS) was developed for As(III) determination in waters, by extraction with sodium diethyldithiocarbamate (NaDDTC) as complexing agent, and by sorption of the As(III)-DDTC complex in a micro-column filled with 5 mg C18 reversed phase (10 µL dry sorbent), followed by elution with ethanol. A complete pre-concentration/elution cycle took 208 s, with 30 s sample load time (1.7 mL) and 4 s elution time (71 µL). The interface and software for the synchronous control of two peristaltic pumps (RUN/ STOP), an autosampler arm, seven solenoid valves, one injection valve, the electrothermal atomizer and the spectrometer Read function were constructed. The system was characterized and validated by analytical recovery studies performed both in synthetic solutions and in natural waters. Using a 30 s pre-concentration period, the working curve was linear between 0.25 and 6.0 µg L-1 (r = 0.9976), the retention efficiency was 94±1% (6.0 µg L-1), and the pre-concentration coefficient was 28.9. The characteristic mass was 58 pg, the mean repeatability (expressed as the variation coefficient) was 3.4% (n=5), the detection limit was 0.058 µg L-1 (4.1 pg in 71 µL of eluate injected into the coil), and the mean analytical recovery in natural waters was 92.6 ± 9.5 % (n=15). The procedure is simple, economic, less prone to sample loss and contamination and the useful lifetime of the micro-column was between 200-300 pre-concentration cycles.

Polímeros biomiméticos em química analítica. Parte 1: preparo e aplicações de MIP ("Molecularly Imprinted Polymers") em técnicas de extração e separação

MIPs are synthetic polymers that are used as biomimetic materials simulating the mechanism verified in natural entities such as antibodies and enzymes. Although MIPs have been successfully used as an outstanding tool for enhancing the selectivity or different analytical approaches, such as separation science and electrochemical and optical sensors, several parameters must be optimized during their synthesis. Therefore, the state-of-the-art of MIP production as well as the different polymerization methods are discussed. The potential selectivity of MIPs in the extraction and separation techniques focusing mainly on environmental, clinical and pharmaceutical samples as applications for analytical purposes is presented.

Preparative separation of flavonoids from the medicinal plant Davilla elliptica St. Hill. by high-speed counter-current chromatography

High-speed counter-current chromatography (HSCCC) is a major tool for the fast separation of natural products from plants. It was used for the preparative isolation of the flavonoid monoglucosides present in the aerial parts of the Davilla elliptica St. Hill. (Dilleniaceae). This species is used in Brazilian folk medicine for the treatment of gastric disorders. The optimum solvent system used was composed of a mixture of ethyl acetate-n-propanol-water (140:8:80, v/v/v) and led to a successful separation of quercetin-3-O-alpha-L-rhamnopyranoside and myricetin-3-O-alpha-L-rhamnopyranoside in approximately 3.0 hours with purity higher than 95%. Identification was performed by ¹H NMR, 13C NMR and HPLC-UV-DAD analyses.

Development of a flotation method for preconcentration-separation of trace amounts of some metal ions in plant tissues prior to their FAAS determinations

An efficient flotation method based on the combination of flame atomic absorption spectrometry (FAAS) and separation and preconcentration step for determination of Cr3+, Cu 2+, Co2+, Ni2+, Zn2+, Cd 2+, Fe3+ and Pb2+ ions in various real samples by the possibility of applying bis(2-hydroxyacetophenone)-1,4-butanediimine (BHABDI) as a new collector was studied. The influence of pH, amount of BHABDI as collector, sample matrix, type and amount of eluting agent, type and amount of surfactant as floating agent, ionic strength and air flow rates i.e. variables affecting the efficiency of the extraction system was evaluated. It is ascertained that metal ions such as iron can be separated simultaneously from matrix in the presence of 0.012 mM ligand, 0.025% (w/v) of CTAB to a test sample of 750 mL at pH 6.5. These ions can be eluted quantitatively with 6 mL of 1.0 mol L-1 HNO3 in methanol which lead to the enrichment factor of 125. The detection limits for analyte ions were in the range of 1.3-2.4 ng mL-1. The method has been successfully applied for determination of trace amounts of ions in various real samples.

Separation and preconcentration trace amounts of gold by using modified organo nanoclay closite 15A

The application of organo nanoclay 5-(4-dimethylamino-benzylidene) rhodanine-immobilized as a new, easily prepared, and stable solid sorbent for preconcentration trace amounts of Au(III) ions in aqueous solution is presented. The sorption of Au(III) ions was quantitative in the pH range of 2-4, and quantitative desorption occurred instantaneously with 10.0 mL of a mixture containing 0.5 mol L-1 Na2S2O3 and KSCN. Various parameters, such as the effect of pH, breakthrough volume, extraction time, and interference of a large number of anions and cations have been studied. The proposed method has been applied for determination of trace amount of gold in water samples.

Effect of the structure of commercial poly(ethylene oxide-b-propylene oxide) demulsifier bases on the demulsification of water-in-crude oil emulsions: elucidation of the demulsification mechanism

Water-in-crude oil emulsions are formed during petroleum production and asphaltenes play an important role in their stabilization. Demulsifiers are added to destabilize such emulsions,however the demulsification mechanism is not completely known. In this paper, the performances of commercial poly(ethylene oxide-b-propylene oxide) demulsifiers were studied using synthetic water-in-oil emulsions and model-systems (asphaltenes in organic solvent). No change in the asphaltene aggregate size induced by the demulsifier was observed. The demulsification performance decreased as the asphaltene aggregate size increased, so it can be suggested that the demulsification mechanism is correlated to the voids between the aggregates adsorbed on the water droplets surface.

Preparative separation and purification of sesquiterpenoids from tussilago farfara l. by high-speed counter-current chromatography

Preparative high-speed counter-current chromatography (HSCCC) was successfully applied for separation and purification of sesquiterpenoids from an extract of Tussilago farfara L. with a two-phase solvent system composed of n-hexane-ethyl acetate- methanol-water (1:0.5:1.1:0.3, v/v/v/v). The separation produced a total of 32 mg of tussilagone, 18 mg of 14-acetoxy-7β-(3'-ethyl cis-crotonoyloxy)-lα-(2'-methyl butyryloxy)-notonipetranone and 21 mg of 7β-(3'-ethyl cis-crotonoyloxy)-lα-(2'- methyl butyryloxy)-3,14-dehydro-Z-notonipetranone from 500 mg of the crude extract in one step separation with the purity of 99.5, 99.4 and 99.1%, respectively, as determined by HPLC. The structures of these compounds were identified by ESI-MS, ¹H-NMR and 13C-NMR.

Electrocatalysis in wastewater treatment: recent mechanism advances

Over 50 years, several scientists and industries have developed new alternatives for wastewater treatment and remediation. Recently, electrochemical technology has been largely developed mainly because of its versatility and environmental compatibility. Scientific contributions about role of the electrode material have allowed determining that the influence of material in the selectivity is an important parameter. However, to interpret this behavior, comprehensive physical chemistry models for organics destruction, related to electrochemical phenomena and material surfaces, were proposed in the last decades. So, this paper presents a critical and comprehensive review about the principles and recent mechanism advances in electrocatalysis for wastewater treatment.

Dispersive liquid-liquid microextraction for the simultaneous separation of trace amounts of zinc and cadmium ions in water samples prior to flame atomic absorption spectrometry determination

In the proposed method, carbon tetrachloride and ethanol were used as extraction and dispersive solvents. Several factors that may be affected on the extraction process, such as extraction solvent, disperser solvent, the volume of extraction and disperser solvent, pH of the aqueous solution and extraction time were optimized. Under the optimal conditions, linearity was maintained between 1.0 ng mL-1 to 1.5 mg mL-1 for zinc and 1.0 ng mL-1 to 0.4 mg mL-1 for cadmium. The proposed method has been applied for determination of trace amount of zinc and cadmium in standard and water samples with satisfactory results.