Water cavities of sH clathrate hydrate stabilized by molecular hydrogen: phase equilibrium measurements

In this experimental phase equilibrium study, we show for the first time that it is possible to stabilize structure sH of hydrogen clathrate hydrate with the help of some selected promoters. It was established that the formation pressures of these systems are significantly higher than that of structure sII of hydrogen clathrate hydrate when tetrahydrofuran (THF) is used as a promoter. Although no experimental evidence is available yet, it is estimated that the hydrogen storage capacity of structure sH can be as high as 1.4 wt % of H2, which is about 40% higher compared to the hydrogen storage capacity in structure sII.     

Development of liquid phase microextraction method based on solidification of floated organic drop for extraction and preconcentration of organochlorine pesticides in water samples

A simple and efficient liquid-phase microextraction (LPME) in conjunction with gas chromatography-electron capture detector (GC-ECD) has been developed for extraction and determination of 11 organochlorine pesticides (OCPs) from water samples. In this technique a microdrop of 1-dodecanol containing pentachloronitrobenzene (internal standard) is delivered to the surface of an aqueous sample while being agitated by a stirring bar in the bulk of solution. Following completion of extraction, the sample vial was cooled by putting it into an ice bath for 5 min. Finally 2 μL of the drop was injected into the GC for analysis. Factors relevant to the extraction efficiency were studied and optimized. Under the optimized extraction conditions (extraction solvent: 1-dodecanol; extraction temperature: 65 °C; sodium chloride concentration: 0.25 M; microdrop and sample volumes: 8 μL and 20 mL respectively; the stirring rate: 750 rpm and the extraction time: 30 min), figures of merit of the proposed method were evaluated. The detection limits of the method were in the range of 7-19 ng L⁻¹ and the RSD% for analysis of 2 μg L⁻¹ of OCPs was below 7.2% (n = 5). A good linearity (r² ≥ 0.993) and a relatively broad dynamic linear range (25-2000 ng L⁻¹) were obtained. After 30 min of extraction, preconcentration factors were in the range of 708-1337 for different organochlorine pesticides and the relative errors ranged from −10.1 to 10.9%. Finally the proposed method was successfully utilized for preconcentration and determination of OCPs in different real samples.     

Extraction and determination of organophosphorus pesticides in water samples by a new liquid phase microextraction-gas chromatography-flame photometric detection

A rapid, sensitive and efficient liquid phase microextraction (LPME) method was developed to determine trace concentrations of some organophosphorus pesticides in water samples. This method combines liquid phase microextraction with gas chromatographic (GC) analysis in a simple and inexpensive apparatus involving very little organic solvent consumption. It involves exposing a floated drop of an organic solvent on the surface of aqueous solution in a sealed vial. Experimental parameters which control the performance of LPME such as type of organic solvent, organic solvent and sample volumes, sample stirring rate, sample solution temperature, salt addition and exposure time were investigated and optimized. Finally, the enrichment factor, dynamic linear range (DLR), limit of detection (LOD) and precision of the method were evaluated by the water samples spiked with organophosphorus pesticides. Using optimum extraction conditions, very low detection limits (0.01-0.04 μg L⁻¹) and good linearities (0.9983 < r² < 0.9999) were achieved. The LPME was performed for determination of organophosphorus pesticides in different types of natural water samples and acceptable recoveries (96-104%) and precisions (3.5 < R.S.D.% < 8.9) were obtained. The results suggested that the newly proposed LPME method is a rapid, accurate and effective sample preparation method and could be successfully applied for extraction and determination of organophosphorus pesticides in water samples.     

On-line metals preconcentration and simultaneous determination using cloud point extraction and inductively coupled plasma optical emission spectrometry in water samples

A new on-line cloud point extraction (CPE) system coupled to ICP-OES was designed for simultaneous extraction, preconcentration and determination of Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Fe³⁺ and Mn²⁺ ions in water samples. This is based on the complexation of the metal ions with 1-(2-thenoyl)-3,3,3-trifluoraceton reagent (TTA) at pH 6.0 in the presence of non-ionic surfactant of Triton X-114. The micellar solution was heated above 60 °C and loaded through a column packed with cotton, which acts as a filter for retaining the analyte-entrapped surfactant-rich phase. Then the surfactant-rich phase was eluted using propanol:0.5 mol L⁻¹ nitric acid solution (75:25, v/v) at a flow rate of 3.0 mL min⁻¹ and directly introduced into the nebulizer of the ICP-OES. Several factors influencing the instrumental conditions and extraction were evaluated and optimized. Under the optimum conditions, the enhancement factors of the proposed method for target ions were between 42 and 97, the detection limits (DLs) were in the range of 0.1-2.2 μg L⁻¹. The relative standard deviations (R.S.D.s) at 100 μg L⁻¹ concentration levels of each ion were found to be less than 4.6%. Also, the calibration graphs were linear in the range of 0.5-100 μg L⁻¹ with the correlation coefficients within the range of 0.9948-0.9994.Finally, the developed method was successfully applied to the extraction and determination of the mentioned metal ions in the tap, well, sea and mineral water samples and satisfactory results were obtained.     

Identification and characterization of smallest pore-forming protein in the cell wall of pathogenic <Emphasis Type="Italic">Corynebacterium urealyticum</Emphasis> DSM 7109

Background

Corynebacterium urealyticum, a pathogenic, multidrug resistant member of the mycolata, is known as causative agent of urinary tract infections although it is a bacterium of the skin flora. This pathogenic bacterium shares with the mycolata the property of having an unusual cell envelope composition and architecture, typical for the genus Corynebacterium. The cell wall of members of the mycolata contains channel-forming proteins for the uptake of solutes.

Results

In this study, we provide novel information on the identification and characterization of a pore-forming protein in the cell wall of C. urealyticum DSM 7109. Detergent extracts of whole C. urealyticum cultures formed in lipid bilayer membranes slightly cation-selective pores with a single-channel conductance of 1.75 nS in 1 M KCl. Experiments with different salts and non-electrolytes suggested that the cell wall pore of C. urealyticum is wide and water-filled and has a diameter of about 1.8 nm. Molecular modelling and dynamics has been performed to obtain a model of the pore. For the search of the gene coding for the cell wall pore of C. urealyticum we looked in the known genome of C. urealyticum for a similar chromosomal localization of the porin gene to known porH and porA genes of other Corynebacterium strains. Three genes are located between the genes coding for GroEL2 and polyphosphate kinase (PKK2). Two of the genes (cur_1714 and cur_1715) were expressed in different constructs in C. glutamicum ΔporAΔporH and in porin-deficient BL21 DE3 Omp8 E. coli strains. The results suggested that the gene cur_1714 codes alone for the cell wall channel. The cell wall porin of C. urealyticum termed PorACur was purified to homogeneity using different biochemical methods and had an apparent molecular mass of about 4 kDa on tricine-containing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE).

Conclusions

Biophysical characterization of the purified protein (PorACur) suggested indeed that cur_1714 is the gene coding for the pore-forming protein in C. urealyticum because the protein formed in lipid bilayer experiments the same pores as the detergent extract of whole cells. The study is the first report of a cell wall channel in the pathogenic C. urealyticum.

     

Preparation of ion-imprinted polyvinyl sulfonate-grafted silica particles for trace enrichment of Th(IV) prior to determination by inductively coupled plasma-mass spectrometry

Grafting from polymerisation technique has been used to prepare Th(IV) ion-imprinted polyvinyl sulfonate (IIPVS)-bonded silica particles. The graft polymerisation of vinyl sulfonate (VS) on the surface of silica particles was achieved in aqueous medium through thermal decomposition of surface-bound azo initiators (60°C) in the presence of thorium ion. The prepared material was characterised by Fourier transform infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis. The entrapped template ion was then removed using 2 M HCl. The experimental batch rebinding data were successfully described by the Langmuir–Freundlich model. The prepared material was then packed to a PTFE micro-column (20 mm × 3.0 mm, id) to evaluate its efficiency in column operations prior to determination by inductively coupled plasma-mass spectrometry (ICP-MS). The limit of detection of the method and breakthrough capacity of the column was evaluated as 0.074 µg L^?1 and 0.83 mg g^?1, respectively. The selectivity of the prepared polymer towards Th(IV) ion was investigated in the presence of some foreign competitor ions, including U(VI). Finally, the proposed method has been used to determine Th(IV) ion in real samples.     

A simple approach for the preparation of simazine molecularly imprinted nanofibers via self-polycondensation for selective solid-phase microextraction

A novel molecularly imprinted sol-gel material based on polysiloxane nanofiber was introduced as a solid-phase microextraction coating on a stainless steel wire for the extraction of simazine. The nanostructured molecularly imprinted fiber was prepared by a simple single step method at room temperature, using methyltriethoxysilane as the sol-gel precursor and simazine as the template molecule. The fiber was applied for the extraction of simazine in different water samples followed by gas chromatography and mass spectrometry detection. The extraction capacity of the molecularly imprinted fiber was 8 ng, and it had better extraction efficiency than the non-imprinted fiber and commercial fibers (PDMS and PA). The fiber had also a good selectivity for simazine and its analogous compounds. Important parameters affecting the extraction and desorption efficiency, such as salt concentration, stirring rate, pH of sample solution, extraction time and temperature, temperature and time of desorption, were investigated. The intra- and inter-day relative standard deviations were in the range of 4.3–7.6%. The fiber-to-fiber reproducibility was 7.7–8.5%. The method showed a good linearity (r²> 0.9980) in the range of 0.02–20 μg L⁻¹ with the detection limit of 0.005 μg L⁻¹. The relative recoveries were also in the range of 94–97% for different water samples.     

Sulfonated nanohydroxyapatite functionalized with 2-aminoethyl dihydrogen phosphate (HAP@AEPH2-SO3H) as a reusable solid acid for direct esterification of carboxylic acids with alcohols

Research on Chemical Intermediates - Sulfonated nanohydroxyapatite functionalized with 2-aminoethyl dihydrogen phosphate (HAP@AEPH2-SO3H) efficiently catalyzed direct esterification of carboxylic...