Preparation of a clay-modified carbon paste electrode based on 2-thiazoline-2-thiol-hexadecylammonium sorption for the sensitive determination of mercury.
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A montmorillonite from Wyoming-USA was used to prepare an organo-clay complex, named 2-thiazoline-2-thiol-hexadecyltrimethylammonium-clay (TZT-HDTA-clay), for the purpose of the selective adsorption of the heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). Adsorption isotherms of Hg2+, Pb2+, Cd2+, Cu2+, and Zn2+ from aqueous solutions as a function of the pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The organo-clay complex was very selective to Hg(II) in aqueous solution in which other metals and ions were also present. The accumulation voltammetry of Hg(II) was studied at a carbon paste electrode chemically modified with this material. The mercury response was evaluated with respect to the pH, electrode composition, preconcentration time, mercury concentration, "cleaning" solution, possible interferences and other variables. A carbon paste electrode modified by TZT-HDTA-clay showed two peaks: one cathodic peak at about 0.0 V and an anodic peak at 0.25 V, scanning the potential from -0.2 to 0.8 V (0.05 M KNO3 vs. Ag/AgCl). The anodic peak at 0.25 V presents excellent selectivity for Hg(II) ions in the presence of foreign ions. The detection limit was estimated as 0.1 microg L(-1). The precision of determination was satisfactory for the respective concentration level. (+info)
An improved method for the flow-injection determination of iodine using the luminol chemiluminescence reaction in a reversed micellar medium of cetyltrimethylammonium chloride in 1-hexanol-cyclohexane.
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To eliminate the use of chlorinated hydrocarbons, we have improved the method for the flow-injection (FI) determination of iodine based on the chemiluminescence reaction of iodine with luminol in a chloroform-free reversed micellar medium of the surfactant cetyltrimethylammonium chloride (CTAC) using a mixture of 1-hexanol-cyclohexane as a bulk solvent. The FI procedure used simply involves the mixing of an iodine solution in cyclohexane with the chemiluminescent reagent solution of luminol in the reversed micellar medium of CTAC in 0.38 M 1-hexanol in cyclohexane/water (buffered with sodium carbonate). The optimum conditions for the iodine determination were evaluated and a detection limit (DL) of 0.05 ng cm(-3) iodine was achieved. The calibration graph obtained was linear with a dynamic range from the DL to 10 ng cm(-3) iodine. The relative standard deviations (n=5) observed at all concentrations within the linear range were less than 2.5%. The improved FI method is rapid and equally sensitive like the original one and was found to be suitable for the determination of trace iodine. (+info)
Structural transitions of confined model proteins: molecular dynamics simulation and experimental validation.
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Proteins fold in a confined space not only in vivo, i.e., folding assisted by molecular chaperons and chaperonins in a crowded cellular medium, but also in vitro as in production of recombinant proteins. Despite extensive work on protein folding in bulk, little is known about how and to what extent the thermodynamics and kinetics of protein folding are altered by confinement. In this work, we use a Go-like off-lattice model to investigate the folding and stability of an all beta-sheet protein in spherical cages of different sizes and surface hydrophobicity. We find whereas extreme confinement inhibits correct folding, a hydrophilic cage stabilizes the protein due to restriction of the unfolded configurations. In a hydrophobic cage, however, strong attraction from the cage surface destabilizes the confined protein because of competition between self-aggregation and adsorption of hydrophobic residues. We show that the kinetics of protein collapse and folding is strongly correlated with both the cage size and the surface hydrophobicity. It is demonstrated that a cage of moderate size and hydrophobicity optimizes both the folding yield and kinetics of structural transitions. To support the simulation results, we have also investigated the refolding of hen-egg lysozyme in the presence of cetyltrimethylammoniumbromide (CTAB) surfactants that provide an effective confinement of the proteins by micellization. The influence of the surfactant hydrophobicity on the structural and biological activity of the protein is determined with circular dichroism spectrum, fluorescence emission spectrum, and biological activity assay. It is shown that, as predicted by coarse-grained simulations, CTAB micelles facilitate the collapse of denatured lysozyme, whereas the addition of beta-cyclodextrin-grafted-PNIPAAm, a weakly hydrophobic stripper, dissociates CTAB micelles and promotes the conformational rearrangement and thereby gives an improved recovery of lysozyme activity. (+info)
Sorption of wastewater containing reactive red X-3B on inorgano-organo pillared bentonite.
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Bentonite is a kind of natural clay with good exchanging ability. By exchanging its interlamellar cations with various soluble cations, such as quaternary ammonium cations and inorganic metal ions, the properties of natural bentonite can be greatly improved. In this study, hexadecyltrimethylammonium bromide (HDTMA), CaCl(2), MgCl(2), FeCl(3), AlCl(3) were used as organic and inorganic pillared materials respectively to produce several kinds of Ca-, Mg-, Fe-, Al-organo pillared bentonites. Sorption of reactive red X-3B on them was studied to determine their potential application as sorbents in wastewater treatment. The results showed that these pillared bentonites had much improved sorption properties, and that the dye solutions' pH value had some effect on the performance of these inorgano-organo pillared bentonites. Isotherms of reactive X-3B on these pillared bentonites suggested a Langmuir-type sorption mechanism. (+info)
Enzymatic hydrolysis of microcrystalline cellulose in reverse micelles.
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The activities of cellulases from Trichoderma reesei entrapped in three types of reverse micelles have been investigated using microcrystalline cellulose as the substrate. The reverse micellar systems are formed by nonionic surfactant Triton X-100, anionic surfactant Aerosol OT (AOT), and cationic surfactant cetyltrimethyl ammonium bromide (CTAB) in organic solvent media, respectively. The influences of the molar ratio of water to surfactant omega0, one of characteristic parameters of reverse micelles, and other environmental conditions including pH and temperature, on the enzymatic activity have been studied in these reverse micellar systems. The results obtained indicate that these three reverse micelles are more effective than aqueous systems for microcrystalline cellulose hydrolysis, and cellulases show "superactivity" in these reverse micelles compared with that in aqueous systems under the same pH and temperature conditions. The enzymatic activity decreases with the increase of omega0 in both AOT and Triton X-100 reverse micellar systems, but reaches a maximum at omega0 of 16.7 for CTAB reverse micelles. Temperature and pH also influence the cellulose hydrolysis process. The structural changes of cellulases in AOT reverse micelles have been measured by intrinsic fluorescence method and a possible explanation for the activity changes of cellulases has been proposed. (+info)
Functional analysis of an endo-1,6-beta-D-glucanase gene (neg-1) from Neurospora crassa.
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The 1,6-beta-D-glucanase gene (neg1) of Neurospora crassa was disrupted by repeat-induced point mutations. Sequence analysis of the neg1 gene in the R12-1 mutant showed that 9 nucleotides within the coding region of the gene changed from GC to AT. The base transition of C to A at position 662 resulted in a codon. No apparent phenotypic changes were observed in the mutant, but Congo-red, SDS, and cetyltrimethyl ammonium bromide (CTAB), which affect fungal cell walls or membranes, markedly inhibited the hyphal growth of the mutant at a concentration that does not inhibit growth in the wild type. (+info)
Cationic lipids and surfactants as antifungal agents: mode of action.
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OBJECTIVES: To determine the mechanism of antimicrobial action for cationic lipid dioctadecyldimethylammonium bromide (DODAB) and hexadecyltrimethylammonium bromide (CTAB) against Candida albicans. METHODS: Determination of DODAB or CTAB adsorption isotherms; cell viability; cell electrophoretic mobility (EM); and leakage of small phosphorylated compounds, proteins or DNA from fungus or haemoglobin from erythrocytes. RESULTS: High affinity isotherms for CTAB and DODAB adsorption onto fungus cells (10(8) cfu/mL) yield limiting adsorption at 7.8 and 3.7 x 10(9) molecules per cell, respectively. Negatively charged C. albicans cells (10(6) cfu/mL) remain viable whereas positively charged ones die. At 0.3 mM CTAB or 0.01 mM DODAB, EM is zero and fungus viability is 50%. Cells start to die at submicellar CTAB concentrations and fungus lysis does not play a significant role in the mechanism of antifungal action. Over 0.1-10 mM CTAB or DODAB, there is no leakage of tested compounds from C. albicans cells despite the low cell viability. In contrast to the fungus, under isotonic conditions, cationic amphiphiles induce haemolysis over a range of low DODAB (>0.01 mM) and CTAB (>0.001 mM) concentrations. CONCLUSIONS: The critical phenomenon determining antifungal effect of cationic surfactants and lipids is not cell lysis but rather the change of cell surface charge from negative to positive. (+info)
Interaction of apoA-II from human high density lipoprotein with lysolecithin.
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The effects of lysolecithin and hexadecyltrimethylammonium bromide on the structure and stability of apoA-II from human high density lipoprotein have been evalued by circular dichroism and fluorescence measurements. There is a profound enhancement in the stability of apoA-II to guanidinium hydrochloride denaturation when it forms a phospholipid complex with lysolecithin micelles. This complex is not only resistant to guanidinium hydrochloride denaturation, but it can be formed in a 6 M solution of this denaturant. The behavior of apoA-II in the native human high density protein is much closer to that of the lysolecithin apoA-II complex than to that of the free apoA-II. (+info)