Use of cationic surfactant-xylenol orange indicator in metals complexometry by back-titration with EDTA.

The interaction of the xilenol orange and commercial disinfectant containing itself cationic-surfactant allowed the use indicator up to pH 11 by back-titration with EDTA, and the determination of total or partial concentration of metallic ions samples using the same indicator at the highest pH range.

Dioctadecyldimethylammonium bromide vesicles prepared by the surfactant removal method

Dioctadecyldimethylammonium bromide (DODAB) is a double chain vesicle-forming cationic surfactant, whereas octa-ethyleneglycol mono-n-dodecyl ether (C12E8) is a single chain micelle-forming nonionic surfactant. At room temperature (ca. 22 degrees C) C12E8 molecules self-assemble in water as micelles while DODAB is insoluble. A mixture of DODAB and C12E8, however, can be soluble in water at room temperature depending on the relative amount of the compounds. We report the formation of small unilamellar vesicles (SUVs) by dialyzing at room temperature a mixture of 1.0 mM DODAB with 10 mM C12E8 in water. Extended bilayers are formed as well in equilibrium with vesicles. Such structures are viewed by a cryogenic transmission electron microscopy (cryo-TEM) image. (c) 2006 Elsevier B.V. All rights reserved.

Immobilization and electrochemical properties of anionic complexes on a V2O5/surfactant nanocomposite

in this work, we report a new way of modifying an electrode by combining the intrinsic conductivity property of vanadium pentoxide xerogel with its water insolubility in the presence of the cationic surfactant N-cetyl-N,N,N,trimethyl-ammonium bromide (CTA(+)Br(-)). The obtained hybrid compound enables the immobilization of electroactive anions such as hexacyanoferrate (III) ([Fe(CN)(6)](3-)) and its analogue pentacyanonitrosylferrate (II) ([Fe(CN)(5)NO](2-)), rather than cations. (C) 2002 Elsevier B.V. B.V. All rights reserved.

beta-ZnMoO4 microcrystals synthesized by the surfactant-assisted hydrothermal method: Growth process and photoluminescence properties

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The mechanism of dephosphorylation of bis(2,4-dinitrophenyl) phosphate in mixed micelles of cationic surfactants and lauryl hydroxamic acid

(Figure Presented) Mixed micelles of cetyltrimethylammonium bromide (CTABr) or dodecyltrimethylammonium bromide (DTABr) and the α-nucleophile, lauryl hydroxamic acid (LHA) accelerate dephosphorylation of bis(2,4-dinitrophenyl) phosphate (BDNPP) over the pH range 4-10. With a 0.1 mole fraction of LHA in DTABr or CTABr, dephosphorylation of BDNPP is approximately 10 4-fold faster than its spontaneous hydrolysis, and monoanionic LHA - is the reactive species. The results are consistent with a mechanism involving concurrent nucleophilic attack by hydroxamate ion (i) on the aromatic carbon, giving an intermediate that decomposes to undecylamine and 2,4-dinitrophenol, and (ii) at phosphorus, giving an unstable intermediate that undergoes a Lossen rearrangement yielding a series of derivatives including N,N-dialkylurea, undecylamine, undecyl isocyanate, and carbamyl hydroxamate. © 2009 American Chemical Society.

Enhancement of voltammetric determination of quinizarine based on the adsorption at surfactant-adsorbed-layer in disposable electrodes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of surfactants and polyethylene glycol on the activity and stability of a lipase from oilseeds of Pachira aquatica

Lipases from oilseeds have a great potential for commercial exploration as industrial enzymes. Lipases are used mixed with surfactants in cleaning and other formulated products, and accordingly, both components must be compatible with each other. This work presents the results of the effects of anionic, cationic and nonionic surfactants, polyethylene glycol and urea on the activity and stability of a lipase extracted of oilseeds from Pachira aquatica. The enzyme was purified and the spectrophotometric assays were done using p-nitrophenyl acetate (p-NPA) as substrate pH 7.5 and 25 degrees C. The activity was significantly enhanced by the cationic surfactant CTAB. Bile salts increased the lipase activity in the tested concentration range, whereas anionic and nonionic surfactants showed an inhibitory effect. Aqueous solutions of PEG activated the lipase and maximum activation (161%) occurred in PEG 12,000. This effect on lipase that can be due to exposition of some hydrophobic residues located in the vicinity of the active site or aggregation.

Aggregation behavior of aqueous dioctadecyldimethylammonium bromide/monoolein mixtures: A multitechnique investigation on the composition and temperature

A recently described non-viral gene delivery system [dioctadecyldimethylammonium bromide (DODAB)/monoolein (MO)] has been studied in detail to improve knowledge on the interactions between lamellar (DODAB) and non-lamellar-forming (MO) lipids, as a means to enhance their final cell transfection efficiency. Indeed, the morphology, fluidity, and size of these cationic surfactant/neutral lipid mixtures play an important role in the ability of these systems to complex nucleic acids. The different techniques used in this work, namely dynamic light scattering (DLS), fluorescence spectroscopy, differential scanning calorimetry (DSC), cryogenic transmission electron microscopy (cryo-TEM), light microscopy (LM), and surface pressure-area isotherms, allowed fully characterization of the phase behavior and aggregate morphology of DODAB/MO mixtures at different molar ratios. Overall, the results indicate that the final morphology of DODAB/MO aggregates depends on the balance between the tendency of DODAB to form zero-curvature bilayer structures and the propensity of MO to form non-bilayer structures with negative curvature. These results also show that in the MO-rich region, an increase in temperature has a similar effect on aggregate morphology as an increase in MO concentration. (C) 2012 Elsevier B.V. All rights reserved.

ZnO architectures synthesized by a microwave-assisted hydrothermal method and their photoluminescence properties

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Structural organization of cetyltrimethylammonium sulfate in aqueous solution: the effect of Na2SO4

We used dynamic light scattering (DLS), a steady-state fluorescence, time resolved fluorescence quenching (TRFQ), tensiometry, conductimetry, and isothermal titration calorimetry (ITC) to investigate the self-assembly of the cationic surfactant cetyltrimethylammonium sulfate (CTAS) in aqueous solution, which has SO42- as divalent counterion. We obtained the critical micelled concentration (cmc), aggregation number (N-agg), area per monomer (a(0)), hydrodynamic radius (R-H), and degree of counterion dissociation (alpha) of CTAS micelles in the absence and presence of up to 1 M Na2SO4 and at temperatures of 25 and 40 degrees C. Between 0.01 and 0.3 M salt the hydrodynamic radius of CTAS micelle R-H approximate to 16 angstrom is roughly independent on Na2SO4 concentration; below and above this concentration range R-H increases steeply with the salt concentration, indicating micelle structure transition, from spherical to rod-like structures. R-H increases only slightly as temperature increases from 25 to 40 degrees C, and the cmc decreases initially very steeply with Na2SO4 concentration up to about 10 mM, and thereafter it is constant. The area per surfactant at the water/air interface, a(0), initially increases steeply with Na2SO4 concentration, and then decrases above ca. 10 mM. Conductimetry gives alpha = 0.18 for the degree of counterion dissociation, and N-agg obtained by fluorescence methods increases with surfactant concentration but it is roughly independent of up to 80 mM salt. The ITC data yield cmc of 0.22 mM in water, and the calculated enthalpy change of micelle formation, Delta H-mic = 3.8 kJ mol(-1), Gibbs free energy of micellization of surfactant molecules, Delta G(mic) = -38.0 kJ mol(-1) and entropy T Delta S-mic = 41.7 kJ mol(-1) indicate that the formation of CTAS micelles is entropy-driven. (c) 2006 Elsevier B.V. All rights reserved.

Zirconia needles synthesized inside hexagonal swollen liquid crystals

We report the synthesis of zirconia microneedles by the direct nucleation of particles inside a hexagonal swollen liquid crystal (SLC) (cell parameter a = 27 nm) prepared by mixing with the proper ratio, an aqueous solution of sulfated zirconium colloids, a cationic surfactant (cetylpyridinium chloride), cychlohexane as swelling agent with an oil over water ratio of 2.5 (vol.), and 1-pentanol as cosurfactant. After a slow crystallogenesis that can be enhanced by an initial induction step under moderate temperature, particles in the centimeter range can be obtained, with a very high shape ratio (over 100). These particles are made of crystalline octahydrate zirconium oxychloride containing pores of 20 nm diameter, aligned along the main axis of the liquid crystal, as the fingerprint of the oil cylinders present in the hexagonal phase. The morphology of these particles confirms that the shaping mechanism is based on true liquid crystal templating (TLCT). Further thermal treatment of these particles, after extraction from the SLC, leads to the crystallization of zirconia with the same needlelike morphology as the zirconium oxychloride.

Effect of different surfactants on the shape, growth and photoluminescence behavior of MnWO4 crystals synthesized by the microwave-hydrothermal method

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Síntese e caracterização de um esterquat: um tipo de surfactante catiônico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Caracterização bioquímica de lipase extraída de sementes oleaginosas de Pachira aquatica

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

On the incorporation of the non-steroidal anti-inflammatory naproxen into cationic O/W microemulsions

Microemulsions (ME) containing hexadecyltrimethylammonium bromide (HTAB)/ethanol as surfactant, isopropylmyristate (IM) or butylstearate (BS) as oil phase and aqueous buffer were studied. Pseudo-ternary phase diagrams of the investigated systems were obtained at constant surfactant/cosurfactant molar ratio (1:5) by titration in order to characterize the proportions between the components to obtain clear systems. Oil in water microemulsions were prepared in a wide range of phase volume (phi). UV-vis absorption spectra of naproxen at pH 5.5 showed that the solubility of Np increases significantly in the presence of O/W ME in high phase volumes. For both, IM and BS microemulsions, the dynamic light scattering experiments showed that the size of the oil droplets remains constant in low values of phi, increasing abruptly in high phi values. Phase solubility study revealed that for both IM and BS microemulsions, the drug incorporation followed a straight-line profile in all range of phi. The data could be analyzed through the phase-separation model and the association constants (K) calculated varied from 27 to 90 M-1, depending on the pH and on the microemulsion oil phase. (c) 2005 Elsevier B.V. All rights reserved.