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The optimum culture conditions of Monodus subterraneus UTEX 151 for eicosapentaenoic acid (EPA) production were at 25 degrees C, initial pH 7.0 and continuous illumination at 10 Klux light. The gas chromatographic data indicated that the fatty acid composition 20:5n-3 was predominant, at approximately 31%. In addition, 16:1, was the major monounsaturated fatty acid, while the 22:6n-3 was absent. Cultivation in 20 mM sodium acetate slightly enhanced the content of EPA from 31% up to 34% of the total fatty acids. Light micrographs of M. subterraneus UTEX 151 showed that the cell shape changed from spherical to ellipsoidal, as cell maturity was achieved. When the cells were in stationary phase, these became elongated spindle-shaped ellipses. TEM data demonstrated lipid body formation occurring in the thylakoid space of the chloroplast. Lipid body size varied with growth phase stage and they finally formed round clusters. The ultrastructure of M. subterraneus UTEX 151 vegetative cells of early and stationary growth stage showed the presence of chloroplasts, with many lipid bodies in the cell. Starch granules and lipid bodies occupied an--equal volume in the cell.
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PMID:Morphology and eicosapentaenoic acid production by Monodus subterraneus UTEX 151. 1601 19

Aqueous solutions of the anionic surfactant potassium oleate (K-oleate) were studied using small-angle neutron scattering (SANS), steady-state rheology, and cryogenic transmission electron microscopy (cryo-TEM). The micellar structural changes induced by the addition of potassium chloride (KCl) and sodium polystyrenesulfonate (PSS) of different molecular weights were investigated. Upon addition of KCl, a transition from spherical to wormlike micelles was detected from the SANS data and confirmed by the cryo-TEM pictures. The rheological measurements revealed a strong dependence of the low-shear viscosity on the concentration of salt: a broad maximum in the viscosity curve was observed upon addition of KCl, characteristic of the growth of micelles into long worms, followed by branching. The addition of PSS to salt-free solutions of K-oleate had a significant effect on the scattering patterns, revealing partial growth of the spherical micelles into rodlike micelles. In contrast, in the presence of high salt concentrations, addition of PSS to solutions of wormlike micelles did not bring any noticeable modifications in the scattering. However, in the same salt conditions, a clear effect was observed on the low shear viscosity upon addition of PSS, which was found to depend significantly on molecular weight. This suggests a novel way of impacting the viscosity of solutions of wormlike micelles.
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PMID:Wormlike micelles mediated by polyelectrolyte. 1608 65

Polysaccharide multilayer nanocapsules have been fabricated in aqueous media by the layer-by-layer self-assembly of chitosan (CHI) and sodium alginate (ALG) on monodisperse polystyrene (PS) nanoparticles with a diameter of 180 nm as template, followed by removal of the templates through dissolving in THF. The pH and added salt concentration of the polyelectrolyte deposition solutions were optimized to ensure the alternating deposition. Consequently, the most suitable pH values were found to be 6.0-8.0 for ALG and 3.5 for CHI and were used in the deposition. The concentration of added NaCl used in the adsorption solutions was 0.5 M, which led to an average thickness of about 13 nm for 5 bilayers of CHI/ALG shell-wall. zeta-potential indicated the stepwise and alternating adsorption of CHI and ALG to form multilayer film on the PS nanoparticles. The characteristic bands of PS residue almost disappeared in the IR spectrum of the nanocapsule after dipped in THF, confirming thorough removal of PS templates from the core-shell particles. TEM, SEM and AFM were utilized to observe the nanocapsules of about 225 nm in diameter (by TEM). A hydrophilic drug model, acridine hydrochloride (AH), was chosen to investigate the loading and release properties of the nanocapsules. The positively charged AH spontaneously deposited into the capsule due to the electrostatic interaction with the negatively charged styrene sulfonate residues from the PS template inside the capsule. The rate of AH release became slightly slower when the capsule wall was cross-linked with glutaraldehyde, but the accumulative released amount for the cross-linked capsule was obviously reduced. These nanocapsules made from nature polysaccharides have a potential application in controlled drug release.
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PMID:Multilayer nanocapsules of polysaccharide chitosan and alginate through layer-by-layer assembly directly on PS nanoparticles for release. 1612 96

A new, facile and generally applicable synthesis of functionalized gold nanoparticles is presented. It is based on the surfactant-free generation of weakly stabilized nanoparticles by the reduction of HAuCl4 with sodium naphthalenide in diglyme. These nanoparticles were found to lack long-term stability. However, stabilization in both unpolar and polar solvents could straightforwardly be achieved by subsequent addition of various capping ligands. The resulting ligand-capped gold nanoparticles were investigated by TEM microscopy, UV-vis, and FT-IR spectroscopy. Particle core size can be tuned by the amount of reduction agent. The strict separation of the reduction step and the functionalization step in this one-pot synthesis offers an easy and fast access to highly functionalized gold nanoparticles.
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PMID:Surfactant-free synthesis and functionalization of gold nanoparticles. 1615 72

The aqueous solutions of the anionic hybrid fluorocarbon/hydrocarbon surfactant sodium 1-oxo-1[4-(tridecafluorohexyl)phenyl]-2-hexanesulfate (FC6HC4) shows peculiar rheological behavior. At 25 degrees C the viscosity vs concentration curve goes successively through a maximum and a minimum, while the viscosity vs temperature curve of the 10 wt% aqueous FC6HC4 solution goes through a marked maximum at 36 degrees C [Tobita et al., Langmuir 13 (1997) 5054]. In an attempt to explain these properties the microstructure of aqueous solutions of FC6HC4 has been investigated by means of digital light microscopy, transmission electron microscopy at cryogenic temperature (cryo-TEM), rheology, and self-diffusion NMR. At 20 degrees C, the increase of the FC6HC4 concentration was found to result in a progressive change of structure of the surfactant assemblies from mainly spherical micelles at 0.5 wt% to mainly cylindrical micelles at 10 wt%. At intermediate concentrations small disk-like micelles and small complete and incomplete vesicles coexisting with cylindrical micelles were visualized. The occurrence of stretched cylindrical micelles is responsible for the effect of the surfactant concentration on the solution viscosity. Cryo-TEM, rheology, and self-diffusion NMR all suggest that an increase of the temperature brings about a growth of the assemblies present in the 10 wt% solution of FC6HC4. The structure of the assemblies present at the temperature where the viscosity is a maximum could not be elucidated by cryo-TEM because of the probable occurrence of an on-the-grid phase transformation, the result of blotting during specimen preparation. Nevertheless, the results show that the observed large assemblies break up at higher temperature to give rise to a more labile bicontinuous structure that consists of multi-connected disordered lamellae, with many folds and creases, and that may well be the L3 phase.
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PMID:Microstructures in the aqueous solutions of a hybrid anionic fluorocarbon/hydrocarbon surfactant. 1625 19

Room-temperature synthesis of Pd nanoparticles protected by polyvinylpyrrolidone (PVP) has been successfully achieved by merely adding sodium hydroxide (NaOH) acting as accelerator for the reduction of Pd(II) in ethylene glycol (EG) without any externally added reducing agent. The Pd particle sizes were controlled in the range from 8.6 to 2.4 nm by changing the concentration of NaOH from 0 to 3.2x10(-1) M. The particle formation was monitored by UV-vis spectroscopy and the microstructure of Pd nanoparticles was analyzed by TEM and XRD. The product of adding NaOH in EG was characterized by FTIR and a -CHO group which possesses reductive ability was identified. In addition, the prepared Pd nanoparticle could serve as an effective activator for electroless copper deposition (ECD) on epoxy substrate, which is an essential process in the printed circuit board (PCB) industry. In contrast to existing commercial activators, the new activator shows superior stability and excellent performance for ECD.
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PMID:Chemical preparation of Pd nanoparticles in room temperature ethylene glycol system and its application to electroless copper deposition. 1628 74

A simple and effective method for synthesizing silica hollow spheres is presented. The synthesis utilizes vesicles from oppositely charged surfactants sodium dodecyl sulfate (SDS) and tetrapropylammonium bromide (TPAB) aqueous solution as template for the silica growth. Tetraethyl orthosilicate (TEOS) is added to the vesicular template as a precursor for the silica formation. Ultrasound was employed to accelerate the formation of vesicles template. The morphology of the silica spheres is uniform and well-defined (diameter: 200 nm-5 microm, wall thickness: 50 nm). The product was also characterized by FTIR, TG-DTA, N2 adsorption. TEM images reveal that the spheres have structure stability after calcinations at 550 degrees C.
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PMID:Synthesis of silica hollow spheres assisted by ultrasound. 1629 99

Well-crystallized zinc oxide nanorods have been fabricated by single step solid-state reaction using zinc acetate and sodium hydroxide, at room temperature. The sodium lauryl sulfate (SLS) stabilized zinc oxide nanorods were characterized by using X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and photoluminescence spectroscopy. The X-ray diffraction revealed the wurtzite structure of zinc oxide. The size estimation by XRD and TEM confirmed that the ZnO nanorods are made of single crystals. The growth of zinc oxide crystals into rod shape was found to be closely related to its hexagonal nature. The mass ratio of SLS:ZnO in the nanorods was found to be 1:10 based on the thermogravimetric analysis. Blue shift of photoluminescence emission was noticed in the ZnO nanorods when compared to that of ZnO bulk. FT-IR analysis confirmed the binding of SLS with ZnO nanorods. Apart from ease of preparation, this method has the advantage of eco-friendliness since the solvent and other harmful chemicals were eliminated in the synthesis protocol.
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PMID:Spectroscopic characterization of zinc oxide nanorods synthesized by solid-state reaction. 1645 53

Understanding the interaction between silicate ions and surfactants is critical for the design and development of mesoporous siliceous materials. We examined the interaction between sodium silicate ions and three different cationic surfactants [namely, cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB), and dodecyltrimethylammonium bromide (DTAB)] and an anionic surfactant [sodium dodecyl sulfate (SDS)] in dilute solution at room temperature. From the combination of several techniques, such as conductometric and potentiometric titrations, dynamic light scattering, and isothermal titration calorimetry, the phase behavior of the sodium silicate and CTAB system was determined. We observed that the aggregation behavior of the silicate-CTAB system is similar to that of a polymer-surfactant system. The formation of the silicate-CTAB complex is induced by the adsorption of SiOH and SiO- groups, aided by CTAB unimers. The electrostatic attraction and hydrophobic interaction are the dominant forces controlling the formation of silicate-CTAB complexes. When these complexes are saturated with CTAB unimers, free CTAB micelles are then produced. TEM micrographs revealed that a stable Si-O-Si network is absent within the silicate-CTAB complexes, and surprisingly, stable silicate-CTAB complexes with ordered structure were observed. The present finding is important for understanding the interaction between silicate and surfactant in the synthesis of mesoporous structure in the dilute solution regime.
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PMID:Interaction between silicates and ionic surfactants in dilute solution. 1646 67

The computer aided analysis of the EPR spectra of radical surfactant probes inserted in cetyltrimethylammonium bromide micelles provided information on the kinetics of formation of micelle templated silico-aluminas (MTSA) at 343 K, obtained by means of silica and alumina alkaline solutions at different Si/Al ratios (from infinity to 4). Mainly two spectral components were analyzed and relatively quantified in the EPR spectra: (1) the micellar component, due to probes inserted in the surfactant aggregates, whose mobility decreases over the synthesis time, thus reporting on the progressive modification of the micelle structure and the solid condensation; (2) the interacting component, mainly arising from the electrostatic interactions between the surfactant heads and the charged surface sites. This last component increases its relative intensity over the synthesis time, informing about condensation and structuration of the silico-alumina at the micelle surface. X-ray diffraction (XRD), nitrogen sorption isotherms at 77 K, thermogravimetric analysis, TEM and chemical analysis were performed to characterize both as-synthesized and calcined MTSA materials. Nitrogen sorption isotherms allowed us to evaluate the pore diameter, the specific surface area and the pore volume. At Si/Al<15 a decrease in pore volume and specific surface area was interpreted as due to the contemporaneous presence of a hexagonal MTSA and an amorphous material, which was ascertained by means of XRD as the only present at Si/Al=4. The amorphous structure at Si/Al<15 used Na+ as contraions, whereas the surfactants are no more needed to neutralize the negatively charged groups at the solid surface. The hypothesis of a "break" at Si/Al=15 was supported by EPR: the interactions between the surfactant probe heads and the negatively charged surface groups are drastically reduced at Si/Al<15. On the contrary, at Si/Al>15, increasing amounts of alumina slow the kinetics of the synthesis but enhance electrostatic interactions between the surfactant heads and the negatively charged surface groups. Dilution of the synthesis mixture decreased the extent of the interactions, due to partial protonation of the silanol groups, and slowed the synthesis process.
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PMID:Synthesis of micelle templated silico-aluminas with different alumina contents. 1650 97


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