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Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We present the phase behavior and thermodynamics of the catanionic mixture of the gemini surfactant hexanediyl-alpha,omega-bis(dodecyldimethylammonium bromide), designated here as 12-6-12Br(2), and sodium dodecyl sulfate (SDS) over the full range of composition, at the water-rich corner. Visual and turbidity measurements of the mixtures provide some basic macroscopic information on phase behavior. The structure of the aggregates formed spontaneously in the mixtures has been observed with TEM. As the molar fraction of SDS, X(SDS), is increased, at constant total surfactant concentration, the aggregation morphologies change gradually from gemini-rich micelles, through multiphase regions containing a precipitate (catanionic surfactant) and a vesicle region, to SDS-rich micelles. From isothermal titration calorimetry measurements, the phase boundaries and corresponding enthalpy changes for phase transitions have been obtained. The formation of the different microstructures, in particular, the spontaneously formed vesicles in the SDS-rich side, is discussed on the basis of geometric and electrostatic effects occurring in the SDS-gemini mixture.
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PMID:Phase behavior and thermodynamics of a mixture of cationic gemini and anionic surfactant. 1653 60

The Ni-Fe bimetallic particles have been laboratory prepared using sodium borohydride (NaBH4) as the reductant to reduce Ni2+ and Fe2+ in aqueous solution simultaneously, and characterized by TEM, XRD, BET and XPS. The particles were proved to be nanoscale amorphous alloy with an average diameter of about 30 nm and a BET surface area of 20.9 m2 g(-1). Experiments for dechlorination of pentachlorophenol (PCP) by the Ni-Fe bimetallic nanoscale particles in aqueous solutions were carried out under the enhancement of ultrasound. Major factors that influence the dechlorination efficiency, such as initial pH value, Ni content in the Ni-Fe particles, and output power of ultrasonic irradiation, were investigated. The results indicated that Ni-Fe nanoscale bimetallic particles were very effective for the dechlorination of PCP. Dechlorination efficiency was 46% in 30 min under the optimal condition without assistance of ultrasound, whereas it increased to 96% when ultrasonic irradiation was present. Initial pH value showed apparent effect on the dechlorination. As the pH varied from acidic condition to neutral condition, the dechlorination efficiency decreased dramatically. In addition, the dechlorination efficiency was improved with increased Ni/Fe ratio and ultrasonic output power. Less chlorinated phenols including tetrachlorophenol, trichlorophenol, dichlorophenol, monochlorophenol were formed during the initial reaction, and phenol was determined by GC-MS as sole product in the end of reaction.
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PMID:Rapid and complete dechlorination of PCP in aqueous solution using Ni-Fe nanoparticles under assistance of ultrasound. 1662 Sep 11

The mechanism(s) of resistance or decreased susceptibility to cefepime (FEP) and/or imipenem (IMP) in three consecutive isolates of Enterobacter aerogenes (Ea1, Ea2 and Ea3) cultured from bronchial aspirates of the same patient after treatment with ceftriaxone and FEP were studied. Identification was performed with the VITEK 2 system. All three isolates showed identical pulsed-field gel electrophoresis patterns and were resistant (minimum inhibitory concentrations (MICs)) to cefoxitin (MIC, >1024 mg/L), cefotaxime (CTX; MIC, 32-128 mg/L) and ceftazidime (CAZ; MIC, 32-128 mg/L) but susceptible to meropenem (MIC, <or=0.5 mg/L) according to the National Committee for Clinical Laboratory Standards (NCCLS). MICs of FEP were 0.5 mg/L (Ea1), 2 mg/L (Ea2) and 16 mg/L (Ea3), whereas MICs of IMP were <or=0.5 mg/L (Ea1 and Ea3) and 8 mg/L (Ea2). Clavulanic acid (CLV) did not affect the MICs of CTX and FEP. In contrast, the MICs of CTX were reduced 32-128 times by BRL 42715 (BRL) or cloxacillin (CLX), whereas the MICs of FEP were reduced 2-128 times by BRL and 16-64 times by CLX. Production of extended-spectrum beta-lactamases (ESBLs) was not detected using the disk diffusion method (NCCLS) or Etest (CTX/CTX-CLV and CAZ/CAZ-CLV). TEM- or SHV-type ESBL genes were not detected by polymerase chain reaction amplification. The three isolates showed the same pattern of five beta-lactamases (isoelectric points 7.9-8.3, inhibited by CLX but not by CLV) by isoelectric focusing of crude extracts. Hydrolysis (nmol/mg) of cefaloridine (CF) was 3741.0 (Ea1), 4000.6 (Ea2) and 3797.4 (Ea3), suggesting that AmpC is hyperproduced. Hydrolysis of FEP was much lower than that of CF: 1.3 (Ea1), 2.1 (Ea2) and 17.3 (Ea3). The nucleotide sequences of the ampR-ampC genes of Ea1 and Ea2 were identical to that of E. aerogenes strain deposited in GenBank (accession no.). For Ea3, however, a point mutation in position 311 of ampC caused a change of Val-->Glu. Three outer membrane proteins (OMPs) of 51 kDa, 40 kDa and 38 kDa were observed in the three isolates by sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) (10% polyacrylamide gels with 4 M urea), although expression of the 40 kDa OMP was reduced in Ea2. In conclusion, decreased susceptibility to FEP and IMP in Ea2 is related to reduced expression of a 40 kDa OMP and hyperproduction of AmpC, whereas resistance to FEP in Ea3 is associated with hyperproduction of an altered AmpC.
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PMID:In vivo selection of Enterobacter aerogenes with reduced susceptibility to cefepime and carbapenems associated with decreased expression of a 40 kDa outer membrane protein and hyperproduction of AmpC beta-lactamase. 1669 50

Thermolysis of [M(SeCH2CH2CH2NMe2)2] (M = Zn, Cd, Hg), prepared by the reactions of sodium salt of 3-(N,N-dimethylamino)propaneselenolate with metal acetates, afforded metal selenides (MSe). The metal selenides were characterized by XRD, EDAX, SEM, AFM, and TEM techniques. Nanoparticles of HgSe were prepared by pyrolysis in a quartz boat, solvothermal, and sonochemical methods. EDAX showed 1:1 Hg/Se ratio, while XRD and SAED patterns confirmed the formation of cubic HgSe. These particles are spherical in nature with an average diameter of 15 nm (from TEM).
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PMID:Synthesis and characterization of metal selenide (ZnSe, CdSe, HgSe) nanoparticles. 1673 62

Biphasic beta-rhenanite (beta-NaCaPO(4))-hydroxyapatite (Ca(10)(PO(4))(6)(OH)(2)) biomaterials were prepared by using a one-pot, solution-based synthesis procedure at the physiological pH of 7.4, followed by low-temperature (300-600 degrees C) calcination in air for 6 h. Calcination was for the sole purpose of crystallization. An aqueous solution of Ca(NO(3))(2). 4H(2)O was rapidly added to a solution of Na(2)HPO(4) and NaHCO(3), followed by immediate removal of gel-like, poorly-crystallized precursor precipitates from the mother liquors of pH 7.4. Freeze-dried precursors were found to be nanosize with an average particle size of 45 nm and a surface area of 128 m(2)/g. Upon calcination in air, precursor powders crystallized into biphasic (60% HA-40% rhenanite) biomaterials, while retaining their submicron particle sizes and high surface areas. beta-rhenanite is a high solubility sodium calcium phosphate phase. Samples were characterized by XRD, FTIR, SEM, TEM, ICP-AES, TG, DTA, DSC, and surface area measurements.
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PMID:A new rhenanite (beta-NaCaPO(4)) and hydroxyapatite biphasic biomaterial for skeletal repair. 1676 21

Mixed catanionic surfactant systems based on amino acids were investigated with respect to the formation of liquid crystal dispersions and the stability of the dispersions. The surfactants used were arginine-N-lauroyl amide dihydrochloride (ALA) and N(alpha)-lauroyl-arginine-methyl ester hydrochloride (LAM), which are arginine-based cationic surfactants; sodium hydrogenated tallow glutamate (HS), a glutamic-based anionic surfactant; and the anionic surfactants sodium octyl sulfate (SOS) and sodium cetyl sulfate (SCS). It is demonstrated that in certain ranges of composition there is a spontaneous formation of vesicular, cubic, and hexagonal structures. The solutions were characterized with respect to internal structure and size by cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and turbidity measurements. Vesicles formed spontaneously and were found for all systems studied; their size distribution is presented for the systems ALA/SCS/W and ALA/SOS/W; they are all markedly polydisperse. The aging process for the system ALA/SOS/W was monitored both by turbidity and by cryo-TEM imaging; the size distribution profile for the system becomes narrower and the number average radius decreases with time. The presence of dispersed particles with internal cubic structure (cubosomes) and internal hexagonal structure (hexosomes) was documented for the systems containing ALA and HS. The particles formed spontaneously and remained stably dispersed in solution; no stabilizer was required. (Cubosome and hexosome are USPTO registered trademarks of Camurus AB, Sweden.) The spontaneous formation of particles and their stability, together with favorable biological responses, suggests a number of applications.
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PMID:Spontaneous formation of vesicles and dispersed cubic and hexagonal particles in amino acid-based catanionic surfactant systems. 1676 81

Gold nanoparticles with an average diameter of approximately 8 nm (Au approximately 15,000) were irradiated with a tightly focused pulse laser at 355 nm in an aqueous solution of sodium dodecyl sulfate (SDS). Transient absorption spectra of the solution were measured at 25-100 ns after the laser irradiation. The observed transient absorption around 720 nm is assignable to the 2p <-- 1s transition of solvated electrons produced via multiple ionization of the gold nanoparticles. The nascent charge state of the gold nanoparticles was estimated from the transient absorbance. The dependence of the charge state on the SDS concentration shows a gradual increase from approximately +60 to approximately +70 in the 2 x 10(-4) to 3 x 10(-4) M range and an abrupt increase up to approximately +710 at the critical micelle concentration (CMC) of SDS, 8 x 10(-3) M. TEM measurements after laser irradiation reveal that the gold nanoparticles fragment into Au(approximately 1000) at a SDS concentration of 3 x 10(-4) M, whereas they are significantly dissociated into Au(approximately 100) above the CMC. The observed correlation between the nascent charge states and the extent of size reduction of the gold nanoparticles after the laser treatment indicates that the size reduction is caused by the Coulomb explosion of the highly charged gold nanoparticles. The mechanism of laser-induced size reduction is quantitatively discussed based on the liquid drop model.
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PMID:Mechanism of laser-induced size-reduction of gold nanoparticles as studied by nanosecond transient absorption spectroscopy. 1680 Apr 73

The NiO nanoparticles with the size of 9-30 nm were prepared by solid state method using nickel acetate and sodium hydroxide as the raw materials, and Tween 80 as the dispersant. The structure, morphology, size, and infrared and UV-Vis spectra were characterized by XRD, TEM, FTIR and UV-Vis, respectively. The XRD and TEM revealed that the products are spherical with cubic structure. The infrared absorption band of the NiO nanoparticles (437 cm(-1)) red-shifts 47 cm(-1) compared with that of bulk NiO(484 cm(-1)). The UV-Vis optical absorption is related with the size of the particles. The bulk NiO has no absorption in the UV-Vis region, while the 10 nm NiO nanoparticles have stronger absorption observed at the wavelength about 309 nm, and the direct band gap energy is estimated to be about 4.2 eV which is obviously blue-shifted 0.55 eV compared to that of bulk NiO (3.65 eV). The surface effect and quantum size effect of the NiO nanoparticles indicated that the products will have potential application in the optical and electrical areas.
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PMID:[Study on the preparation and spectral characteristics of nano-NiO]. 1683 41

The crystallization of PbS in aqueous solutions containing the surfactant sodium dodecyl sulfate (SDS) and hydrophilic polymers resulted in a novel type of metastable nanotubes, the walls of which consist of layers of ordered PbS nanoparticles, apparently separated by layers of surfactant molecules. Information on the mechanism of formation of these structures was obtained by focusing on the roles of the polymer, and of the insoluble lead dodecyl sulfate (Pb(DS)2) present in the system. TEM investigations of the early stages of crystallization revealed the coexistence of PbS and Pb(DS)2 precipitates, the latter being surprisingly important for nanotube formation, and allowed to follow the evolution of layered structures from combination of the two types of crystals. Six different hydrophilic polymers have been used, which interact with SDS with varying strengths. Surprisingly, and in contrast to previous hypotheses, layered nanostructures were observed in all polymer solutions, regardless of the strength of polymer-surfactant interactions. This indicates that, although the presence of a polymer is necessary, polymer-SDS interactions are not a driving force for the formation of the layered structures and nanotubes. On the contrary, the interactions between the polymer chains and the growing particles appear to be of the utmost importance. Results presented here can be interpreted in terms of two alternative mechanisms for layered nanostructure and nanotube formation.
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PMID:Formation mechanism of nanotubes comprising layers of PbS nanoparticles in polymer-surfactant solutions. 1684 6

Vesicles can be formed spontaneously in aqueous solution of a single anionic surfactant sodium dodecyl benzenesulfonate (SDBS) just under the inducement of salt, which makes the formation of vesicle much easier and simpler. The existence of vesicles was demonstrated by TEM image using the negative-staining method. The mechanism of the formation may be attributed to the compression of salt on the electric bilayer of the surfactant headgroups, which alters the packing parameter of the surfactant. The addition of the zwitterionic surfactant lauryl sulfonate betaine (LSB) makes the vesicles more stable, expands the range of formation and vesicle size, and reduces the polydispersity of the vesicles. The vesicle region was presented in a pseudoternary diagram of SDBS/LSB/brine. The variations of vesicle size with the salinity and mixing ratios, as well as the surfactant concentration, were determined using the dynamic light scattering method. It is found that the vesicle size is independent of the surfactant concentration but subject to the salinity and the mixing ratio of the two surfactants.
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PMID:Salt-induced vesicle formation from single anionic surfactant SDBS and its mixture with LSB in aqueous solution. 1685 6


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