UMLS:C0276640 - FACTA Search

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Query: UMLS:C0276640 (TEM)
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In a recent study, we showed that the surfactant 1,2-distearoyl-sn-glycero-3-phosphatidylethanolamine-N-[methoxy(polyethylene glycol)-2000 (DSPE-PEG2000) induced mixed micelles of either threadlike or discoidal shape when mixed with different types of lipids. In this study, we have exchanged the PEG-lipid for the more conventional surfactants octaethylene glycol monododecyl ether (C12E8), hexadecyltrimethylammonium bromide (CTAB), and sodium dodecyl sulfate (SDS). Cryo-TEM investigations show that also these surfactants are able to induce the formation of long-lived discoidal micelles. Generally, the preference for either discoidal or threadlike micelles can be tuned by the choice of lipids and environmental conditions in much the same way as observed for the lipid/PEG-lipid system. Our investigation showed, furthermore, that the choice of surfactant may influence the type of mixed micelles formed. It is argued that the formation of discoidal rather than threadlike micelles may be rationalized as an effect of increasing bending rigidity. Our detailed theoretical model calculations show that the bending rigidity becomes significantly raised for aggregates formed by an ionic rather than a nonionic surfactant.
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PMID:On the formation of discoidal versus threadlike micelles in dilute aqueous surfactant/lipid systems. 1821 80

The compaction of calf thymus DNA (CT-DNA) by cationic liposomes constituted by a 1:1 mixture of a cationic lipid, 1,2-distearoyl-3-(trimethylammonio)propane chloride (DSTAP), and a zwitterionic lipid, 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE, null net charge at pH = 7.4), has been evaluated in aqueous buffered solution at 298.15 K by means of conductometry, electrophoretic mobility, cryo-TEM, and fluorescence spectroscopy techniques. The results reveal that DSTAP/DOPE liposomes are mostly spherical and unilamelar, with a mean diameter of around 77 +/- 20 nm and a positively charged surface with a charge density of sigmazeta = (21 +/- 1) x 10(-3) C m(-2). When CT-DNA is present, the genosomes DSTAP/DOPE/CT-DNA, formed by means of a surface electrostatic interaction, are generally smaller than the liposomes. Furthermore, they show a tendency to fuse forming cluster-type structures when approaching isoneutrality, which has been determined by the electrochemical methods at around (L/D)phi = 5.6. The analysis of the decrease on the fluorescence emission of the fluorophore ethidium bromide, EtBr, initially intercalated between DNA base pairs, as long as the genosomes are formed has permitted us to confirm the electrostatic character of the DNA-liposome interaction.
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PMID:Compaction process of calf thymus DNA by mixed cationic-zwitterionic liposomes: a physicochemical study. 1822 Mar 88

We studied the phase behavior and aggregation in mixed aqueous solutions of the anionic UV-absorber 2-phenylbenzimidazole-5-sulfonic acid sodium salt, PhBSA (Na salt), and the cationic surfactant cetyltrimethylammonium bromide, CTAB. The mixtures of the two components behave similarly to catanionic surfactant mixtures. The samples on the PhBSA-rich side have low viscosity and are turbid. The turbidity, due to uni- and multilamellar vesicles (SUVs and MLVs), increases with the mole ratio of CTAB. The interbilayer distance inside the MLV changes with the mole ratio of the two components from a few 10 nm for the 7:3 (molar ratio of PhBSA, Na salt, to CTAB) system to practically zero for the 5:5 mixture. The latter mixture forms a precipitate within less than 1 h. With the exception of the 5:5 mixture, all samples on the PhBSA-rich side are stable for many days. After that period, within one more day, the turbid vesicle phases are transformed into more or less clear hydrogels. We found that the gelation is due to the formation of very long stiff tubules about 14 nm in diameter, which is independent of the mixing ratio of the samples. The hydrogels and the tubules melt around 45 degrees C. On the CTAB-rich side, the 4:6 sample behaves like the 6:4 sample, whereas at 3:7 a precipitate was found to form shortly after mixing. At still smaller PhBSA (Na salt) to CTAB ratios, only clear, viscoelastic solutions are found that do not change with time. We determined the micellar structures in the samples by cryo-TEM and by SAXS. The rheological properties of the hydrogels and of the viscoelastic samples were characterized by oscillating rheological measurements. DSC measurements indicated that the tubules are in a semicrystalline state and melt at around 45 degrees C. The semicrystalline bilayer of the tubules seems to have a 1:1 composition of PhBSA to CTAB. The excess PhBSA seems to be adsorbed on the tubules. It is assumed that the stiffness of the bilayer of the vesicles and the stiffness of the tubules are due to the stiffness of the PhBSA molecule.
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PMID:Phase behavior of aqueous mixtures of 2-phenylbenzimidazole-5-sulfonic acid and cetyltrimethylammonium bromide: hydrogels, vesicles, tubules, and ribbons. 1827 77

Male Wistar rats were treated with aflatoxin B1 (AFB1). Live as well as methanol-fixed cauda epididymal spermatozoa were stained with acridine orange (AO) and ethidium bromide (EB) and observed under a fluorescence microscope. Giemsa-stained smears were observed in a bright field microscope. Unstained smears were observed with phase contrast illumination. The axoneme of more than 10% of the spermatozoa of treated rats had the outer dense fibres (ODFs), in varying numbers, and the associated axonemal microtubule doublets of the flagellum extruded either at midpiece-principal piece junction or connecting piece. This could be perceived in all light microscopic preparations, but AO-EB staining offered an advantage of the assessment of the viability as well. TEM observation of sections of the testis and cauda epididymidis also revealed ODF extrusion, as seen in the transverse sections of sperm flagella missing one or more ODFs and the associated axonemal microtubule doublets. In a few such sections, the extruded elements were seen in the cytoplasm, outside the mitochondrial sheath or peripheral sheath. Marginal to severe mitochondrial pathologies were observed in the spermatozoa and elongated spermatids, suggesting a link between AFB1-induced sperm mitochondrial pathology and extrusion of ODFs. However, the possibility that AFB1 treatment would disrupt the cytoskeletal proteins of the flagellum, resulting in the extrusion of ODFs, cannot be excluded. This sperm abnormality is reported for the first time as produced by a dietary toxin. Dietary aflatoxins, therefore, could also be contributory factors for the deterioration of the reproductive health of men.
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PMID:Spermatotoxic effect of aflatoxin B1 in rat: extrusion of outer dense fibres and associated axonemal microtubule doublets of sperm flagellum. 1829 23

Combined dynamic and static light scattering (DLS, SLS) and cryogenic transmission electron microscopy (cryo-TEM) were used to investigate extruded cationic vesicles of dioctadecyldimethylammonium chloride and bromide (DODAX, X being Cl(-) or Br(-)). In salt-free dispersions the mean hydrodynamic diameter, D(h), and the weight average molecular weight, M(w), are larger for DODAB than for DODAC vesicles, and both D(h) and M(w) increase with the diameter (varphi) of the extrusion filter. NaCl (NaBr) decreases (increases) the DODAB (DODAC) vesicle size, reflecting the general trend of DODAB to assemble as larger vesicles than DODAC. The polydispersity index is lower than 0.25, indicating the dispersions are rather polydisperse. Cryo-TEM micrographs show that the smaller vesicles are spherical while the larger ones are oblong or faceted, and the vesicle samples are fairly polydisperse in size and morphology. They also indicate that the vesicle size increases with phi and DODAB assembles as larger vesicles than DODAC. Lens-shaped vesicles were observed in the extruded preparations. Both light scattering and cryo-TEM indicate that the vesicle size is larger or smaller than phi when phi is smaller or larger than the optimal phi approximately 200 nm.
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PMID:Extruded vesicles of dioctadecyldimethylammonium bromide and chloride investigated by light scattering and cryogenic transmission electron microscopy. 1840 74

We report characterization of the nanostructures of complexes formed between the redox-active lipid bis(n-ferrocenylundecyl)dimethylammonium bromide (BFDMA) and DNA using small-angle neutron scattering (SANS) and cryogenic transmission electron microscopy (cryo-TEM). A particular focus was directed to the influence of lipid oxidation state (where reduced BFDMA has a net charge of +1 and oxidized BFDMA has a charge of +3) on the nanostructures of the solution aggregates formed. Complexes were characterized over a range of charge ratios of reduced BFDMA to DNA (1.1:1, 2.75:1, and 4:1) in solutions of 1 mM Li2SO4. For these complexes, a single peak in the SANS data at 1.2 nm(-1) indicated that a nanostructure with a periodicity of 5.2 nm was present, similar to that observed with complexes of the classical lipids DODAB/DOPE and DNA (multilamellar spacing of 7.0 nm). The absence of additional Bragg peaks in all the SANS data indicated that the periodicity did not extend over large distances. Both inverse Fourier transform analysis and form factor fitting suggested formation of a multilamellar vesicle. These results were confirmed by cryo-TEM images in which multilamellar complexes with diameters between 50 and 150 nm were observed with no more than seven lamellae per aggregate. In contrast to complexes of reduced BFDMA and DNA, Bragg peaks were absent in SANS spectra of complexes formed by oxidized BFDMA and DNA at all charge ratios investigated. The low-q behavior of the SANS data obtained using oxidized BFDMA and DNA complexes suggested that large, loose aggregates were formed, consistent with complementary cryo-TEM images showing predominantly loose disordered aggregates. Some highly ordered spongelike and cubic phase nanostructures were also detected in cryo-TEM images. We conclude that control of BFDMA oxidation state can be used to manipulate the nanostructures of lipid-DNA complexes formed using BFDMA.
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PMID:Characterization of the nanostructure of complexes formed by a redox-active cationic lipid and DNA. 1841 68

Aqueous micellar solutions of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) and sodium nitrate (NaNO(3)) were examined using steady and dynamic rheology, small-angle neutron scattering (SANS) and cryogenic-transmission electron microscopy (cryo-TEM). Upon addition of NaNO(3), the CTAB spherical micelles transform into long, flexible wormlike micelles, conveying viscoelastic properties to the solutions. The zero-shear viscosity (eta(0)) versus NaNO(3) concentration curve exhibits a well-defined maximum. Likewise, upon increase in temperature, the viscosity decreases. Dynamic rheological data of the entangled micellar solutions can be well described by the Maxwell model. Changes in the structural parameters of the micelles with addition of NaNO(3) were inferred from SANS measurements. The intensity of scattered neutrons at the low q region was found to increase with increasing NaNO(3) concentration. This suggests an increase in size of the micelles and/or decrease of intermicellar interactions with increasing salt concentration. Analysis of the SANS data using prolate ellipsoidal structure and Yukawa form of interaction potential between micelles indicates that addition of NaNO(3) leads to a decrease in the surface charge of the ellipsoidal micelles and consequently an increase in their length. The structural transition from spherical to entangled threadlike micelles, induced by the addition of NaNO(3) to CTAB micelles is further confirmed by cryo-TEM.
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PMID:Viscoelastic micellar water/CTAB/NaNO(3) solutions: rheology, SANS and cryo-TEM analysis. 1848 41

The influences of amphiphiles on the catalytic dechlorination of 1,2,4-trichlorobenzene (124TCB) bythe nanoscale Pd/Fe particles were comprehensively examined. The fresh and reacted Pd/ Fe particles were characterized with XRD, TEM, SEM, FTIR spectrometry, and goniometry. Adsorption of amphiphiles on the Pd/Fe particles, iron dissolution, and H2 evolution in the Pd/Fe-water system were quantified to expound the influences of the various amphiphiles on the dechlorination process. The Langmuir-Hinshelwood model is used to elucidate the dechlorination kinetics, and it provides insight into the influence of amphiphiles on 124TCB partitioning to the interfacial layer and the resulting dechlorination rates. The rate constants increased by a factor of 1.5--2.5 with the presence of cationic cetyltrimethylammonium bromide (CTAB). In the anionic sodium deodecyl sulfate(SDS) or nonionic nonylphenol ethoxylate (NPE) and octylphenolpoly (ethylene glycol ether)x (TX-100) surfactant solutions, the 124TCB dechlorination rates were slightly increased over those observed in ultrapure water. However, when concentrations of the surfactants were above their CMCs, the dechlorination rates decreased. The findings also showed that DPC (dodecylpyridinium chloride) and NOM (natural organic matter) might be the competitive H2 acceptors to 124TCB, and they significantly retarded its catalytic dechlorination by the Pd/Fe particles. CTAB at a concentration below the CMC appeared to be the most benign to the 124TCB dechlorination.
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PMID:Influences of amphiphiles on dechlorination of a trichlorobenzene by nanoscale Pd/Fe: adsorption, reaction kinetics, and interfacial Interactions. 1860 79

A 1:1 mixture of the cationic lipid 3beta-[ N-( N', N'-dimethylaminoethane)-carbamoyl]cholesterol hydrochloride (DC-Chol) and the zwitterionic lipid, 1,2-dioleoyl- sn-glycero-3-phosphoetanolamine (DOPE), has been used to compact calf-thymus DNA (CT-DNA) in aqueous buffered solution at 298.15 K. The formation process of this lipoplex has been analyzed by means of electrophoretic mobility, cryo-TEM, dynamic light scattering, and fluorescence spectroscopy techniques. The experimental results indicate that DC-Chol/DOPE liposomes are mostly spherical and unilamellar, with a mean diameter of around 99 +/- 10 nm and a bilayer with a thickness of 4.5 +/- 0.5 nm. In the presence of CT-DNA, DC-Chol/DOPE/CT-DNA lipoplexes are formed by means of a strong entropically driven surface electrostatic interaction, as confirmed by zeta potential and fluorescence results, as a consequence of which DNA is compacted and condensed at the surface of the cationic liposomes. The negative charges of DNA phosphate groups are neutralized by the positive charges of cationic liposomes at the isoneutrality L/ D ratio, ( L/ D) varphi around 4, obtained from electrophoretic, fluorescence, and DLS measurements. The decrease in the fluorescence emission intensity of ethidium bromide, EtBr, initially intercalated between DNA base pairs, as long as the association between the biopolymer and the cationic liposomes takes place has permitted one to confirm its electrostatic character as well as to evaluate the different microenvironments of varying polarity of DNA-double helix, liposomes, and/or lipoplexes. Electronic microscopy reveals a rich scenario of possible nanostructures and morphologies for the lipoplexes, from unilamellar DNA-coated liposomes to multilamellar lipoplexes passing through cluster-like structures and several intermediate morphologies.
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PMID:A physicochemical characterization of the interaction between DC-Chol/DOPE cationic liposomes and DNA. 1872 99

Phase inversion of aqueous two-phase systems with excess cationic surfactant (abbreviated as ATPS-C) formed by aqueous mixtures of 1,3-propanediyl bis(dodecyl dimethylammonium bromide) (abbreviated as 12-3-12) and sodium dodecyl sulfonate (abbreviated as AS) at 318.15 K was investigated. The experimental results indicate that addition of NaF, NaCl, NaHCO 3, or NaNO 3 can result in phase inversion of ATPS-C formed by 12-3-12/AS systems; however, addition of NaBr cannot lead to phase inversion. TEM micrographic experiments illustrate that there is no direct relationship between the microstructures of the concentrated phase in ATPS-C and phase inversion. To interpret the phase-inversion phenomena of ATPS-C, the phase composition, phase density, and phase volume ratio between the dilute phase and the concentrated phase in ATPS-C were investigated. Phase composition analysis results illustrate that for the ATPS-C formed by 0.10 mol.kg (-1) 12-3-12/AS mixed system, the concentration of Br (-) counterions in the dilute phase of ATPS-C increases with addition of NaF, NaCl, NaHCO 3, or NaNO 3. At the same time, the molar ratio between the F (-) (Cl (-), HCO 3 (-), or NO 3 (-)) counterions and Br (-) counterions in the concentrated phase of ATPS-C increases also. It illustrates that part of the bromide counterions which are the natural counterions of the surfactant 12-3-12 in excess are exchanged by other anionic counterions when an additional salt is added to the system. The investigation indicates that the common ground of the added F (-), Cl (-), HCO 3 (-), or NO 3 (-) counterions is that they all make a smaller density contribution than that of Br (-) counterions, although they have a weaker or stronger counterion binding ability with the mixed positively charged aggregates in ATPS-C than that of Br (-) counterion. Density experiments illustrate that the density increase of the dilute phase is larger than that of the concentrated phase in the ATPS-C with addition of NaF, NaCl, NaHCO 3, or NaNO 3; thus, phase inversion occurs. The densities of the added inorganic sodium salt aqueous solution and the order of the Hofmeister series for the added inorganic anions with respect to the chaotropic headgroup of 12-3-12 play important roles in the phase inversion of ATPS-C.
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PMID:Salt-induced phase inversion in aqueous cationic/anionic surfactant two-phase systems. 1876 79

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