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The phase behavior of zwitanionic and catanionic mixtures of perfluoro and hydrocarbon surfactants has been studied for the case of lithium perfluorooctanoate (LiPFO) as anionic surfactant and tetradecyldimethylamine oxide (TDMAO) as zwitterionic or tetradecyltrimethyl ammonium bromide (TTAB) as cationic surfactant. Samples as a function of the mixing ratio were characterized by means of electric conductivity, light scattering, cryo-TEM, and rheology. Despite the equal chain length of the zwitterionic and cationic surfactant we observe largely different phase behavior in these systems with the formation of precipitates around equimolar mixing for the catanionic system, while no such precipitation is observed for the zwitanionic system. This can be rationalized in terms of the much lower interaction parameter beta (from cmc measurements) for the case of the zwitanionic system. Accordingly, in the zwitanionic mixture a larger range of stable unilamellar vesicles is observed, while for the catanionic system larger vesicles are present, with a much stronger tendency for formation of multilamellar vesicles. Another interesting effect is that only for the case of the zwitanionic mixture a substantial increase of viscosity is observed prior to the formation of vesicles, which means that here the transition from spherical micelles to vesicles takes place via strongly anisometric micellar aggregates, which are not observed for the case of the catanionic mixtures. From these results it can be concluded that the structure and stability of vesicles formed in these mixtures are largely controlled by the extent of the electrostatic interactions which allows modification accordingly.
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PMID:Comparison of vesicle formation in zwitanionic and catanionic mixtures of hydrocarbon and fluorocarbon surfactants: phase behavior and structural progression. 1974 44

The compaction of DNA by cationic liposomes constituted by a mixture of a cationic lipid, dioctadecyldimethylammonium bromide (DODAB), and a zwitterionic lipid, 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) or 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), has been evaluated by means of experimental studies (electrophoretic mobility, conductometry, cryogenic electron transmission microscopy or cryo-TEM, and fluorescence spectroscopy) as well as theoretical calculations. This information reveals that DODAB/DOPE and DODAB/DLPC liposomes are mostly spherical and unilamellar, with a mean diameter of around 70 and 61 nm, respectively, a bilayer thickness of 4.5 nm, and gel-to-fluid transition temperatures, T(m), of around 19 and 28 degrees C, respectively. Their positively charged surfaces efficiently compact the negatively charged DNA by means of a strong entropically driven surface interaction that yields DODAB/DOPE-DNA and DODAB/DLPC-DNA lipoplexes as confirmed by zeta potential and ethidium bromide fluorescence intercalation assays. These experiments have permitted as well the evaluation of the different microenvironments of varying polarity of the DNA helix, liposomes, and/or lipoplexes. DODAB/DOPE-DNA and DODAB/DLPC-DNA lipoplexes have been characterized by isoneutrality ratios (L/D)(phi) of around 4.7 and 4.8, respectively, a more fluid membrane than that of the parent liposomes, and T(m) around 24 and 28 degrees C, respectively, as revealed by fluorescence anisotropy. Cryo-TEM micrographs reveal a rich scenario of nanostructures and morphologies, from unilamellar DNA-coated liposomes to multilamellar lipoplexes passing through cluster-like structures. Phase diagrams (aggregation and re-entrant condensation phenomena), calculated by means of a phenomenological theory, have confirmed the experimental concentration domains and the isoneutrality conditions. The influence of helper lipid in the compaction process, as well as the optimum choice among those herein chosen, has been analyzed.
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PMID:A theoretical and experimental approach to the compaction process of DNA by dioctadecyldimethylammonium bromide/zwitterionic mixed liposomes. 1987 82

An application of increasing importance is the use of gold nanorods (AuNRs) as nanosensors and nanoprobes. We explored the possibility of using AuNRs as detectors for various temperature exposures. We measured the effects of freeze-thaw processes on AuNRs in aqueous solution by visual inspection (thermochromism), transmission electron microscopy (TEM; morphological reshaping and aggregation), and absorbance spectroscopy (plasmon peak shifts). TEM images revealed that AuNRs coalesced after prolonged exposures to -20 degrees C. The results suggest that solute rejection and cetyltrimethylammonium bromide (CTAB) bilayer crystallization underlie the mechanism of AuNR aggregation during freezing. This non-reversible aggregation appears to be unique to CTAB-protected AuNRs. Due to their unique freezing properties, we propose that AuNRs may have utility as freeze-thaw temperature nanoprobes.
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PMID:The effect of temperature and freeze-thaw processes on gold nanorods. 1992 58

PANI/TiO2 nano-composites with different amount of nanometer TiOz were synthesized by using reverse micelle formed from cationic surfactant cetyltrimethyl ammonium bromide (CTAB) as the template. The structure and properties of PANI/TiO2 nano-composites were investigated by FTIR, UV-Vis, TG, TEM and photoluminescence spectroscopy. The self-assembly mechanism of PANI/TiO2 nanorods composites in reversed micelle was discussed briefly. The results indicate that the synthesized nano-composites are PANI/TiO2 nanorods with an average diameter and length around 30-40 nm and 400 nm respectively. The infrared spectrum shows that a strong interaction exists between PANI and TiO2 nano-particles. The thermal stability of PANI/TiO2 nanorods improves with the contents of TiO2 increasing. The absorption of PANI/TiO2 nano-composites was found to be very intense in the range of violet and visible light by UV-Vis spectrum. The fluorescence of PANI/TiO2 nanorods was excited at 416 nm, and the intensity of fluorescence was strengthened greatly with increasing TiO2 concentration. The mechanism of the strengthened fluorescence quantum efficiency and fluorescence intensity of PANI/TiO2 was investigated through the charge transfer and exciton dissociation in PANI/TiO2 nanorods composites.
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PMID:[Synthesis of PANI/TiO3 nanorods composites by reverse micelle template and their properties]. 1995 Jun 63

A systematic study is performed of the influence of surfactant and temperature on the aspect ratio and monodispersity of Au nanorods, synthesized by a seed-mediated growth technique in water using cetyltrimethylammonium bromide (CTAB) as surfactant. The changes in aspect ratio with temperature show an "anomalous" behavior, where the aspect ratio first decreases with increasing temperature, reaching a minimum at about 55 degrees C, and after that increases again reaching a maximum at about 80 degrees C. A physical explanation of the observed behavior is proposed. It has also been studied how the CTAB concentration in the cleansing water used in the post-synthesis treatment of the samples affected the stability of the gold suspension. It was found that without the presence of a surfactant such as CTAB in the washing medium, only very few centrifugations can be carried out without considerable loss of product. Characterization of prepared samples was performed with UV-Vis and TEM.
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PMID:CTAB promoted synthesis of Au nanorods--temperature effects and stability considerations. 1995 87

Herein, we report the effect of gold nanoparticles (GNPs) in enhancing lipase activity in reverse micelles of cetyltrimethylammonium bromide (CTAB)/water/isooctane/n-hexanol. The size and concentration of the nanoparticles were varied and their specific roles were assessed in detail. An overall enhancement of activity was observed in the GNP-doped CTAB reverse micelles. The improvement in activity becomes more prominent with increasing concentration and size of the GNPs (0-52 microM and ca. 3-30 nm, respectively). The observed highest lipase activity (k(2)=1070+/-12 cm(3) g(-1) s(-1)) in GNP-doped CTAB reverse micelles ([GNP]: 52 microm, ca. 20 nm) is 2.5-fold higher than in CTAB reverse micelles without GNPs. Improvement in the lipase activity is only specific to the GNP-doped reverse micellar media, whereas GNP deactivates and structurally deforms the enzyme in aqueous media. The reason for this activation is probably due to the formation of larger-sized reverse micelles in which the GNP acts as a polar core and the surfactants aggregate around the nanoparticle ('GNP pool') instead of only water. Lipase at the augmented interface of the GNP-doped reverse micelle showed improved activity because of enhancement in both the substrate and enzyme concentrations and increased flexibility in the lipase conformation. The extent of the activation is greater in the case of the larger-sized GNPs. A correlation has been established between the activity of lipase and its secondary structure by using circular dichroism and FTIR spectroscopic analysis. The generalized influence of GNP is verified in the reverse micelles of another surfactant, namely, cetyltripropylammonium bromide (CTPAB). TEM, dynamic light scattering (DLS), and UV/Vis spectroscopic analysis were utilized to characterize the GNPs and the organized aggregates. For the first time, CTAB-based reverse micelles have been found to be an excellent host for lipase simply by doping with appropriately sized GNPs.
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PMID:Influence of gold nanoparticles of varying size in improving the lipase activity within cationic reverse micelles. 2001 61

We have studied the effect of Cr(III)(phen)3 [(tris(1,10-phenanthroline) chromium(III) chloride)] on lymphocytes in order to find out if metallothioneins (MTs) are produced in the process. We also investigated whether zinc pretreatment is able to protect cells from apoptosis reported to occur for this compound. Our results indicate that MT synthesis is induced by Cr(III)(phen)3, and it has been identified as the MT-3 isoform through RT-PCR which has not been reported earlier. By zinc pretreatment, this apoptosis is reversed as inferred from cytotoxicity studies, Annexin-V/PI staining, ethidium bromide/acridine orange staining and DNA fragmentation pattern and ultrastructural investigations using TEM and SEM. The zinc pretreatment reduces the amount of ROS produced by Cr(III)(phen)3. The MT-1a and 1b synthesized by zinc (also evidenced through RT-PCR experiments) is possibly able to scavenge ROS which is one of the early signaling molecules that lead to apoptosis. Zinc pretreatment also reverses the changes in downstream signaling events such as mitochondrial membrane potential, ATP levels and the activation of caspase-3. This is the first report on the induction of MT-3 in lymphocytes due to a metal stress or any other stimuli. Even though MT-3 is synthesized here, apoptosis still occurs due to ROS production on Cr(III)(phen)3 exposure when the cells have not been primed with zinc.
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PMID:Zinc protects human peripheral blood lymphocytes from Cr(III)(phenanthroline)3-induced apoptosis. 2004 34

The gelation and aggregation properties of a newly synthesized structurally simplified tetrahexyl pyromellitamide 2 have been studied and compared to the previously reported tetra(ethylhexanoate) pyromellitide 1, indicating that the ester groups in the latter significantly impede its aggregation. Morphology studies (AFM and TEM) on the aggregates formed by tetrahexyl pyromellitamide 2 in cyclohexane revealed highly uniform aggregates with different dimensions at different starting concentrations, suggesting that this molecule aggregates in a hierarchical fashion from a one-dimensional supramolecular polymer through hollow tubes or compressed helices to a network structure and then to a gel. This hypothesis is further supported by viscosity measurements that indicate a crossover point where individual supramolecular fibers get entangled at concentrations above ca. 3 mM in cyclohexane. Addition of 1 equiv of tetraalkylammonium salts of chloride or bromide, however, caused the viscosities of these pyromellitamide solutions to drop by a factor of 2-3 orders of magnitude, demonstrating the sensitivity of these aggregates to the presence of small anions. The sensitivity to anions does depend on the solubility of the salts used as small anion salts with little solubility in cyclohexane did not show this effect. Time-dependent viscosity studies showed that the aggregation of pyromellitamide 2 follows an exponential rate law, possibly related to the columnar rearrangements that are associated with the observed 6 angstroms contraction in d spacing in the XRD pattern of these gels. These results, particularly on the importance of kinetics of aggregation of self-assembled pyromellitamide gels, will be useful for future development of related materials for a number of applications, including tissue engineering and drug delivery.
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PMID:Pyromellitamide gelators: exponential rate of aggregation, hierarchical assembly, and their viscoelastic response to anions. 2005 45

The binding characteristics and molecular mechanism of the interaction between a typical ionic liquid (IL), 1-butyl-3-methylimidazolium chloride ([bmim]Cl), as a green solvent and DNA were investigated for the first time by conductivity measurements, fluorescence spectroscopy, dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), circular dichroism spectroscopy, (31)P nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy, isothermal titration calorimetry (ITC), and quantum chemical calculations. It was found that the critical aggregation concentration of [bmim]Cl is decreased in the presence of DNA, and the addition of [bmim]Cl induced a continuous fluorescence quenching of the intercalated probe ethidium bromide (EtBr), indicating that the interaction between the ionic liquid and DNA is sufficiently strong to exclude EtBr from DNA. DLS results show that [bmim]Cl can induce a coil-to-globule transition of DNA at a low IL concentration, which was confirmed by the cryo-TEM images of DNA-IL complexes. With [bmim]Cl added, the resulting globular DNA structures and the extended DNA coils are first compacted, and then grow in size. During the binding process, DNA maintains the B-form, but the base packing and helical structure of DNA are altered to a certain extent. The (31)P NMR and IR spectra indicate that the cationic headgroups of bmim(+) groups interact with the phosphate groups of DNA through electrostatic attraction, and the hydrocarbon chains of bmim(+) groups interact with the bases through strong hydrophobic association. ITC results reveal the interaction enthalpy between [bmim]Cl and DNA and show that the hydrophobic interaction between the hydrocarbon chains of [bmim]Cl and the bases of DNA provides the dominant driving force in the binding. On the basis of quantum chemical calculations, it can be inferred that at a low IL concentration, the cationic headgroups of [bmim]Cl would be localized within several angstroms of the DNA phosphates, whereas the hydrophobic chains would be arranged parallel to the DNA surface. When the IL concentration is above 0.06 mol/L, the cationic headgroups are near DNA phosphates, and the hydrocarbon chains are perpendicularly attached to the DNA surface.
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PMID:Binding characteristics and molecular mechanism of interaction between ionic liquid and DNA. 2008 58

In conventional cationic-anionic (catanionic) surfactant mixtures with excess monovalent salt, two lamellar phase (L(alpha)) regions are usually observed in both the cation-rich and anion-rich solutions, and precipitates form when there is an equal molar ratio of the cationic and anionic surfactants. The phase- and temperature-dependent behavior of the calcium dodecyl sulfate (CDS)-tetradecyltrimethylammonium bromide (TTABr)-water system with excess CaBr(2) is reported. A birefringent L(alpha)-phase is observed in the cation-rich solution while the precipitates in both the anion-rich and the cation-rich regions. The introduction of the Ca(2+) ion is proposed to alter the electrostatic shielding of the surfactant headgroups. Stable vesicles were characterized by TEM and rheology. The formation of the vesicles is driven by electrostatic and hydrophobic interactions between the cationic and anionic surfactants. The results from TEM show that the temperature markedly influences the molecular interactions and changes the structure of molecular bilayers, leading to the instability of the vesicles. The vesicles were used to prepare microcrystals of calcium oxalate monohydrate (CaC(2)O(4) x H(2)O) by adding dimethyl oxalate to L(alpha) solution. X-ray diffraction and scanning electron microscopy indicate that the vesicle phases play an important role in affecting the formation and growth of the CaC(2)O(4) crystals. Namely, the microcrystals formed in the reaction are mainly bricklike (dodecahedrons) and starlike (icositetrahedrons). The two morphologies have not been previously observed in COM. Furthermore, they are larger than those prepared without surfactant, which may also explain a role for surfactants in calcium oxalate biomineralization.
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PMID:Preparation of calcium oxalate by vesicle modification in the catanionic surfactant system CDS/TTABr/H2O. 2009


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