Self-Assembly of Magnetic Bacillus-Shaped Bilayer Vesicles in Catanionic Surfactant Solutions.

Bacillus-shaped bilayer vesicles of nanoscale size are very rare structures of stable surfactant self-assembly, because they are both thermodynamically and electrostatically unfavorable in solution. It is evidently demonstrated that appropriately aqueous mixtures of single-tailed cationic and anionic (catanionic) surfactants can produce rigidly bacillus-shaped bilayer vesicles with both flat parts and bent edges. The crucial requirement for forming bacillus-shaped bilayer vesicles is the use of cationic surfactants with relatively hydrophobic [FeCl3Br]- as counterions. [FeCl3Br]- can strongly associate with cationic surfactants to partition into the hydrophobic bilayer of bacillus-shaped bilayer vesicles, significantly increasing the edge energy of cationic surfactants to make them distribute in the low curvature part of bilayers. This causes the formation of bacillus-shaped bilayer vesicles, but not completely bent spherical vesicles, in the case of cationic surfactant excess. The specificity of hydrophobic counterions, [FeCl3Br]-, could also make the catanionic mixtures do not precipitate at the stoichiometric point. This new self-assembly on catanionic systems is culminated in the discovery of beautifully structured colloidal objects which are of practical use for molecular templating and controlled drug or DNA release.

Formation of core-shell Au@Ag nanorods induced by catecholamines: A comparative study and an analytical application.

Gold nanorods (AuNRs) stabilized by cetyltrimethylammonium bromide (CTAB) were synthesized and an interaction of catecholamines (CAs) with silver ions in the presence of the obtained AuNRs was studied. The reaction results into formation of core-shell Au@Ag nanorods (Au@AgNRs) and leads to a hypsochromic shift of the long-wave surface plasmon resonance (SPR) band in the absorption spectrum of AuNRs. The influence of a CA structure, excess of CTAB, interaction time, pH, concentration of AuNRs, silver ions and CAs on this interaction was studied. Based on correlation of the NRs spectral characteristics with the concentration of CAs, a method for spectrophotometric determination of dobutamine, epinephrine, norepinephrine and dopamine with detection limits 27, 18, 16 and 13 µg L(-1), respectively, has been developed. The method can be applied to the analysis of medicines.

Shape control of mesoporous silica nanomaterials templated with dual cationic surfactants and their antibacterial activities.

Mesoporous silica nanomaterials of different shapes (film, platelet, sphere, rod) were synthesized simply by tuning the mole ratio of dual cationic surfactant templates, cetyltrimethylammonium bromide (CTAB) and tetrabutylammonium iodine (TBAI). The film showed the most potent antibacterial activity against mycobacteria.

Synthesis and properties of PDMS/montmorillonite-cetyltrimethylammonium bromide-heparin films.

In this study, poly(dimethylsiloxane)(PDMS)/montmorillonite-cetyltrimethylammonium bromide-heparin (PDMS/MMT-CTAB-HEP) films were prepared by solution intercalation technique. The cetyltrimethylammonium bromide-heparin (CTAB-HEP) was intercalated into montmorillonite (MMT) layers forming MMT-CTAB-HEP (modified MMT). The structure and properties of the film were characterized by XRD, TG and SEM. The modified MMT was homogeneously dispersed within the PDMS matrix. The effect of modified MMT on mechanical properties of the film was also investigated. As the modified MMT content was lower than 2wt%, the films showed excellent mechanical properties. The blood compatibility of PDMS/MMT-CTAB-HEP films was further evaluated by hemolysis test and platelet adhesion. Both hemolysis and platelet adhesions tests showed that PDMS/MMT-CTAB-HEP film had better blood compatibility than pure PDMS.

Polymers containing hydroxamate groups: nanoreactors for hydrolysis of phosphoryl esters.

A polyhydroxamicalkanoate (PHA) polymer containing the functional groups hydroxamic acid and carboxylic acid with the ability to accelerate dephosphorylation reactions is proposed. The methodology used to prepare this polymer favored the position of the two functional groups next to each other, which allows for the cooperativity between these groups. This cooperative effect has an important role when one wants to mimic enzymes. The catalytic effect promoted by the polymer was evaluated on the cleavage of the bis(2,4-dinitrophenyl) phosphate (BDNPP) and diethyl 2,4-dinitrophenyl phosphate (DEDNPP) esters. Indeed, PHA was very efficient and promiscuous because it increased the rate of both reactions by a factor of up to 10(6)-fold. Isothermal titration calorimetry (ITC) experiments showed that the presence of PHA aids the formation of cetyltrimethylammonium bromide (CTABr) micelles. Thus, the effect of the cationic surfactant CTABr on the dephosphorylation of BDNPP by PHA was also investigated, and it was observed that, when CTABr is added to PHA, the reaction is ca. 15-fold faster compared to the reaction when only PHA is present.

CTAB promoted synthesis of Au nanorods--temperature effects and stability considerations.

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.

Facile synthesis of polyaniline "sunflowers" with arrays of oriented nanorods.

Polyaniline (PANI) "sunflowers" made of arrays of oriented nanorods were synthesized by chemical oxidative polymerization of aniline in the presence of cetyltrimethylammonium bromide (CTAB) and suitable concentration of HNO3 at about 0 degrees C (ice bath). The reaction conditions, such as the concentration of reagents and reaction temperature were systematically investigated and controlled on the preparation of PANI "sunflowers". The results also suggest that HNO3 probably plays a key role in forming PANI "sunflowers". A possible forming mechanism of the PANI nanostructures is offered.

Encapsulation of myoglobin in a cetyl trimethylammonium bromide micelle in vacuo: a simulation study.

A recently published paper describes encapsulation of myoglobin into cetyl trimethylammonium bromide (CTAB) micelles by electrospray ionization followed by detection using mass spectrometry [Sharon, M., et al. (2007) J. Am. Chem. Soc. 129, 8740-8746]. Here we present molecular dynamics simulations aimed at elucidating the structural transitions that accompany the encapsulation and dehydration processes. Myoglobin associates with CTAB surfactants in solution, but no complete reverse micelle is formed. Upon removal of most of the water and exposure of the system to vacuum, a stable protein-surfactant reverse micelle forms. The surfactants shield the protein to a large extent from dehydration-related conformational changes, in the same manner that a water shell does, as previously described by Patriksson et al. [(2007) Biochemistry 46, 933-945]. Solvated CTAB micelles undergo a rapid inversion when transported to the gas phase and form very stable reverse micelles, independent of the amount of water present.

Tailoring of horseradish peroxidase activity in cationic water-in-oil microemulsions.

Horseradish peroxidase (HRP) in cationic water-in-oil (W/O) microemulsions has always been ignored in reverse micellar enzymology, mainly because cationic surfactants are inhibitors of enzyme peroxidase. In the present study, for the first time, we have successfully introduced the cationic W/O microemulsion as an attractive host for efficient HRP activity. To this notion, much improved activity of HRP was observed in the W/O microemulsion of cetyltrimethylammonium bromide (CTAB) with an increase in n-hexanol concentration and W0 ([water]/[surfactant]), presumably due to the increased interfacial area of the microemulsions. In support of our above observation, six surfactants were synthesized with an increased headgroup size where the methyl groups of CTAB were subsequently replaced by the n-propyl and 2-hydroxyethyl groups, respectively, to prepare mono-, di-, and tripropylated/hydroxyethylated n-hexadecylammonium bromide. The peroxidase activity enhanced with headgroup size and also followed an overall trend similar to that found in the case of CTAB. Possibly, the reduced positive charge density at the augmented interfacial area by means of increase, either in headgroup size, cosurfactant concentration, and/or W0, is not capable of inactivating HRP. Also, the larger space at the interface may facilitate easier solubilization of the enzyme and increase the local concentration of enzyme and substrate, leading to the higher activity of HRP. The best activity was obtained with surfactant N-hexadecyl-N,N,N-tripropylammonium bromide, the highest ever found in any cationic W/O microemulsions, being almost 3 times higher than that found in water. Strikingly, this observed highest activity is comparable with that observed in an anionic bis(2-ethylhexyl)sulfosuccinate sodium salt (AOT)-based system, the best W/O microemulsions used for HRP.

DNA-network-templated self-assembly of silver nanoparticles and their application in surface-enhanced Raman scattering.

A large-scale lambda-DNA network on a mica surface was successfully fabricated with a simple method. Silver nanoparticles capped with the cationic surfactant cetyltrimethylammonium bromide (CTAB) were self-assembled onto a two-dimensional DNA network template by electrostatic interaction and formed nanoporous silver films, which can be used as active surface-enhanced raman scattering (SERS) substrates. Two probe molecules, Rhodamine 6G (R6G) and 4-aminothiophenol (4-ATP), were studied on these substrates with very low concentrations, and great enhancement factors for R6G (0.21 x 10(10)-4.09 x 10(11)) and 4-ATP (approximately 1.70 x 10(5)) were observed. It was found that the enhancement ability was affected by the DNA concentration and the electrostatic absorption time of the CTAB-stabilized silver nanoparticles on the DNA strands. These SERS substrates formed by the self-assembly of silver nanoparticles on DNA network also show good stability and reproducibility in our experiments.