Sodium effect on self-organization of amphiphilic carboxylates: formation of structured micelles and superlattices.

Not only the self-aggregation of dendritic polycarboxylates into structurally persistent micelles, but also that of the micelles themselves into superlattices is controlled by alkali-metal counterions and shows a pronounced sodium effect. Our combined experimental and computational work has revealed the formation of superlattices for the first time. The behavior of a variety of amphiphilic carboxylates and the different effects of the alkali cations Li(+), Na(+), and K(+) have been investigated by conductivity measurements, cryogenic transmission electron microscopy (cryo-TEM), and molecular-dynamics (MD) simulations. Together, these show that sodium salts of the amphiphiles give the most stable micelles, followed by lithium and potassium. Our results suggest that ion multiplets in bridging positions, rather than contact ion pairs, are responsible for the enhanced stability and the formation of hexagonally ordered superlattices with sodium counterions. Potassium ions do not form such ion multiplets and cannot therefore induce aggregation of the micelles. This sodium effect has far-reaching consequences for a large number of biological and technical systems and sheds new light on the origin of specific-ion effects.

Nanotube surfactant design: the versatility of water-soluble perylene bisimides.

The synthesis of perylene-based single-walled carbon nanotube (SWCNT) surfactants and the dispersion and exfoliation of SWCNTs in water by a variety of designed surfactants is investigated. The quality of the nanotube dispersions is evaluated by optical absorption and emission spectroscopy, zeta-potential measurements and statistical atomic force microscopy (AFM). Significantly the dispersion efficiency can be increased at higher pH, as water solubility of the surfactants is ensured by peripheral derivatization with carboxyl-functionalized first- and second-order Newkome dendrimers. Even at very low perylene concentrations of 0.1 g L(-1) and a nanotube-to-surfactant ratio of 1:1, the nanotube supernatant after centrifugation contains up to 73% of the pristine material with exfoliation degrees (the number of fractions of individualized nanotubes N(I)/N(T)) of up to 76%. The adsorption of the perylene core to the nanotube scaffold is indicated by red-shifted perylene-absorption and SWCNT-emission features except for the smallest perylene amphiphile, where solubilization is presumably based on a micellar arrangement. The nanotube fluorescence is significantly altered and reduced in intensity compared to nanotubes dispersed in sodium dodecylbenzene sulfonate (SDBS) being strongly dependent on the structure of the perylene surfactant. We attribute this observation to the homogeneity of the surfactant coverage, e.g., the supramolecular arrangement onto the nanotube backbone. This study represents a step forward in understanding the structure-property relationship of nanotube surfactants. Furthermore high-quality nanotube dispersions with increased degrees of exfoliation are highly desirable, as the efficiency of nanotube separation techniques relies on highly individualized samples.

In vitro behavior of layer-by-layer deposited molecular oligoelectrolyte films on Ti-6Al-4V surfaces.

Layer-by-layer self-assembled films of molecular oligoelectrolytes were used to modify Ti-6Al-4V surfaces in order to test their ability as potential drug delivery system. With regard to medical application the in vitro behavior of the modified material was investigated. The Ti-6Al-4V (6% aluminium, 4% vanadium) material was treated in a layer-by-layer (LbL) process with 2, 4, 6 and 8 layers of molecular oligoelectrolytes 1 and 2 and thereby doped with a fluorescent reporter molecule 2. Human osteoblasts were cultured for a period up to 5 days on the modified material. Ti-6Al-4V surfaces without modification were used as control. In order to investigate the in vitro behavior of the coating as well as the influence of components of the coating on osteoblastic cells, respectively, cell proliferation, differentiation and attachment of hFOB cells were observed by means of cell number, osteoblastic gene expression and fluorescence microscopy. Degradation behavior of the OEM (oligoelectrolyte multilayer film) was examined using optical spectroscopy. Measurement data imply that the layer-by-layer coating was successfully assembled on the Ti surface and endures steam sterilization. The fluorescence signal in cell culture medium increased strictly linear with increasing pre-assembled number of layers on the surface. Proliferation rates of the cells in experimental groups did not differ significantly from each other (P >or= 0.783). Differentiation pattern was not significantly changed by the coating. The fluorescent reporter component of the film was absorbed by osteoblastic cells and was detected by fluorescence microscopy.

Layer-by-layer deposition of molecular oligoelectrolytes-investigation of assembling and degradation behaviour.

The assembly and degradation behavior of oligoelectrolyte multilayer films (OEMs) self assembled by layer-by-layer deposition of positively and negatively charged oligoelectrolytes 1-6 was investigated. Next to colorless oligoelectrolytes we have employed representatives involving chromophores, in particular porphyrins. This allows for the systematic observation of both assembly and disassembly of the OEMs using optical spectroscopy, where chromophore containing building blocks serve as reporter electrolytes. The OEMs investigated in this study were built in a consistent, monomolecular matter and show linear correlation between the absorption and the number of layers. Using the concept of reporter electrolytes we have introduced for the first time also the use of non-chromophoric oligoelectrolytes, such as the new synthesized cationic system 2 as building blocks for OEMs. Moreover, we have investigated for the first time the degradation behavior of OEMs. We demonstrated that two different mechanisms of degradation proceed at the same time. The direct degradation is accompanied by a second release mechanism.