Langmuir and Gibbs magnetite NP layers at the air/water interface

The interfacial properties of Fe(3)O(4)@MEO(2)MA(90)-co-OEGMA(10) NPs, recently developed and described as promising nanotools for biomedical applications, have been investigated at the air/water interface. These Fe(3)O(4) NPs, capped with catechol-terminated random copolymer brushes of 2-(2-methoxyethoxy) ethyl methacrylate (MEO(2)MA) and oligo(ethylene glycol) methacrylate (OEGMA), with molar fractions of 90% and 10%, respectively, proved to be surface active. Surface tension measurements of aqueous dispersions of the NPs showed that the adsorption of the NPs at the air/water interface is time- and concentration-dependent. These NPs do not behave as classical amphiphiles. Once adsorbed at the air/water interface, they do not exchange with NPs in bulk, but they are trapped at the interface. This means that all NPs from the bulk adsorb to the interface until reaching maximum coverage of the interface, which corresponds to values between 6 × 10(-4) and 8 × 10(-4) mg/cm(2) and a critical equilibrium surface tension of ～47 mN/m. Moreover, Langmuir layers of Fe(3)O(4)@MEO(2)MA(90)-co-OEGMA(10) NPs have been investigated by measuring surface pressure-area compression-expansion isotherms and in situ X-ray fluorescence spectra. The compression-expansion isotherms showed a plateau region above a critical surface pressure of ～25 mN/m and a pronounced hysteresis. By using a special one-barrier Langmuir trough equipped with two surface pressure microbalances, we have shown that the NPs are squeezed out from the interface into the aqueous subphase, and they readsorb on the other side of the barrier. The results have been supported by TEM as well as AFM experiments of transferred Langmuir-Schaefer films on solid supports. This study shows the ability of Fe(3)O(4)@MEO(2)MA(90)-co-OEGMA(10) NPs to transfer from hydrophilic media (an aqueous solution) to the hydrophobic/hydrophilic interface (air/water interface) and back to the hydrophilic media. This behavior is very promising, opening studies of their ability to cross biological membranes.     

Multifunctional, polymorphic, ionic fullerene supramolecular materials: self-assembly and thermotropic properties

An N-methylfulleropyrrolidine (2) bearing three eicosyloxy chains on the laterally substituted phenyl group can be further functionalized to give the ionic fullerene derivative, i.e., N,N-dimethylfulleropyrrolidinium iodide (1). The spectroscopic, electrochemical, self-assembly, and liquid crystalline properties of 1 have been investigated and compared to its neutral precursor 2. Changes in electronic structure upon ionization are observed in the UV spectra. Additionally, a positive potential shift of electrochemical reductions for 1 compared to those of 2 is noted in both homogeneous solution and film state. Driven by the π-π, van der Waals, and electrostatic interactions, the ionic compound 1 is able to form a variety of functional and polymorphic self-assembled structures both from solution and on substrates, including hierarchically organized flakelike microparticles with high water repellency, doughnut-shaped objects with rough surfaces, and long one-dimensional C(60) nanowires (>1 μm). The thermotropic behavior of 1 has also been investigated, and a smectic liquid crystalline phase was observed at elevated temperatures. Further investigations of the thermotropic behavior of 1 revealed that a deionization back-reaction from 1 to the neutral precursor 2 gradually occurred. The mechanism of this deionization reaction is presented and discussed. These investigations provide insight into the effects of added ionicity to alkylated fullerene derivatives, in particular on their self-assembly features and functionality.     

Ultrasonic approach for formation of erbium oxide nanoparticles with variable geometries

Ultrasound (20 kHz, 29 W·cm(-2)) is employed to form three types of erbium oxide nanoparticles in the presence of multiwalled carbon nanotubes as a template material in water. The nanoparticles are (i) erbium carboxioxide nanoparticles deposited on the external walls of multiwalled carbon nanotubes and Er(2)O(3) in the bulk with (ii) hexagonal and (iii) spherical geometries. Each type of ultrasonically formed nanoparticle reveals Er(3+) photoluminescence from crystal lattice. The main advantage of the erbium carboxioxide nanoparticles on the carbon nanotubes is the electromagnetic emission in the visible region, which is new and not examined up to the present date. On the other hand, the photoluminescence of hexagonal erbium oxide nanoparticles is long-lived (μs) and enables the higher energy transition ((4)S(3/2)-(4)I(15/2)), which is not observed for spherical nanoparticles. Our work is unique because it combines for the first time spectroscopy of Er(3+) electronic transitions in the host crystal lattices of nanoparticles with the geometry established by ultrasound in aqueous solution of carbon nanotubes employed as a template material. The work can be of great interest for "green" chemistry synthesis of photoluminescent nanoparticles in water.     

Local control of antibody binding to hapten-presenting interfaces: Steric and electrostatic interaction

The binding of labeled antibodies to hapten substituted monolayers at the air/water interface has been studied by means of fluorescence microscopy. Haptens with various spacer lengths between the epitope and a hydrocarbon chain, anchoring the molecule to the interface, have been synthesized. With DMPC,^a unspecific binding has been shown to predominate over specific binding due to electrostatic interactions. At high surface pressures the bound antibody is detached because of steric interference with the lipid head groups. Due to a reduction of electrostatic interactions, no unspecific binding is observed to monolayers of cholesterol, which carries a small dipole moment. Mixed monolayers of cholesterol and DMPC separate into two fluid phases, with preferential antibody binding to the cholesterol-enriched phase.