Polymer-stabilized phospholipid vesicles with a controllable, pH-dependent disassembly mechanism.

In this letter, we report a facile method to prepare robust phospholipid vesicles using commonly available phospholipids that are stabilized via the formation of an interpenetrating, acid-labile, cross-linked polymer network that imparts a site for controlled polymer destabilization and subsequent vesicle degradation. The polymer network was formed in the inner lamella of the phospholipid bilayer using 2,2-di(methacryloyloxy-1-ethoxy)propane (DMOEP) and butyl methacrylate (BMA). Upon exposure to acidic conditions, the highly cross-linked polymer network was partially converted to smaller linear polymers, resulting in substantially reduced vesicle stability upon exposure to chemical and physical insults. Isolated polymers had pH-dependent-solubility in THF. Transmission electron microscopy and dynamic light scattering revealed time-dependent enhanced vesicle stability in high concentrations of surfactant and vacuum conditions at elevated pH, whereas exposure to acidic pH rapidly decreased the vesicle stability, with complete destabilization observed in less than 24 h. The resultant transiently stabilized vesicles may prove useful for enhanced drug delivery and chemical sensing applications and allow for improved physiological clearance.

Synthesis of neutral spin-delocalized electron acceptors for multifunctional materials.

A new synthetic route to stable spin-delocalized radicals, annelated nitronyl nitroxides, has been developed on the basis of the condensation of benzofuroxan with aryl nitrones. The electronic structure of the resulting radicals was investigated through absorption spectroscopy, EPR, electrochemistry, and computation (DFT-UB3LYP). The annelated radicals exhibit electronic transitions in the near IR (850-900 nm) and are excellent electron acceptors (E(red) approximately 0.0 vs SCE) ideal for the development of multifunctional magnetic materials.

Field induced formation of mesoscopic polymer chains from functional ferromagnetic colloids.

The assembly and direct imaging of ferromagnetic nanoparticles into one-dimensional mesostructures (1-D) are reported. Polymer-coated ferromagnetic colloids (19 nm, 24 nm) were assembled at a crosslinkable oil-water interface under both magnetic field induced and zero-field conditions and permanently fixed into 1-D mesoscopic polymer chains (1-9 mum) in a process referred to as Fossilized Liquid Assembly (FLA). In the FLA process, nanoparticle chains were fixed at the oil interface through photopolymerization, enabling direct visualization of organized mesostructures using atomic force microscopy. Using the FLA methodology, we systematically investigated different conditions and demonstrated that dispersed ferromagnetic colloids possess sufficient dipolar interactions to organize into mesoscopic assemblies. Application of an external magnetic field during assembly enabled the formation of micron-sized chains which were aligned in the direction of the applied field. This universal methodology is an attractive alternative technique to cryogenic transmission electron microscopy (cryo-TEM) for the visualization of nanoparticle assembly in dispersed organic media.

Polymer-coated ferromagnetic colloids from well-defined macromolecular surfactants and assembly into nanoparticle chains.

A novel synthetic route to polymer-coated ferromagnetic colloids of metallic cobalt has been developed. Well-defined end-functional polystyrenes were synthesized using controlled radical polymerization and used as surfactants in the thermolysis of dicobaltoctacarbonyl to afford uniform ferromagnetic nanoparticles. The presence of the polymer shell enabled prolonged colloidal stability of dispersions in a wide range of organic solvents and formed glassy encapsulating coatings around ferromagnetic cores in the solid state. These polymer-coated colloids assembled into robust, micron-sized nanoparticle chains when cast onto supporting surfaces due to dipolar associations of magnetic cores. Hierarchical assemblies were also prepared by blending polystyrene-coated cobalt colloids with larger silica beads.