Hierarchical self-assembly of amphiphilic calix[6]arene wheels and viologen axles in water.

We have designed and synthesized two amphiphilic calix[6]arene derivatives, CA8 and CA18, that combine the potential to act as wheel components for pseudorotaxane structures with the self-assembly features typical of surfactant molecules in aqueous solution. Their endo-cavity recognition and selfaggregation properties were compared with those of a non-amphiphilic analogue, C8. TEM, DLS, and fluorescence experiments show that in water the amphiphilic calixarenes form vesicle- and micelle-like aggregates. The size, nature and properties of such aggregates depend on the length of the alkyl chain anchored at the lower rim of the calix[6]arene skeleton, as well as on the inclusion of a molecular guest into the wheel. Specifically, the release of a fluorescent guest entrapped inside the CA8 vesicles is accelerated in the presence of dioctylviologen axles that can pierce the calixarene cavity.

Biofunctionalization of anisotropic nanocrystalline semiconductor-magnetic heterostructures.

Asymmetric binary nanocrystals (BNCs) formed by a spherical γ-Fe(2)O(3) magnetic domain epitaxially grown onto a lateral facet of a rodlike anatase TiO(2) nanorod have been functionalized with PEG-terminated phospholipids, resulting in a micellar system that enables the BNC dispersion in aqueous solution. The further processability of the obtained water-soluble BNC including PEG lipid micelles and their use in bioconjugation experiments has been successfully demonstrated by covalently binding to bovine serum albumin (BSA). The whole process has also been preliminarily performed on spherical iron oxide nanocrystals (NCs) and TiO(2) nanorods (NRs), which form single structural units in the heterostructures. Each step has been thoroughly monitored by using optical, structural, and electrophoretic techniques. In addition, an investigation of the magnetic behavior of the iron oxide NCs and BNCs, before and after incorporation into PEG lipid micelles and subsequently bioconjugation, has been carried out, revealing that the magnetic characteristics are mostly retained. The proposed approach to achieving water-soluble anisotropic BNCs and their bioconjugates has a large potential in catalysis and biomedicine and offers key functional building blocks for biosensor applications.