Controlled aggregation of functionalized gold nanoparticles with a novel conjugated oligomer.

A new route is developed to control the self-assembly of gold nanoparticles (AuNPs) functionalized with a novel pyridyl-ended porphyrin-oligo(p-phenylene vinylene) conjugated oligomer (P-OPV-Py) into branched-rods, chain-networks, uniform fractal-like Au clusters, and larger nanoparticles. The techniques of optical spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS) are used to characterize the self-assembly in various solvent systems (pure toluene, CHCl(3)/toluene, THF/toluene and n-butanol/toluene). A combination of the ligand/AuNPs molar ratio and relative concentration serves as the driving force to control the size and shape of P-OPV-Py capped AuNPs.     

Shape-persistent macrocycles: from molecules to materials

Shape-persistent macrocycles with an interior in the nanometer regime allow the attachment of (functional) side groups at defined positions at the ring. These side groups can have either a fixed orientation relative to the molecular backbone or they can adapt their orientation according to an external stimulus. The properties and applications of the compounds depend strongly on the orientation of these side groups. Macrocycles with intraannular or adaptable long alkyl groups display a new design principle for discotic liquid crystals. Macrocycles with extraannular (oligo)alkyl groups can be used for surface patterning in the nanometer regime and rings with extraannular oligostyryl groups are able to aggregate to supramolecular hollow polymer brushes.     

Macrocyclic glycoclusters: from amphiphiles through nanoparticles to glycoviruses

Macrocyclic glycocluster amphiphiles are intended to be a covalent-bundle mimic of clustering glycolipid motifs on the cell membrane. They are irreversibly micellized to give glycocluster nanoparticles (GNPs); their masked hydrophobicity endows them with remarkable saccharide specificities in the interactions with biological saccharide receptors. The GNPs also exhibit unprecedented hydrogen-bond capacities; they are agglutinated with Na(2)HPO(4) and assembled on plasmid DNA in a number-, size-, and shape-controlled manner to give artificial glycoviral particles capable of transfection. Thus, the intrinsic function of viruses, that is, cell invasion followed by gene expression, is also intrinsic to size-regulated (approximately 50 nm) glycoviruses. The growth of glycocluster amphiphiles through nanoparticles to glycoviruses reveals a hierarchical adhesion control of the saccharide clusters.     

Assembly of a tetrathiafulvalene-anthracene dyad on the surfaces of gold nanoparticles: tuning the excited-state properties of the anthracene unit in the dyad

Due to the unique features of the tetrathiafulvalene (TTF) unit, such as the electron-donating ability and presence of methylthio groups, dyad 1 can be assembled on the surfaces of gold nanoparticles, as indicated by absorption, electrochemical, and fluorescent-spectral studies. Dyad 1 can also be disassembled by the addition of thiols. Assembly of dyad 1 on the surfaces of gold nanoparticles leads to the formation of a triad (A1-D-A2), which in turn modulates the photoinduced electron-transfer process within dyad 1. Accordingly, the fluorescence intensity of dyad 1, after assembly with gold nanoparticles, increases, and the fluorescence lifetime is prolonged. Furthermore, the assembly of dyad 1 on gold nanoparticles facilitates photodimerization of the anthracene units of dyad 1. Both fluorescence and photodimerization are associated with the excited-state behavior of the anthracene unit, thus it may be concluded that the excited-state properties of the anthracene unit can be tuned upon complexation with gold nanoparticles.     

Seed‐Mediated and Iodide‐Assisted Synthesis of Gold Nanocrystals with Systematic Shape Evolution from Rhombic Dodecahedral to Octahedral Structures

We report the development of a seed‐mediated and iodide‐assisted method for the synthesis of monodisperse gold nanocrystals with systematic shape evolution from rhombic dodecahedral to octahedral structures. Particle growth is complete in 15 min at room temperature, so the process is fast and energy‐efficient. By progressively increasing the volume of KI used in a growth solution while keeping the amount of ascorbic acid added constant, nanocrystals with morphologies that vary from rhombic dodecahedral to rhombicuboctahedral, edge‐ and corner‐truncated octahedral, corner‐truncated octahedral, and octahedral structures were synthesized. The nanocrystals are monodisperse in size and readily form self‐assembled structures on substrates. By simply adjusting the volume of gold seed solution added to a growth solution, particle sizes of the octahedral gold nanocrystals can be tuned with average opposite corner‐to‐corner distances of 42, 48, 54, 60, 68, 93, 107, and 125 nm. In the presence of HAuCl₄, iodide may act as a reducing agent. Variation of its volume in the solution may slightly modulate the reduction rate and affect the final crystal morphology. Intermediate structures collected during crystal growth reveal the presence of many twisted structures that surround a developing nanocrystal core. This nanocrystal growth mechanism and the less important role of surfactant in directing the polyhedral nanocrystal morphology is discussed.