N-Heterocyclic Carbene-Modified Au-Pd Alloy Nanoparticles and Their Application as Biomimetic and Heterogeneous Catalysts.

The preparation of water-soluble, N-heterocyclic-carbene-stabilized Au-Pd alloy nanoparticles by a straightforward ligand exchange process is presented. Extensive analysis revealed excellent size retention and stability over years in water. The alloy nanoparticles were applied as biomimetic catalysts for aerobic oxidation of d-glucose, for which monometallic Au and Pd nanoparticles showed no or negligible activity. The alloy nanoparticles were further applied as titania-supported heterogeneous catalysts for the mild hydrogenation of nitroarenes and the semihydrogenation of 1,2-diphenylacetylene with a solvent-dependent selectivity switch between E- and Z-stilbene.

A Modular System for the Design of Stimuli-Responsive Multifunctional Nanoparticle Aggregates by Use of Host-Guest Chemistry.

A self-assembly approach for the design of multifunctional nanomaterials consisting of different nanoparticles (gold, iron oxide, and lanthanide-doped LiYF4 ) is developed. This modular system takes advantage of the light-responsive supramolecular host-guest chemistry of ß-cyclodextrin and arylazopyrazole, which enables the dynamic and reversible self-assembly of particles to spherical nanoparticle aggregates in aqueous solution. Due to the magnetic iron oxide nanoparticles, the aggregates can be manipulated by an external magnetic field leading to the formation of linear structures. As a result of the integration of upconversion nanoparticles, the aggregates are additionally responsive to near-infrared light and can be redispersed by use of the upconversion effect. By varying the nanoparticle and linker concentrations the composition, size, shape, and properties of the multifunctional nanoparticle aggregates can be fine-tuned.

Stimulus-Responsive Assembly of Nanoparticles using Host-Guest Interactions of Cyclodextrins.

The design of multifunctional nanomaterials that respond to external stimuli and mimic the capacity of biological materials to respond and adapt to their environment has become a focus of interest in nanotechnology. In this Concept, we describe the development of supramolecular nanoparticle assemblies constructed by use of host-guest interactions between cyclodextrins and suitable guest molecules. The nanoparticle assembly is reversible and can be directed by applying different stimuli that act either on the guest molecules or the nanoparticles. This strategy can be extended to mesoscale assembly of microparticles. We highlight the newest research work in this field of nanochemistry and point out future perspectives and opportunities.

Stabilization of High Oxidation State Upconversion Nanoparticles by N-Heterocyclic Carbenes.

The stabilization of high oxidation state nanoparticles by N-heterocyclic carbenes is reported. Such nanoparticles represent an important subset in the field of nanoparticles, with different and more challenging requirements for suitable ligands compared to elemental metal nanoparticles. N-Heterocyclic carbene coated NaYF4 :Yb,Tm upconversion nanoparticles were synthesized by a ligand-exchange reaction from a well-defined precursor. This new photoactive material was characterized in detail and employed in the activation of photoresponsive molecules by low-intensity near-infrared light (λ=980 nm).

Near-infrared photoswitching of cyclodextrin-guest complexes using lanthanide-doped LiYF4 upconversion nanoparticles.

This communication reports a new type of supramolecular cyclodextrin-guest complexes using cyclodextrin coated upconversion nanoparticles as hosts and monovalent and divalent azobenzenes and arylazopyrazoles as guests. A potentially biocompatible photocontrol of the interaction by isomerization of the azobenzene or arylazopyrazole was achieved by laser irradiation at 980 nm and a very low light intensity of 0.22 W cm-2.