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The reactivities of enamines and predistorted (strained) dipolarophiles toward perfluoroaryl azides (PFAAs) were explored experimentally and computationally. Kinetic analyses indicate that PFAAs undergo (3 + 2) cycloadditions with enamines up to 4 orders of magnitude faster than phenyl azide reacts with these dipolarophiles. DFT calculations were used to identify the origin of this rate acceleration. Orbital interactions between the cycloaddends are larger due to the relatively low-lying LUMO of PFAAs. The triazolines resulting from PFAA-enamine cycloadditions rearrange to amidines at room temperature, while (3 + 2) cycloadditions of enamines and phenyl azide yield stable, isolable triazolines. The 1,3-dipolar cycloadditions of norbornene and DIBAC also show increased reactivity toward PFAAs over phenyl azide but are slower than enamine-azide cycloadditions.

Graphene-titanium dioxide (TiO2) hybrid nanomaterials have received much attention due to their high potential in enhancing the photocatalytic efficiency. In the hybrid system, graphene acts as an electron acceptor to ensure the fast charge transfer to the current collector. Three-dimensional (3D) graphene in this context represents a new format of graphene material to further enhance the photocatalytic efficiency. 3D graphene has been shown to be a good candidate for making hybrid materials due to its outstanding properties, including increased surface area, multiple conductivity pathways, absence of intersheet contact resistance, reduced agglomeration of two-dimensional (2D) graphene sheets, and ease of handling and control. The examples included in this chapter have shown the high potential of 3D graphene in developing high-efficiency photocatalysts based on 3D graphene-TiO2 hybrid nanomaterials.

The Diels–Alder (DA) reaction, a classic cycloaddition reaction involving a diene and a dienophile to form a cyclohexene, is among the most versatile organic reactions. Theories have predicted thermodynamically unfavorable DA reactions on pristine graphene owing to its low chemical reactivity. We hypothesized that metals like Ni could enhance the reactivity of graphene towards DA reactions through charge transfer. The results indeed showed that metal substrates enhanced the reactivity of graphene in the DA reactions with a diene, 2,3-dimethoxy butadiene (DMBD), and a dienophile, maleic anhydride (MAH), with the activity enhancement in the order of Ni > Cu, and both are more reactive than graphene supported on silicon wafer. The rate constants were estimated to be two times higher for graphene supported on Ni than on silicon wafer. The computational results support the experimentally obtained rate trend of Ni > Cu, both predicted to be greater than unsupported graphene, which is explained by the enhanced graphene–substrate interaction reflected in charge transfer effects with the strongly interacting Ni. This study opens up a new avenue for enhancing the chemical reactivity of pristine graphene through substrate selection. [ABSTRACT FROM AUTHOR]

Glyconanomaterials, nanomaterials carrying multiple carbohydrate ligands, provide an excellent platform for sensitive protein recognition. Using nanomaterials as the scaffold, multivalent interactions between glycan ligands and proteins have been demonstrated. However, the quantitative analysis of the binding affinity of these glyconanomaterials has been lacking. In this Article, we report a new method to measure the binding affinity of glyconanoparticle (GNP)--protein interactions based on a fluorescent competition binding assay, which yielded the apparent dissociation constant ([K.sub.d]) of GNPs with the interacting protein. Au nanoparticles conjugated with underivatized mono-, oligo-, and polysaccharides were synthesized using our recently developed photo-coupling chemistry. The 'affinities of these GNPs with lectins were measured and were several orders of magnitude higher than the corresponding free ligands with lectins. The effect of iigand display on the binding 'affinity of GNPs was, furthermore, studied where GNPs of varying linker type, spacer length, ligand density, and nanoparticle size were prepared and [K.sub.d] values determined. The long spacer linker containing hydrocarbon and ethylene oxide units gave the highest binding affinity as well as assay sensitivity. The binding 'affinity increased with ligand density in general, showing a drastic increase in affinity at low ligand density. In addition, the affinity enhancement was more pronounced on smaller NPs than the larger ones. These results not only demonstrate that the binding affinity of GNPs is highly influenced by how the ligands are presented on the nanoparticles but also pave the way for tailor-made glyeonanomaterials with tunable affinity by way of ligand display. 10.1021/ac102114z

We report that UV-crosslinked polystyrene (PS) thin films can be used as an inexpensive wet chemical etch resist to create microstructures on silicon wafers. When spin-coated PS films were irradiated, the polymer undergoes UV-induced crosslinking. Patterned PS films were successfully used as the protective layer withstanding chemical etching with the buffered HF solution. Removal of the polymer films by sonicating in water generated microstructures in silicon wafers. This simple and environmentally friendly procedure employs inexpensive commodity polymer and eliminates the use of organic solvents and harsh conditions in the subsequent development process. POLYM. ENG. SCI., 49:945-948, 2009. [C] 2009 Society of Plastics Engineers, INTRODUCTION The production of electronic devices such as capacitor arrays, circuit boards, and CCD displays relies on the fabrication of integrated circuits, complex three-dimensional structures of alternating, patterned layers of [...]