The molybdenum dioxo catalyst CNH/MoO2 is prepared via direct grafting of (dme)MoO2Cl2 (dme = 1,2-dimethoxyethane) onto the graphitic surfaces of carbon nanohorn (CNH) substrates. The structure of this heterogeneous catalyst was characterized by SMART-EM, XPS, and ICP, and is found to have single isolated MoO2 species on the surface as well as a few multi-Mo species. The CNH/MoO2 complex exhibits excellent catalytic activity for polyethylene terephthalate (PET) hydrogenolysis, N-oxide reductions, and reductive carbonyl coupling, representing an informative model catalyst for structural and mechanistic investigations.

Cyclodextrins (CDs) are doughnut-shaped cyclic oligosaccharides having a cavity and two rims. Inclusion binding in the cavity has long served as a classic model of molecular recognition, and rim binding has been neglected. We found that CDs recognize guests by size-sensitive binding using the two rims in addition to the cavity, using single-molecule electron microscopy and a library of graphitic cones as a solid-state substrate for complexation. For example, with its cavity and rim binding ability combined, γ-CD can recognize a guest of radius between 4 and 9 Å with a size-recognition precision of better than 1 Å, as shown by structural analysis of thousands of individual specimens and statistical analysis of the data thereof. A 2.5 ms resolution electron microscopic video provided direct evidence of the process of size recognition. The data suggest the occurrence of the rim binding mode for guests larger than the size of the CD cavity and illustrate a unique application of dynamic molecular electron microscopy for deciphering the spatiotemporal details of supramolecular events.