Takatsugu Tanaka

Imaging the passage of a single hydrocarbon chain through a nanopore.

Molecular transport through nanoscale pores in films, membranes and wall structures is of fundamental importance in a number of physical, chemical and biological processes. However, there is a lack of experimental methods that can obtain information on the structure and orientation of the molecules as they pass through the pore, and their interactions with the pore during passage. Imaging with a transmission electron microscope is a powerful method for studying structural changes in single molecules as they move and for imaging molecules confined inside carbon nanotubes. Here, we report that such imaging can be used to observe the structure and orientation of a hydrocarbon chain as it passes through nanoscale defects in the walls of a single-walled carbon nanotube to the vacuum outside, and also to study the interactions between the chain and the nanopore. Based on experiments at 293 K and 4 K we conclude that the major energy source for the molecular motions observed at 4 K is the electron beam used for the imaging.

Imaging of Conformational Changes of Biotinylated Triamide Molecules Covalently Bonded to a Carbon Nanotube Surface

A diamide molecule bearing a biotin terminus was bonded via an amide linkage to the surface of an aminated single-walled carbon nanotube and examined by a high-resolution transmission electron microscope. The still and movie images allowed us to study not only the conformation of the molecule but also its time evolution. An iterative sequence of modeling and simulation allowed us to assign one plausible conformation out of >10(8) possibilities. The images also provide direct support for the accepted wisdom that the curved regions of pristine carbon nanotubes are chemically reactive.

Photoinduced electron transfer of nanohybrids of carbon nanohorns with amino groups and tetrabenzoic acid porphyrin in aqueous media

Amino carbon nanohorns (CNH–NH2) are covalently and non-covalently functionalized with tetrabenzoic acid porphyrin (H2P(CO2H)4) forming dispersible nanohybrids in aqueous solution; the nanohybrids are characterized by spectroscopy and electron microscopy. Photoinduced electron-transfer processes of the nanohybrids of carbon nanohorns in aqueous solution are revealed with time-resolved absorption and fluorescence measurements. From the observed fluorescence quenching of the H2P(CO2H)4 moieties by CNH–NH2, charge separation via the excited singlet state of the H2P moieties, generating radical cations localized in the H2P moieties and electrons trapped in CNH, is suggested. In the presence of methylviologen dication (MV2+) and a hole-shifting reagent, electron pooling is observed by the light-illumination of the H2P(CO2H)4 moieties in CNH–NH2 nanohybrids, suggesting that the electron generated by the charge-separation migrates to MV2+ in aqueous solution.