Shuji Aonuma

Optically active single-walled carbon nanotubes

The optical, electrical and mechanical properties of single-walled carbon nanotubes (SWNTs) are largely determined by their structures, and bulk availability of uniform materials is vital for extending their technological applications. Since they were first prepared, much effort has been directed toward selective synthesis and separation of SWNTs with specific structures. As-prepared samples of chiral SWNTs contain equal amounts of left- and right-handed helical structures, but little attention has been paid to the separation of these non-superimposable mirror image forms, known as optical isomers. Here, we show that optically active SWNT samples can be obtained by preferentially extracting either right- or left-handed SWNTs from a commercial sample. Chiral gable-type diporphyrin molecules bind with different affinities to the left- and right-handed helical nanotube isomers to form complexes with unequal stabilities that can be readily separated. Significantly, the diporphyrins can be liberated from the complexes afterwards, to provide optically enriched SWNTs.

A facile and scalable process for size-controllable separation of nanodiamond particles as small as 4 nm.

Interest in nanometer-sized particles has increased in recent years, especially from the viewpoint of nanobiology and nanomedicine. Among them are gold, silver, and silica nanoparticles, quantum dots, magnetic beads, carbon nanotubes, and nanodiamond (ND) particles. Since the physical properties of these nanoparticles are largely dependent on their size and shape, control of their structure is vital for advancing both fundamental studies and technological applications. In this context, sizeselective preparation has been established for gold, silver, and silica nanoparticles, quantum dots, and magnetic beads (iron oxide). We have also investigated structure-based separation of single-walled carbon nanotubes by using molecular recognition or ultrasonic atomization. Quite recently, shape, as well as size, was successfully controlled in the preparation of silver and gold nanoparticles. The availability of a wide spectrum of nanoparticle size and shape enables precise investigation of their effects in biological systems. In contrast, the size and shape control of ND is much less developed than that of other nanoparticles. This restricts the potential applications of ND particles, in spite of their many prominent physical properties. Although the biological and medicinal applications of ND have been extensively investigated quite recently due to its biocompatibility, it is somewhat difficult to fully investigate the effect of its size in,

A rosette cooling cell: more effective container for solubilization of single-walled carbon nanotubes under probe-type ultrasonic irradiation.

Probe-type ultrasonication has been employed for surfactant-aided solubilization, or individualization, of single-walled carbon nanotubes (SWNTs). The resulting solution can be used not only for spectroscopic analyses such as absorption, photoluminescence, and circular dichroism, but also for separation by density gradient ultracentrifugation, dielectrophoresis, chromatography, and polymer wrapping. In spite of its importance, the sonochemical processing of SWNTs has not been considered seriously. Herein, we report on a more efficient cooling cell for probe-type ultrasonication. As compared with a conventional cylindrical cell, the concentration of the SWNTs solubilized in water was found to be almost double in a rosette cooling cell after ultracentrifugation. The efficiency of a rosette cell can be attributed to the higher efficiency in circulation and cooling of the SWNT dispersion as well as enhancement of the cavitation process.

Design, synthesis, and preliminary ex vivo and in vivo evaluation of cationic magnetic resonance contrast agent for rabbit articular cartilage imaging

Since early-stage diagnosis of osteoarthritis (OA) is necessary to retard the progress of the disease, magnetic resonance (MR) and computed tomography (CT) imaging agents have been applied to evaluate the integrity of the extracellular matrix (ECM) in the articular cartilage (AC). Although several negatively charged contrast agents were employed, they provided indirect images of the AC based on the coulombic repulsion with anionic glycosaminoglycans (GAGs) in the ECM. To achieve direct imaging of the ECM, positively charged contrast agents have quite recently been designed for optical and CT imaging. In this paper, we report on a positively charged MR contrast agent, DOTA-Gd-G2R8, which was applied preliminarily to ex vivo and in vivo imaging of rabbit AC. In the ex vivo imaging, the contrast agent was accumulated in the AC in high concentration due to the strong coulombic attraction between the negative charge of the GAGs and the positive charge of the octaarginine (R8). The thickness of the AC measured in the MR image was found to be comparable to that determined by the histological staining of the slice. The AC was also observed in vivo by MR imaging with the use of DOTA-Gd-G2R8.

g-Tensor analyses of β'-type Pd(dmit)2 metal complexes

ESR measurements and g -tensor analyses were performed for metal complexes, g -type Pd(dmit) 2 . The ESR g -values of g -type Pd(dmit) 2 are found to be beyond one radical description which is a good approximation for conventional molecular based conductors. In this paper we focus on the anomalous behavior of the ESR g -values in g -type Pd(dmit) 2 . We discuss the possible explanation of the electronic structure of g -type Pd(dmit) 2 metal complexes from microscopic points of view. metal complexes dmit ESR

Synthesis, properties and molecular-orbital calculations of new π-acceptors as ortho-analogues of DCNQI

New π-acceptor molecules, DCNA, DF-DCNA and DBr-DCNA have been synthesized as ortho-analogues of DCNQI, in which two cyanoimino groups are located positions next to each other. Molecular orbital calculations by several methods have been made and compared with the actual molecular geometry and reduction potentials.

Methyl Rotation and Reentrant Metal-Insulator Transition in Deuterated (DMe-DCNQ1) 2 Cu System

We studied the thermal property of metal complex salts (DMe-DCNQI) 2 Cu formed of DMe-DCNQI molecules of which some of hydrogen atoms are substituted by deuterium atoms. In those systems, we have discovered peaks in the specific heat originating from the orientation freedom of deuterated methyl groups. In systems containing methyl groups with one deuterium atom (CH 2 D), we found Schottky type of specific heat. In system with CHD 2 , we observed peaks not of Schottky type. To find out the origin and mechanism of these anomalies, we carried out the thermal study of the mixed crystals composed of molecules with CH 2 D and those with CHD 2 . We clarified the conformational ordering of CHD 2 molecular along c axis in the DCNQI-Cu system. Methyl Rotation Thermal properties Order-disorder transition M-I transition Phase Transition Mott Transition CDW Specific heat Deuteration