Takumi Oshima

Facile Synthesis of Highly Water-Soluble Fullerenes More Than Half-Covered by Hydroxyl Groups

Using a novel hydrogen peroxide heating method, we synthesized milky white, water-soluble polyhydroxylated fullerenes (fullerenols) with 36-40 hydroxyl groups (estimated average) along with 8-9 secondary bound water molecules. The fullerenols exhibited high water solubility up to 58.9 mg/mL in a neutral (pH = 7) condition. Dynamic light scattering analysis showed a high dispersion property, to give a narrow particle size distribution within 0.7-2.0 nm.

Antioxidant Activity of Supramolecular Water-Soluble Fullerenes Evaluated by β-Carotene Bleaching Assay

We investigated the antioxidant activity of supramolecular water-soluble fullerenes, polyvinylpyrrolidone (PVP)-entrapped C60, and γ-cyclodextrin (CD)-bicapped C60, based on comparable β-carotene bleaching assay. Antioxidant activity against reactive oxygen species (ROS) generated by three different methods, (i) autoxidation of linoleic acid, (ii) hydrogen peroxide promoter, and (iii) photoirradiation, was evaluated as percent of inhibition relative to a control experiment in view of the bleaching rate constant (k obs) as well as the persistent absorbancy of β-carotene. Water-soluble fullerenes exhibit significant inhibitory effects on the oxidative discoloration of β-carotene in any system.

Kinetic Study of the Diels–Alder Reaction of Li+@C60 with Cyclohexadiene: Greatly Increased Reaction Rate by Encapsulated Li+

We studied the kinetics of the Diels-Alder reaction of Li(+)-encapsulated [60]fullerene with 1,3-cyclohexadiene and characterized the obtained product, [Li(+)@C60(C6H8)](PF6(-)). Compared with empty C60, Li(+)@C60 reacted 2400-fold faster at 303 K, a rate enhancement that corresponds to lowering the activation energy by 24.2 kJ mol(-1). The enhanced Diels-Alder reaction rate was well explained by DFT calculation at the M06-2X/6-31G(d) level of theory considering the reactant complex with dispersion corrections. The calculated activation energies for empty C60 and Li(+)@C60 (65.2 and 43.6 kJ mol(-1), respectively) agreed fairly well with the experimentally obtained values (67.4 and 44.0 kJ mol(-1), respectively). According to the calculation, the lowering of the transition state energy by Li(+) encapsulation was associated with stabilization of the reactant complex (by 14.1 kJ mol(-1)) and the [4 + 2] product (by 5.9 kJ mol(-1)) through favorable frontier molecular orbital interactions. The encapsulated Li(+) ion catalyzed the Diels-Alder reaction by lowering the LUMO of Li(+)@C60. This is the first detailed report on the kinetics of a Diels-Alder reaction catalyzed by an encapsulated Lewis acid catalyst rather than one coordinated to a heteroatom in the dienophile.

Stereochemistry of the copper perchlorate or copper bromide-catalyzed decomposition of aryldiazomethanes to stilbenes

Several phenyldiazomethanes easily decompose to cis- and trans-stilbenes when treated with catalytic amounts of copper perchlorate or copper bromide at 20°C. The preferential formation of cis isomer is particularly noteworthy. The stereochemistry and the mechanism of these reactions will be discussed.

Facile and Exclusive Formation of Aziridinofullerenes by Acid-catalyzed Denitrogenation of Triazolinofullerenes

Variously substituted [6,6]closed aziridinofullerenes were exclusively obtained from acid-catalyzed denitrogenation of triazolinofullerenes without formation of relevant [5,6]open azafulleroids, which are the major products on noncatalyzed denitrogenation. The mechanistic consideration by DFT calculations suggested a reaction sequence involving initial pre-equilibrium protonation of the triazoline N(1) atom, generation of aminofullerenyl cation by nitrogen-extrusion, and final aziridination.

Synthesis of a lithium-encapsulated fullerenol and the effect of the internal lithium cation on its aggregation behavior

AbstractA lithium-encapsulated fullerenol Li@C60(OH)18, as an example of a polar solvent-soluble endohedral fullerene derivative, has been synthesized and fully characterized by infrared spectroscopy, nuclear magnetic resonance spectroscopy, UV spectroscopy, electron spin resonance (ESR) spectroscopy, matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS), elemental analysis, thermogravimetric analysis, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and the particle size was determined using the induced grating (IG) method, and scanning probe microscopy. The encapsulated Li+ was clearly detected by 7Li NMR at very high field in the range −15 to −19 ppm, an intermediate lithium-encapsulated fullerenol was detected by MALDI-TOF-MS, and the molar ratio of lithium-encapsulated fullerenol to empty fullerenol was quantitatively determined to be 12:88 by ICP-AES. The solid-state ESR and particle size measurements using the IG method showed the characteristic anionic behavior with no external counter cations, in what can be called a “cation-encapsulated anion nanoparticle”, revealing the drastic differences between its properties and those of empty C60(OH)16.

One‐step Synthesis of Water‐soluble Fullerenols Bearing Nitrogen‐containing Substituents

We found a facile one‐step synthetic method for water‐soluble fullerenols bearing 8–16 nitrogen‐containing substituents as well as more than 16 hydroxyl groups from commercially available C60 as a starting material. The water solubility of one of the products showed the same as the highest one reported (>200 mg/mL). Other fullerenols bearing hydrogen or diethylamino group on the same fullerene cage were also synthesized by the modified method using hydrogen peroxide as a simple hydroxylation reagent.

Facile synthetic methods of acetals and crown ethers from the reaction of diphenyldiazomethane with 2,3-dichloro-5,6-dicyanobenzoquinone in the presence of alcohols

Abstract The reaction of diphenyldiazomethane with 2,3-dichloro-5,6-dicyano-benzoquinone in the presence of alcohols and thiols gave the corresponding benzophenone acetals and thioacetals at 20–25°C in 1,2-dichloro-ethane. The mechanism of the reaction will be discussed.

Systematic evaluation and mechanistic investigation of antioxidant activity of fullerenols using β -carotene bleaching assay

Antioxidant activity of hydroxylated fullerenes, so-called fullerenols, against lipid peroxyl radical was evaluated by β-carotene bleaching assay. All samples showed moderate to high antioxidant activity (%AOA), especially for C60(OH)12 (70.1) and C60(OH)44 (66.0) as compared with 8, 24, 26, and 36 hydroxylated ones (31.7-62.8). The detection of the possible products was conducted in the model reaction of both fullerenols and C60 with methyl linoleate by MALDI-TOF-MS. These results suggested that the two possible mechanisms, such as C-addition to double bonds and H-abstraction from-OH groups, are involved in the present radical scavenging reaction.

Thermal [2+2] cycloaddition of morpholinoenamines with C60 via a single electron transfer.

The thermal reaction of C(60) with five- and six-membered morpholinocycloalkenes in refluxing toluene exclusively gave the [2+2] cycloadducts in high yields. However, a seven-membered homologue sluggishly reacted with C(60) because of the increasing steric hindrance. This cycloaddition reaction is likely to proceed via a single electron transfer (SET), a radical-coupling, and subsequent ion cyclization rather than the prior proton transfer between the radical ions.