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PubMed2005

Effects of fullerene substituents on structure and photoelectrochemical properties of fullerene nanoclusters electrophoretically deposited on nanostructured SnO2 electrodes.

Two kinds of fullerene derivatives have been designed to examine the effect of the fullerene substituents on the structure and photoelectrochemical properties of fullerene clusters electrophoretically deposited on nanostructured SnO(2) electrodes. The cluster sizes increase and the incident photon-to-current efficiencies decrease with introduction of large substituents into C(60). The trend for photocurrent generation efficiency as well as surface morphology on the electrode can be explained by the steric bulkiness around the C(60) molecules. A C(60) molecule with two alkoxy chains is suggested to give a bilayer vesicle structure, irrespective of the hydrophobic nature of both the C(60) and alkoxy chain moieties. Such information will be valuable for the design of photoactive molecules, which are fabricated onto electrode surfaces to exhibit high energy conversion efficiency.

Journal Article↗
PubMed2005

The first synthesis of a methano[60]fullerene with an electron-donating group at the methano-bridge carbon: synthesis and reaction of aminomethano[60]fullerene.

[reaction: see text] Aminomethano[60]fullerene was synthesized for the first time as a trifluoromethanesulfonic acid salt by applying the Curtius rearrangement of azidocarbonylmethano[60]fullerene as the key reaction. Aminomethano[60]fullerene thus obtained was found to be able to react with various acyl chlorides to afford the corresponding amides.

Journal Article↗
PubMed2006

Ionisation of fullerenes and fullerene clusters using ultrashort laser pulses.

We give a brief review of the literature concerning the ultra-short pulse ionisation of fullerenes in the gas phase. Emphasis is placed on the excitation time dependence of different ionisation regimes as manifested by photoelectron spectroscopy. The ionisation rates are modelled for the intermediate situation where the excitation energy is equilibrated between electronic degrees of freedom but not yet coupled to vibrational degrees of freedom. The model is shown to describe many aspects of the experiments. New results are presented on the intra-cluster molecular fusion of fullerene molecules when van der Waals bound clusters of fullerenes are exposed to ultra-short laser pulses. Pump-probe measurements give a decay time constant for the intra-cluster fusion reaction of 520 +/- 55 fs. A comparison with monomer ionisation results suggests that the time window for the fusion reaction is influenced by the coupling of the electronic excitation energy to vibrational degrees of freedom of the molecules in the cluster.

Journal Article↗
PubMed2006

Geometric and electronic structures of metal-substitutional fullerene C59Sm and metal-exohedral fullerenes C60Sm.

The geometric and electronic structures of metal-substituted fullerene C59Sm and exohedral fullerenes C60Sm are studied using the density-functional theory. The geometric optimization shows that the replacement of a C atom with a Sm in C60 yields a stable substitutionally doped fullerene C59Sm, and among the five possible optimized geometries for C60Sm, the most favorable exohedral sites are above the center of a hexagon and a pentagon ring. The calculations for electronic structures show that the magnetic moment of Sm is preserved for all the stable structures as tiny hybridization takes place between the orbitals of the Sm atom and those of their neighboring carbons. Because of the small energy gaps and the half occupation of the highest occupied molecular orbitals, all the stable C60Sm isomers are inferred to be conductors.

Journal Article↗
PubMed2006

Conversion pathways between a fullerene and a ring among C(20) clusters by a sphere contracting walk method: Remarkable difference in local potential energy landscapes around the fullerene and the ring.

Conversion pathways from a fullerene to a ring and vice versa among C(20) clusters have been explored. A new technique has been developed for discovering multistep reaction pathways, which can be searched by finding constrained energy minima on spheres whose surfaces are contracting from the starting point to the terminal. Local landscapes that appeared on the pathways were found to be considerably different around the fullerene and the ring, from which one can make a new interpretation for no generation of the C(20) fullerene in laser vaporization of graphite.

Journal Article↗
PubMed2003

Computations of model narrow nanotubes closed by fragments of smaller fullerenes and quasi-fullerenes.

New type of carbon nanotubes-narrow nanotubes-has recently been observed with diameters of 4-5 A. It has been postulated that the narrow nanotubes are closed by fullerene fragments of C(20) and C(36). This paper presents computational results on related model nanotubes with stoichiometries such as C(80), C(84), C(96), C(108), or C(120). The computations were carried out at the PM3, AM1, SAM1, HF/3-21G, HF/4-31G, and B3LYP/6-31G(*) levels. Two C(36) fullerenes were considered, D(6h) and D(2d). At the PM3 level and with the C(84) nanotube stoichiometry, the D(2d) cage closure gave a lower energy (by 185 kcal/mol and a diameter of 5.42 A). There is another possible candidate, a C(32) cage with D(4d) symmetry (two four-membered rings). At the PM3 level and with the C(96) nanotube stoichiometry, the D(4d) closure (with a diameter of 5.43 A) had energy lower by 210 kcal/mol than that of the D(6h) nanotube closure. On the other hand, four-membered rings should not play a significant role for narrow nanotubes with a diameter of 4 A, where the dodecahedron-related closure should be exclusive. Still narrower nanotubes are briefly discussed.

Fullerenes↗
PubMed2002

Supramolecular fullerene-porphyrin chemistry. Fullerene complexation by metalated "jaws porphyrin" hosts.

Porphyrins and fullerenes are spontaneously attracted to each other. This new supramolecular recognition element is explored in discrete, soluble, coordinatively linked porphyrin and metalloporphyrin dimers. Jawlike clefts in these bis-porphyrins are effective hosts for fullerene guests. X-ray structures of the Cu complex with C60 and free-base complexes with C70 and a pyrrolidine-derivatized C60 have been obtained. The electron-rich 6:6 ring-juncture bonds of C60 show unusually close approach to the porphyrin or metalloporphyrin plane. Binding constants in toluene solution increase in the order Fe(II) < Pd(II) < Zn(II) < Mn(II) < Co(II) < Cu(II) < 2H and span the range 490-5200 M-1. Unexpectedly, the free-base porphyrin binds C60 more strongly than the metalated porphyrins. This is ascribed to electrostatic forces, enhancing the largely van der Waals forces of the pi-pi interaction. The ordering with metals is ascribed to a subtle interplay of solvation and weak interaction forces. Conflicting opinions on the relative importance of van der Waals forces, charge transfer, electrostatic attraction, and coordinate bonding are addressed. The supramolecular design principles arising from these studies have potential applications in the preparation of photophysical devices, molecular magnets, molecular conductors, and porous metal-organic frameworks.

Carbon↗
PubMed2006

Highly regioselective transformation of out/out-equatorial bis(formylmethano)[60]fullerenes: construction of dissymmetric [60]fullerene-centered triads.

Three kinds of out/out-equatorial bis(formylmethano)[60]fullerenes (1b-d) were obtained by the tether-directed bifunctionalization of [60]fullerene with bis(alpha-formylsulfonium ylide)s. The condensation of aromatic amines with 1b-d proceeded with an unexpectedly high regioselectivity to give one of two possible regioisomers of mono-imines as the main products (the ratio of the regioisomers, up to 97:3). By the transformation of the remaining formyl group in the mono-imines thus obtained, the corresponding dissymmetric bis-imines were efficiently synthesized.

Amines↗
PubMed2005

Syntheses, structure, and derivatization of potassium complexes of penta(organo)[60]fullerene-monoanion, -dianion, and -trianion into hepta- and octa(organo)fullerenes.

Two-electron reduction of penta(organo)[60]fullerenes C(60)Ar(5)H (Ar = Ph and biphenyl) by potassium/mercury amalgam afforded potassium complexes of the corresponding open-shell radical dianions [K+(thf)n]2[C60Ar5(2-.)]. These compounds were characterized by UV-visible-near-IR and electron spin resonance spectroscopy in solution. Anaerobic crystallization of [K+(thf)n]2[C60(biphenyl)(5)(2-.)] that exists largely as a monomer in solution gave black crystals of its dimer [K+(thf)3]4[(biphenyl)5C60-C60(biphenyl)5(4-)], in which the two fullerene units are connected by a C-C single bond [1.577(11) A] as determined by X-ray diffraction. Three-electron reduction of C60Ar5H with metallic potassium gave a black-green trianion [K+(thf)n]3[C60Ar5(3-)]. The reaction of the trianion with an alkyl halide RBr (R = PhCH(2) and Ph(2)CH) regioselectively afforded a hepta-organofullerene C60Ar5R2H, from which a potassium complex [K+(thf)n][C60(biphenyl)5(CH2Ph)(2)(-)] and a palladium complex Pd[C60(biphenyl)5(CH2Ph)2](pi-methallyl) as well as octa-organofullerene compounds C60(biphenyl)5(CH2Ph)3H2 and Ru[C60(biphenyl)5(C2Ph)3H]Cp were synthesized. These compounds possess a dibenzo-fused corannulene pi-electron conjugated system and are luminescent.

Journal Article↗
PubMed2001

The reaction of fullerene C(60) with phthalazine: the mechanochemical solid-state reaction yielding a new C(60) dimer versus the liquid-phase reaction affording an open-cage fullerene.

The reaction of fullerene C(60) with phthalazine was studied both in solution and in the solid state using the high-speed vibration-milling technique. The reaction in solution gave open-cage fullerene derivative 1 in 44% yield by a one-pot reaction. In contrast, the solid-state reaction afforded dimeric derivative 2 as the sole product. Dimeric derivative 2 was found to undergo intramolecular [2 + 2] cycloaddtion between the two C(60) cages located in close proximity to give a new C(60) dimer 6 in quantitative yield. The structures of these new derivatives of C(60) were determined by spectroscopic methods, and the electrochemical behavior of 2 and 6 was also studied.

Journal Article↗
PubMed2003

Accurate calculation, prediction, and assignment of 3He NMR chemical shifts of helium-3-encapsulated fullerenes and fullerene derivatives.

Helium-3 NMR chemical shifts of various (3)He-encapsulated fullerenes ((3)He@C(n)()) and their derivatives have been calculated at the GIAO-B3LYP/3-21G and GIAO-HF/3-21G levels with AM1 and PM3 optimized structures. A good linear relationship between the computed (3)He NMR chemical shifts and the experimental data has been determined. Comparisons of the calculation methods of (3)He NMR chemical shifts show that GIAO-B3LYP/3-21G with AM1-optimized structures yields the best results. The corrected (3)He NMR chemical shifts were calculated from the correction equation that is obtained through linear regression fitting of the experimental and calculated (3)He NMR chemical shifts over a wide range of (3)He-encapsulated fullerene compounds. The corrected (3)He NMR chemical shifts match the experimental data very well. The current computational method can serve as a prediction tool and can be applied to the assignments and reassignments of the (3)He NMR chemical shifts of (3)He@C(n)() and their derivatives.

Journal Article↗
PubMed2000

Synthesis of fluorous fullerene adducts: reversible solubilization of fullerenes in perfluorinated solvents

Fullerene (C60) Diels-Alder adducts with perfluoroalkylated 1,3-cyclopentadiene (1a,b) were synthesized and studied. The perfluoroalkylated cyclopentadiene was found to be less reactive toward C60 than cyclopentadiene itself, possibly because of the electron-withdrawing effect of the side chain. Because of the same effect, the temperature of the retro-Diels-Alder reaction for the fluorinated adducts was lower (70 degrees C) than the reported value (95 degrees C) for the cyclopentadiene adducts of C60. Higher adducts of the fluorous diene and C60 were found to be soluble in perfluorohexane and to show visible partitioning between organic (toluene) and fluorous phases. Also, the Diels-Alder addition of the fluorous diene was accompanied by extensive oxidation of the fullerene core, as revealed by MALDI-TOF data.

Journal Article↗
PubMed1996

Comparison of immunological effects of Fullerene C60 and raw soot from Fullerene production on alveolar macrophages and macrophage like cells in vitro.

Two carbon modifications, C60 and Raw Soot (RS) from fullerene production, were incubated with macrophages and macrophage-like cells. Their effects were compared both to DQ12 Quartz as a positive particle control known to damage BAM and HL60M, and LPS or zymosan as biological inducers of immunological reactions. C60 as well as RS are not cytotoxic as compared to DQ12. C60 seems to induce a lower chemotactic activity than RS and DQ12. Furthermore, C60 is of no or only very little influence on the formation of reactive oxygen species (ROS). RS itself is oxidatively active both with H2DFC-DA in in vitro cell culture and with KMB in a cell free incubation under the influence of light. It is not yet clear whether the in vitro effects of RS are caused by ROS formation by the cells and/or the oxidative activity due to light as indicated from the results with KMB.

Acetylglucosaminidase↗
PubMed2004

Selective preparation of oxygen-rich [60]fullerene derivatives by stepwise addition of tert-butylperoxy radical and further functionalization of the fullerene mixed peroxides.

tert-Butylperoxy radicals add to C(60) selectively to form multi-adducts C(60)(O)(m)(OO(t)Bu)(n) (m = 0, n = 2, 4, 6; m = 1, n = 0, 2, 4, 6) in moderate yields under various conditions. Visible light irradiation favors epoxide formation. High concentration of tert-butylperoxy radicals mainly produces the hexa-homoadduct C(60)(OO(t)Bu)(6) 6; low concentration and long reaction time favor the epoxy-containing C(60)(O)(OO(t)Bu)(4) 7. The reaction can be stopped at the bis-adducts with limited TBHP. A stepwise addition mechanism is discussed involving mono-, allyl-, and cyclopentadienyl C(60) radical intermediates. m-CPBA reacts with the 1,4-bis-adduct to form C(60)(O)(OO(t)Bu)(2) and C(60)(O)(3)(OO(t)Bu)(2). The C-O bond of the epoxy ring in 7 can be cleaved with HNO(3) and CF(3)COOH. Nucleophilic addition of NaOMe to 7 follows the S(N)1 and extended S(N)2' mechanism, from which four products are isolated with the general formula C(60)(O)(a)(OH)(b)(OMe)(c)(OO(t)Bu)(d). Visible light irradiation of the hexa-adduct 6 results in partial cleavage of both the C-O and O-O bonds of peroxide moieties and formation of the cage-opened compound C(60)(O)(O)(2)(OO(t)Bu)(4). All the fullerene derivatives are characterized by spectroscopic data. A single-crystal structure has been obtained for an isomer of C(60)(O)(OH)(2)(OMe)(4)(OO(t)Bu)(2).

Journal Article↗