Free-electron attachment to coronene and corannulene in the gas phase.

Electron attachment to the polyaromatic hydrocarbons coronene and corannulene is studied in the electron energy range of about 0-14 eV using a high-resolution crossed electron-neutral beam setup. The major anions observed are the parent anions peaking at about 0 eV with cross sections of 3.8 x 10(-20) and 1 x 10(-19) m(2), respectively. The only fragment anions formed in coronene and corannulene are the dehydrogenated coronene and corannulene anions. Other anions observed in the negative mass spectra at about 0 eV can be ascribed to impurities of the sample. High-level quantum-mechanical studies are carried out for the determination of electron affinities, hydrogen binding energies, and structures of both molecules. The behavior of coronene and corannulene upon electron attachment is compared with that of other polyaromatic hydrocarbons studied previously.

Embracing C(60) with multiarmed geodesic partners.

1,3,5,7,9-Pentakis(4-methoxyphenylthio)corannulene (3), 1,3,5,7,9-pentakis(2-naphthylthio)corannulene (4), and 1,3,6,8-tetrakis(4-methoxyphenylthio)corannulene (5b) have been synthesized by chlorination of corannulene with ICl in CH(2)Cl(2) at 25 degrees C and subsequent nucleophilic aromatic substitution with the appropriate sodium thiophenolate in DMEU at 25 degrees C. (1)H NMR titration studies demonstrate that these novel bowl-shaped hosts form 1:1 complexes with C(60) in toluene-d(8) solution with association constants of 454, 368, and 280 M(-1), respectively.

Groundwork for a rational synthesis of C60: cyclodehydrogenation of a C60H30 polyarene.

A C60H30 polycyclic aromatic hydrocarbon (PAH) that incorporates all 60 carbon atoms and 75 of the 90 carbon-carbon bonds required to form the fullerene C60 has been synthesized in nine steps by conventional laboratory methods. Laser irradiation of this C60H30 PAH at 337 nanometers induces hydrogen loss and the formation of C60, as detected by mass spectrometry. A specifically labeled [13C3]C60H30 retains all three 13C atoms during the cage formation process. A structurally related C48H24 PAH that lacks the three peripheral benzene rings cannot be transformed into C60, whereas the next higher homolog, a C80H40 PAH, degrades to the C60H30 PAH, which then loses hydrogen to give [60]fullerene. These control experiments verify that the C60 is formed by a molecular transformation directly from the C60H30 PAH and not by fragmentation and recombination in the gas phase.

Regional cerebral hyperperfusion and nitric oxide pathway dysregulation in Fabry disease: reversal by enzyme replacement therapy.

BACKGROUND: Fabry disease is an X-linked lysosomal deficiency of alpha-galactosidase A that results in cellular accumulation of galacto-conjugates such as globotriosylceramide, particularly in blood vessels. It is associated with early-onset stroke and kidney and heart failure. METHODS AND RESULTS: Using [(15)O] H(2)O and PET, we found increased resting regional cerebral blood flow in Fabry disease without evidence of occlusive vasculopathy or cerebral hypoperfusion. Because nitric oxide is known to play an important role in vascular tone and reactivity, we studied plasma nitrate, nitrite, and low-molecular-weight S-nitrosothiol levels by chemiluminescence. Skin biopsy specimens and archived brain tissue were also examined immunohistochemically for nitrotyrosine. Plasma nitrate, nitrite, and low-molecular-weight S-nitrosothiol were in the normal range; however, enhanced nitrotyrosine staining was observed in dermal and cerebral blood vessels. After a double-blind, placebo-controlled trial of alpha-galactosidase A therapy, the resting regional cerebral blood flow in the treated group was significantly reduced, with a notable decrease of nitrotyrosine staining in dermal blood vessels. CONCLUSIONS: These findings suggest a chronic alteration of the nitric oxide pathway in Fabry disease, with critical protein nitration that is reversible with enzyme replacement therapy.

Lithium reduction of the bowl-shaped C60 fragment diindeno[1,2,3,4-defg;1',2',3',4'-mnop]chrysene: an interplay between experiment and calculation.

Diindeno[1,2,3,4-defg;1',2',3',4'-mnop]chrysene (DIC) (one of the smallest symmetrical bowl-shaped fragments of C60) and its tetra-tert-butyl derivative are reduced with lithium metal to yield dianions and tetraanions. Due to the high degree of symmetry (C2v) of DIC and its derivative, their NMR spectra cannot be assigned using the standard two-dimensional NMR techniques. A novel carbon-edited NOESY method was used to complete the assignments of the neutral and dianion species, whereas the tetraanions are aided by DFT calculations for their assignment. Experimental charge-distribution patterns were obtained and match those of the calculations. An extension of the empirical approach for estimating the charge distribution from the 13C NMR spectra enables a direct comparison between experimentally derived charge-distribution data and the computed electron density in each of the lowest unoccupied molecular orbitals. The overall picture evolving from the orbital structure of DIC is presented and reflects the surface reactivity of C60.

Fullerometallic ion chemistry: reactions of C(60)Fe+ and C(20)H(10)Fe+ in the gas phase.

Fe+ has been attached to buckminsterfullerene, C(60), and corannulene, C(20)H(10), in the gas phase, and the reactivities of C(60)Fe+ and C(20)H(10)Fe+ have been measured with several small inorganic and organic molecules in helium bath gas at 0.35 Torr using a selected-ion flow tube (SIFT) mass spectrometer. Comparisons with measured reactivities of the bare Fe+ ion indicate that the presence of C(60) and C(20)H(10) leads to enhancements in reactivity at room temperature of up to 5 orders of magnitude. Ligation was the only chemistry observed with D(2), N(2), CO(2), CH(4), C(2)H(2), C(2)H(4), SO(2), C(6)D(6), NH(3), H(2)O, and CO, but other channels were observed to compete with adduct formation in the reactions with N(2)O and O(2). The number of molecules sequentially ligated to the ion was different: up to five molecules of ligand added sequentially to Fe+, up to four molecules of ligand were observed to attach to C(60)Fe+, while only up to three molecules added to C(20)H(10)Fe+. C(60)+ and C(20)H(10)+ were observed to be unreactive toward the same ligands. The kinetic results show the influence of carbonaceous surfaces on metal ion reactivity and are interpreted in terms of the nature of the coordination of Fe+ to the carbonaceous surface. Catalytic effects of the carbonaceous surfaces were identified for the reactions with N(2)O and O(2).

Estimation of the electron affinities of C60, corannulene, and coronene by using the kinetic method.

Novel anions that contain one molecule each of C60 and the polycyclic aromatic hydrocarbon coronene are generated in the gas phase by electron attachment desorption chemical ionization. Collision-induced dissociation reveals that these cluster ions are loosely bonded. Fragmentation of the mass-selected cluster anion yields, as the only products, the intact radical anions of the constituent molecules, namely, the C60 radical anion and the coronene radical anion, in almost identical relative abundances. This result is interpreted as evidence that the cluster ion can be considered as the anion radical of one molecule solvated by the other molecule. The known very high electron affinity of C60 (2.66 eV) and the comparable degree to which C60 and the PAH compete for the electron suggests that dissociation may be controlled by the electron affinity of a portion of the C60 surface, that is, in this case the kinetic method yields information on the local electron affinity of C60. The electron affinity of the bowl-shaped compound corannulene is estimated for the first time to be 0.50 ± 0.10 eV by the kinetic method by using a variety of reference compounds. Unlike coronene, corannulene reacts with C -• (60) in the gas phase to form a covalently bonded, denydrogenated cluster ion. Support for the concept of "local" electron affinity of C60 comes from a theoretical calculation on the electronic structure of C60 anions, which shows evidence for localization of the charge in the C60 molecule. The possibility of electron tunneling in the C60-coronene system is discussed as an alternative explanation for the unusual observation of equal abundances of C60 anions and coronene anions upon dissociation of the corresponding cluster ion.

Stable high-order molecular sandwiches: hydrocarbon polyanion pairs with multiple lithium ions inside and out.

Stable ten-component sandwich compounds have been characterized in which four lithium ions reside between two tetraanions derived from corannulene or its alkyl-substituted derivatives and four additional lithium ions decorate the exterior. In tetrahydrofuran solution, the four lithium ions inside the sandwich can exchange environments with the four external lithium atoms, but the two tetraanion decks of the sandwich never separate from one another on the time scale of nuclear magnetic resonance. Theoretical calculations point to a "stacked bowl" conformation and a low energy barrier for synchronous double inversion of the tetraanion bowls in the solvated sandwich compounds.