A soluble bisanthene derivative, 4,11-dimesitylbisanthene, has been synthesized in three steps from bianthrone. In hot toluene, this bisanthene undergoes a clean Diels-Alder reaction with diethyl acetylenedicarboxylate to give a rearomatized 1:1 cycloadduct and, more slowly, a rearomatized 2:1 cycloadduct. In a competition experiment with the shorter "periacene" perylene, only the bisanthene reacts, and the perylene remains unchanged. The experimental results stand in complete accord with density functional calculations (B3LYP/6-31G*), which predict that the activation energies for Diels-Alder cycloadditions in the bay regions of periacenes should diminish monotonically as the length of the molecule increases. This structure-activity relationship offers hope that single-chirality carbon nanotubes can be grown from suitable hydrocarbon templates, without metal catalysis, by a Diels-Alder cycloaddition/rearomatization strategy, using acetylene or a "masked acetylene" as the dienophile.

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Transition metal-catalyzed double ring closures of 1,1-diaryl-2,2-diethynylethylenes yield polycyclic aromatic hydrocarbons and heterocycles that contain a newly formed naphthalene ring system embedded in a larger polycyclic network. The diynes required for this procedure are readily synthesized from diaryl ketones by the Corey-Fuchs olefination and subsequent Sonogashira coupling with trimethylsilylacetylene followed by desilylation. This procedure provides easy access to new compounds such as 3,11-di-tert-butyl[4]helicene and 1,8,9-perinaphthothioxanthene. Double naphthoannulation of 9,10-anthraquinone by this procedure closes four new benzene rings in a single operation to give coronene, although the yield in this case is presently low.

3We measured total mercury (THg) and monomethyl mercury (MMHg) concentrations and 4 mercury (Hg) isotopic compositions in sediment and aquatic organisms from the Yuba River 5

Sediments were analyzed for total Hg concentration (THg) and isotopic composition from streams and rivers in the vicinity of the Y-12 National Security Complex (Y12) in Oak Ridge, TN (USA). In the stream directly draining Y12, where industrial releases of mercury (Hg) have been documented, high THg (3.26 to 60.1 μg/g) sediments had a distinct Hg isotopic composition (δ(202)Hg of 0.02 ± 0.15‰ and Δ(199)Hg of -0.07 ± 0.03‰; mean ± 1SD, n = 12) compared to sediments from relatively uncontaminated streams in the region (δ(202)Hg = -1.40 ± 0.06‰ and Δ(199)Hg of -0.26 ± 0.03‰; mean ± 1SD, n = 6). Additionally, several streams that are nearby but do not drain Y12 had sediments with intermediate THg (0.06 to 0.21 μg/g) and anomalous δ(202)Hg (as low as -5.07‰). We suggest that the low δ(202)Hg values in these sediments provide evidence for the contribution of an additional Hg source to sediments, possibly derived from atmospheric deposition. In sediments directly downstream of Y12 this third Hg source is not discernible, and the Hg isotopic composition can be largely explained by the mixing of low THg sediments with high THg sediments contaminated by Y12 discharges.