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Detailed experimental measurements and theoretical calculations suggest that their dianions (ER-n2- , n=3-5) are stabilized by both the aromatic fluorenyl anion substituents and the central aromatic rings with formally [4n+2] delocalized π electrons. In addition, the dianions of the extended radialenes (ER-42 - and ER-52 - ) show unique open-shell diradical character with a small singlet-triplet energy gap. For comparison, their linear counterparts (L-3 and L-4) were also synthesized; their dianions exhibit very different redox and optical properties from their respective macrocycles.Micrometer- and nanometer-scale photopatterning using 2-nitrophenylpropyloxycarbonyl-protected aminosiloxane monolayers.An approach to nanopatterning is reported in which a scanning near-field optical microscope coupled to a near-UV laser is used to selectively deprotect 2-nitrophenylpropyloxycarbonyl (NPPOC)-protected aminosiloxane monolayers on glass. UV deprotection was studied for unpatterned samples using X-ray photoelectron spectroscopy (XPS) and contact angle measurements.

Highly efficient photodeprotection of the NPPOC moiety was observed upon irradiation at both 325 and 364 nm, and complete deprotection was found to occur within minutes. The resulting amine-terminated surfaces were then derivatized using trifluoroacetic anhydride (TFAA) and aldehyde-functionalized polymer nanoparticles. Contact angle and XPS measurements postderivatization indicated that surface functionalization was extensive, with the NPPOC-deprotected surfaces and aminopropylsiloxane control materials exhibiting essentially identical characteristics. Micrometer-scale patterns were fabricated using mask-based exposure, functionalized with polymer nanoparticles, and characterized by atomic force microscopy. Nanometer-scale patterns were fabricated using near-field exposure and characterized by friction force microscopy. The nanopatterns were derivatized with TFAA. The resulting images exhibited a clear contrast inversion that was due to an inversion of surface polarity in the patterned areas and confirmed that high spatial resolution (ca.

Visualizing electron delocalization in contorted polycyclic aromatic Electron delocalization in contorted polycyclic aromatic hydrocarbon (PAH) molecules was examined through 3D isotropic magnetic shielding (IMS) contour maps built around the molecules using pseudo-van der Waals surfaces. The resulting maps of electron delocalization provided an intuitive, yet detailed and quantitative evaluation of the aromatic, non aromatic, and antiaromatic character of the local and global conjugated cyclic circuits distributed over the molecules. An attractive pictural feature of the 3D IMS contour maps is that they are reminiscent of the Clar π-sextet model of aromaticity. The difference in delocalization patterns between the two faces of the electron circuits in contorted PAHs was clearly visualized. For π-extended contorted PAHs, some splits of the π system resulted in recognizable patterns typical of smaller PAHs. The differences between the delocalization patterns of diastereomeric chiral PAHs could also be visualized. Mapping IMS on pseudo-van der Waals surfaces around contorted PAHs allowed visualization of their superimposed preferred circuits for electron delocalization and hence their local and global This journal is © The Royal Society of Chemistry.

Multiple Tyrosine Residues Contribute to GABA Binding in the GABA(C) Receptor Lummis SC, Harrison NJ, Wang J, Ashby JA, Millen KS, Beene DL, Dougherty DA.The ligand binding site of Cys-loop receptors is dominated by aromatic amino acids. In salcaprozate (C) receptors, these are predominantly tyrosine residues, with a number of other aromatic residues located in or close to the binding pocket. Here Order now examine the roles of these residues using substitution with both natural and unnatural amino acids followed by functional characterization. Tyr198 (loop B) has previously been shown to form a cation-π interaction with GABA; the current data indicate that none of the other aromatic residues form such an interaction, although the data indicate that both Tyr102 and Phe138 may contribute to stabilization of the positively charged amine of GABA. Tyr247 (loop C) was very sensitive to substitution and, combined with data from a model of the receptor, suggest a π-π interaction with Tyr241 (loop C); here again functional data show aromaticity is important. In addition the hydroxyl group of Tyr241 is important, supporting the presence of a hydrogen bond with Arg104 suggested by the model.

At position Tyr102 (loop D) size and aromaticity are important; this residue may play a role in receptor gating and/or ligand binding. The data also suggest that Tyr167, Tyr200, and Tyr208 have a structural role while Tyr106, Trp246, and Tyr251 are not critical. Comparison of the agonist binding site "aromatic box" across the superfamily of Cys-loop receptors reveals some interesting parallels and divergences.Investigation of the toxicokinetics of petroleum hydrocarbon distillates with The Canada-wide standards for petroleum hydrocarbons in soils regulate petroleum hydrocarbons based on four distillate ranges: F1 (C6-C10), F2 (>C10-C16), F3 (>C16-C34), and F4 (>C34).