Single-Molecule Junction Conductance through Diaminoacenes

The study of electron transport through single molecules is essential to the development of molecular electronics. Indeed, trends in electronic conductance through organic nanowires have emerged with the increasing reliability of electron transport measurements at the single-molecule level. Experimental and theoretical work has shown that tunneling distance, HOMO-LUMO gap and molecular conformation influence electron transport in both saturated and pi-conjugated nanowires. However, there is relatively little experimental data on electron transport through fused aromatic rings. Here we show using diaminoacenes that conductivity depends not only on the number of fused aromatic rings in the molecule, which defines the molecular HOMO-LUMO gap, but also on the position of the amino groups on the rings. Specifically, we find that conductance is highest with minimal disruption of aromaticity in fused aromatic nanowires.Comment: 2 pages, 3 figure

Measurement of the W mass by direct reconstruction in e+e−e^+ e^- collisions at 172 GeV

The mass of the W boson is obtained from reconstructed invariant mass distributions in W-pair events. The sample of W pairs is selected from 10.65~pb$^{-1}$ collected with the ALEPH detector at a mean centre-of-mass energy of 172.09 \GEV. The invariant mass distribution of simulated events are fitted to the experimental distributions and the following W masses are obtained: $WW \to q\overline{q}q\overline{q } m_W = 81.30 +- 0.47(stat.) +- 0.11(syst.) GeV/c^2$, $WW \to l\nu q\overline{q}(l=e,\mu) m_W = 80.54 +- 0.47(stat.) +- 0.11(syst.) GeV/c^2$, $WW \to \tau\nu q\overline{q} m_W = 79.56 +- 1.08(stat.) +- 0.23(syst.) GeV/C62$. The statistical errors are the expected errors for Monte Carlo samples of the same integrated luminosity as the data. The combination of these measurements gives: $m_W = 80.80 +- 0.11(syst.) +- 0.03(LEP energy) GeV/^2$

Multilayer chitosan-based open tubular capillary anion exchange column with integrated monolithic capillary suppressor

China Scholarship Council; US National Science Foundation [CHE-0821969]; NASA [NNX11AO66G]We describe a multilayered open tubular anion exchange column fabricated by alternately pumping solutions of chitosan and glutaraldehyde. The column is terminated in an integrally bonded monolithic suppressor cast around a mandrel of a tungsten wire, composed of an acrylic acid (AA)-ethylene dimethacrylate (EDMA) monolith that is made with sufficient porogen for the monolith to function as a membrane. For a 4.5 m long 75 mu m bore column coated with 24 successive layers of the condensation polymer (estimated to contain similar to 72 molecular layers) and coupled to 1 cm length of a suppressor fabricated with 55-60% AA, effective separation of several common anions (F-, Cl-, NO2-, Br-, NO3-, average number of theoretical plates similar to 12,000) and adequate suppression of 1 mM KOH used as eluent was observed at a flow rate of 800 nL min(-1) to obtain sub-picomol detection limits at an operating pressure of similar to 1 bar. The separation is not time efficient but the system can be meritorious in unique niche applications where a small form factor is desired and liquid volume and power consumption are more important than separation speed. (C) 2011 Elsevier B.V. All rights reserved

A Selective and Sensitive Hg2+ Aminonaphthalimide-aza-crown-ether Cellular Chemosensor

Crown ether ionophores linked to napthalimide fluorophores provide a powerful and versatile class of fluorescent chemosensors. Here we demonstrate the unusual Hg2+ ion selectivity of an aza-crown ether ionophore linked to a 4-aminonapthalimide by 1,4-phenylenediamine. Binding, computational, and fluorescence studies reveal an intramolecular charge transfer mechanism. The sensor demonstrates exceptional selectivity for Hg2+ in aqueous ethanol and detects both Hg2+and Zn2+ in aqueous acetonitrile. The sensor\u27s Hg2+ sensitivity is retained in live cells at biologically relevant concentrations of Hg2+, making it a potentially versatile and convenient tool for environmental and biological assay and monitoring applications

NMR Analyses of-1,3-Bridged Calix[4]arene Conformations

Calix[4]arenes are cyclic oligomers known for their unique molecular architecture that provides a versatile platform for various applications in supramolecular chemistry. When strategically coupled with fluorescent molecules, their molecular recognition enables highly selective and sensitive chemosensors. The introduction of bridging groups at 1,3 phenolic positions within the calix[4]arene framework has the potential to yield distinctive structural features and enhanced functional properties. Despite their opportunities, calix[4]arene preparation requires careful characterization of conformationally restricted rotomers. We used a combination of experimental and computational techniques to elucidate the three-dimensional structure and conformational dynamics of a 1,3-bridged calix[4]arene derivative. Nuclear magnetic resonance (NMR) spectroscopy, Density Functional Theory (DFT) based optimization, and Boltzmann-weighted NMR chemical shift calculations are used to determine the precise molecular structure of the binding domain in our novel calix[4]arene derivative, including conformation, bond distance, and angle details