Lewis acid—base interactions enhance explosives sensing in silacycle polymers

Sanchez, Jason C.; DiPasquale, Antonio G.; Mrse, Anthony A.; Trogler, William C.
September 2009
Analytical & Bioanalytical Chemistry;Sep2009, Vol. 395 Issue 2, p387
Academic Journal
The high sensitivity of silole- and silafluorene-containing polymers for detecting organic nitro, nitrate, and nitramine explosives cannot be solely attributed to favorable analyte–polymer hydrophobic interactions and amplified fluorescence quenching due to delocalization along the polymer chain. The Lewis acidity of silicon in conjugated poly(silafluorene-vinylene)s is shown to be important. This was established by examining the 29Si NMR chemical shifts (Δ) for the model trimer fragment of the polymer CH3–silafluorene–( trans-C2H2)–silafluorene–( trans-C2H2)–silafluorene–CH3. The peripheral and central silicon resonances are up-field from a TMS reference at −9.50 and −18.9 ppm, respectively. Both resonances shift down-field in the presence of donor analytes and the observed shifts (0 to 1 ppm) correlate with the basicity of a variety of added Lewis bases, including TNT. The most basic analyte studied was acetonitrile and an association constant ( Ka) of 0.12 M−1 was calculated its binding to the peripheral silicon centers using the Scatchard method. Spin-lattice relaxation times ( T1) of 5.86(3) and 4.83(4) s were measured for the methyl protons of acetonitrile in benzene- d6 at 20 °C in the absence and presence of the silafluorene trimer, respectively. The significant change in T1 values further supports a binding event between acetonitrile and the silafluorene trimer. These studies as well as significant changes and shifts observed in the characteristic UV–Vis absorption of the silafluorene group support an important role for the Lewis acid character of Si in polymer sensors that incorporate strained silacycles. The nitro groups of high explosives may act as weak Lewis-base donors to silacycles. This provides a donor–acceptor interaction that may be crucial for orienting the explosive analyte in the polymer film to provide an efficient pathway for inner-sphere electron transfer during the electron-transfer quenching process. [Figure not available: see fulltext.]


Related Articles

  • Aggregation of [70]fullerene in presence of acetonitrile: A chemical kinetic experiment. Datta, Kakali; Mukherjee, Asok K. // Journal of Chemical Physics;4/14/2006, Vol. 124 Issue 14, p144509 

    [70]fullerene solutions in carbon tetrachloride and o-xylene exhibit a noteworthy spectral variation with time when acetonitrile is added. This has been ascribed to self-aggregation of [70]fullerene caused by the repulsion between polar acetonitrile and hydrophobic [70]fullerene, and the...

  • Templated formation of giant polymer vesicles with controlled size distributions. Howse, Jonathan R.; Jones, Richard A. L.; Battaglia, Giuseppe; Ducker, Robert E.; Leggett, Graham J.; Ryan, Anthony J. // Nature Materials;Jun2009, Vol. 8 Issue 6, p507 

    Unilamellar polymer vesicles are formed when a block copolymer self-assembles to form a single bilayer structure, with a hydrophobic core and hydrophilic surfaces, and the resulting membrane folds over and rearranges by connecting its edges to enclose a space. The physics of self-assembly...

  • Local wettability modification by thermochemical nanolithography with write-read-overwrite capability. Wang, D. B.; Szoszkiewicz, R.; Lucas, M.; Riedo, E.; Okada, T.; Jones, S. C.; Marder, S. R.; Lee, J.; King, W. P. // Applied Physics Letters;12/10/2007, Vol. 91 Issue 24, p243104 

    The wettability of a thin polymer film was modified twice by thermochemical nanolithography. By means of a first local chemical modification induced by an atomic force microscope tip heated to 110±20 °C, hydrophilic patterns are written over an originally hydrophobic polymer surface. By...

  • Monte Carlo study of the phase structure of compact polymer chains. Irback, Anders; Sandelin, Erik // Journal of Chemical Physics;6/22/1999, Vol. 110 Issue 24, p12256 

    Studies the phase behavior of single homopolymers in a simple hydrophobic/hydrophilic off-lattice model with sequence independent local interactions. Monte Carlo methods used in the study; Dynamics of the algorithms; Measurement of specific heat and bond-bond correlation function.

  • Avoiding Viscosity Loss on Tinting. Saucy, Daniel // Paint & Coatings Industry;Aug2008, Vol. 24 Issue 8, p34 

    The article discusses the advantages of associative rheology modifiers for reducing viscosity loss on tinting while maintaining an excellent flow-sag balance in waterborne paint. A decreased viscosity manifests itself in various ways, including low sag resistance and poor brush loading....

  • Effect of a Hydrophobic Phospholipid Lining of the Gastric Mucosa in Bioadhesion. Joseph Robinson // Pharmaceutical Research;Jan2008, Vol. 25 Issue 1, p16 

    Abstract Purpose  The role of a model hydrophobic phospholipid simulating lining of the gastric mucosa, as to adhesion of polymers with different surface functional groups and surface hydrophobicities, was evaluated using an in vitro gastric mucus model. Materials and...

  • Double slapper initiation of the PBX. Mendes, R.; Plaksin, I.; Campos, J.; Ribeiro, J. // AIP Conference Proceedings;2000, Vol. 505 Issue 1, p915 

    The interaction of two divergent detonation waves (DW), initiated simultaneously by two flyer plates in a PBX based on a bimodal particle distribution of RDX was studied. The slappers are generated by the interaction, of a single (25 mm in diameter) flyer plate against a twin pierced barrel....

  • RDX.  // Hutchinson Dictionary of Scientific Biography;2005, p1 

    Or hexogen a very powerful explosive compound.

  • The Continuing Acetonitrile Shortage: How to Combat it or Live with It. Majors, Ronald E. // LC-GC North America;Jun2009, Vol. 27 Issue 6, p458 

    The article discusses the topics on dealing with acetonitrile such as shorter column with smaller particles, reduction of the column internal diameter, and changing the type or amount of stationary phase. It notes that the current trend in higher throughput liquid chromatography (LC) is the use...


Read the Article


Sorry, but this item is not currently available from your library.

Try another library?
Sign out of this library

Other Topics