Invariance of the dissipative action at ultrahigh strain rates above the strong shock threshold

We have directly resolved shock structures in pure aluminum in the first few hundred picoseconds subsequent to a dynamic load at peak stresses up to 43 GPa and strain rates in excess of 10(10) s(-1). For strong shocks we obtain peak stresses, strain rates, and rise times. From these data, we directly validate the invariance of the dissipative action in the strong shock regime, and by comparing with data obtained at much lower strain rates show that this invariance is observed over at least 5 orders of magnitude in the strain rate. Over the same range, we similarly validate the fourth-power scaling of the strain rate with the peak stress (the Swegle-Grady relation).     

Novel synthesis of sulfones from α,α-dibromomethyl aromatics

A novel, high yielding preparation of sulfones from α,α-dibromomethyl aromatics through reaction with a sulfinate salt is reported.     

The intramolecular Morita-Baylis-Hillman-type alkylation reaction

From the initial development of a homologous Morita-Baylis-Hillman reaction utilizing epoxides as electrophiles, the method was expanded to enable the exclusively organocatalyzed intramolecular allylation of enones and to develop the intramolecular MBH-type alkylation of activated alkenes. We successfully utilized both enones and unsaturated thioesters as the activated alkene component. This work, carried out using stoichiometric amounts of the trialkylphosphine, gave an array of functionalized five- and six-membered carbocycles in high yields. With the cycloalkylation of enones and thioesters, conditions that allowed the use of substoichometric amounts of the phosphine catalyst were developed. As a result both five- and six-membered rings can be formed efficiently with little to no loss in yield upon comparison to yields obtained when stoichiometric amounts of trialkylphosphines were employed. We isolated, for the first time, an MBH-type intermediate exhibiting unprecedented trans geometry of the phosphonium salt and acyl group.     

Blue fluorescent dye-protein complexes based on fluorogenic cyanine dyes and single chain antibody fragments

Fluoromodules are complexes formed upon the noncovalent binding of a fluorogenic dye to its cognate biomolecular partner, which significantly enhances the fluorescence quantum yield of the dye. Previously, several single-chain, variable fragment (scFv) antibodies were selected from a yeast cell surface-displayed library that activated fluorescence from a family of unsymmetrical cyanine dyes covering much of the visible and near-IR spectrum. The current work expands our repertoire of genetically encodable scFv-dye pairs by selecting and characterizing a group of scFvs that activate fluorogenic violet-absorbing, blue-fluorescing cyanine dyes, based on oxazole and thiazole heterocycles. The dye binds to both yeast cell surface-displayed and soluble scFvs with low nanomolar K(d) values. These dye-protein fluoromodules exhibit high quantum yields, approaching unity for the brightest system. The promiscuity of these scFvs with other fluorogenic cyanine dyes was also examined. Fluorescence microscopy demonstrates that the yeast cell surface-displayed scFvs can be used for multicolor imaging. The prevalence of 405 nm lasers on confocal imaging and flow cytometry systems make these new reagents potentially valuable for cell biological studies.     

An investigation into the one-pot Heck olefination-hydrogenation reaction

Herein is described an operationally simple process concerning the observation that, following either inter-, or intramolecular Heck olefination, stirring of the so formed substituted alkenyl product under an atmosphere of hydrogen efficiently effects alkene hydrogenation. Overall this two-operation, one-pot "reductive Heck" sequence is notable since direct reductive Heck processes, using additives such as formate salts, are restricted to a limited range of substrates. In total 25 examples are reported (yields ranging from 0 to 95%), which were selected in order to probe the scope and limitations of this method. Finally, the utility of this sequence was demonstrated in a short synthesis of the calcimimetic agent, cinacalcet.     

Kinetic discrimination in recognition of DNA quadruplex targets by guanine-rich heteroquadruplex-forming PNA probes

Guanine-rich peptide nucleic acid probes hybridize to DNA G quadruplex targets with high affinity, forming PNA-DNA heteroquadruplexes. We report a surprising degree of kinetic discrimination for PNA heteroquadruplex formation with a series of DNA targets. The fastest hybridization is observed for targets folded into parallel morphologies.