Hunting for the Magnesium(I) Species: Formation, Structure, and Reactivity of some Donor-Free Grignard Compounds

Magnesium bromide radicals have to be prepared as high-temperature molecules and trapped as a metastable solution because a seemingly simple reduction of donor-free Grignard compounds failed. However, the essential role of magnesium(I) species during the formation of Grignard compounds could be demonstrated experimentally.     

Filter-free integrated sensor array based on luminescence and absorbance measurements using ring-shaped organic photodiodes

An optical waveguiding sensor array featuring monolithically integrated organic photodiodes as integrated photo-detector, which simplifies the readout system by minimizing the required parts, is presented. The necessity of any optical filters becomes redundant due to the proposed platform geometry, which discriminates between excitation light and sensing signal. The sensor array is capable of measuring luminescence or absorption, and both sensing geometries are based on the identical substrate. It is demonstrated that background light is virtually non-existent. All sensing and waveguide layers, as well as in- and out-coupling elements are assembled by conventional screen-printing techniques. Organic photodiodes are integrated by layer-by-layer vacuum deposition onto glass or common polymer foils. The universal and simple applicability of this sensor chip is demonstrated by sensing schemes for four different analytes. Relative humidity, oxygen, and carbon dioxide are measured in gas phase using luminescence-based sensor schemes; the latter two analytes are also measured by absorbance-based sensor schemes. Furthermore, oxygen and pH in aqueous media were enabled. The consistency of calibration characteristics extending over different sensor chips is verified.

Dual fluorophore PNA FIT-probes - extremely responsive and bright hybridization probes for the sensitive detection of DNA and RNA

Fluorescently labeled oligonucleotides are commonly employed as probes to detect specific DNA or RNA sequences in homogeneous solution. Useful probes should experience strong increases in fluorescent emission upon hybridization with the target. We developed dual labeled peptide nucleic acid probes, which signal the presence of complementary DNA or RNA by up to 450-fold enhancements of fluorescence intensity. This enabled the very sensitive detection of a DNA target (40 pM LOD), which was detectable at less than 0.1% of the beacon concentration. In contrast to existing DNA-based molecular beacons, this PNA-based method does not require a stem sequence to enforce dye-dye communication. Rather, the method relies on the energy transfer between a "smart" thiazole orange (TO) nucleotide, which requires formation of the probe-target complex in order to become fluorescent, and terminally appended acceptor dyes. To improve upon fluorescence responsiveness the energy pathways were dissected. Hydrophobic, spectrally mismatched dye combinations allowed significant (99.97%) decreases of background emission in the absence of a target. By contrast, spectral overlap between TO donor emission and acceptor excitation enabled extremely bright FRET signals. This and the large apparent Stokes shift (82 nm) suggests potential applications in the detection of specific RNA targets in biogenic matrices without the need of sample pre-processing prior to detection.     

No stirring necessary: parallel carbonylation of aryl halides with CO and various alcohols under pressure

The parallel carbonylation of aryl halides with 6-25 bar of CO in 1-mL vials in a standard autoclave was investigated. 4-Bromoacetophenone and 2-chloropyridine were used as model substrates with 102 different O-nucleophiles (primary and secondary alcohols, phenols). No inertization during the loading was necessary. Fifty esters (43 new, yield up to 60%) were isolated and characterized. Ether, ester, ketone, and sometimes even olefin functions were usually tolerated. The new method is suitable for screening and small scale products synthesis.     

Direct determination of selected metals in refractory powder micro samples with exploding thin film excitation

The direct determination of metallic elements in powder micro samples is explored. Emphasis is placed on refractory materials prepared as alcoholic suspensions of their powders. Silver thin films are vacuum deposited on polypropylene strips and on polycarbonate membrane filters. Based on a parametric study, explosions conducted at 700 torr in Ar(60%)O₂(40%) using 4 kV, 180 J discharges are most satisfactory. Particle size studies suggest complete vaporization of particles smaller than ～10 μm independent of their boiling points. High circuit inductance and capacitance as well as O₂ added to the plasma support gas promote vaporization of larger particles. Particles which pass through a 5 μm mesh sieve can be analyzed with aqueous solution standards. Analytical curves and precision data are presented for Zr, V, Mo and Ni. Interparticle concomitant effects are not significant. Feasibility studies are presented for the direct analysis of airborne particles collected on metallized membrane filters.     

Synthesis and Photochemistry of 2,2-Dimethyl-3(2H)-thiophenone,a Ketonic Tautomer of 3-Hydroxythiophene. Preliminary Communication

On irradiation (λ = 366 nm), the 4-thia-2-cyclopentenone 3a behaves in complete analogy to the oxa-enone 3c undergoing regio- and stereospecific cyclodimerization, regiospecific cycloaddition with 2-methylpropene and cycloaddition with 2,3-dimethyl-2-butene to afford cyclobutane derivatives. In contrast, the 4 -aza-2-cyclopentenone 3b does not undergo the above-mentioned reactions but only slow photodecomposition.