Electron transfer reactions between excited diarylmethyl and triarylmethyl carbocations and aromatic donors

The excited singlet states of a variety of diarylmethyl and triarylmethyl carbocations were characterized by fluorescence spectroscopy. The dibenzosuberenyl, xanthenyl and 9-phenylxanthenyl cations are strongly fluorescent (\u3a6 = 0.1-0.3) and have fluorescence lifetimes in the 30-40 ns range in 2,2,2-trifluoroethanol. The fluorescence of each of these cations is efficiently quenched by a variety of substituted aromatics (e.g. cumene, anisole, toluene) with rate constants in excess of 10\u2079 M\u207b\ub9 s\u207b\ub9. There is a correlation between the observed rate constants and the oxidation potential of the aromatic quencher which suggests that an electron transfer process occurs to generate a dibenzosuberenyl radical/silane radical cation pair. This hypthesis is confirmed by irradiation of the dibenzosuberenyl cation in the presence of benzyltrimethylsilane. This reaction produces 5-benzyldibenzocycloheptene, which is formed by addition of the benzyl radical produced via cleavage of the silane radical cation to either the dibenzosuberenyl radical or cation. Quenching studies suggest that the efficiency of product formation is controlled by the competition between cage escape and back electron transfer for the initial geminate radical/radical ion pair.NRC publication: Ye

High-Throughput Array Production Using Precision Glass Syringes

The advantages of using 1, 96, or 384 precision glass syringes in automated high-throughput microdispensers in creating highly uniform and reproducible DNA, protein, and organic compound array filters and slides are described. Using the Hydra® Microdispenser and TangoTM Liquid Handling system, 0.1–5 ng (in 50–300 nL) PCR-amplified, human cancer-related genes and housekeeping genes were spotted onto nylon membranes and coated slides. Protein solutions of 50μg/mL to 1 mg/mL were spotted onto coated slides or onto MaxiSorpTM 96-well plates. Up to 6144 spots/membrane and up to 1000 spots/slide were printed. The size of the spots created by glass syringes was uniform and reproducible (precision variation of less than 5%) from spot to spot and membrane to membrane. Using a Tango 384 system, a total of ten 6144-spot filters can be produced in approximately 25 min, translating into a spotting speed of 2.5 min/membrane