Sample preparation for high throughput accurate mass analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

An automated sample preparation for high throughput accurate mass determinations by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) has been developed. Sample preparation was performed with an automated workstation and automated mass analyses were performed with a commercial MALDI-TOF mass spectrometer. The method was tested with a 41-sample library. MALDI-TOFMS was found to give the needed sensitivity, accurate mass measurement, and soft ionization necessary for structure confirmation, even of mixtures. A mass accuracy of 5 ppm or less was obtained in over 80% of known compound measurements. A mass accuracy better than 10 ppm was obtained for all measurements of known compounds. Analyses of parallel synthesis products resulted in 77% of the measurements with a mass accuracy of 5 ppm or better.     

Hesseltins B-G, novel meroterpenoids from a new Penicillium species

Six new meroterpenoid compounds, hesseltins B-G, were isolated from Penicillium species along with the previously described hesseltin A. A further 14 compounds, which turned out to be photoisomers, were detected during purification and were subsequently isolated. The structures of these analogues were elucidated by comparison of their NMR spectral data with that of hesseltin A. None of the new hesseltins showed antiviral activity in a Herpes simplex virus type 2 assay.     

Stimulated emission three-pulse photo-echo peakshift: a mixed pump-probe and photon-echo technique for studying excited-state dynamics

A novel four-pulse photon-echo technique for exploring condensed phase dynamics at different parts of the excited-state potential energy surface is presented. In contrast to traditional three-pulse photon-echo signals, the introduction of a fourth pump pulse allows the use of photon-echo techniques to probe excited-state phenomena. Here, a "proof of principle" experiment is presented where the excited-state solvent dynamics of the coumarin 153 chromophore dissolved in methanol is explored. The fluctuations of the stimulated emission transition is probed, in contrast to the ground-state absorption transition explored in traditional echo measurements. Distinctly different excited-state dynamics, in contrast to ground-state signals, is observed and discussed.     

Electrically forced coaxial nanojets for one-step hollow nanofiber design

The outer liquid of a two-liquid coaxial electrified jet is gelled before the onset of natural instabilities to yield hollow nanofibers. By using sol-gel chemistry, innocuous solvents such as glycerol and olive oil, and electrohydrodynamics, it is possible to make such structures in a rather straightforward manner.     

Nucleic acid analysis using an expanded genetic alphabet to quench fluorescence

Organic chemistry has made possible the synthesis of molecules that expand on Nature's genetic alphabet. Using the previously described nonstandard DNA base pair constructed from isoguanine and 5-methylisocytosine, we report a highly specific and sensitive method that allows for the fast and specific quantitation of genetic sequences in a closed tube format. During PCR amplification, enzymatic site-specific incorporation of a quencher covalently linked to isoguanine allows for the simultaneous detection and identification of multiple targets. The specificity of method is then established by analysis of thermal denaturation or melting of the amplicons. The appropriate functions of all reactions are further verified by incorporation of an independent target into the reaction mixture. We report that the method is sensitive down to the single copy level, and specificity is demonstrated by multiplexed end-point genotypic analysis of four targets simultaneously using four separate fluorescent reporters. The method is general enough for quantitative and qualitative analysis of both RNA and DNA using previously developed primer sets. Though the method described employs the commonly used PCR, the enzymatic incorporation of reporter groups into DNA site-specifically should find broad utility throughout molecular biology.     

Fluorescent properties and resonance energy transfer of 3,4-bis(2,4-difluorophenyl)-maleimide

A fluorescent compound 3,4-bis(2,4-difluorophenyl)-maleimide from the 3,4-diaryl-substituted maleimides was synthesized and determined to have a Stokes shift of 140 nm (λ(abs) 341 nm, λ(em) 481 nm), a high fluorescent quantum yield (Φ(fl) 0.61) and an extinction coefficient ε((340)) of 48?400 M(-1) cm(-1) in dichloromethane. For the first time we demonstrated the successful implementation of a 3,4-diaryl-substituted maleimide molecule as a donor component in FRET experiments.     

Synthesis of α-2′-deoxynucleosides

α-Thymidine (4) was synthesized from thymidine (1) in 3 steps in 36% overall yield without using chro-matography and with the possibility of increasing the yield to 85% by reusing the remaining α,β-mixture. 1-(2-Deoxy-3,5-di-O-p-toluoyl-α-D-erythro-pentofuranosyl)thymine (3) was further converted to 1-(2-deoxy-α-D-erythro-pentofuranosyl)-5-methylcytosine (5) .     

Characterization of poly(3,4-ethylenedioxythiophene):tosylate conductive polymer microelectrodes for transmitter detection

In this paper we investigate the physical and electrochemical properties of micropatterned poly(3,4-ethylenedioxythiophene):tosylate (PEDOT:tosylate) microelectrodes for neurochemical detection. PEDOT:tosylate is a promising conductive polymer electrode material for chip-based bioanalytical applications such as capillary electrophoresis, high-performance liquid chromatography, and constant potential amperometry at living cells. Band electrodes with widths down to 3 μm were fabricated on polymer substrates using UV lithographic methods. The electrodes are electrochemically stable in a range between -200 mV and 700 mV vs. Ag/AgCl and show a relatively low resistance. A wide range of transmitters is shown to oxidize readily on the electrodes. Kinetic rate constants and half wave potentials are reported. The capacitance per area was found to be high (1670 ± 130 μF cm(-2)) compared to other thin film microelectrode materials. Finally, we use constant potential amperometry to measure the release of transmitters from a group of PC 12 cells. The results show how the current response decreases for a series of stimulations with high K(+) buffer.