Electroacoustic miniaturized DNA-biosensor

A micrometer-sized electroacoustic DNA-biosensor was developed. The device included a thin semi-crystalline polyethylene terephthalate (PET) dielectric layer with two Ag microband electrodes on one side and a DNA thiol-labeled monolayer adsorbed on a gold surface on the other. A resonance wave was observed at 29 MHz with a network analyzer, upon AC voltage application between the two Ag electrodes, corresponding to electromechanical coupling induced by molecular dipoles of the PET polymer chain in the dielectric layer. It was found that the device size and geometry were well adapted to detect DNA hybridization, by measuring the capacity of the resonance response evolution: hybridization induced polarization of the dielectric material that affected the electromechanical coupling established in the dielectric layer. The 0.2 mm(2) sensor sensitive area allows detection in small volumes and still has higher detection levels for bioanalytical applications, the non-contact configuration adopted avoids electric faradic reactions that may damage biosensor sensitive layers, and finally, PET is a costless raw material, easy to process and well adapted for large scale production. The well-balanced technological and economic advantages of this kind of device make it a good candidate for biochip integration.     

Electrochemical detection of osmium tetroxide-labeled PCR-products by means of protective strands

This communication reports about how single-stranded 136 base polymerase chain reaction (PCR) products labeled with electrochemically active osmium tetroxide bipyridine can be detected voltammetrically by hybridization with probe strands immobilized on gold electrodes. These electroactive ssDNA targets have been obtained by means of Lambda Exonuclease treatment of the double-stranded PCR products followed by hybridization of the remaining single strands with short protective strands and covalent labeling with osmium tetroxide bipyridine. Square-wave voltammetric signals of these osmium labels have been obtained only upon hybridization with the immobilized probe strands. An optimal 50 °C hybridization temperature has been found with a saturation of the probe layer at 30 min hybridization time and 7.5 nmol/l target concentration. The blank capture probe layer alone did not yield any signal. Unprotected strands produced almost no interference. Such double-selective switch-on electrochemical hybridization assays hold great promise for the specific detection of PCR products.     

Synthesis,Structure, and Properties of the High‐Pressure Modification of CePdSn – a 5 K Antiferromagnet

The high‐pressure (HP) modification of CePdSn was synthesized under multianvil high‐pressure (10.5 GPa) high‐temperature (1100 °C) conditions from the normal‐pressure (NP) modification. The structures of both modifications were studied by X‐ray powder and single crystal diffraction: TiNiSi type, Pnma, a = 754.1(2), b = 470.6(1), c = 798.4(3) pm, wR2 = 0.0333, 945 F² values, 20 variables for NP‐CePdSn and ZrNiAl type, , a = 760.03(5), c = 416.06(3) pm, wR2 = 0.0443, 248 F² values, 13 variables for HP‐CePdSn. The structural chemistry of both modifications is goverened by platinum centered trigonal prisms. The platinum and tin atoms in NP‐CePdSn and HP‐CePdSn build up a three‐dimensional [PdSn] network in which the cerium atoms fill channels. Susceptibility measurements on HP‐CePdSn reveal an experimental magnetic moment of 2.55(1) μ_B/Ce atom in the paramagnetic region. At 5 K a paramagnetic‐to‐antiferromagnetic transition is evident from magnetization and specific heat measurements.     

Gel-free IEF in a membrane-sealed multicompartment cell for proteome prefractionation

A minidevice for performing gel-free proteome prefractionation via conventional IEF in soluble carrier ampholyte buffers is reported here. It consists of a compact block of polyoxymethylene in which eight samples and two electrode chambers are machined. Each of the eight sample chambers can be filled with up to 120 microL of sample and has the following size: 7 mm width, 3 mm depth and 10 mm height. The anodic and cathodic compartments have the same width and height as the sample chambers, but with a depth of 6 mm, thus accepting up to 250 microL of electrodic solutions. Focusing is in general accomplished in 2 h with a voltage gradient of up to 1000 V (7 cm electrode distance). Easy fractionation and collection of the content of the eight chambers is achieved by simply pressing a rubber diaphragm against the edges of the thin walls separating each well, this automatically breaking liquid continuity. The performance of this device has been tested by subfractionating total cell lysates of a human cancer cell line (U2Os) and of Escherichia coli bacterial cells, and by analysing the content of each chamber by mono-dimensional SDS-PAGE and 2-D maps.     

Diagonal chromatographic selection of cysteinyl peptides modified with benzoquinones

The derivatization of cysteine-containing peptides with benzoquinone compounds is rapid, quantitative and specific in acidic media. The conversion of cysteines into hydrophobic benzoquinone-adducted residues in peptides is used here to alter the chromatographic properties of cysteinyl peptides during liquid chromatography separation. The benzoquinone derivatization is shown to allow the accurate selection of cysteine-containing peptides of bovine serum albumin tryptic digest by diagonal reversed-phase chromatography, which consists of one primary and a series of secondary identical liquid chromatographic separations, before and after a cysteinyl-targeted modification of the peptides by benzoquinone compounds. Figure Diagonal chromatographic selection of cysteinyl peptides modified with benzoquinones Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Calibrant delivery for mass spectrometry

This article describes a means of sampling ions that are created at a location remote from the primary ion source used for mass spectral analysis. Such a source can be used for delivery of calibrant ions on demand. Calibrant ions are sprayed into an atmospheric pressure chamber, at a position substantially removed from the sampling inlet. A gas flow sweeps the calibrants towards the sampling inlet, and a new means for toggling the second ion beam into the instrument can be achieved with the use of a repelling field established by an electrode in front of the sampling inlet. The physical separation of two or more sources of ions eliminates detrimental interactions due to gas flows or fields. When using a nanoflow electrospray tip as the primary ion source, the potential applied to the tip completely repels calibrant ions and there is no compromise in terms of electrospray performance. When calibrant ions are desired, the potential applied to the nanoflow electrospray tip is lowered for a short period of time to allow calibrant ions to be sampled into the instrument, thus providing a means for external calibration that avoids the typical complications and compromises associated with dual spray sources. It is also possible to simultaneously sample ions from multiple ion beams if necessary for internal mass calibration purposes. This method of transporting additional ion beams to a sampling inlet can also be used with different types of atmospheric pressure sources such as AP MALDI, as well as sources configured to deliver ions of different polarity.     

A one-pot chemoenzymatic synthesis for the universal precursor of antidiabetes and antiviral bis-indolylquinones

Bis-indolylquinones represent a class of fungal natural products that display antiretroviral, antidiabetes, or cytotoxic bioactivities. Recent advances in Aspergillus genomic mining efforts have led to the discovery of the tdiA-E-gene cluster, which is the first genetic locus dedicated to bis-indolylquinone biosynthesis. We have now genetically and biochemically characterized the enzymes TdiA (bis-indolylquinone synthetase) and TdiD (L-tryptophan:phenylpyruvate aminotransferase), which, together, confer biosynthetic abilities for didemethylasterriquinone D to Aspergillus nidulans. This compound is the universal intermediate for all bis-indolylquinones. In this biochemical study of a bis-indolylquinone synthetase and a fungal natural product transaminase, we present a one-pot chemoenzymatic protocol to generate didemethylasterriquinone D in vitro. As TdiA resembles a nonribosomal peptide synthetase, yet catalyzes carbon-carbon-bond formation, we discuss the implications for peptide synthetase chemistry.     

Conversion of perhydropolysilazane into a SiOx network triggered by vacuum ultraviolet irradiation: access to flexible, transparent barrier coatings

The photochemical conversion of 200-500 nm layers of perhydropolysilazane --(SiH2-NH)n-- (PHPS) in the presence of oxygen into an SiOx network was studied. Different UV sources in the wavelength range of 160-240 nm, that is, 172 nm Xe2* and 222 nm KrCl* excimer, and 185 nm Hg low-pressure (HgLP) lamps were used for these purposes. The role of both ozone and O(1D) as well as of catalytic amounts of tertiary amines in the degradation process of PHPS and the formation of SiOx were studied. In this context, the kinetics of the entire reaction were elucidated and allowed both a continuous and discontinuous process to be established for the production of fully transparent, flexible barrier coatings. Barrier improvement factors (BIFs) of 400 were achieved with one single layer on 23 microm poly(ethyleneterephthalate) (PET), which translated into oxygen transmission rates (OTRs) of 0.20 cm3 m(-2) day(-1) bar(-1). Double layers prepared by this technique allowed the realization of OTRs of or=800.     

Stereochemical consequences of threefold symmetry in asymmetric catalysis: distorting C3 Chiral 1,1,1-tris(oxazolinyl)ethanes ("trisox") in CuII Lewis acid catalysts

The underlying conceptual differences in exploiting two- and threefold rotational symmetry in the design of chiral ligands for asymmetric catalysis have been addressed in a comparative study of the catalytic performance of bisoxazoline (BOX) and tris(oxazolinyl)ethanes (trisox) containing copper(II) Lewis acid catalysts. The differences become apparent in constructing new catalysts by systematically "deforming" the stereodirecting ligand by inverting chiral centres or replacing chiral by achiral oxazolines. The catalytic alpha-amination of ethyl 2-methylacetoacetate with dibenzyl azodicaboxylate, which occurs with high enantioselectivity for both Ph(2)-BOX and Ph(3)-trisox copper catalysts, has been employed as the test reaction. In the trisox-copper complex [Cu(II)(iPr(3)-trisox)(kappa(2)-O,O'-MeCOCHCOOEt)](+)[BF(4)](-) (1), which was characterised by X-ray diffraction, two of the oxazoline groups are coordinated to the central copper atom, whilst the third oxazoline unit is dangling with the N-donor pointing away from the metal centre. A similar arrangement is found for the stereochemically "mixed" C(1)-trisox complex [Cu(II){(Ph(3)-trisox(R,S,S)}(kappa(2)-O,O'-MeCOCHCOOEt)(H(2)O)](+)[ClO(4)](-) (2), in which the phenyl substituents adopt a first coordination sphere meso arrangement. The almost identical selectivity of the Ph(3)-trisox(R,R,R)- and Ph(2)-BOX(R,R)-derived catalysts is as expected from the proposed model of the active catalyst based on a partially decoordinated podand. The behaviour of the "desymmetrised" trisox-Cu catalysts may be rationalised in terms of a general steady-state kinetic model for the three possible active bisoxazoline-copper species, which are expected to be in rapid exchange with each other in solution. This applies to both the trisox derivatives with stereochemically inverted and achiral oxazoline rings. The study underscores previous observations of superior performance of the catalysts bearing C(3)-chiral stereodirecting ligands as compared to systems of lower symmetry.