Transportation of megawatt millijoule laser pulses via optical fibers?

Laser ignition is considered to be one of the most promising future concepts for internal combustion engines. It combines the legally required reduction of pollutant emissions and higher engine efficiencies. The igniting plasma is generated by a focused pulsed laser beam. Having pulse durations of a few nanoseconds, the pulse energy E _p for reliable ignition amounts to the order of 10 mJ. Different methods of laser ignition with an emphasis on fiber-based systems will be discussed and evaluated.     

Catalytic Activation of Imines by Chalcogen Bond Donors in a Povarov [4+2] Cycloaddition Reaction

Recently, chalcogen bonding has been investigated in more detail in organocatalysis and the scope of activated functionalities continues to increase. Herein, the activation of imines in a Povarov [4+2] cycloaddition reaction with bidentate cationic chalcogen bond donors is presented. Tellurium-based Lewis acids show superior properties compared to selenium-based catalysts and inactive sulfur-based analogues. The catalytic activity of the chalcogen bonding donors increases with weaker binding anions. Triflate, however, is not suitable due to its participation in the catalytic pathway. A solvent screening revealed a more efficient activation in less polar solvents and a pronounced effect of solvent (and catalyst) on endo : exo diastereomeric ratio. Finally, new chiral chalcogen bonding catalysts were applied but provided only racemic mixtures of the product.     

Improvements of a combined size exclusion chromatography and solid phase extraction approach for the clean-up of marine sediment samples for trace analysis of pesticides

 Two methods based on gel permeation chromatography (GPC) [size exclusion chromatography] for the analysis of traces (ng/kg) of nitrogen and phosphorus containing pesticides (like triazines or phosphothionates) from marine sediment samples are compared: A macro GPC with Biobeads SX-3 and a chromatography on a high-performance (HP-GPC) column with UV-detection. Results for eight triazine herbicides, two triazine metabolites, the phenylurea derivative linuron, two acetanilides and two organophosphorus compounds are given. Concentrations obtained with the HP-GPC are compared with those obtained with a macro GPC approach in an earlier study. Received: 4 October 1996/Revised: 20 December 1996/Accepted: 24 December 1996     

Monitoring the heterogeneity in single cell responses to drugs using electrochemical impedance and electrochemical noise

Impedance spectroscopy is a widely used technique for monitoring cell–surface interactions and morphological changes, typically based on averaged signals from thousands of cells. However, acquiring impedance data at the single cell level, can potentially reveal cell-to-cell heterogeneity for example in response to chemotherapeutic agents such as doxorubicin. Here, we present a generic platform where light is used to define and localize the electroactive area, thus enabling the impedance measurements for selected single cells. We firstly tested the platform to assess phenotypic changes in breast cancer cells, at the single cell level, using the change in the cell impedance. We next show that changes in electrochemical noise reflects instantaneous responses of the cells to drugs, prior to any phenotypical changes. We used doxorubicin and monensin as model drugs and found that both drug influx and efflux events affect the impedance noise signals. Finally, we show how the electrochemical noise signal can be combined with fluorescence microscopy, to show that the noise provides information on cell susceptibility and resistance to drugs at the single cell level. Together the combination of electrochemical impedance and electrochemical noise with fluorescence microscopy provides a unique approach to understanding the heterogeneity in the response of single cells to stimuli where there is not phenotypic change.

A light addressable single-cell impedance technique for cell adhesion monitoring and measurement of a cell''s drug response based on electrochemical noise is introduced.     

Incorporation of β-Alanine in Cu(II) ATCUN Peptide Complexes Increases ROS Levels,DNA Cleavage and Antiproliferative Activity**

Redox-active Cu(II) complexes are able to form reactive oxygen species (ROS) in the presence of oxygen and reducing agents. Recently, Faller et al. reported that ROS generation by Cu(II) ATCUN complexes is not as high as assumed for decades. High complex stability results in silencing of the Cu(II)/Cu(I) redox cycle and therefore leads to low ROS generation. In this work, we demonstrate that an exchange of the α-amino acid Gly with the β-amino acid β-Ala at position 2 (Gly2→β-Ala2) of the ATCUN motif reinstates ROS production (^•OH and H₂O₂). Potentiometry, cyclic voltammetry, EPR spectroscopy and DFT simulations were utilized to explain the increased ROS generation of these β-Ala2-containing ATCUN complexes. We also observed enhanced oxidative cleavage activity towards plasmid DNA for β-Ala2 compared to the Gly2 complexes. Modifications with positively charged Lys residues increased the DNA affinity through electrostatic interactions as determined by UV/VIS, fluorescence, and CD spectroscopy, and consequently led to a further increase in nuclease activity. A similar trend was observed regarding the cytotoxic activity of the complexes against several human cancer cell lines where β-Ala2 peptide complexes had lower IC₅₀ values compared to Gly2. The higher cytotoxicity could be attributed to an increased cellular uptake as determined by ICP-MS measurements.     

Arene Ruthenium(II) Complexes Bearing the κ-P or κ-P,κ-S Ph2P(CH2)3SPh Ligand

Neutral [Ru(η⁶-arene)Cl₂{Ph₂P(CH₂)₃SPh-κP}] (arene = benzene, indane, 1,2,3,4-tetrahydronaphthalene: 2a, 2c and 2d) and cationic [Ru(η⁶-arene)Cl(Ph₂P(CH₂)₃SPh-κP,κS)]X complexes (arene = mesitylene, 1,4-dihydronaphthalene; X = Cl: 3b, 3e; arene = benzene, mesitylene, indane, 1,2,3,4-tetrahydronaphthalene, and 1,4-dihydronaphthalene; X = PF₆: 4a–4e) complexes were prepared and characterized by elemental analysis, IR, ¹H, ¹³C and ³¹P NMR spectroscopy and also by single-crystal X-ray diffraction analyses. The stability of the complexes has been investigated in DMSO. Complexes have been assessed for their cytotoxic activity against 518A2, 8505C, A253, MCF-7 and SW480 cell lines. Generally, complexes exhibited activity in the lower micromolar range; moreover, they are found to be more active than cisplatin. For the most active ruthenium(II) complex, 4b, bearing mesitylene as ligand, the mechanism of action against 8505C cisplatin resistant cell line was determined. Complex 4b induced apoptosis accompanied by caspase activation.     

SUBPOL: a novel SUcrose-Based Polymer support for solid-phase peptide synthesis and affinity chromatography applications

A novel SUcrose-Based Polymer support (SUBPOL) with tailored morphology suitable for the use in solid-phase peptide synthesis (SPPS) is described, and its application as a hydrophilic affinity matrix for the specific removal of fibrinogen from human plasma is demonstrated. After suspension polymerization of partly methacrylated 2,1':4,6-di-O-isopropylidene sucrose and subsequent removal of the protecting groups, hydrophilic spherical polymer beads were obtained. The morphology of the resulting resin was controlled by variation of the porogen as well as the average degree of substitution with respect to the methacryloyl groups of the monomer mixture. After introduction of amino groups for a permanent attachment of immobilized peptide ligands, prevention of unintended esterification during SPPS was achieved by silylation of remaining hydroxy groups. Alternatively, a Rink amide linker was introduced prior to SPPS to allow cleavage and subsequent analysis of the peptide assembled on the SUBPOL resins. Two hexapeptides of sequence kwiivw and hffflw, consisting of d-amino acids, as well as a 19-mer peptide corresponding to the sequence GSGVRGDFGSLAPRVARQL of the VP1 protein from the foot-and-mouse disease virus (FMDV) were successfully prepared both manually or in a semi-automated process on SUBPOL resins according to the Fmoc/tBu strategy. Yields and purities were comparable to peptides prepared on commercially available polystyrene resins. A specific affinity adsorbent containing the fibrinogen-binding pentapeptide GPRPK was prepared by SPPS on SUBPOL resins of different morphology, and the strong impact of the affinity matrix on adsorption performance was demonstrated.     

UV/Vis Spectroscopic Properties of N -(2′-Hydroxy-4′- N , N -dimethyl-aminobenzylidene)-4-nitroaniline in Various Solvents and Solid Environments

 N-(2′-Hydroxy-4′-N,N-dimethylaminobenzylidene)-4-nitroaniline [HDBN] has been used as a model for investigating intra- and intermolecular D–A (donor–acceptor) interactions in various environments by means of UV/Vis spectroscopy. UV/Vis spectra of HDBN have been measured in various solvents, ethanolic solutions of different pH, adsorbed on silica, and in the solid state. A bathochromic shift of ν_max is observed with increasing the dipolarity/polarizability and HBD (hydrogen bond donor) capacity of the solvent, which is described by means of a multiple LSE (linear solvation energy) relationship in terms of the empirical Kamlet-Taft solvent polarity parameters. The adsorption of HDBN on Aerosil^? 300-silica particles in non-HBA (hydrogen bond acceptor) solvents is explained in the same sense. Mobile protons and sol–gel entrapping cause a hypsochromic shift due to protonation of the lone electron pair of the 4′-N,N-dimethylamino group. Hydroxide ions attack the 2′-hydroxy group which causes a bathochromic shift. A strong intramolecular hydrogen bond between the 2′-hydroxyl hydrogen and the imine nitrogen atom is present in the solid-state structure causing an unprecedented bathochromic shift.     

New Interfaces for Coupling TLC with TOF SIMS

JPC – Journal of Planar Chromatography – Modern TLC - Two interfaces have been tested for coupling thin-layer chromatography (TLC) with time-of-flight secondary-ion mass spectrometry...