THE INTERACTIONS OF PYRENYLMETHYL TRIBUTYLPHOSPHONIUM BROMIDE WITH SINGLE STRAND POLYNUCLEOTIDES

The binding of the water soluble derivative of pyrene, pyrenylmethyl tri-n-butylphosphonium bromide (PMTP), to single strand polynucleotides has been characterised by changes in the absorption spectra, fluorescence spectra, the fluorescence lifetime and the time-resolved fluorescence anisotropy of PMTP. For polyguanylic acid at low ionic strength, there are two modes of binding; external ionic binding and intercalation between the bases. The former results in PMTP excimer formation and the latter involves a charge-transfer complex between PMTP and guanine bases. Polyadenylic acid and polyinosinic acid show only external binding and poly[C] exhibits an interaction which is a combination of external binding and partial intercalation. Single strand DNA binds PMTP by intercalation and external binding at low ionic strength. In the presence of 0.2 M sodium chloride, only binding by intercalation between the bases occurs for poly[G]. Single strand DNA bound PMPT by partial intercalation, as well as full intercalation between the bases, but polyadenylic acid, polycytidylic acid and polyinosinic acid showed no significant binding in the presence of 0.2 M sodium chloride. The differences in the binding of PMTP are attributed to variations in the rigidity and form the structures of single strand polynucleotides adopt in solution. A full analysis of the binding isotherms has been made using methods based on Scatchard plots and the McGhee and von Hippel approach, which are critically compared.     

Ground-state energy of a quantum chain with competing interactions

We show rigorously that the ground state of a quantum chain with competing ferromagnetic nearest and antiferromagnetic next nearest interactions undergoes a transition from ferromagnetic to helical type, in the isotropic case, for a certain value of the relevant ratio of coupling constants. Boundaries of the phase diagram are also determined in the anisotropic case. The stability of a special quantum state (corresponding to a classical modulated phase of =/3) is analyzed by an extension of Holstein-Primakoff arguments, along a line of constant ratio of couplings, showing in particular a sequence of (instability) gaps. Finally, a natural adaptation of a variational wave function due to Huse and Elser is used to study several portions of the phase diagram, with very good agreement with previous theoretical results.     

Angular dependence of Bose-Einstein correlations in interactions of π+ andK + mesons with protons and nuclei at 250 GeV/c

The angular dependence of Bose-Einstein correlations is studied in interactions of ⁺ andK ⁺ mesons with protons and nuclei at 250 GeV/c. The pion source is found to be elongated along the interaction axis in the c.m.s., with the ratioa between transverse and longitudinal dimension equal to 0.55±0.06 for the case of proton, 0.53±0.13 for the case ofAl and 0.33±0.21 for the case ofAu target. For meson-proton interactions, indication for an increase of the elongation is found with increasing event multiplicity, pair momentum and particle transverse momentum.Now at UIA, Wilrijk, Belgium     

Evaluation of recombinant green fluorescent protein, under various culture conditions and purification with HiTrap hydrophobic interaction chromatography resins

To determine the influence of various culture conditions, transformed cells of Escherichia coli expressing recombinant green fluorescent protein (GFPuv) were grown in nine cultures with four variable conditions (storage of inoculated broth at 4°C prior to incubation, agitation speed, isopropyl-β-d-thiogalactopyranoside [IPTG] concentration, and induction time). The pelleted cells were resuspended in extraction buffer and subjected to the three-phase partitioning (TPP) extraction method. To determine the most appropriate purification resin, protein extracts were eluted through one of four types of HiTrap hydrophobic interaction chromatography (HIC) columns prepacked with methyl, butyl, octyl, or phenyl resins and analyzed further on a 12% sodium dodecylsulfatepolyacrylamidegel. With Coomassie staining, a single band between 27 (standard GFPuv) and 29 kDa (molecular weight standard) was visualized for every HIC column sample. TPP extraction with HIC elution provided about 90% of the GFPuv recovered and eight-fold GFPuv enrichment related to the specific mass. Rotary speed and IPTG concentration showed, respectively, greater negative and positive influences on GFPuv expression at the beginning of the logarithmic phase for the set culture conditions (37°C, 24-h incubation).     

Gas chromatographic quantification of amino acid enantiomers in food matrices by their N(O,S)-ethoxycarbonyl heptafluorobutyl ester derivatives

Several amino acid enantiomer derivatives were prepared with different chloroformates and analysed by gas chromatography (GC) on a Chirasil-L-Val GC column, at a temperature below 200 degrees C. Among them the N(O,S)-ethoxycarbonyl heptafluorobutyl esters presented the best compromise between short retention times, high yield responses and good resolution for almost all the tested amino acids. These derivatives proved to be suited for quantification of amino acids in aqueous media, with L-p-chlorophenylalanine as internal standard. The developed procedure was applied to several food samples for determination of their free amino acid profiles.     

A thieno-2H-chromene alpha-amino acid derivative: synthesis and photochromic properties

[structure: see text] A new photochromic thieno-2H-chromene alpha-amino acid derivative was prepared by C-N palladium-catalyzed cross-coupling of a bromothieno-2H-chromene with the aminated aromatic side chain of the methyl ester of a N,N-diprotected amino acid. Its good photochromic properties demonstrated by flash photolysis and continuous irradiation indicate a possible application in ophthalmic lenses. It may also be inserted into peptides to give photoinduced reversible structural changes.