Orientierungsverhalten von segmentierten Polyurethanen in Abhängigkeit von der Folienpräparation und dem Zeitpunkt der Orientierungsbestimmung

Zusammenfassung Bei der Drehung von entmischten Block-Copolymeren treten kontinuums- und molekularmechanische Dremomente an den Domänen der härteren Phase auf. Dies führt im Fall der segmentierten Polyurethane zu einer anfänglichen Negativorientierung der Hartsegmente, die als Hinweis auf eine stark anisotrope Domänenform zu verstehen ist, wobei die Hartsegmente in Richtung der kurzen Domänenachse liegen. Hiervon ausgehend werden in der vorliegenden Arbeit Zusammenhänge zwischen der Probenpräparation (ca. 6m dicke Folien) und der Negativorientierung erarbeitet, um so ein Kriterium für die von Fall zu Fall unterschiedliche Domänenmorphologie zu gewinnen. Gleichzeitig ergeben sich Hinweise auf unterschiedliche Relaxationsmechanismen, die sich überlagern und so teilweise eine Erhöhung, teilweise eine Erniedrigung der Orientierung bedingen.Herrn Prof. Dr. F. H. Müller gewidmet.     

7-Deazaguanosine: Synthesis of an oligorbonucleotide building block and disaggregation of the U-G-G-G-G-U G4 structure by the modified base

Building blocks derived from 7-deazaguanosine (c⁷G, 1 ) were prepared for solid-phase oligoribonucleotide synthesis. Compound 1 was converted into the isobutyurl derivative 2b and the (dimethylamino)methylidene compound 3 (Scheme 1). After tritylation (→ 4a , b ), silylation was studied with regard to regioselectivity. It was found that the triisopropylsilyl group in combination with the (dimethylamino)methylidene residue gave the highest 2′ -selectivity (→ 5e ). The 2′ -O -silyl derivative 5e was reacted with PCl₃ affording the 3′ -phosphonate 7 which was used in solid-phase oligoribonucleotide synthesis. Oligonucleotides derived from U-G-G-G-G-U with an increasing number of c⁷G residues instead of G were synthesized. Aggregation was studied by polyacrylamidegel electrophoresis and CD Spectroscopy. Disaggregation of the G₄-structure of U-G-G-G-G-U was observed when c⁷G replaced G, demonstrating that guanine N(7) participates in the aggregation process.     

Generation of larger numbers of separated microbial populations by cultivation in segmented-flow microdevices

The high speed production of fluid segments for the highly parallelized cultivation of monoclonal cell populations was carried out by the use of microchip segmentor modules. Aqueous fluid segments, embedded in a non-miscible carrier liquid, were produced with frequencies up to 30 s(-1) and showed a high homogeneity in size. This corresponds with the production of about 2.5 million samples per day. The segment volumes can be adapted between about 4 nl and 100 nl. The typical segment size for cultivation experiments is in the range between 40 nl and 80 nl. Nutrient medium can be applied instead of pure water. It is possible to aliquot a cell suspension in such a way that most of the aqueous fluid segments contain only one cell. In model experiments with four microbial species chip-produced aliquots of 60 nl, each containing one or a few cells, were incubated in Teflon capillary tubes. Rapid growth of the microcultures was observed. Cell densities were found to be as high as in conventional shake flask cultures.     

In-situ characterization of thin polymer films for applications in chemical sensing of volatile organic compounds by spectroscopic ellipsometry

Polymer coatings are applied in many kinds of chemical sensors. The interaction with organic vapours changes the physical properties of the coating material. For optical sensors, changes in the coating volume and the complex refractive index are most important. Spectroscopic ellipsometry has been applied for the first time to the in-situ characterization of thin poly(dimethylsiloxane) films in contact with tetrachloroethene, toluene and cyclohexane vapours. The differences in bulk refractive index between organic solvent and polymer are large for toluene and tetrachloroethene and both effects were studied separately. Cyclohexane has a bulk refractive index very close to the investigated poly(dimethylsiloxane) films. Therefore the calculation of the volume fraction of the analyte in the mixture phase with the polymer is subject to large errors for vapour concentrations below 5000 ppm. Paper presented at the ANAKON ’95, Schliersee, München, Germany     

Photoreduction of Cyclic α-Fluoroketones

Irradiation of the α-fluoroketones 1a and 6a in i-PrOH selectively affords the parent ketone 1b and 6b , respectively. It is concluded that in this solvent heterolytic C-F bond cleavage of the anion radical-formed by electron transfer to the excited fluoroketone-is a faster process than the subsequent protonation by the cation radical of the solvent. In cyclohexane 1b and 6b are only formed in minor amounts, the fluorinated RH-reduction product 4 now being the major product from 1a . In non-reducing solvents as t-BuOH or benzene 2-fluorocyclohexanone (1a) exhibits a similar behavior as cyclohexanone (1b) on excitation. The quantum yields for α-cleavage are alike for both compounds, but oxetane formation with 2-methylpropene as olefinic component occurs much more readily with 1a than with 1b .     

Recent advances in the biosynthesis and accumulation of anthocyanins

This review describes biochemistry, molecular biology and regulation of anthocyanin biosynthesis, with particular emphasis on mechanistic features and late steps of anthocyanin biosynthesis including glycosylation and vacuolar sequestration. The literature from 1997 to the beginning of 2002 is reviewed, and 163 references are cited.     

An automated technique for thermoacoustimetry of solids

An automated technique for thermoacoustimetry of solids is described. The technique is illustrated by measurements on Green River and Kentucky oil shales.     

Computational study of the influence of solvent on (16)O/(18)O equilibrium isotope effects in phosphate deprotonation reactions

Results from theoretical calculations of (16)O/(18)O equilibrium isotope effects (EIEs) on deprotonation of phosphate and methyl phosphate monoanions as well as their deuterated counterparts are reported. The EIEs are calculated from the Bigeleisen equation using harmonic vibrational frequencies from several quantum mechanical methods (HF, DFT, MP2, and AM1). All methods correctly predict the qualitative trends in the EIEs related to the different isotope substitutions. However, the calculated gas-phase values are found to be systematically higher than those experimentally observed in aqueous solution. On the other hand, the addition of explicit solvent molecules (up to 24 waters) in the first solvation shells of the phosphate ion substantially improves the calculated EIE, which approaches the experimental value with increasing size of the water cluster. The large effects of surrounding water molecules on the phosphate deprotonation EIE can be explained by the strong solute-solvent interactions, which result in solvent coupled vibrational modes of the phosphate ions.     

Mass transfer characteristics of plasmids in monoliths

The hydrodynamic properties and pore-structure of monoliths based on functionalized poly(glycidyl methacrylate-ethylene dimethacrylate) were characterised by pulse response experiments using different probes representing a wide range of molecular mass. On a small scale, band spreading was found to be caused to the extent of more than 90% by extra-column effects. These monoliths have large channel diameters, providing a suitable chromatography adsorbent for processing of large molecules. Dynamic and static binding capacity for plasmid DNA was investigated. For our model plasmid, consisting of 4.9 kbp, a capacity of 7 mg/mL was observed in comparison to 0.3 mg/mL for a conventional medium designed for protein separation. When plasmids were loaded on the monolith a gradual increase in pressure drop was observed. The channels filled up and the cross-sectional area available for liquid flow decreased. Therefore, a higher pressure drop was observed during elution. This is caused by (i) shrinking of the channels as effect of the high salt concentration, (ii) high viscosity of the mobile phase due to high concentration of plasmids, and (iii) an increase of the hydrodynamic radius of the plasmid with salt concentration from 45 nm at 150 mM to 70 nm at 2 M NaCl, as measured by dynamic light scattering. These types of monoliths are considered to be the preferred adsorbents for plasmid separation.     

PHOTOCHEMICAL STABILITY OF BIOLOGICALLY ACTIVE COMPOUNDS. IX. CHARACTERIZATION OF THE SPECTROSCOPIC PROPERTIES OF THE 4-AMINOQUINOLINES, CHLOROQUINE AND HYDROXYCHLOROQUINE, AND OF SELECTED METABOLITES BY ABSORPTION, FLUORESCENCE AND PHOSPHORESCENCE MEASUREMENTS

Abstract The spectroscopic properties of the antimalarials chloroquine, hydroxychloroquineand selected metabolites were investigated by absorption, fluorescence and phosphorescence measurements. The antimalarials exhibit both fluorescence and phosphorescence. Fluorescence dominates for the deprotonated forms of the 4-aminoquinolines, while phosphorescence dominates when the compounds are protonated. The phosphorescence lifetimes of the 4-aminoquinolines were measured. Both the protonated and the deprotonated forms have long phosphorescence lifetimes indicating a long-lived triplet state.