4,678 research outputs found
Torsion and bending of nucleic acids studied by subnanosecond time-resolved fluorescence depolarization of intercalated dyes
Subnanosecond timeāresolved fluorescence depolarization has been used to monitor the reorientation of ethidium bromide intercalated in native DNA, synthetic polynucleotide complexes, and in supercoiled plasmid DNA. The fluorescence polarization anisotropy was successfully analyzed with an elastic model of DNA dynamics, including both torsion and bending, which yielded an accurate value for the torsional rigidity of the different DNA samples. The dependence of the torsional rigidity on the base sequence, helical structure, and tertiary structure was experimentally observed. The magnitude of the polyelectrolyte contribution to the torsional rigidity of DNA was measured over a wide range of ionic strength, and compared with polyelectrolyte theories for the persistence length. We also observed a rapid initial reorientation of the intercalated ethidium which had a much smaller amplitude in RNA than in DNA
Time-resolved spectroscopy of macromolecules: Effect of helical structure on the torsional dynamics of DNA and RNA
The torsional rigidity of DNA and RNA is measured via the fluorescence depolarization technique
Study of volatile contaminants in reclaimed water
Different methods were evaluated for reducing the volatile contaminants found in water recovered from urine by distillation. The use of activated carbon, addition of potassium permanganate, and the use of oxidation catalyst are described along with laboratory tests. It is concluded that catalytic decomposition appears to be feasible, and further investigation is recommended
Ethynyl (C2H) in massive star formation: Tracing the initial conditions?
APEX single-dish observations at sub-millimeter wavelengths toward a sample
of massive star-forming regions reveal that C2H is almost omni-present toward
all covered evolutionary stages from Infrared Dark Clouds via High-Mass
Protostellar Objects to Ultracompact HII regions. High-resolution data from the
Submillimeter Array toward one hot-core like High-Mass Protostellar Object show
a shell-like distribution of C2H with a radius of ~9000AU around the central
submm peak position. These observed features are well reproduced by a 1D cloud
model with power-law density and temperature distributions and a gas-grain
chemical network. The reactive C2H radical (ethynyl) is abundant from the onset
of massive star formation, but later it is rapidly transformed to other
molecules in the core center. In the outer cloud regions the abundance of C2H
remains high due to constant replenishment of elemental carbon from CO being
dissociated by the interstellar UV photons. We suggest that C2H may be a
molecule well suited to study the initial conditions of massive star formation.Comment: Accepted for Astrophysical Journal Letters, 4 pages, 3 figures, for a
high-resolution version, see http://www.mpia.de/homes/beuther/papers.htm
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