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PubMed1985

Boundary centrifugation in isovolumetric and isokinetic cesium sulfate density gradients: application to cartilage proteoglycans and other macromolecules.

A boundary sedimentation methodology is described that avoids plateau dilution and simplifies the calculation of centrifugal parameters. The technique is designed for the preparative ultracentrifuge and uses a newly developed sectorial cell. It is based on previous developments of the transport method and depends on isokinetic or isovolumetric Cs2SO4 density and viscosity gradients. These gradients are prepared with a single-chamber mixing device, and the only two parameters required for their calculations are presented in a tabulated form for general use with most available rotors and cell sizes. Conditions are specified (1) to assure that the density and shape of the sedimenting molecules remain invariant through the selected electrolytic gradient, (2) to monitor the gradient profiles, and (3) to verify attainment of isokinetic or isovolumetric sedimentations. A set of equations is presented to calculate the average and transport sedimentation coefficients and the differential sedimentation coefficient distribution for both the isokinetic and isovolumetric centrifugal regimes. The method was applied to slowly diffusing polydisperse proteoglycan monomers, to a paucidisperse DNA from bacteriophage PM2, and to a diffusible monodisperse system (purified bovine serum albumin). In all cases, the expected results were obtained.

Animals↗
PubMed2003

Linking cesium and strontium uptake to kaolinite weathering in simulated tank waste leachate.

Weathering behavior of kaolinite was studied in batch systems under geochemical conditions characteristic of tank waste released to the vadose zone at the Hanford Site, WA (0.05 M Al(T), 2 M Na+, 1 M N03-, pH approximately 14, Cs+ and Sr2+ present as co-contaminants). Time series experiments were conducted from 0 to 369 d, with initial Cs+ and Sr2+ concentrations ranging from 10(-5) to 10(-3) M. Dissolution of kaolinite increased soluble Si and Al to maximum levels at 7 d (Cs and Sr concentrations of 10(-5) and 10(-4) M) or 33 d (Cs and Sr concentrations of 10(-3) M). Subsequent precipitation of Si and Al was coupled to the formation of oxalate-extractable solids that incorporated Cs and Sr. Strontium sorption was nearly complete within 24 h for initial Sr concentrations (Sr0) < or = 10(-4) whereas Cs uptake increased over the full year of the experiment for all initial Cs concentrations. Spectroscopic analyses revealed neoformed solids including the zeolite Na-Al silicate (Al-chabazite), and feldspathoids sodium aluminum nitrate silicate (NO3-sodalite), and sodium aluminum nitrate silicate hydrate (NO3-cancrinite), which can incorporate Cs. Single-pulse 27Al solid-state nuclear magnetic resonance (NMR) spectroscopyyielded first-order rate constants (k)for mineral transformation that decreased from 3.5 x 10(-3) to 2 x 10(-3) d(-1) as Cs and Sr concentrations were increased from 10(-5) to 10(-3) M. Discrete strontium silicate solids were also observed. The incongruent dissolution of kaolinite promoted the sequestration of contaminants into increasingly recalcitrant solid phases over the 1-yr time period.

Adsorption↗
PubMed2004

Microscale distribution of cesium sorbed to biotite and muscovite.

Individual 1-3 mm biotite and muscovite clasts from Hanford sediment were contacted with 0.08 M CsNO3. They were examined using electron or X-ray microprobe methods, as intact specimens or sectioned perpendicular to their basal planes. Cs+ was observed to preferentially sorb to mica edges, steps on mica surfaces, or fractured regions. The localization of Cs conformed to hypothesized strong binding to frayed edge sites in preference to sites on basal planes. In section, Cs+ was found to penetrate the mica interior, forming discrete zones of concentration, particularly in muscovite. In biotite, Cs was more abundant, permeating the clasts, but also forming discrete zones of higher concentration. Concentrated Cs on both clast edges and within clast interiors corresponded to microscopic but relatively extensive zones where K was depleted. The localization of sorbed Cs in areas where K was depleted suggested that weathering reactions had caused the formation of frayed edge sites within the micas. Cs+ accessed crystal interiors by diffusion along channels following crystal defects, cracks, or partings where pore fluids had previously migrated to form the interior alteration zones. On the nanometer scale, areas with localized Cs were disrupted, confirming that frayed edge sites were developed in clast interiors.

Adsorption↗
PubMed2006

Dissolution nature of cesium fluoride by water molecules.

The structures, stabilities, thermodynamic quantities, dissociation energies, infrared spectra, and electronic properties of CsF hydrated by water molecules are investigated by using density functional theory, Møller-Plesset second-order perturbation theory (MP2), coupled cluster theory with singles, doubles, and perturbative triples excitations (CCSD(T)), and ab initio molecular dynamic (AIMD) simulations. It is revealed that at 0 K three water molecules (as a global minimum structure) begin to half-dissociate the Cs-F, and six water molecules (though not a global minimum energy structure) can dissociate it. By the combination of the accurate CCSD(T) conformational energies for Cs(H2O)6 at 0 K with the AIMD thermal energy contribution, it reveals that the half-dissociated structure is the most stable at 0 K, but this structure (which is still the most stable) changes to the dissociated structure above 50 K. The spectra of CsF(H2O)(1-6) from MP2 calculations and the power spectra of CsF(H2O)6 from 50 and 100 K AIMD simulations are also reported.

Algorithms↗
PubMed1988

[One year after Chernobyl. Cesium-137 levels in premature, newborn and nursing infants and in younger and older children of Bonn and environs].

From May to August 1987, 137Cs activity was measured in a total-body counter (4 pi counter) in 33 premature and mature newborns (group I), 40 infants and young children up to 2 4/12 years of age (group II), and 15 children between 3 and 6 8/12 years (group III), all from Bonn or its environs. The mean of measurements in group II, at 3.7 Bq/kg body-weight, was lower than that of group I (5.8 Bq) and III (9.4 Bq). Mean radiation exposure, calculated from these data, was 1.7 mrem/a for group I, 1.1 mrem/a for group II, and 2.8 mrem/a for group III. A comparison with present Cs values in adults and measurements made at the end of the 1950's and beginning of 60's showed good agreement. There were no significant differences, as regards Cs activity, between newborns or infants who had been formula-fed or breast-fed. The measured radiation exposure of the three groups is about 1% of natural radiation exposure. Thus, present-day results indicate that there will be no damage to health outside the natural scatter.

Accidents↗
PubMed1981

Right-handed alternating DNA conformation: poly(dA-dT) adopts the same dinucleotide repeat with cesium, tetraalkylammonium, and 3 alpha, 5 beta, 17 beta-dipyrrolidinium steroid dimethiodide cations in aqueous solution.

We demonstrate that poly(dA-dT) can adopt two conformations in solution, with the relative proportions dependent on the nature and concentration of the counter ion and cationic ligands. The synthetic DNA exhibits a dinucleotide repeat conformation on addition of CsF and Me4NCl at molar concentrations, with the NMR spectral changes reflecting a common conformational change at one glycosidic torsion angle and one phosphodiester linkage. We also observe the same dinucleotide repeat in the neighbor-exclusion 3 alpha, 17 beta-dipyrrolidin-1'-yl-5 beta- delta 9,11-androstene dimethiodide (3 alpha, 5 beta, 17 beta-dipyrandenium) complex, with the steroid diammonium ligand binding in the groove of the stacked poly(dA-dT) duplex and the complex stabilized through the interaction of one of the charged ends with the backbone phosphate. We demonstrate further that 3 alpha, 5 beta, 17 beta-dipyrandenium bound to poly(dA-dT) at low binding ratios induces a switch to the dinucleotide repeat conformation at adjacent steroid-free duplex regions. This observation contrasts with a previous demonstration that the diastereoisomeric 3 beta, 5 alpha, 17 beta-dipyrandium binds to poly(dA-dT) by partial insertion between unstacked tilted base pairs. The NMR parameters rule out a left-handed alternating DNA structure (Z DNA) for the observed poly(dA-dT) dinucleotide repeat conformation, but right-handed alternating DNA models are under consideration. The facile interconversion of poly(dA-dT) between two conformations, one of which exhibits a dinucleotide repeat and can be induced by ligand binding, may provide a mechanism for the recognition of specific nucleic acid sequences by DNA-binding proteins.

Androstenes↗