Labeling the human skeleton with 41Ca to assess changes in bone calcium metabolism

Bone research is limited by the methods available for detecting changes in bone metabolism. While dual X-ray absorptiometry is rather insensitive, biochemical markers are subject to significant intra-individual variation. In the study presented here, we evaluated the isotopic labeling of bone using ⁴¹Ca, a long-lived radiotracer, as an alternative approach. After successful labeling of the skeleton, changes in the systematics of urinary ⁴¹Ca excretion are expected to directly reflect changes in bone Ca metabolism. A minute amount of ⁴¹Ca (100 nCi) was administered orally to 22 postmenopausal women. Kinetics of tracer excretion were assessed by monitoring changes in urinary ⁴¹Ca/⁴⁰Ca isotope ratios up to 700 days post-dosing using accelerator mass spectrometry and resonance ionization mass spectrometry. Isotopic labeling of the skeleton was evaluated by two different approaches: (i) urinary ⁴¹Ca data were fitted to an established function consisting of an exponential term and a power law term for each individual; (ii) ⁴¹Ca data were analyzed by population pharmacokinetic (NONMEM) analysis to identify a compartmental model that describes urinary ⁴¹Ca tracer kinetics. A linear three-compartment model with a central compartment and two sequential peripheral compartments was found to best fit the ⁴¹Ca data. Fits based on the use of the combined exponential/power law function describing urinary tracer excretion showed substantially higher deviations between predicted and measured values than fits based on the compartmental modeling approach. By establishing the urinary ⁴¹Ca excretion pattern using data points up to day 500 and extrapolating these curves up to day 700, it was found that the calculated ⁴¹Ca/⁴⁰Ca isotope ratios in urine were significantly lower than the observed ⁴¹Ca/⁴⁰Ca isotope ratios for both techniques. Compartmental analysis can overcome this limitation. By identifying relative changes in transfer rates between compartments in response to an intervention, inaccuracies in the underlying model cancel out. Changes in tracer distribution between compartments were modeled based on identified kinetic parameters. While changes in bone formation and resorption can, in principle, be assessed by monitoring urinary ⁴¹Ca excretion over the first few weeks post-dosing, assessment of an intervention effect is more reliable ∼150 days post-dosing when excreted tracer originates mainly from bone.     

Synthesis of Fluorinated Dienylic Stannanes Via the Wadsworth-Emmons Reaction

Geminal difluorination of dithiolane 9 affords bis benzyl ether 4b which is converted to beta-fluoroenals 3Z/3E. Reaction of these enals with the stannylmethyl Wadsworth-Emmons reagent 2 produces dienyl esters 14Z/14E which are converted to highly functionalized dienylic stannanes 1Z and 1E.     

Magnesium isotope ratio measurements by negative thermal ionisation mass spectrometry using molecular fluoride ions

A new technique for accurate Mg isotope ratio measurements has been developed with MgF₂ as sample compound. With the help of a fluorinating agent negatively charged MgF₃ molecular ions were formed in the ion source of a thermal ionisation mass spectrometer. An evaporation study has been performed and the results clearly show that Mg is evaporated from the filament as MgF₂ molecules. The MgF₂ technique has been applied in the certification of a candidate ²⁶Mg-enriched Spike Isotope Reference Material. The result from this new technique has been compared with results obtained for the same material using ICP-MS. Received: 14 December 1998 / Revised: 5 March 1999 / Accepted: 11 March 1999     

Prediction of nonlinear optical responses of organic compounds.

The nonlinear optical quantities, second and third harmonics (beta and gamma), were predicted using a quantitative structure-property relationship (QSPR) approach. Molecular orbital ab initio calculations were applied to generate easily accessible variables to be used in the partial least-squares analysis. Simplified equations are presented that could be used to predict the experimental beta and gamma responses, prior to further investigations of potentially interesting molecules for use in optical materials.     

Vortmann's Methode, direct Chlor neben Brom zu bestimmen

Ohne Zusammenfassung     

On the correlation between deuteron quadrupole coupling constants,O-H and O-D stretching frequencies and hydrogen-bond distances in solid hydrates

Correlation curves are reported relating deuteron quadrupole coupling constants (e²qQ/h) to O-H and O-D stretching frequencies (v_OH and v_OD) for isotopically-dilute HDO molecules. Correlation curves are also given relating these quantities to hydrogen-bond distances.The best correlations are found to be between (e²qQ/h) and v_OH andv_OD whereas the correlations involving intermolecular geometries show considerably greater scatter.Complications caused by the effects of anharmonicity on the stretching vibrations and of vibrational averaging of the quadrupole coupling and geometrical parameters are discussed in light of the observed correlations. It is concluded that, although these effects are large, their magnitude is also strongly correlated with the stretching frequencies, quadrupole couplings and geometrical parameters.     

Methods of calibration in the direct analysis of solid samples by electrothermal atomic absorption spectrometry

One of the major problems involved in the direct analysis of solid samples by electrothermal atomic absorption spectrometry (ETAAS) lies in the calibration step because non-spectral interference effects are often pronounced. Three standardization techniques have been described and used in solid sampling-ETAAS: (i) standard additions method; (ii) calibration relative to a certified reference material; and (iii) calibration curve technique. However, an adequate statistical evaluation of the uncertainty in the analyte concentration in the solid sample is most frequently neglected, and reported errors may be seriously underestimated. This can be attributed directly to the complexity of the statistical expressions required to accurately account for errors in each of the calibration techniques mentioned above, and the general lack of relevant reference literature. The object of this work has been to develop a computer package which will perform the necessary statistical analyses of solid sampling-ETAAS data; the result is the program “SOLIDS” described here in the form of an electronic publication in Spectrochimica Acta Electronica, the electronic section of Spectrochimica Acta Part B. The program could also be useful in other analytical fields where similar calibration methods are used. The hard copy text, outlining the calibration models and their associated errors, is accompanied by a diskette containing the program, some data files, and a manual. Use of the program is exemplified in the text, with some of the data files discussed included on the diskette which, together with the manual, should enable the reader to become familiarized with the operation of the program, and the results generated.     

Concentration enrichment of urea at cellulose surfaces: results from molecular dynamics simulations and NMR spectroscopy

A combined solid-state NMR and Molecular Dynamics simulation study of cellulose in urea aqueous solution and in pure water was conducted. It was found that the local concentration of urea is significantly enhanced at the cellulose/solution interface. There, urea molecules interact directly with the cellulose through both hydrogen bonds and favorable dispersion interactions, which seem to be the driving force behind the aggregation. The CP/MAS ¹³C spectra was affected by the presence of urea at high concentrations, most notably the signal at 83.4 ppm, which has previously been assigned to C4 atoms in cellulose chains located at surfaces parallel to the (110) crystallographic plane of the cellulose Iβ crystal. Also dynamic properties of the cellulose surfaces, probed by spin-lattice relaxation time ¹³CT ₁ measurements of C4 atoms, are affected by the addition of urea. Molecular Dynamics simulations reproduce the trends of the T ₁ measurements and lends new support to the assignment of signals from individual surfaces. That urea in solution is interacting directly with cellulose may have implications on our understanding of the mechanisms behind cellulose dissolution in alkali/urea aqueous solutions.     

Three-dimensional real-time tracking of nanoparticles at an oil-water interface

Single-particle tracking with real-time feedback control can be used to study three-dimensional nanoparticle transport dynamics. We apply the method to study the behavior of adsorbed nanoparticles at a silicone oil-water interface in a microemulsion system over a range of particles sizes from 24 nm to 2000 nm. The diffusion coefficient of large particles (>200 nm) scales inversely with particle size, while smaller particles exhibit an unexpected increase in drag force at the interface. The technique can be applied in the future to study three-dimensional dynamics in a range of systems, including complex fluids, gels, biological cells, and geological media.