PubMed · 4532866
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E Kirkegaard, S Poulsen, I Moller. 1974. [What about fluoride tablets?].. https://pubmed.ncbi.nlm.nih.gov/4532866/
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19F/29Si Hartmann-Hahn continuous wave cross-polarization (CP) has been applied under fast magic-angle spinning (MAS) to a powder sample of octadecasil. Strong oscillations occur during CP on a sideband matching condition between the isolated 29Si-19F spin pairs formed by the silicons in the D4R units and the fluoride anions. The magnitude of the dipolar coupling constant was deduced directly from the line-splitting between the intense singularities of the Pake-like patterns obtained by Fourier transformation of the oscillatory polarization transfer. The corresponding Si-F internuclear distance, r = 2.62 +/- 0.05 A, is found to be in very good agreement with the X-ray crystal structure and the value of 2.69 +/- 0.04 A recently reported from rotational echo double resonance (REDOR) and transferred echo double resonance (TEDOR) nuclear magnetic resonance (NMR) experiments. Furthermore, the CP technique is still reliable under fast MAS where both REDOR and TEDOR sequences suffer from severe artefacts due to finite pulse lengths. In octadecasil, a spinning frequency of approximately 14 kHz is shown to be necessary for an effective suppression of 19F-19F spin diffusion. The influences of experimental missettings and radiofrequency (RF) field inhomogeneity are taken into account.
The most important requirement for effective topical fluoride prophylaxis from toothpaste containing fluoride is that the active fluoride agent must be chemically free, and the rapid spread of the dissolved fluoride ions over the tooth surface. Abrasive compounds in the toothpastes and the brief residence time at the site of action, the oral cavity and tooth surface must not prevent the liberation. Using a two-chamber diffusion cell and an ion-selective fluoride electrode, the content of fluoride ions in five different fluoride-containing toothpastes was determined by direct potentiometry as a function of time and the different abrasive compounds employed. The investigation has demonstrated that a reduction of the release rate of fluoride ions by nearly 50% is seen when calcium carbonate and calcium hydrogen phosphate dihydrate are used as abrasive compounds and combined with sodium fluoride.
Organic vapor deposited thin films of pure biomolecules, polymer films and biomolecules dispersed in gelatin and biological tissue have been analyzed in a magnetic sector secondary ion mass spectrometer using an SF5+ primary ion beam at keV impact energies. In comparison to Ar+ bombardment under identical conditions, bombardment with SF5+ gives a 10 to 50 fold enhancement in the secondary ion yields for characteristic molecular ions. The SF5+ primary ion beam can be focussed to a small spot allowing molecular ion images to be obtained at micrometer spatial resolution with enhanced sensitivity. More importantly, the decay in molecular ion signal as a function of primary ion dose commonly observed in SIMS using monoatomic primary ions is either eliminated or greatly reduced, allowing molecular depth profiles to be obtained of organic thin films. By continuing to sample intact molecules as sputtering proceeds into the sample, the total number of detected characteristic secondary ions is increased by as much as a factor of approximately 700 for SF5+ bombardment as compared to Ar+ bombardment under identical analytical conditions. This effect is thought to be a result of the high erosion rate and the low penetration depth inherent in the use of a polyatomic primary projectile.