Blood plasma model predictions for the proposed bone-seeking radiopharmaceutical [(117m)Sn]Sn(IV)-N,N',N'-trimethylenephosphonate-poly(ethyleneimine).

In an attempt to elucidate the in vivo stability of the prospective radiopharmaceutical [(117m)Sn]Sn(IV)-PEI-MP, where PEI-MP stands for N,N',N'-trimethylenephosphonate-polyethyleneimine, glass electrode potentiometry was used to determine the stability constants of the Sn(4+) ion as complexed with a variety of physiological amino acids. In addition, linear free energy relationship (LFER) correlation plots were used to extrapolate the constants of the major blood plasma ligands, based on data from Cu(2+), Pb(2+), and Zn(2+). In so doing, a thermodynamic model of blood plasma was established for Sn(4+) from which the complexation tendencies of Sn(4+) were predicted in the event of the intravenous administration of such a drug. It was found that the Sn(IV)-PEI-MP could succumb to competition by the glutamine amino acid, which forms more stable complex(es), whilst the PEI-MP gets taken up largely by Ca(2+). Also, this study shows the value of the in vitro experiments and modeling performed for radiopharmaceutical research and for attempts to reduce the number of animal experiments.

Sorption of tin on human teeth.

The sorption of tin ions on human teeth from water and other drinks has been studied by the radioactive tracer technique using the isotope 113Sn (T(1/2) = 115.1 d) as a tracer. The tooth holds a minimum amount of tin from coffee and a maximum amount is held from water and from tea with sugar. The same technique was also used to study the desorption of tin already taken up on the teeth. It has been found that sorbed tin is hardly desorbed from the teeth specimens. The high uptake of tin on human teeth from various drinks showed that teeth act as a natural sieve holding trace elements.