Interfacial reaction of Sn(II) on mackinawite (FeS)

The interaction of Sn(II) with metastable, highly reactive mackinawite is a complex process due to transient changes of the mackinawite surface in the sorption process. In this work, we show that tin redox state and local structure as investigated by Sn-K X-ray absorption spectroscopy (XAS) change with pH. We observe at pH<7 that divalent Sn forms two short (2.38 Å) Sn-S bonds to the S-terminated surface of mackinawite, and two longer (2.59 Å) Sn-S bonds pointing most likely towards the solution phase, in line with a SnS4 innersphere sorption complex. Precipitation of SnS or formation of a solid solution with mackinawite could be excluded. At pH>9, Sn(II) is completely oxidized to Sn(IV) by an Fe(II)/Fe(III) (hydr)oxide, most likely green rust, forming on the surface of mackinawite. Six O atoms at 2.04 Å and 6 Fe atoms at 3.29 Å indicate a structural incorporation by green rust, with Sn(IV) substituting for Fe in the crystal structure. The transition between Sn(II) and Sn(IV) and between sulfur and oxygen coordination takes place at a pH of 7 to 8 and an Eh of -250 mV, close to the thermodynamically predicted transitions from mackinawite to Fe (hydr)oxide and from sulfide to sulfate. The uptake processes of Sn(II) by mackinawite are largely in line with the uptake processes of divalent cations with soft Lewis-acid character like Cd, Hg and Pb, and lead to a strong retention of Sn with logRd values from 5 to 7 across the investigated pH range of 5 to 11.

Labeling conditions, in vitro properties and biodistributions of various Sn-labeled complexes

Conditions for preparing Sn-EDTMP, Sn-DTPMP, Sn-TTHMP, Sn-HEDTMP and Sn-DTPA in aqueous solution in open air environments, and their in vitro properties including adsorption on hydroxyapatite (HA) and collagen (I) and binding to bovine serum albumin (BSA) were studied using (117m)Sn and 113Sn as tracers. Biodistributions of SnO2.xH2O.yEDTMP, SnO2.xH2O.yDTPMP, SnO2.xH2O.yTTHMP, SnO2.xH2O.yHEDTMP, SnO2.xH2O.yDTPA in normal mice were also tested. Based on the above experiments, the relationship between in vitro biochemical properties and biodistributions of these SnO2.xH2O.yLigands was investigated. The results show that Sn(IV)-Ligands are prone to hydrolysis into SnO2.xH2O.yLigands in aqueous solutions in open air environments, especially when the ligand is DTPA, when the molar ratio of metal to ligand is higher than 1:200, or when the pH of the solution is higher than 10. The in vitro experiments show that all of the SnO2.xH2O.yLigands bind strongly to BSA, and the binding percentages of SnO2.xH2O.yLigands to BSA are much higher than those of the corresponding Sn(IV)-Ligands. The biodistribution data indicate that all of the SnO2.xH2O.yLigands locate mainly in bone with little uptake in liver. When the binding percentages of SnO2.xH2O.yLigands to BSA are similar, those SnO2.xH2O.yLigands with higher adsorption on HA and collagen (I) undergo lower liver uptake.

Preparation and properties of 99Tcm-exametazime using stannous ion augmentation of fractionated cold kits

Fractionation of 99Tcm-exametazime enables several patients doses to be prepared from one vial. To overcome the disadvantages of storage at -70 degrees C, storage at higher temperatures was investigated with replacement of stannous ions before use. Kits were fractionated using a nitrogen-purged 0.9% w/v sodium chloride injection, sub-dispensed into five nitrogen-filled vials in an aseptic environment and stored at -20 degrees C. Under these conditions, exametazime vials failed quality control in approximately 1 week. However, the addition of stannous pyrophosphate solution (10 micrograms Sn(II) in 0.1 ml, prepared by aseptic dilution of a red blood cell labelling kit) immediately before 99Tcm-pertechnetate produced 90.1 +/- 1.6% (n = 8) lipophilic complex with a normal rate of decomposition. Biodistribution studies of this product in mice compared with the full kit showed identical brain and other organ uptakes. This product was used for cerebral imaging in patients with 90.5 +/- 3.3% lipophilic complex (n = 647) at approximately 3 min and produced excellent clinical results. It is concluded that stannous ion augmentation ('reboot') using approved Sn(II)-pyrophosphate kits is a viable option for institutions with facilities for aseptic preparation of fractionated exametazime kits, enabling substantial cost savings. Other advantages include removal of restrictions on generator eluate and 'rejuvenation' of expired kits.