The chelate Dy(PPP)27− (where PPP5− is tripolyphosphate) is a very effective shift reagent for the 23Na NMR signal. However, it is also quite toxic to living animals. In addition to the effects of the equilibrium competitions of the biological metal cations Mg2+ and Ca2+ with Na+ for Dy(PPP)27−, this toxicity is most likely due to the potentially irreversible effects of ligand dissociation in vivo. In order to avoid this latter problem, two PPP moieties have been covalently linked so as to take advantage of the chelate effect. Thus, this paper reports the synthesis of the new shift reagent DybPPPpob5− (where bPPPpob8− is o-bis((3-(tripolyphosphato)propyl)oxy)benzene). In vitro 23Na and 31P NMR experiments show that (1) DybPPPpob5− is an upfield shift reagent (like Dy(PPP)27−), which shifts the 23Na signal more than a third as well as Dy(PPP)27−, (2) the 23Na shift has a pH profile similar to that of Dy(PPP)27−, (3) competition by Ca2+ and Mg2+ with Na+ for DybPPPpob5− is not as severe as it is for Dy(PPP)27− and (4) DybPPPpob5− hydrolysis is catalyzed by alkaline phosphatase but neither as rapidly nor as extensively as that of Dy(PPP)27−. This latter result presumably implies that an uncoordinated PPP moiety of an incompletely dissociated DybPPPpob5− chelate can still act as a substrate for the enzyme. The hydrolysis is slow enough that, with proper care, DybPPPpob5− may be useful as an in vivo shift reagent.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry