Abstract
1, 4, 7-Triazacyclononame- N, N′,N′-tris(methylenephosphonate monoethylester) (NOTPME) has been synthesized, characterized and analyzed for use as a 31P NMR indicator of intracellular Mg 2+ and Zn 2+ ions. The 31P NMR spectrum of this chelate in the presence of metal ions shows characteristics resonances for the free chelate, Mg(NOTPME) −, Zn(NOTPME) − and Ca(NOTPME) −. The K ??? values indicate that this chelate has a 10-fold higher affinity for Mg 2+ than for Ca 2+ at physiological pH values. In the presence of Mg 2+, NOTPME is readily loaded into red blood cells. A 31P NMR spectrum of red cells taken after several washing shows resonances characteristics of entrapped NOTPME and the Mg(NOTPME) − complex, the relative areas of which report an intracellular free Mg 2+ concentration of 0.32 mM. The 31P chemical shifts of the free chelate and its metal complexes are far downfield from the typical phosphorus-containing metabolites observed in biological systems, thus making it possible to monitor intracellular cation concentration and cell energetics simultaneously.
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