NOTPME: a 31P NMR probe for measurement of divalent cations in biological systems

FEBS Lett. 1991 Mar 11;280(1):121-4. doi: 10.1016/0014-5793(91)80218-r.


1,4,7-Triazacyclononane-N,N',N''-tris(methylenephosphonate monoethylester) (NOTPME) has been synthesized, characterized and analyzed for use as a 31P NMR indicator of intracellular Mg2+ and Zn2+ ions. The 31P NMR spectrum of this chelate in the presence of metal ions shows characteristic resonances for the free chelate, Mg(NOTPME)-, Zn(NOTPME)-, and Ca(NOTPME)-. The Kd values indicate that this chelate has a 10-fold higher affinity for Mg2+ than for Ca2+ at physiological pH values. In the presence of Mg2+, NOTPME is readily loaded into red blood cells. A 31P NMR spectrum of red cells taken after several washings shows resonances characteristic of entrapped NOTPME and the Mg(NOTPME)- complex, the relative areas of which report an intracellular free Mg2+ 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 concentrations and cell energetics simultaneously.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Cations, Divalent / metabolism*
  • Erythrocytes / metabolism*
  • Humans
  • Magnesium / metabolism
  • Magnetic Resonance Spectroscopy*
  • Organophosphorus Compounds*
  • Phosphorus Radioisotopes


  • Cations, Divalent
  • Organophosphorus Compounds
  • Phosphorus Radioisotopes
  • 1,4,7-triazacyclononane-N,N',N''-tris(methylenephosphonate monoethyl ester)
  • Magnesium