trans-1,2-Diaminocyclohexane-N,N,N',N'-tetraacetic acid is superior to ethylenediamine-N,N,N',N'-tetraacetic acid for sequestering Mg2+ in 31P NMR experiments involving ATP spectra at neutral and acidic pH.

The use of ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA) to sequester Mg2+ from samples containing ATP at acidic or neutral pH prior to 31P NMR spectroscopic analysis leads to significant broadening of the gamma- and beta-phosphorus resonances of ATP as compared to ATP alone. It was found that the use of trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) reduces the broadening of the ATP resonances. At pH 7.0, 30 mM EDTA in the presence of 5 mM ATP and 7 mM Mg2+ leads to a threefold increase in the peak width of the gamma phosphorus of ATP as compared to 5 mM ATP alone. When 30 mM CDTA is used in the place of EDTA, the peak width decreased to about 80% of the peak width of ATP alone. When the experiment is repeated at pH 8.5, both EDTA and CDTA lead to narrow peak widths with no significant difference between the two spectra. At pH 6.0, the use of EDTA leads to a spectrum that is very noisy, with a 10-fold increase in the peak width as compared to ATP in the absence of Mg2+ at this pH, whereas the increase with CDTA is only 50%. These results do not reflect the difference in chelating strength between EDTA and CDTA: The free Mg2+ concentration in the presence of each chelator, as calculated by the computer program given in the Appendix, was nearly equal at each pH. The results, however, reflect a difference in the lability of the metal-ligand bond between EDTA and CDTA.