RELAXATION OF SOLVENT PROTONS BY SOLUTE GD3-CHELATES, REVISITED()

The magnetic field dependence (NMRD profile) of 1/T-1 of solvent proto ns in an aqueous solution of Gd(DTPA)(2-) was remeasured at 5, 15, 25, 30, and 35 degrees C. The data were reanalyzed with the usual low-fie ld theory, using recently published values for tau(M), the residence l ifetime of the single inner-coordinated waters of solute Gd(DTPA)(2-). (These tau(M) values are significantly longer than earlier estimates) . Values were obtained for three dynamic parameters: tau(R), the rotat ional relaxation time of solute ions, and tau(SO) end tau(V), the low- field relaxation time of the Gd3+ magnetic moment and the related corr elation time. These Gd(DTPA)(2-) values, together with recent results for tau(M) for Gd(DTPA-BMA) - a nonionic structural analog of Gd(DTPA) (2-) with an unusually long tau(M) - were used to calculate NMRD profi les at 5 and 35 degrees C. These profiles agree very well with new dat a given here for a solution of Gd(DTPA-BMA). This reaffirms the import ance of knowing the temperature-dependent values of tau(M) a priori in order to obtain unambiguous quantitative theoretical analyses of NMRD profiles of chelates of known structure. Additionally, the theory of inner sphere relaxation is extended to high fields, at which the magne tic energy of a solute moment is greater than its thermal energy.