Physicochemical Characterization of Four Gadolinium(III) DTPA-like Complexes

摘要

The analysis of ~(17)O NMR transverse relaxation rates and EPR transverse electronic relaxation rates for aqueous solutions of the four DTPA-like (DTPA=diethylenetriamine-.N,N,.N',.N'',N''-pentaacetic acid) complexes,[Gd(DTPA-PY)(H_2O)]~- (DTPA-PY=N'-(2-pyridylmethyl)),[Gd(DTPA-HP)(H_2O)_2]~- (DTPA-HP=N'-(2-hydroxypropyl)),[Gd(DTPA-H1P)(H_2O)_2]~- (DTPA-H1P=N'-(2-hydroxy-1-phenylethyl)) and [Gd(DTPA-H2P)(H_2O)_2]~- (DTPA-H2P=N'-(2-hydroxy-2-phenylethyl)),at various temperatures allows us to understand the water exchange dynamics of these four complexes.The water-exchange lifetime (tau_M) parameters for [Gd(DTPA-PY)(H_2O)]~-,[Gd(DTPA-HP)(H_2O)_2]~-,[Gd(DTPA-H1P)(H_2O)_2]~- and [Gd(DTPA-H2P)(H_2O)_2]~- are of 585,98,163,and 69 ns,respectively.Compared with [Gd(DTPA)(H_2O)]~(2-) (tau_M=303 ns),the tau_M value of [Gd(DTPA-PY)(H_2O)]~- is slightly higher,but the other three complexes values are significantly lower than those of [Gd(DTPA)(H_2O)]~(2-).This difference is explained by the fact that the gadolin-ium(III) complexes of DTPA-HP,DTPA-H1P,and DTPA-H2P have two inner-sphere waters.The ~2H longitudinal relaxation rates of the labeled diamagnetic lanthanum complex allow the calculation of its rotational correlation time (tau_R).The tau_R values calculated for DTPA-PY,DTPA-HP,DTPA-H1P,and DTPA-H2P are of 127,110,142 and 147 ps,respectively.These four values are higher than the value of [La(DTPA)]~(2-) (tau_R=103 ps),because the rotational correlation time is related to the magnitude of its molecular weight.