| Abstract: | The analysis of 17O 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)(H2O)]? (DTPA‐PY = N′‐(2‐pyridylmethyl)), [Gd(DTPA‐HP)(H2O)2]? (DTPA‐HP = N′‐(2‐hydroxypropyl)), [Gd(DTPA‐H1P)(H2O)2]? (DTPA‐H1P = N′‐(2‐hydroxy‐1‐phenylethyl)) and [Gd(DTPA‐H2P)(H2O)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 (τM) parameters for [Gd(DTPA‐PY)(H2O)]?, [Gd(DTPA‐HP)(H2O)2]?, [Gd(DTPA‐H1P)(H2O)2]? and [Gd(DTPA‐H2P)(H2O)2] are of 585, 98, 163, and 69 ns, respectively. Compared with [Gd(DTPA)(H2O)]2? (τM = 303 ns), the τM value of [Gd(DTPA‐PY)(H2O)]? is slightly higher, but the other three complexes values are significantly lower than those of [Gd(DTPA)(H2O)]2?. This difference is explained by the fact that the gadolinium(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 (τR). The τR 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? (τR = 103 ps), because the rotational correlation time is related to the magnitude of its molecular weight. |
