Physicochemical characterization of the dimeric lanthanide complexes [en{Ln(DO3A)(H2O)}2] and [pi{Ln(DTTA)(H2O)}2]2−: a variable-temperature 17O NMR study

✍ Scribed by Tzu-Ming Lee; Tsan-Hwang Cheng; Ming-Hung Ou; C. Allen Chang; Gin-Chung Liu; Yun-Ming Wang

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 156 KB
• Volume: 42
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1315

✦ Synopsis

Abstract

The Gd(III) complexes of the two dimeric ligands [en(DO3A)~2~] {N,N^′^‐bis[1,4,7‐tris(carboxymethyl)‐1,4,7,10‐tetraazacyclododecan‐10‐yl‐methylcarbonyl]‐N,N^′^‐ethylenediamine} and [pi(DTTA)~2~]^8−^ [bisdiethylenetriaminepentaacetic acid (trans‐1,2‐cyclohexanediamine)] were synthesized and characterized. The ^17^O NMR chemical shift of H~2~O induced by [en{Dy(DO3A)}~2~] and [pi{Dy(DTTA)}~2~]^2−^ at pH 6.80 proved the presence of 2.1 and 2.2 inner‐sphere water molecules, respectively. Water proton spin–lattice relaxation rates for [en{Gd(DO3A)(H~2~O)}~2~] and [pi{Gd(DTTA)(H~2~O)}~2~]^2−^ at 37.0 ± 0.1° C and 20 MHz are 3.60 ± 0.05 and 5.25 ± 0.05 mM^−1^ s^−1^ per Gd, respectively. The EPR transverse electronic relaxation rate and ^17^O NMR transverse relaxation time for the exchange lifetime of the coordinated H~2~O molecule and the ^2^H NMR longitudinal relaxation rate of the deuterated diamagnetic lanthanum complex for the rotational correlation time were thoroughly investigated, and the results were compared with those reported previously for other lanthanide(III) complexes. The exchange lifetimes for [en{Gd(DO3A)(H~2~O)}~2~] (769 ± 10 ns) and [pi{Gd(DTTA)(H~2~O)}~2~]^2−^ (910 ± 10 ns) are significantly higher than those of [Gd(DOTA)(H~2~O)]^−^ (243 ns) and [Gd(DTPA)(H~2~O)]^2−^ (303 ns) complexes. The rotational correlation times for [en{Gd(DO3A)(H~2~O)}~2~] (150 ± 11 ps) and [pi{Gd(DTTA)(H~2~O)}~2~]^2−^ (130 ± 12 ps) are slightly greater than those of [Gd(DOTA)(H~2~O)]^−^ (77 ps) and [Gd(DTPA)(H~2~O)]^2−^ (58 ps) complexes. The marked increase in relaxivity (r~1~) of [en{Gd(DO3A)(H~2~O)}~2~] and [pi{Gd(DTTA)(H~2~O)}~2~]^2−^ result mainly from their longer rotational correlation time and higher molecular weight. Copyright © 2004 John Wiley & Sons, Ltd.