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

Tzu Ming Lee, Tsan Hwang Cheng, Ming Hung Ou, C. Allen Chang, Gin Chung Liu, Yun-Ming Wang*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

23 Scopus citations

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′-ethylenediamme} and [pi(DTTA)2] 8- [bisdiethylene-triaminepentaacetic acid (trans-1,2- cyclohexanediamine)] were synthesized and characterized. The 17O NMR chemical shift of H2O 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)(H2O)}2] and [pi{Gd(DTTA)(H2O)}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 17O NMR transverse relaxation time for the exchange lifetime of the coordinated H2O molecule and the 2H 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 2O)}2] (769 ± 10 ns) and [pi{Gd(DTTA)(H 2O)}2]2- (910 ± 10 ns) are significantly higher than those of [Gd(DOTA)(H2O)]- (243 ns) and [Gd(DTPA)(H2O)]2- (303 ns) complexes. The rotational correlation times for [en{Gd(DO3A)(H2O)}2] (150 ± 11 ps) and [pi{Gd(DTTA)(H2O)}2]2- (130 ± 12 ps) are slightly greater than those of [Gd(DOTA)(H2O)] - (77 ps) and [Gd(DTPA)(H2O)]2- (58 ps) complexes. The marked increase in relaxivity (r1) of [en{Gd(DO3A)(H2O)}2] and [pi{Gd(DTTA)(H 2O)}2]2- result mainly from their longer rotational correlation time and higher molecular weight.

Original languageEnglish
Pages (from-to)329-336
Number of pages8
JournalMagnetic Resonance in Chemistry
Volume42
Issue number3
DOIs
StatePublished - 1 Mar 2004

Keywords

  • O NMR
  • H NMR
  • EPR
  • Gd(III) complexes
  • NMR
  • Paramagnetic complexes
  • Proton relaxation

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