Number of inner-sphere water molecules in Gd3+ and Eu3+ complexes of DTPA-amide and -ester conjugates

C. F G C Geraldes, A. D. Sherry, W. P. Cacheris, Kuan Kah-Tiong Kuan, R. D. Brown, S. H. Koenig, M. Spiller

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Abstract

The inner-sphere water coordination number for Eu3+ and Gd3+ complexed with five DTPA analogs, in which one or two terminal carboxylate groups are functionalized as propyl amides or propyl esters, have been studied using phosphorescence lifetime and nuclear magnetic relaxation dispersion (NMRD) measurements. Both methods show that the water coordination number does not increase above that observed for the analogous DTPA complexes. The phosphorescence lifetime results indicate that all five Eu3+ complexes have one inner-sphere water molecule at 25°C. The NMRD profiles for three of the Gd3+ complexes at 25°C are also consistent with one inner-sphere water molecule, whereas two complexes have profiles consistent only with a mixture of complexes, 50% containing a single water molecule and 50% with none. Lowering the temperature alters the population of these species such that all five Gd3+ complexes have significantly less bound water on average at 5°C. These results explain the anomalous temperature dependencies of the NMRD curves reported previously for the Gd(DTPA)-protein conjugates. We suggest that the Gd(DTPA)-conjugate systems have a fluxional coordination sphere whereby the amount of inner-sphere coordinated water varies from near zero at 5°C to a high of two near 37°C.

Original languageEnglish (US)
Pages (from-to)191-199
Number of pages9
JournalMagnetic Resonance in Medicine
Volume8
Issue number2
Publication statusPublished - 1988

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ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging
  • Radiological and Ultrasound Technology

Cite this

Geraldes, C. F. G. C., Sherry, A. D., Cacheris, W. P., Kah-Tiong Kuan, K., Brown, R. D., Koenig, S. H., & Spiller, M. (1988). Number of inner-sphere water molecules in Gd3+ and Eu3+ complexes of DTPA-amide and -ester conjugates. Magnetic Resonance in Medicine, 8(2), 191-199.