pH-dependent modulation of relaxivity and luminescence in macrocyclic gadolinium and europium complexes based on reversible intramolecular sulfonamide ligation

M. P. Lowe, D. Parker, O. Reany, S. Aime, M. Botta, G. Castellano, E. Gianolio, R. Pagliarin

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254 Scopus citations

Abstract

A series of macrocyclic Eu, Gd, and Tb complexes has been prepared in which the intramolecular ligation of a β-arylsulfonamide nitrogen is rendered pH-dependent, giving rise to changes in the hydration state, q, at the lanthanide center. In complexes based on DO3A, variation of the p-substituent in the arylsulfonamide moiety determines'the apparent protonation constant log KMLH with values of 5.7, 6.4, and 6.7 for the -CF3, -Me, and -OMe substituents, respectively. Introducti0n of three β-carboxyalkyl substituents, αto three ring nitrogens, inhibits displacement of the bound water by added protein and also suppresses intermolecular binding by endogenous anions (lactate, HCO3-). Measurements of the pH dependence of the form and intensity of the Eu complexes revealed that intramolecular carboxylate coordination occurred competitively. This was reduced either by enhancing the electron density at the sulfonamide nitrogen or by enlarging the chelate ring from 7-8. Amplification of the relaxivity changes in the pH range 8-5 occurred on protein binding, and over the pH range 7.4-6.8 a 48% change in relaxivity was defined for [Gd·3a] (298 K, 65.6 MHz) in 50% human serum solution.

Original languageEnglish
Pages (from-to)7601-7609
Number of pages9
JournalJournal of the American Chemical Society
Volume123
Issue number31
DOIs
StatePublished - 8 Oct 2001
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry

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