Coupling fast water exchange to slow molecular tumbling in Gd3+ chelates

Why faster is not always better

Stefano Avedano, Mauro Botta, Julian S. Haigh, Dario L. Longo, Mark Woods

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

The influence of dynamics on solution state structure is a widely overlooked consideration in chemistry. Variations in Gd3+ chelate hydration with changing coordination geometry and dissociative water exchange kinetics substantially impact the effectiveness (or relaxivity) of monohydrated Gd3+ chelates as T1-shortening contrast agents for MRI. Theory shows that relaxivity is highly dependent upon the Gd3+-water proton distance (rGdH), and yet this distance is almost never considered as a variable in assessing the relaxivity of a Gd3+ chelate as a potential contrast agent. The consequence of this omission can be seen when considering the relaxivity of isomeric Gd3+ chelates that exhibit different dissociative water exchange kinetics. The results described herein show that the relaxivity of a chelate with "optimal" dissociative water exchange kinetics is actually lower than that of an isomeric chelate with "suboptimal" dissociative water exchange. When the rate of molecular tumbling of these chelates is slowed, an approach that has long been understood to increase relaxivity, the observed difference in relaxivity is increased with the more rapidly exchanging ("optimal") chelate exhibiting lower relaxivity than the "suboptimally" exchanging isomer. The difference between the chelates arises from a non-field-dependent parameter: either the hydration number (q) or rGdH. For solution state Gd3+ chelates, changes in the values of q and rGdH are indistinguishable. These parametric expressions simply describe the hydration state of the chelate - i.e., the number and position of closely associating water molecules. The hydration state (q/rGdH 6) of a chelate is intrinsically linked to its dissociative water exchange rate kex, and the interrelation of these parameters must be considered when examining the relaxivity of Gd3+ chelates. The data presented herein indicate that the changes in the hydration parameter (q/r GdH 6) associated with changing dissociative water exchange kinetics has a profound effect on relaxivity and suggest that achieving the highest relaxivities in monohydrated Gd3+ chelates is more complicated than simply "optimizing" dissociative water exchange kinetics.

Original languageEnglish (US)
Pages (from-to)8436-8450
Number of pages15
JournalInorganic Chemistry
Volume52
Issue number15
DOIs
StatePublished - Aug 5 2013

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Barreling
chelates
Water
Hydration
water
Kinetics
hydration
Contrast Media
kinetics
exchanging
Isomers
Magnetic resonance imaging
Protons
Ion exchange
Molecules

ASJC Scopus subject areas

  • Inorganic Chemistry
  • Physical and Theoretical Chemistry

Cite this

Coupling fast water exchange to slow molecular tumbling in Gd3+ chelates : Why faster is not always better. / Avedano, Stefano; Botta, Mauro; Haigh, Julian S.; L. Longo, Dario; Woods, Mark.

In: Inorganic Chemistry, Vol. 52, No. 15, 05.08.2013, p. 8436-8450.

Research output: Contribution to journalArticle

Avedano, Stefano ; Botta, Mauro ; Haigh, Julian S. ; L. Longo, Dario ; Woods, Mark. / Coupling fast water exchange to slow molecular tumbling in Gd3+ chelates : Why faster is not always better. In: Inorganic Chemistry. 2013 ; Vol. 52, No. 15. pp. 8436-8450.
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