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[sup 17]O NMR study of water exchange on [Gd(DTPA)(H[sub 2]O)][sup 2[minus]] and [Gd(DOTA)(H[sub 2]O)][sup [minus]] related to NMR imaging

Journal Article · · Inorganic Chemistry; (United States)
DOI:https://doi.org/10.1021/ic00070a013· OSTI ID:6768760
 [1]; ;  [2];  [3]
  1. Institut de Chimie Minerale et Analytique, Lausanne (Switzerland) Kossuth Univ., Debrecen (Hungary)
  2. Institut de Chimie Minerale at Analytique, Lausanne (Switzerland)
  3. Kossuth Univ., Debrecen (Hungary)
+ Show Author Affiliations
The water-exchange rate constants for the [Gd(DTPA)(H[sub 2]O)][sup 2[minus]] and [Gd(DOTA)(H[sub 2]O)][sup [minus]] complexes as determined by variable-temperature [sup 17]O NMR are respectively k[sub ex[sup 298]] = (4.1 [+-] 0.3) x 10[sup 6] and (4.8 [+-] 0.4) x 10[sup 6] s[sup [minus]1]. The activation volumes ([Delta]V[sup [double dagger]]), measured up to 200 MPa, are 12.5 [+-] 0.2 and 10.5 [+-] 0.2 cm[sup 3] mol[sup [minus]1], indicating an extreme dissociative activation mode for the water-exchange mechanism. The mechanism (D) is further supported by the large activation enthalpies ([Delta]H[sup [double dagger]] = +52.0 [+-] 1.4 and +48.8 [+-] 1.6 kJ mol[sup [minus]1]) and positive entropies ([Delta]S[sup [double dagger]] = +56.2 [+-] 5 and +46.6 [+-] 6 kJ mol[sup [minus]1] K[sup [minus]1]) obtained for the [Gd(DTPA)(H[sub 2]O)][sup 2[minus]] and [Gd(DOTA)(H[sub 2]O)][sup [minus]] complexes, respectively, In the first coordination sphere of these two monoaqua complexes there is only space for one water molecule, and thus the bond breaking of the coordinated water should be the rate-determining step. The [sup 17]O relaxation contribution of the second coordination sphere. All these considerations lead to the conclusion that the effectiveness of [Gd(DTPA)(H[sub 2]O)][sup 2[minus]] and [Gd(DOTA)(H[sub 2]O)][sup [minus]] as contrast agents in MRI is not limited by the relatively low water-exchange rates but by T[sub 1m], the longitudinal relaxation time of water protons in the first coordination sphere.
OSTI ID:
6768760
Journal Information:
Inorganic Chemistry; (United States), Journal Name: Inorganic Chemistry; (United States) Vol. 32:18; ISSN 0020-1669; ISSN INOCAJ
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
CATALYST SUPPORTS
CHEMICAL REACTIONS
COMPLEXES
EVEN-ODD NUCLEI
GADOLINIUM COMPLEXES
HYDRATES
HYDROGEN COMPOUNDS
ISOTOPES
LIGHT NUCLEI
MAGNETIC RESONANCE
NUCLEAR MAGNETIC RESONANCE
NUCLEI
OXYGEN 17
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
RARE EARTH COMPLEXES
RESONANCE
STABLE ISOTOPES
WATER