NMR Evidence of a Long Exchange Lifetime for the Coordinated Water in Ln(III)-Bis(methyl amide)-DTPA Complexes (Ln = Gd, Dy)

Abstract

The magnetic field dependence of the water proton longitudinal relaxation rate for the paramagnetic complex Gd-BMA-DTPA has been measured and analyzed at different temperatures. Interestingly we have found that the solvent relaxivity is largely affected by the residence lifetime (ZM) of the water molecule in the coordination site on the metal chelate. The calculated values for ZM at 298 K is 0.81 ps, i.e. 4-fold longer than the values recently reported for Gd-DTPA and much longer than the values commonly assumed in the analysis of NMRD profiles of poly(amino carboxylate) complexes. This result has been also confirmed by an alternative approach for the structurally analogous Dy(III) complex. In this latter case, from the measurement of the paramagnetic contribution to 'H NMR chemical shift and transverse relaxation rate of the solvent water protons, we evaluated the residence lifetime ZM by solving iteratively the Swift-Connick equations.

Synthesis and relaxometry of high-generation (G = 5, 7, 9, and 10) PAMAM dendrimer-DOTA-gadolinium chelates

“…Previous reports (7,16) indicate an increase in the rotational correlation times as the generation of the dendrimer increases from G ϭ 2-6. From 17 O NMR studies, the rotational correlation time per dendrimer generation for G ϭ 3-5 increased by approximately 25%. However, maximum ion relaxivities were not attained because slow water exchange between the metal ion and the bulk solution limits the ion relaxivities (7).…”

“…The subsequent increase in molecular weight results in increased 1/T1 relaxation rates for the Gd 3ϩ ion relaxivity (1,8). However, based on variable temperature and pressure 17 O nuclear magnetic resonance (NMR) studies, Tóth et al (7) found that the expected increase in the relaxation rates from an increase in the rotational correlation time as the generation of the dendrimer increased was not observed because of slow water exchange between the metal ion and the bulk solvent. The highest generation dendrimer that has been studied to date is G ϭ 6 (1).…”

Impact of rigidification on relaxometric properties of a tricyclic tetraazatriacetic gadolinium chelate

“…The NMRD curves were analyzed according to the classical inner-sphere model described by Solomon (3) and Bloembergen (4) and to the outer-sphere model described by Freed (5). In agreement with previous studies, the number of water molecules coordinated to the Gd 3þ ion (q) was fixed to 2; d, the distance of closest approach for the outer-sphere contribution, was set at 0.36 nm (21,22) ] and the rotational correlation time t R were optimized for the outer-and inner-sphere contributions simultaneously. A satisfactory fit of the data could be obtained (Fig.…”

In vitro Relaxometric and Luminescence Characterization of P792 (Gadomelitol, Vistarem®), an Efficient and Rapid Clearance Blood Pool MRI Contrast Agent

“…[27] In these fittings, the number of water molecules coordinated to the Gd 3+ ion was fixed to 1 in agreement with the luminescence data. Some other parameters were also fixed: r, the distance between the proton nuclei of the innersphere water molecule and the Gd 3+ (0.31 nm); D, the relative diffusion constant (3 × 10 -9 m 2 s -1 ); and d, the distance of closest approach for the outersphere contribution (0.36 nm [28,29] ). τ V and τ SO (the electronic relaxation time at zero field), describing the elec- Figure 5.…”