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Solvate structures in water‐methanol solutions of MRI contrast agents: Electron spin echo envelope modulation in gadolinium chelates
Author(s) -
Clarkson R. B.,
Hwang J.H.,
Belford R. L.
Publication year - 1993
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.1910290414
Subject(s) - gadolinium , chemistry , coordination sphere , deuterium , quadrupole , mri contrast agent , solvent , nuclear magnetic resonance , chelation , envelope (radar) , ligand (biochemistry) , molecule , crystallography , analytical chemistry (journal) , inorganic chemistry , atomic physics , crystal structure , physics , telecommunications , radar , receptor , biochemistry , organic chemistry , chromatography , computer science
Electron Spin Echo Envelope Modulation (ESEEM) data are reported for three gadolinium (III) chelates, Gd‐EDTA, Gd‐DTPA, and Gd‐TTHA, in frozen D 2 O/CH 3 OD glasses. This series includes Gd‐DTPA, an MRI contrast agent that is in clinical use. Three‐pulse electron spin echo modulation patterns can be modeled to yield geometrical information; e.g., distances and numbers of Gd +3 ‐OD interactions. Interpreted by a spherical shell model, the data for Gd‐TTHA are accounted for by Gd +3 surrounded by seven deuterons at an effective distance of 3.9 Å. We attribute these deuterons to second‐coordination sphere solvent molecules, since it is likely that Gd +3 is fully coordinated by a TTHA ligand. For analysis of ESEEM from Gd‐EDTA and Gd‐DTPA, the second‐sphere structures of Gd‐EDTA, Gd‐DTPA, and Gd‐TTHA are assumed equivalent. 2 H‐ESEEM from inner‐sphere solvent molecules gives the effective distance between deuterons and Gd +3 to be ≈ 2.7 Å for the inner‐sphere water in both EDTA and DTPA complexes. The results of simulations also give the isotropic hyperfine and quadrupole coupling constants for solvent deuterium in these systems. Possible sources of error in the determination of r and q by this method are discussed.