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Effect of Ligand Chirality and Hyperconjugation on the Thermodynamic Stability of a Tris(aquated) Gd III Complex: Synthesis, Characterization, and T 1 ‐Weighted Phantom MR Image Study
Author(s) -
Khannam Mahmuda,
Sahoo Suban K.,
Mukherjee Chandan
Publication year - 2019
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201900043
Subject(s) - chemistry , ligand (biochemistry) , chirality (physics) , molecule , chemical stability , luminescence , analytical chemistry (journal) , crystallography , stereochemistry , chromatography , organic chemistry , biochemistry , chiral symmetry breaking , receptor , physics , quantum mechanics , quark , optoelectronics , nambu–jona lasinio model
The hexadentate chiral alanine‐based ligand, Li 3 cbda, in a reaction with hydrated GdCl 3 at pH ~ 6.5 provided the corresponding nine‐coordinated, neutral Gd III complex ( 1 ). The hydration state ( q ) of complex 1 was 3.1 ± 0.1, as determined by luminescence decay time measurements of Tb III congener in H 2 O and D 2 O. Complex 1 exhibited thermodynamic stability, log K GdL = 14.64 in 0.15 m NaCl solution at 25 °C. At 1.41 T, pH ≈ 7.4, and 25 °C, the complex offered longitudinal relaxivity, r 1 = 10.95 m m –1 s –1 , which was in accordance with three inner‐sphere water molecules. While, the relaxivity value remained unaffected in the pH range of 4.0 to 7.4, under basic conditions (pH ≥ 10) a reduction in the relaxivity value to 6.68 m m –1 s –1 was observed. A similar phenomenon was also realized in the presence of endogenous anions (100 equivalents of F – and HCO 3 – ), which implied the removal of coordinated‐water molecules under the conditions. Phantom MR imaging under the clinical scanner at 1.5 T showed the enhancement in the image intensity with increasing concentration of the complex. As expected, the image intensity of 1 m m complex 1 was about three times compared to 1 m m MultiHance® solution.