Unexpected Changes in the Population of Coordination Isomers for the Lanthanide Ion Complexes of DOTMA–Tetraglycinate
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TitleUnexpected Changes in the Population of Coordination Isomers for the Lanthanide Ion Complexes of DOTMA–Tetraglycinate
Unexpected Changes in the Population of Coordination Isomers for the Lanthanide Ion Complexes of DOTMA–Tetraglycinate. Cemile Kumas, W. Shirangi Fernando, Piyu Zhao, Martín Regueiro-Figueroa, Garry E. Kiefer, André F. Martins, Carlos Platas-Iglesias, and A. Dean Sherry. Inorganic Chemistry 2016 55 (18), 9297-9305. DOI: 10.1021/acs.inorgchem.6b01390
[Abstract] Lanthanide complexes with DOTA–tetraglycinate (DOTA-(gly)4) heavily favor the square antiprismatic (SAP) coordination isomer in aqueous solution, a structural feature that has made them useful as water-based paraCEST agents. In an effort to create amide-based paraCEST agents with rapid water exchange rates, we prepared the analogous tetraglycinate complexes with DOTMA, a ligand known to favor the twisted square antiprismatic (TSAP) coordination structures. Unexpectedly, NMR investigations show that the LnDOTMA–(gly)4 complexes, like the LnDOTA–(gly)4 complexes, also favor the SAP isomers in solution. This observation led to density functional theory (DFT) calculations in order to identify the energy terms that favor the SAP structures in lanthanide complexes formed with macrocyclic DOTA– and DOTMA–tetraamide ligands. The DFT calculations revealed that, regardless the nature of the ligand, the TSAP isomers present more negative hydration energies than the SAP counterparts. The extent to which the TSAP isomer is stabilized varies, however, depending on the ligand structure, resulting in different isomeric populations in solution.
This document is the Accepted Manuscript version of a Published Work that appeared in final form in "Inorganic Chemistry", copyright © American Chemical Society after peer review and technical editing by the publisher.