Isomeric DTPA-amide macrocycles of p-xylenediamine and their complexation with Gd3+

Rosa Elena Navarro, Yedith Soberanes, Sheyla D-Yañez, Olivia Jatomea, José Zeferino Ramírez, Motomichi Inoue

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

© 2015 Elsevier Ltd. All rights reserved. Three DTPA-amide cyclophanes-including conformational isomers-have been isolated by optimizing the conditions of a reaction between diethylenetriaminepentaacetic (DTPA) dianhydride and p-xylenediamine: a 2 + 2-cyclization product, abbreviated as (cy2)H6, that integrates two phenylene groups in the macrocyclic frame and bears six pendant-CH2CO2H arms, and two isomeric 1 + 1-macrocyles, (cy1)H3, carrying three arms. A crucial factor for controlling the ring size is the concentration in the reaction. For (cy2)H6, whose binuclear Gd3+complex is a potential paramagnetic protein sensor, the synthetic method has been established in 70% yield. The isomerism of (cy1)H3is due to the conformation of the rigid macrocyclic frame; the1H NMR and geometry optimization show that the conformation is of quasi-C2symmetry in one (cy1)H3isomer, and of quasi-mirror symmetry in the other. Their distinct conformations define the chemical properties and coordination capability toward Gd3+: in the C2-symmetric isomer, the amino nitrogen is less basic and the N-H bond is more covalent than in the mirror-symmetric isomer; the former forms a mononuclear Gd3+complex whereas the latter does not show sign of complexation with Gd3+.
Original languageAmerican English
Pages (from-to)105-110
Number of pages6
JournalPolyhedron
DOIs
StatePublished - 28 May 2015

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