N-functionalization of poly(ethylene glycol)-linked mono- and bis-dioxocyclams as potential ligands for Gd3+

A number of highly functionalized dioxocyclams with acetic acid side chains on the secondary amine sites and ethylene glycol side chains on 6 and 13-positions (12a, 12b) or a tetra(ethylene glycol) side chain linking the 6 and 13 positions (15) were synthesized and characterized, as was a bis-dioxocyclam bridged across the 6 and 13 positions by tetra(ethylene glycol) groups (16). These were screened for their ability to complex Gd3+. Only ligands 15 and 16, having tetra(ethylene glycol) groups, formed such complexes.