Gadolinium DO3A derivatives mimicking phospholipids; preparation and in vitro evaluation as pH responsive MRI contrast agents

A series of Gd-DO3A derivatives (8a-d) mimicking phospholipids have been prepared. Two of the complexes, Gd-HADB-DO3A (8a) and Gd-HADO-DO3A (8b), have been evaluated as pH responsive MRI contrast agents in vitro. The T-1-relaxivity (r(1)) of Gd-HADO-DO3A (8b) increased 142% on changing the pH from 6 to 8. The pH dependence is thought to arise from the formation of supramolecular structures caused by deprotonation of the amphiphilic complex at alkaline pH.