Gd-DTPA-dopamine-bisphytanyl amphiphile : synthesis, characterisation and relaxation parameters of the nanoassemblies and their potential as MRI contrast agents

Here, a new amphiphilic magnetic resonance imaging (MRI) contrast agent, a GdIII-chelated diethylenetriaminepentaacetic acid conjugated to two branched alkyl chains via a dopamine spacer, Gd-DTPA-dopamine-bisphytanyl (Gd-DTPA-Dop-Phy), which is readily capable of self-assembling into liposomal nanoassemblies upon dispersion in an aqueous solution, is reported. In vitro relaxivities of the dispersions were found to be much higher than Magnevist, a commercially available contrast agent, at 0.47 T but comparable at 9.40 T. Analysis of variable temperature 17O NMR transverse relaxation measurements revealed the water exchange of the nanoassemblies to be faster than that previously reported for paramagnetic liposomes. Molecular reorientation dynamics were probed by 1H NMRD profiles using a classical inner and outer sphere relaxation model and a Lipari-Szabo "model-free" approach. High payloads of GdIII ions in the liposomal nanoassemblies made solely from the Gd-DTPA-Dop-Phy amphiphiles, in combination with slow molecular reorientation and fast water exchange makes this novel amphiphile a suitable candidate to be investigated as an advanced MRI contrast agent. Heads up: Liposomal nanoassemblies, made solely from the novel paramagnetic amphiphile with two branched chains (Gd-DTPA-Dop-Phy), have high potential as advanced magnetic resonance imaging (MRI) contrast agents due to the high payloads of GdIII ions they offer, along with their slow molecular reorientation and fast water exchange.