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Liposomes containing high-spin Fe(iii ) coordination complexes were prepared towards the production of T 1 MRI probes with improved relaxivity. The amphiphilic Fe( iii) complexes were anchored into the liposome with two alkyl chains to give a coordination sphere containing mixed amide and hydroxypropyl pendant groups. The encapsulated complex contains a macrocyclic ligand with three phosphonate pendants, [Fe(NOTP)] 3−, which was chosen for its good aqueous solubility. Four types of MRI probes were prepared including those with intraliposomal Fe(iii) complex (LipoA) alone, amphiphilic Fe(iii) complex (LipoB), both intraliposomal and amphiphilic complex (LipoC) or micelles formed with amphiphilic complex. Water proton relaxivities r 1 and r 2 were measured and compared to a small molecule macrocyclic Fe(iii) complex containing similar donor groups. Micelles of the amphiphilic Fe( iii) complex had proton relaxivity values ( r 1 = 2.6 mM−1 s −1 ) that were four times higher than the small hydrophilic analog. Liposomes with amphiphilic Fe(iii) complex (LipoB) have a per iron relaxivity of 2.6 mM −1 s −1 at pH 7.2, 34 °C at 1.4 T whereas liposomes containing both amphiphilic and intraliposomal Fe(iii) complexes (lipoC) have r 1 of 0.58 mM −1 s −1 on a per iron basis consistent with quenching of the interior Fe(iii) complex relaxivity. Liposomes containing only encapsulated [Fe(NOTP)]3− have a lowered r 1 of 0.65 mM−1s −1 per iron complex. Studies show that the biodistribution and clearance of the different types liposomal nanoparticles differ greatly. LipoB is a blood pool agent with a long circulation time whereas lipoC is cleared more rapidly through both renal and hepatobiliary pathways. These clearance differences are consistent with lower stability of LipoC compared to LipoB.
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Continuous growth phenomenon for direct synthesis of monodisperse water-soluble iron oxide nanoparticles with extraordinarily high relaxivity
The direct synthesis of highly water-soluble nanoparticles has attracted intensive interest, but systematic size control has not been reported. Here, we developed a general method for synthesizing monodisperse water-soluble iron oxide nanoparticles with nanometer-scale size increments from 4 nm to 13 nm in a single reaction. Precise size control was achieved by continuous growth in an amphiphilic solvent, diethylene glycol (DEG), where the growth step was separated from the nucleation step by sequential addition of a reactant. There was only one reactant in the synthesis and no need for additional capping agents and reducing agents. This study reveals the “living growth” character of iron oxide nanoparticles synthesised in an amphiphilic solvent. The synthetic method shows high reproducibility. The as-prepared iron oxide nanoparticles are extremely water soluble without any surface modification. Surprisingly, the synthesized 9 nm iron oxide nanoparticles exhibit extremely high transversal and longitudinal relaxivities of 425 mM −1 s −1 and 32 mM −1 s −1 respectively, which is among the highest transversal relaxivity in the literature for sub-10 nm spherical nanoparticles. This study will not only shed light on the continuous growth phenomenon of iron oxide nanoparticles in an amphiphilic solvent, but could also stimulate the synthesis and application of iron oxide nanoparticles. The continuous growth method could be further extended to other materials for the controlled synthesis of water-soluble nanoparticles.
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- Award ID(s):
- 1757220
- PAR ID:
- 10166225
- Date Published:
- Journal Name:
- Nanoscale
- Volume:
- 12
- Issue:
- 16
- ISSN:
- 2040-3364
- Page Range / eLocation ID:
- 9272 to 9283
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0NR01552K
