ABSTRACT
We report a nanoscale morphology-regulation strategy of self-assembled double-hydrophilic block copolymers with square planar PtII compounds. The selective coordination of PtII on the chelating blocks of poly(acrylic acid)-b-poly(ethylene glycol) (PAA-b-PEG) induced the self-association of metal-chelated unimers by the known cohesive force of PtII. The block-length variation of PAA with constant PEG led to the shape transition from normal core/shell and crew-cut spheres to anisotropic pearl-string structures. On the other hand, PtII adsorption on PEG blocks by extensive hydrogen bonding can further modify the molecular geometry of metal-chelated unimers by decreasing the volume of hydrophilic segments, eventually leading to the shape transition to vesicular structures. This result was well correlated to the structural constraint of PEG conformation estimated by the quantitative 1H NMR analysis. The vesicles also exhibited the enclosing nature for the fluorescent guest molecules, which demonstrated the promising potential for the encapsulating delivery vehicle.
ABSTRACT
Cationic metal-mediated self-assembly of double-hydrophilic block copolymers (DHBCs) has been of great interest for the preparation of hybrid nanoparticles for versatile applications. Among many functional transition-metal ions, manganese (MnII) is a highly attractive element due to its paramagnetic property with a high coordination number. However, MnII does not lead to the efficient self-assembly of DHBCs because of the relatively high aqueous solubility of coordinated MnII. This article reports a facile method for direct conjugation of MnII ions inside sterically stabilized polymer assemblies, composed of pyrene-end-modified DHBCs. Nitroxide-mediated radical polymerization was used to prepare the poly(ethylene glycol)- b-poly(acrylate) DHBC precursor, followed by the end-modification with pyrene maleimide via the radical-exchange reaction. Employing the self-associated DHBC as the nanoscale template, the simple addition of MnII enables a large number of polyvalent MnII ions to be immobilized at the chelating blocks of DHBCs, which can be readily monitored by the excimeric fluorescence emission change of the terminal pyrene fluorophore. The resulting MnII-loaded polymeric nanoparticles (MnII-PNPs) possess nanogel-like scaffolds, which allow for efficient water permeation at the MnII-incorporated interior for enhanced magnetic resonance contrasting effect. Additionally, by comparing the coordination properties of MnII and cisplatin, we endeavor to understand the internal structures and the relevant physicochemical features of metal-chelated nanoparticles.
