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Development of novel oxidation responsive T2 MRI contrast agents based on molecular magnets encapsulated in a polysulfide nanocarrier

Jeanmaire, Damien Peter

[Thesis]. Manchester, UK: The University of Manchester; 2015.

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Abstract

In this thesis, we propose the development of an oxidation responsive T2 contrast agent based on oxidation sensitive poly(propylene sulfide) (PPS) nanoparticles and molecular magnet heterometallic rings. PPS nanoparticles show an oxidation responsive character in the presence of Reactive Oxygen Species (ROS), typically found in inflammatory conditions in the body.We have shown that PPS nanoparticles can be synthesised with a controlled hydrodynamic size and degree of polymerisation. Upon oxidation with different ROS, in particular hydrogen peroxide (H2O2) and hypochlorite (OCl-), the hydrophobic polysulfide network experiences oxidation to poly-sulfoxides/-sulfones, causing a shift in polarity and ingress of water, resulting in particle swelling. The oxidation of the nanoparticles was monitored by dynamic light scattering (DLS) as well as diffusion ordered spectroscopy (DOSY).The polysulfide nanoparticles were then loaded with molecular magnets (heterometallic rings Cr7Ni and Cr12Gd4) using a co-solvent method. It was found that the loading did not significantly change the physical or chemical properties of either the PPS nanoparticles or the molecular magnets. However the composition and outer functionalization of the molecular magnets has an effect on both their loading efficiency and their T2 relaxivity. The nanoparticles’ effect on water proton transvers relaxation was measured before and after oxidation with small amounts of H2O2. The loaded nanoparticles exhibit a binary ‘off/on’ switch effect when exposed to small amounts of hydrogen peroxide. Independent of oxidant concentration, the oxidised nanoparticles increase the relaxivity rate of water protons when compared to their reduced state.