Surface attached manganese oxo clusters as possible contrast agents for MRI.

摘要

Mn12O12(OOCCH3)16(H 2O)4 (referred to as Mn-12, due to the stoichiometry) is considered the prototypical single molecule magnet (SMM), and has been the subject of intense research since it was first synthesized. Most of the research involving Mn-12 has focused on its fundamentally novel magnetic properties and potential use in applications such as quantum computing. Here, Mn-12 acetate was studied in solution; and through examination of its effect on the longitudinal (T1) and transverse (T2) relaxation rates, r1 and r2, respectively, Mn-12 was shown to have promise as a MRI contrast agent. However, one of the major limitations to using SMMs for contrast enhancement is their limited solution stability.;Previous studies have shown the Mn-12 clusters can be attached to any surface that is functionalized with carboxylic acid groups. This thesis describes the incorporation of Mn-12 into three systems: polystyrene nanobeads, co-polymeric material and MCM-41 beads. Through the attachment of Mn-12 to carboxylate terminated polystyrene nanobeads, the solution stability of the cluster was improved, and it was observed that the relaxation properties of Mn-12 were enhanced. This is significant because it demonstrates that the interaction between Mn-12 and H2O can be mediated by the nanostructure the cluster is attached to.;Using a ligand exchange procedure, a series of new substituted Mn-12 clusters, Mn12O12(O2CR)16, were prepared. It was demonstrated that the cluster, Mn12O12(O 2CR)16 for O2CR= vinylbenzoic acid (VBA), can be co-polymerized with styrene to form magnetic polymer nanobeads using miniemulsion, and that full incorporation of the cluster within a polymer matrix produces a water stable nanobead (more than several days) with enhanced relaxivity.;It was found that combination with a polymeric matrix increases the solubility of Mn-12, however, it likely limits the exposure of the cluster to water. By impregnating nanospheres of a carboxylate functionalized porous material known as MCM-41 with Mn-12, magnetic nanospheres with enhanced relaxation properties were prepared. We believe the increased relaxivity may be the result of the increased exposure of the cluster to water molecules. This system was determined to be the most efficient and most stable of all the systems investigated for the use of Mn-12 as a contrast agent.