SGER: A Study of the Enhanced MRI Relaxivity in Gadolinium-Based Endohedral Metallofullerenes

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

This award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports research by Professor Harry Dorn at Virginia Tech to elucidate the structure and magnetic properties of new Gd3 functionalized trimetaspheres, which exhibit enhanced magnetic relaxation properties, by NMR and X-ray crystallography. Because of their high paramagnetism, some lanthanide endohedral metallofullerenes have potential applications as MRI agents; however, the fundamental basis of the dipole-dipole dynamic interactions (i.e., unpaired electron spin density inside/outside the carbon cage with water) responsible for their enhanced relaxivity is not well understood. The goal of this research is to provide a new model for this phenomenon that will catalyze and expedite related research in this area and on fullerene cage functionalization, biodistribution, and toxicology. The dependence of 1H MRI relaxivities in Gd3 functionalized trimetaspheres on the dynamic processes at the exohedral surface of the trimetasphere cage (and corresponding influence on correlation times), will be explored by variable temperature NMR studies and by varying the chain length of the external functional group (e.g., polyethylene glycol, PEGS chain length). The properties and dynamics of the internal trimetallic nitride cluster (Gd3N) will also be determined. Changes in the water exchange rate as a function of the cage surface functionality (hydroxyls) will be measured and the effects on water relaxation rates determined by variable temperature and 17-O NMR water exchange studies. Key physical properties, such as water solubility, light scattering, and magnetic susceptibility will also be quantified. These measurements will be used in developing an improved model for magnetic relaxation rates for endohedral metallofullerenes in water. This work is coordinated with work at a local company, Luna Innovations, and other researchers at Virginia Tech and the Medical College of Virginia on biodistribution and toxicological studies that will provide a better physical and biochemical basis for designing agents that further enhance magnetic relaxation effects in water for use in biological imaging.