DYNAMICS OF DENDRIMERIC MRI CONTRAST AGENTS

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Molecular dynamics play a key role in determining and predicting the efficacy of transition metal magnetic resonance imaging (MRI) contrast agents. We have used EPR and nuclear magnetic relaxation dispersion (NMRD) data on dendrimer-bound and free metal chelate complexes with VO2+ and TEMPOL to obtain precise dynamical information, as well as provide an expanded data base of paramagnetic center/proton relaxation. Both the NMRD and EPR data are consistent with a significant increase in the rotational correlation time on binding chelate to dendrimeric polymer. The NMRD profiles show a peak in the high-field region (6-60 MHz proton Larmor frequency), consistent with increasing rs. Correlation times of 0.7 < r < 2.7 ns are measured by EPR over physiological temperatures, which are much larger than 0.1 ns as predicted by other authors. These results confirm qualitatively the predictions of the Solomon-Bloembergen-Morgan (SBM) theory, and provide an excellent platform from which to expan d our understanding of motional effects on contrast agent-proton relaxation. The first major results of this study were published last year. Work continues, with anisotropic motion a focus of new work.