| Abstract: |
Recent reports have compared Fe8(aq)) versus Magnevist with seemingly conflicting conclusions: one claims a much greater efficiency of Fe8 for magnetic resonance imaging contrast, and the other claims a much lower efficiency. Our study shows that at concentrations below 1.5mM Fe8(aq) had a T{I/}1 relaxivity, r{I/}r1, of 5.4s-1mM-1 which is comparable to Magnevist. Above 1.5mM Fe8(aq) han an r{I/}1 of 1.1s-1mM-1, significantly lower than Magnevist. These results agree with the previous literature over the concentrations they examined. The results for the T{I/}2 relaxivity, r{I?}2, were similar. Here, we show that the concentration dependence of the relaxivity accounts for these discrepancies. Further, the relaxivity data are correlated with frequency-dependent maxima in Χ"/ac of frozen solutions of Fe8 dissolved in deionized water over the temperature range of 1.8-4 K and the frequency range of 200-1400 Hz. The magnetic properties of the single-molecule magnet Fe8 in room temperature and frozen aqueous solution were found to be highly non-linear when examined over a wide concentration range. |
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