The utility of the single-molecule magnet Fe8 as a magnetic resonance imaging contrast agent over a broad range of concentration

Brant Cage*, Stephen E. Russek, Richard Shoemaker, Alex J. Barker, Conrad Stoldt, Vasanth Ramachandaran, Naresh S. Dalal

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

41 Scopus citations


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 1.5 mM Fe8(aq) had a T1 relaxivity, r1, of 5.4 s-1 mM-1 which is comparable to Magnevist. Above 1.5 mM Fe8(aq) had an r1 of 1.1 s-1 mM-1, significantly lower than Magnevist. These results agree with the previous literature over the concentrations they examined. The results for the T2 relaxivity, r2, 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 χac 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.

Original languageEnglish (US)
Pages (from-to)2413-2419
Number of pages7
Issue number12
StatePublished - Jul 23 2007


  • Fe
  • MRI contrast agent
  • NMR
  • Relaxivity
  • SMM
  • ac susceptibility

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry


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