Nitroxides have great potential as contrast agents for Magnetic Resonance Imaging (MRI). Two b - cyclodextrin ( b CD) derivatives bearing one or seven (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) units on the small rim of b CD (CD3 and CD6 respectively) were synthesized. Their e ff ective magnetic moments were measured by DC-SQUID magnetometry obtaining the values m e ff/mB z 1.7 and me ff/m B z 4.2 for CD3 and CD6 respectively. Interestingly, while isothermal magnetization data of CD3 were well described by a Brillouin function for a S ¼ 1/2 single spin system, those associated with CD6 could not be explained in the framework of a non-interacting spins model. For this reason, four different con fi gurations for the seven interacting nitroxides were considered and modeled. The numerical results evidenced that only the con fi gurations with a privileged central spin could take into account the experimental observations, thus justifying the reduced e ff ective magnetic moment of CD6. The water relaxivity (r1 ) in DMSO-d 6 – water (9 : 1 v : v) solutions was also measured for both the derivatives obtaining the values r 1 ¼ 0.323 mM and r 1 ¼ 1.596 mM for CD3 and CD6 respectively.
Effective magnetic moment in cyclodextrin-polynitroxides: Potential supramolecular vectors for magnetic resonance imaging
Caglieris, F.;CANEPA, FABIO MICHELE;
2015-01-01
Abstract
Nitroxides have great potential as contrast agents for Magnetic Resonance Imaging (MRI). Two b - cyclodextrin ( b CD) derivatives bearing one or seven (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) units on the small rim of b CD (CD3 and CD6 respectively) were synthesized. Their e ff ective magnetic moments were measured by DC-SQUID magnetometry obtaining the values m e ff/mB z 1.7 and me ff/m B z 4.2 for CD3 and CD6 respectively. Interestingly, while isothermal magnetization data of CD3 were well described by a Brillouin function for a S ¼ 1/2 single spin system, those associated with CD6 could not be explained in the framework of a non-interacting spins model. For this reason, four different con fi gurations for the seven interacting nitroxides were considered and modeled. The numerical results evidenced that only the con fi gurations with a privileged central spin could take into account the experimental observations, thus justifying the reduced e ff ective magnetic moment of CD6. The water relaxivity (r1 ) in DMSO-d 6 – water (9 : 1 v : v) solutions was also measured for both the derivatives obtaining the values r 1 ¼ 0.323 mM and r 1 ¼ 1.596 mM for CD3 and CD6 respectively.
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