How paramagnetic ions effect relaxation time in NMR?

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Kristof Grohe

Hallo,

Generally, relaxation is caused by electromagnetic fluctuations. These fluctuations can be caused by molecular motion, which again causes changes in dipolar fields or in your case by spin flips of electrons. Electrons have a roughly 600 times higher gyromagnetic ratio than proton. In a paramagnetic ion, the electronic spin relaxation is enhanced by transitions between electronic states.

Regarding NMR relaxation, one has to separate between longitudinal T1 and transversal T2 relaxation. The firs one can basically be understood al flipping between alpha and beta states along B0. A paramagnetic ion causes T1 relaxation when its frequency of electron flips is roughly at the Lamor (resonance) frequency of the nucleus such that alpha beta transitions can be caused by the electron flipping. T2 relaxation while the magnetization is on the xy plane can be imagined as a dephasing of the magnetization vectors of the magnetically equivalent nuclei. These relaxation is caused, additionally to the frequencies at the Lamor frequency by slow frequencies. So, it depends on the relaxation time of the electron if and how much t1 or t2 relaxation is affected by a paramagnetic ion.

I hope that helps a bit.

Many greetings