Rotational correlation time lengthening

The rotational correlation time tr several methods have been proposed to lengthen tr for example, noncova-lent interactions with endogenous macromolecules such as HSA, DNA, specific receptors of the cellular membrane, paramagnetic polymers, liposomes, or micelles. This parameter can be determined by various methods such as NMR of diamagnetic lanthanum complexes or NMR of Gd-complexes. 

The molecular rotational correlation time, Tr, mainly depends on the molecular radius of the complex and thus (if extensive internal flexibility is not present) higher molecular weight induces a lengthening of the Tr and consequently the relaxivity is higher at magnetic fields of 0.5-1.5T. 

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