Gadolinium complexes relaxivity

The gadolinium complex GdHPDOSA can be trapped inside the interior of apoferritin (60). The process is based on the dissociation of the apoprotein into subunits at low pH in a concentrated solution of the complex followed by its reforming at pH 7. The complex molecules that are not trapped inside the protein are eliminated by dialysis. The longitudinal relaxivity of the... 

A general model for electronic relaxation of the Gd3+ S = 7/2 ion in various complexes in solution was presented by Rast el al. [86]. Contrary to the usual assumption, the electronic relaxation in their model is not only due to the effects of the transient zero field splitting, but is also strongly influenced by the static crystal field effect which is modulated by the random Brownian rotation of the complex. Experimental peak-to-peak widths of three gadolinium complexes could be well interpreted as a function of temperature and frequency using three static and one transient crystal field parameters. Moreover, their interpretation of experimental data did not require the addition of any field independent contribution to the line width like the spin-rotation mechanism. 

A structural change in a gadolinium complex may result in a relaxivity change when it goes together with a change in the hydration state of the metal... 

Lowe et al. [7] and Frias et al. [8] described complexes of cyclene-based molecules with lanthanoids. A gadolinium complex which would exhibit pH-dependent relaxivity thanks to a switch in hydration state was prepared. [7] Cyclene bore a sulphonamide substituent in order to achieve a variation of the coordination environment of the lanthanide centre as a function of pH (Scheme 7). 

The gadolinium complex with Cxi displays a reasonable relaxivity and it has been assessed as a potential contrast agent for magnetic resonance imaging. Its stability constant is however too low to make this complex a good candidate for in vivo applications. Until now, no calixarene derivative has proved efficient in this field, contrary to the pendant-arm substituted coronands. 

Xu, J., Franklin, S.J., Whisenhunt, D.W. Jr, and Raymond, K.N. (1995) Gadolinium complex of tris[(3-hydroxy-l-methyl-2-oxo-l,2-didehydropyridine-4-carboxamido)ethyl]-amine a new class of gadolinium magnetic resonance relaxation agents. Journal of the American Chemical Society, 117, 7245-7246. 

Five bis(amid derivatives of DTPA form neutral Gd complexes with similar relaxivity to [Gd(dtpa)(H20)] The structure of a gadolinium complex of a bis(amide) of DTPA (21), a potential contrast agent, has been determined. ... 

Very high relaxivities have been found for three Gd(DTPA-bisamide)alkyl copolymers. A gadolinium complex of a substituted DTPA (25) was undergoing phase III clinical trials at the end of the twentieth century as a liver-specific contrast agent for MRI. ... 

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