First Characterization of the Influence of Paramagnetic Heteropoly Complexes of Tungsten on Relaxation Times of Water. Separation of Various Contributions to Relaxivities

The gadolinium complexes with polyoxometalates as potential MRI contrast agents

“…Moreover, the relaxivities of Gd(BW 11 ) 2 and Gd(CuW 11 ) 2 were much higher than that of Gd(SiW 11 ) 2 and Gd(PW 11 ) 2 [21,22], and this result can be rationalized that the larger negative charge on the complex will orient water molecules with hydrogen atoms closer to the complex. Similar effect was observed in other heteropoly complexes [26] and metal porphyrins [27].…”

Mn(II)-monosubstituted polyoxometalates as candidates for contrast agents in magnetic resonance imaging

“…Those may be attributed to (a) a longer rotational correlation time due to their higher molecular weight and the rigidity of their structure and (b) a shorter distance between the inner-sphere water molecule and Mn stemming from the larger negative charge. Similar effect was observed in other heteropoly complexes [37] and metal porphyrins [38].…”

Correlation of Relaxivity with Coordination Number in Six-, Seven-, and Eight-Coordinate Mn(II) Complexes of Pendant-Arm Cyclen Derivatives

“…For series of structurally related Gd 3+ complexes, it has been generally found that the relaxivity decreases as the charge increases,89,90 although exceptions have also been noted 91. This effect has been rationalized in terms of a water exchange mechanism and enhanced electrostatic interactions between positive charges and the oxygen atom of the water molecule, which lead to slower water exchange rates 89,90. All of the amide-based complexes in Table 3 have 2+ charges while the carboxylates are neutral and Mn 2+ (aq) carries a large positive charge.…”