First characterization of the influence of paramagnetic heteropoly complex of tungsten on relaxation times of water. Separation of various contributions to relaxivities

Spectral studies help measure the T1 relaxation times of water in the aqueous solutions of the three types of paramagnetic transition metal-substituted heteropoly complexes, alpha-(XW11O39Z(H2O))n-, (X = P or Si and Z = Fe3+ or Mn2+), alpha2-(P2W17O61Z(H2O))m- (Z = Mn2+ or Fe3+) and (GdH2W10O36)7- in a 10.7 MHz magnetic field. The net relaxivity of individual heteropoly complexes vary as a function of the metal type, net complex charge, the size, and the rotational correlation time.