HIGH RELAXIVITY LINEAR GD(DTPA)-POLYMER CONJUGATES - THE ROLE OF HYDROPHOBIC INTERACTIONS

A series of linear copolymers of DTPA-class Gd3+ conjugates, linked by alpha,omega-alkyldiamides with a varying number (n) of methylenes sep arating the amide function, were synthesized, Surprisingly, their rela xivities at all fields increased with increasing n. At MRI fields and 35 degrees C, the relaxivities of the n = 10 and n = 12 polymers were unexpectedly high, similar to those of rigid dendrimer-based Gd3+ chel ates, The magnetic field dependence of solvent proton 1/T-1, was measu red for aqueous urea-free and urea-containing polymer solutions, The r esults for urea-free solutions imply an increase of rigidity (required for high relaxivities) with increasing n, arising from hydrophobic in teractions of the methylene groups with solvent, This hypothesis is su pported by a large decrease in the relaxivities upon addition of urea, which is known to weaken hydrophobic interactions, The relaxivities a re also independent of polymer concentration, indicating that the hydr ophobic interactions are intramolecular.