Focal‐point anchoring: Large proton relaxivity observed for gadolinium‐cored dendrimer complexes in water

Water‐soluble Gd³⁺‐cored poly(ether amide) dendrimer complexes, bearing a diethylenetriaminepentaacetic acid Gd³⁺ complex (GdDTPA) core, were synthesized. The longitudinal proton relaxivity (R₁), governed mainly by the rotation correlation time of the paramagnetic Gd³⁺ center, was measured in water (37 °C, 20 MHz). An anchor effect at the focal point of the hydrophilic dendrimer was experimentally evaluated for the first time, through a comparison of the R₁ values with the ones reported for various Gd³⁺ complexes, including linear copolymers of GdDTPA linked by various lengths of aliphatic chains via amide bonds. Unusually large R₁ values for the first‐ and second‐generation Gd³⁺‐cored dendrimer complexes (6.1 and 9.3 mM^?1 s^?1, respectively), even with relatively low molecular weights (1355 and 3877, respectively), suggested a remarkable increase in the local rigidity around the GdDTPA core. The internal rigidity of the dendrimer was supposed to take advantage of the increased nominal molecular weight in water via multihydration to the dendron to increase the rotation correlation time, and this resulted in the observed R₁ gain. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2680–2689, 2004