Increasing the length of the carboxyamide arm of a GdDOTA monoamide (DOTA = 1,4,7,10-tetraaza-1,4,7,10-tetrakis(carboxymethyl)cyclododecane) complex from acetic to propionic accelerates the water exchange rate (k_ex) by nearly two orders of magnitude; the ¹H relaxivity of the corresponding macromolecular derivatives may then be remarkably enhanced in MRI-based molecular imaging applications, as exemplified in the case of micellar systems.