Polynitroxyl functionalized dendrimers as paramagnetic relaxation enhancers : effects of structure on relaxivity

The 1H NMR relaxivity of ortho and para dinitroxide substituted phthalate esters and a series of nitroxyl functionalized poly(propylene imine) dendrimers has been measured in acetonitrile and methanol. Studies of dinitroxide relaxivity indicate that electron exchange rate has only a small effect on relaxivity. In studies on dendritic polynitroxides, the per-nitroxide based relaxivity nearly doubles for the generation 5 nitroxyl functionalized dendrimer as compared to a mononitroxide model. This relaxivity enhancement may be due to crowding of dendrimer surface groups in higher generation dendrimers. Dendritic polynitroxides exhibit high relaxivities, making them exciting candidates for magnetic resonance imaging applications. [on SciFinder (R)