Poly(amidoamine)s carryng TEMPO residues for NMR imaging applications

An amphoteric bio-compatible and stealth-like poly (amidoamine) named ISA23 was obtained from 2,2-bis(acrylamido)acetic acid (BAC) and 2-methylpiperazine. The partial substitution of 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl (Amino-TEMPO) for 2-methylpiperazine as comonomer gave two new PAA-TEMPO conjugates based on ISA23: ISA23-TEMPO1 and ISA23- TEMPO2 with 10 and 40% TEMPO-carrying units per polymer chain, respectively. In this study, a thorough NMR characterization of ISA23 polymer together with NMR and ESR characterizations of the ISA23-TEMPO derivatives and a preliminary evaluation of their potential as NMR labels for imaging applications are reported. Relaxivity measurements performed on ISA23-TEMPO1 and ISA23-TEMPO2 showed relaxivities of 0.4 and 1.8 mM^(-1) s^(-1), respectively, indicating that the PAA-TEMPO adducts have a definite potential as NMR imaging contrast agents. This was confirmed by preliminary magnetic resonance imaging (MRI) determinations.