Characterization of poly(amidoamine) dendrimers and their complexes with Cu2+ by matrix-assisted laser desorption ionization mass spectrometry

Hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimers of generation 2-4 ( Gn-OH, n = 2, 3, and 4; M-r similar to 3.7, 6.9, and 14.3 kDa, respectively ) and dendrimers encapsulating Cu2+ ions have been investigated by matrix-a ssisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectro metry. Umbelliferone (7-hydroxycoumarin) and 2',4',6'-trihydroxyacetophenon e (THAP) were used as the matrices for dendrimers with and without Cu2+ in the interior. The MALDI-TOF results provide accurate molecular weight deter minations of all dendrimers and some multiple copper complexes of G2-OH and G3-OH (accuracy <0.01%). More importantly, this approach provides direct c haracterization of multiple-cation adducts and quantitative evaluation of t he complexing capacity of dendrimers hosting transition-metal ions. The res ults are used to determine dendrimer structure and evaluate polydispersity.