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 (G n -OH, n = 2, 3, and 4; M r ∼ 3.7, 6.9, and 14.3 kDa, respectively) and dendrimers encapsulating Cu 2+ ions have been investigated by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. Umbelliferone (7-hydroxycoumarin) and 2‘,4‘,6‘-trihydroxyacetophenone (THAP) were used as the matrices for dendrimers with and without Cu 2+ in the interior. The MALDI-TOF results provide accurate molecular weight determinations of all dendrimers and some multiple copper complexes of G2-OH and G3-OH (accuracy <0.01%). More importantly, this approach provides direct characterization of multiple-cation adducts and quantitative evaluation of the complexing capacity of dendrimers hosting transition-metal ions. The results are used to determine dendrimer structure and evaluate polydispersity.