Glycine-modified polyamidoamine dendrimers: synthesis and structural characterization using nuclear magnetic resonance, ion-mobility mass spectrometry and capillary electrophoresis

We present here the preparation and the structural characterization of first-generation ammonia-cored polyamidoamine (PAMAM) dendrimers modified with glycine residues. Chemical modification of the dendrimer was done to increase the biocompatibility of these compounds, known to be effective delivery agents for drugs or genes. Fully modified PAMAM [Gly(6)G1(N)] on the one hand and partially modified [Gly(n)G1(N), with n = 0 to 6)] on the other hand were obtained depending on the experimental conditions. The resulting modified PAMAM dendrimers have to be cautiously characterized to understand and interpret their physico-chemical and biochemical properties as well as to control their chemical design. The structural characterization was carried out using ion mobility spectrometry-mass spectrometry (IM-MS), multistage tandem mass spectrometry (MSn), accurate mass measurements by high resolution-mass spectrometry (HR-MS), two dimensional nuclear magnetic resonance (NMR) and capillary electrophoresis (CE). Characteristic fragmentation patterns for these compounds were obtained from ESI/MSn (with n = 2 to 4) experiments. IM-MS and CE analysis showed that a single component was mainly obtained for the complete grafting experimental conditions while a distribution of oligomers was produced for partially grafted products. The physical separation of Gly(n)G1(N) oligomer ions was achieved in the gas phase (IM-MS) as well as in the condensed phase (CE). Besides, the collision cross sections (CCS) were estimated by IM-MS and compared to theoretical values. Then, the glycine grafting yield for Gly(n)G1(N) PAMAM was determined by both NMR and IM-MS experiments.