Mimicking PAMAM Dendrimers with Amphoteric, Hybrid Triazine Dendrimers: A Comparison of Dispersity and Stability

摘要

Two strategies are applied to mimic the amphoteric nature of the surfaces of half-generation PAMAM dendrimers yet retain the very narrow dispersity inherent of triazine dendrimers. Both strategies start with a monodisperse, single-chemical entity, generation two triazine dendrimer presenting 12 surface amines that is available at the kilogram scale. The First method relies on reaction with methyl bromoacetate. Complete conversion of the surface primary amines to tertiary amines occurs to provide 24 surface esters. Extended reaction times lead to quarternization of the amines while other unidentified species are also present. The resulting polyester can be quantitatively hydrolyzed using 4 M aqueous HCl to yield a dendrimer with 12 tertiary amines and 24 carboxylic acids about a hydrophobic triazine core. The second method utilizes Michael additions of methyl acrylate to yield 24 surface esters. This reaction proceeds more rapidly and more cleanly than the former strategy. Hydrolysis of this material proceeds quantitatively using 4 M aqueous HCl to Yield the desired dendrimer. In both cases, MALDI-TOF mass spectrometry provides compelling evidence of reaction progress. Electrophoretic analysis confirms the amphoteric nature of these materials with the former targets having a pI value in tile 1.8 < pI < 3.4 range, and the latter having a pI value in the 4.7 < pI < 5.9. These ranges bookend the pH range within which PAMAM dendrimers become zwitterionic, 3.4 < pI < 4.7. The strategy of using monodisperse amine-terminated dendrimer constructs as core offers significant advantage over PAMAM homopolymers including dispersity, case of characterization and batch-to-batch reproducibility. These triazine dendrimers could ultimately be adopted into materials with applications wherein the demands of purity have hitherto remained unsatisfied.