Quantitative analysis of generation and branch defects in G5 poly(amidoamine) dendrimer

Abstract

Although methods have been developed to synthesize and isolate generation 5 (G5) PAMAM dendrimers containing precise numbers of ligands per polymer particle, the presence of skeletal and generational defects in this material can substantially hamper the process. Here we provide a quantitative analysis of G5 PAMAM dendrimer defects via high performance liquid chromatography, potentiometric titration, mass spectrometry, size exclusion chromatography, and nuclear magnetic resonance. We identified, isolated, and characterized the major structural defects of G5 dendrimer, trailing generations, and dimer, trimer, and tetramer species. We determine that the G5 material present in the as-received mixture contains 93 arms on average. We have developed two model systems capable of generating the experimentally observed mass range and polydispersity at defect rates of 8–15%.

Controlling the number of dendrimers in dendrimicelle nanoconjugates from 1 to more than 100

“…dimers and trimers, in the specic dendrimer batch. The number of defects and amount of impurities are known to increase with increasing dendrimer generation; 32,33 overall, this should result in a net reduction of the charge per weight, which means that there are less negative charges per sample than expected from theoretical calculations. Since the determined PMC indicates the actual (charge) stoichiometry, the observed deviation from 0.5 has been taken into account in the calculations of the aggregation number (see ESI † for details on computation).…”

“…This may be because a commercial sample of G9 PAMAM dendrimer contains a signicant percentage of lower generation dendrimeric structures, as reported previously for G5 PAMAM dendrimers. 33 These smaller (<G9) dendrimers in a G9-C3M dendrimicelle sample will self-assemble with polymers and undergo a formation-dissociation process with increasing polymer concentration, leading to an increase and decay of the intensity as is clear from the DLS curves of the lower generations. 45 …”

Generation 3 PAMAM dendrimer TAMRA conjugates containing precise dye/dendrimer ratios

“…Lower generation dendrimers are also of great interest for biological applications because of their reduced cost and, for some applications, preferred size [21,22]. For controlled photophysical and biodistribution properties, it is important to control MW as well dye/dendrimer ratio [23]. Defects expected in G3 PAMAM include trailing generations (G1 and G2) as well as G3-G3 dimer, which give a molecular weight range from ∼1400 to 14,000 Da for the nominally 6909 Da material [24].…”

Distributions: The Importance of the Chemist’s Molecular View for Biological Materials

“…2−10 Note that G5 PAMAM has a theoretical 128 attachment sites (purified G5 PAMAM monomer, discussed below, has an average of 93 attachment sites). 4 …”

“…(c) Conjugation to an rp-HPLC-purified G5 monomer sample (red trace) has narrowed peak width and improved peak resolution compared to those of the as-received conjugation (black trace). Adapted and reprinted from ref (4). Copyright 2013, with permission from Elsevier.…”