Structure–Function Relationship of PAMAM Dendrimers as Robust Oil Dispersants

Abstract

PAMAM dendrimers have recently been investigated as efficient and biocompatible oil dispersants utilizing their encapsulation capacity; however, their high cationic charge density has been shown to be cytotoxic. It is therefore imperative to mitigate cationic charge-induced toxicity and understand the effects of such changes. Presented here is a synergistic experimental and computational approach to examine the effects of varying terminal surface charge on the capacity of dendrimers to disperse model liner, polycyclic aromatic, and hybrid hydrocarbons. Uncharged dendrimers collapse by forming intramolecular hydrogen bonds, which reduce the hosting capability. On the other hand, changing the surface charges from positive to negative greatly shifts the pK a of tertiary amines of the PAMAM dendrimer interior. As a result, the negatively charged dendrimers have a significant percentage of tertiary amines protonated, ∼30%. This unexpected change in the interior protonation state causes electrostatic interactions with the anionic terminal groups, leading to contraction and a marked decrease in hydrocarbon hosting capacity. The present work highlights the robust nature of dendrimer oil dispersion and also illuminates potentially unintended or unanticipated effects of varying dendrimer surface chemistry on their encapsulation or hosting efficacy, which is important for their environmental, industrial, and biomedical applications.

Deviation from the Unimolecular Micelle Paradigm of PAMAM Dendrimers Induced by Strong Interligand Interactions

“…These results not only explain the phenomena observed in our earlier experimental studies 18,20 but also illuminate the contrasting mechanisms of dendritic polymers for oil 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 dispersion, where both ligand--ligand and ligand--dendrimer interactions contribute to conjure the dendrimer hosting capacity. Such dynamic capacity may serve as a basis for a range of dendrimer applications in environmental remediation, water purification, catalysis, and gene and drug delivery.…”

“…In actual applications of PAMAM as dispersants, the targeted ligands are usually mixtures of different types of ligands. For example, in our previous experiments, 18 the mixture of C16 with 8% PN ligands was used as a "model crude", which displayed a higher binding cooperativity than PHe. Although we did not model the mixture of C16 and PN in the current study, we expect that C16 will be a "good" solvent for PN and PAMAM can disperse the hydrocarbon mixtures in the same manner as C16 alone.…”

“…[31][32][33] Recently, we have successfully applied DMD in simulating dendrimers with various structures. 18 We used a united--atom representation for the dendrimer--hydrocarbon systems in which all heavy atoms and polar hydrogens were explicitly modeled. Inter--atomic interactions including van der Waals (VDW), solvation, electrostatic and hydrogen bond interactions were modeled by a physical force field adapted from Medusa.…”

Applications of Discrete Molecular Dynamics in biology and medicine

“…They demonstrated that highly hydroxylated fullerene nanoparticles form hydrogen bonds with protein surfaces, stabilizing them without inducing structural changes, while less hydroxylated fullerene particles are hydrophobic and can cause proteins to misfold. Geitner et al [30] conducted DMD simulations of poly(amidoamine) dendrimers (PMAMs), a class of highly branched polymers, to determine differences in oil dispersion interactions between cationic, anionic, and neutral charged PMAMs with various hydrocarbons. Their results can be applied to inform design of polymers used in environmental cleanup, water purification, and drug delivery, among other industrial and biomedical applications.…”

Hyperbranched fluorene-alt-carbazole copolymers with spiro[3.3]heptane-2,6-dispirofluorene as the core and their application in white polymer light-emitting devices

“…[1][2][3][4][5] Firstly, they are easy to be synthesized by one-pot polymerization with comparable properties to dendritic polymers or other well dened polymers. 4,8,9 Recently, a number of hyperbranched electroluminescent polymers with the three principle colors (red, 10 green 11,12 and blue 13 ) have been synthesized, and both emission efficiency and thermal stability were effectively improved with respect to their linear analogies. 4,8,9 Recently, a number of hyperbranched electroluminescent polymers with the three principle colors (red, 10 green 11,12 and blue 13 ) have been synthesized, and both emission efficiency and thermal stability were effectively improved with respect to their linear analogies.…”