Abstract
Polyelectrolyte complexation is a versatile platform for the design of self-assembled materials. Here we use rational design to create ionic hydrophobically-patterned peptides that allow us to precisely explore the role of hydrophobicity on electrostatic self-assembly. Polycations and polyanions were designed and synthesized with an alternating sequence of d- and l-chiral patterns of lysine or glutamic acid with either glycine, alanine or leucine due to their increasing hydrophobicity index, respectively. Two motifs were considered for the oppositely charged patterned peptides; one with equal residues of charged and uncharged amino acids and the other with increased charge density. Mass spectroscopy, circular dichroism, H- and F-NMR spectroscopy were used to characterize the polypeptides. Polyelectrolyte complexes (PECs) formed using the sequences were characterized using turbidity measurements, optical microscopy and infrared spectroscopy. Our results show that the critical salt concentration, a key measure of PEC stability, increased with both increasing charge density as well as hydrophobicity. Furthermore, by increasing the hydrophobicity, the amount of PEC formed increased with temperature, contrary to purely ionic PECs. Lastly, we assessed the encapsulation behavior of these materials using a hydrophobic dye. Concluding that encapsulation efficiency increased with hydrophobic content of the complexes providing insight for future work on the application of these materials for drug delivery.
Highlights
Complex coacervates have extremely low interfacial tension with water [7,8] which has led to encapsulation applications in the food industry [9,10] as well as potential applications in the pharmaceutical industry [11,12,13,14]
To evaluate this precipitate-like behavior and the possibility of hydrogen bonding, we studied the stability of p(kX)+p(eX) at both 1 M and 2 M concentrations of urea with the same preparation steps that polyelectrolyte complexes (PECs) were examined with salt (Figure 5)
We presented two different designs of hydrophobically patterned ionic polypeptides that were used to study the effect of hydrophobicity on polyelectrolyte complexes
Summary
Interactions between oppositely charged macromolecules in solution lead to polyelectrolyte complexes (PECs) that phase separate into materials that behave either as a liquid or a solid [1,2,3,4,5].The liquid-liquid phase separation is termed complex coacervation which initially forms polymer-rich droplets that eventually coalesce into a distinct phase. [2,3] The term was introduced by Bungenberg de Jong et al [6], based on their work on ionically interacting polymers in aqueous media.Complex coacervates have extremely low interfacial tension with water [7,8] which has led to encapsulation applications in the food industry [9,10] as well as potential applications in the pharmaceutical industry [11,12,13,14]. Interactions between oppositely charged macromolecules in solution lead to polyelectrolyte complexes (PECs) that phase separate into materials that behave either as a liquid or a solid [1,2,3,4,5]. The liquid-liquid phase separation is termed complex coacervation which initially forms polymer-rich droplets that eventually coalesce into a distinct phase. Complex coacervates have extremely low interfacial tension with water [7,8] which has led to encapsulation applications in the food industry [9,10] as well as potential applications in the pharmaceutical industry [11,12,13,14]. PECs that form solids (precipitates), have glassy behavior, where the glass transition temperature has been shown to be dependent on the number of water molecules surrounding a Molecules 2019, 24, 868; doi:10.3390/molecules24050868 www.mdpi.com/journal/molecules
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