Chirality-selected phase behaviour in ionic polypeptide complexes

Abstract

Polyelectrolyte complexes present new opportunities for self-assembled soft matter. Factors determining whether the phase of the complex is solid or liquid remain unclear. Ionic polypeptides enable examination of the effects of stereochemistry on complex formation. Here we demonstrate that chirality determines the state of polyelectrolyte complexes, formed from mixing dilute solutions of oppositely charged polypeptides, via a combination of electrostatic and hydrogen-bonding interactions. Fluid complexes occur when at least one of the polypeptides in the mixture is racemic, which disrupts backbone hydrogen-bonding networks. Pairs of purely chiral polypeptides, of any sense, form compact, fibrillar solids with a β-sheet structure. Analogous behaviour occurs in micelles formed from polypeptide block copolymers with polyethylene oxide, where assembly into aggregates with either solid or fluid cores, and eventually into ordered phases at high concentrations, is possible. Chirality is an exploitable tool for manipulating material properties in polyelectrolyte complexation.

Selective Uptake and Refolding of Globular Proteins in Coacervate Microdroplets

“…Although urea is known to induce the demicellization of ionic and nonionic surfactants by the modulation of hydrogen bond networks, hydrophobic associations, headgroup solvation, and counterion binding, 42,43 there are few studies on the influence of urea on the process of complex coacervation. 44 In general, there was only a small decrease in both the turbidity (coacervate yield, Supporting Information Figure S5) and positive zeta potential values for samples prepared at high denaturant concentrations (Figure 4). The positive ζ values were attributed to a slight excess of positive PDDA units in the 1:1 coacervate mixture prepared from strong (PDDA) and weak (PAA, 88 and 71% ionization) polyelectrolytes at pH 8 in the absence and presence of 10 M urea, respectively (data not shown).…”

Linear viscoelasticity of complex coacervates

“…The qualitative nature of turbidity-style measurements allows a phenomenological characterization of coacervate phase behavior, rather than a more direct quantification of the binodal phase space [8,15,71,[73][74][75][76][77]83,88,[91][92][93]104,105,108,112,114,. Typical characterization experiments include evaluation of the stoichiometric ratio of polycation to polyanion, the effect of increasing salt concentration, and the effect of variable pH.…”

PRISM-Based Theory of Complex Coacervation: Excluded Volume versus Chain Correlation

“…Experimentalists have begun to systematically explore this space, looking at effects such as chain solubility and length, ion identity, and valency. 1,32,[34][35][36][37][38][47][48][49][50][51] Nevertheless, a comprehensive physical picture of these systems remains to be elucidated.…”

“…1 Polymeric complex coacervates demonstrate a rich phenomenology that is a function of the presence of salt as well as the nature of the charged polyions, 1,32,[34][35][36][37][38][47][48][49][50] with a vast parameter space that spans the molecular features of all four components. Experimentalists have begun to systematically explore this space, looking at effects such as chain solubility and length, ion identity, and valency.…”