Influence of polymer molar mass and mixture stoichiometry on polyelectrolyte complexes of poly(l-arginine) and Poly(l-glutamic acid)

Poly(l-arginine) (PARG) and poly(l-glutamic acid) (PLGA) homopolypeptides were custom synthesized by precision N-carboxyanhydride ring-opening polymerization methods with two molar masses, matched for pairs of cationic anionic polypeptides (degrees n = 100 500). The conformations the probed using circular dichroism (CD) FTIR spectroscopy which revealed presence mainly polyproline II (PPII) conformation. Small-angle X-ray scattering (SAXS) showed concentration-dependent polyelectrolyte peaks form factor high q scaling due to excluded volume behaviour wormlike chains. We then examined complexation in mixtures PARG PLGA masses. Precipitation was generally observed structures precipitates, supernatant resuspended precipitates investigated CD, SAXS cryo-TEM. These that, contrary prior suggestions literature, contain mostly a PPII-like conformation, there is only minimal β-sheet content (which enhanced upon drying sample during preparation certain measurements). have fractal-like structure as cryo-TEM SAXS. Our findings on polypeptide complex contribute understanding phase separation complexes coacervation may shed light formation inter-cellular bodies proteins peptides such Lewy other inclusion bodies.