Effect of organic and inorganic salt environment on the complex coacervation of in situ formed protein nanoparticles and DNA.

Complex coacervation was noticed between in situ formed protein (a primarily hydrophobic Zein protein with pI = 6.2) nanoparticles (size 80-120 nm) and ds-DNA (a high charge density polyanion), in the ionic liquid (IL) solutions of 1-ethyl-3-methyl imidazolium chloride [C2mim][Cl], and 1-octyl-3-methyl imidazolium chloride [C8mim][Cl], in the studied ionic strength range of I = 10-4 to 6 × 10-1 M, which was extended to strong monovalent 1:1 electrolyte (NaCl) to explore the commonality between the organic and inorganic salt (ionic) environment on coacervation. The salt dependent coacervation profile was monitored from the measured turbidity of the interacting solution, and zeta potential, (ζ) and apparent hydrodynamic radius (Rh) of interpolymer complexes, which depicted the following three discernible interaction regimes common to all the salts: (i) Region-I: I = 0.0001-0.01 M, primary binding, (ii) Region-II, I = 0.01-0.1 M, secondary binding, and (iii) Region-III, I = 0.1-0.6 M, saturation binding. The free-energy and the network density calculations favored preferential coacervation in [C2mim][Cl] samples. Nonetheless, commonality in the overall ionic strength dependent coacervation profiles could still be observed.