Abstract
Complex coacervation is an emerging liquid/liquid phase separation (LLPS) phenomenon that behaves as a membrane-less organelle in living cells. Yet while one of the critical factors for complex coacervation is temperature, little analysis and research has been devoted to the temperature effect on complex coacervation. Here, we performed a complex coacervation of cationic protamine and multivalent anions (citrate and tripolyphosphate (TPP)). Both mixtures (i.e., protamine/citrate and protamine/TPP) underwent coacervation in an aqueous solution, while a mixture of protamine and sodium chloride did not. Interestingly, the complex coacervation of protamine and multivalent anions showed upper critical solution temperature (UCST) behavior, and the coacervation of protamine and multivalent anions was reversible with solution temperature changes. The large asymmetry in molecular weight between positively charged protamine (~4 kDa) and the multivalent anions (<0.4 kDa) and strong electrostatic interactions between positively charged guanidine residues in protamine and multivalent anions were likely to contribute to UCST behavior in this coacervation system.
Highlights
Coacervation is a liquid/liquid phase separation (LLPS) phenomenon in aqueous solution caused by the complexation of dissolved polymers in the aqueous solution due to a variety of attractive forces [1,2,3,4]
When protamine and the multivalent ions were mixed in water, the mixed solutions became turbid, and the formation of spherical coacervate droplets in both systems was observed by an optical microscope (Figure 2)
Protamine/multivalent ion coacervates were prepared by mixing protamine and multivalent ion solution at a ratio of 6:4 for further experiments
Summary
Coacervation is a liquid/liquid phase separation (LLPS) phenomenon in aqueous solution caused by the complexation of dissolved polymers in the aqueous solution due to a variety of attractive forces [1,2,3,4]. When an aqueous solution is adjusted to a specific pH and ionic strength at which solvated polymers attract each other, the polymer chains mingle, partially desolvate, and recruit other polymer chains to form dynamic dense polymer droplets within the fluid [1,5]. This dense dynamic polymer droplet is called a coacervate, originating from the Latin word coacervatus, which means “cluster”. 2 2of de Jong and Kruyt as an LLPS resulting from mixing two oppositely charged polyelectrolytes, a as an LLPS resulting from mixing two oppositely charged polyelectrolytes, a positively charged gelatin positively charged gelatin and a negatively charged gum Arabic [1].
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