Coacervation in Biopolymers

Kamla Rawat and Bohidar HB

Abstract

In this review, a detailed discussion on salient features of intermolecular interactions leading to phase separation and coacervation is discussed. Biomolecular solutions exist as gels, coacervates and melts with each of these phases having its signature physico-chemical properties which is discussed in this review. The discussions are supported by robust experimental data obtained from an array of methods like turbidimetry, electrophoresis, viscosity, light scattering etc. The inevitability of the phenomenon of self-organization in biopolymers results in generation of a variety of soft matter phases which do not, however, make it predictable. For instance the associate aggregation is a process which remains obscure, as every protein aggregates in a different manner under different conditions. One known feature to the aggregation of proteins is the strong dependence upon pH, salt concentration, and temperature. Beyond the influence of these factors and their effects on aggregation, the process is not well understood. In summary, a comprehensive account of biomolecular phase states and their inherent attributes are presented in this review. Potential applications of coacervates are many starting from protein purification, drug encapsulation to treatment of organic plumes. This calls for better understanding of the coacervate structure and the transport of biomolecules inside this phase. Several questions pertaining to the structure of coacervates can arise. The foremost of these is, is it a gel-like or a solution-like phase? Though presence of hydrogen bonding and hydrophobic sites on the polyions influence biomolecular binding, they hardly play any role in deciding the persistence length of the polyion unlike the surface charge. Interestingly, we observed that the differential binding (SPB versus EB) was found to be a function of intrinsic persistence length only which we conclude as a significant observation.