Elastin-like polypeptides (ELPs) are a class of biopolymers with the potential to function as a novel drug delivery platform. These protein based polymers are composed of the repeating pentapeptide sequence (GαGβP)n where n is the number of pentapeptide repeats while α and β are guest amino acid residues. ELP constructs have been designed to respond to various external stimuli including temperature, pH, and ionic strength where their response to these stimuli results in the separation of the ELP from solution. This phase separation results in a two-phase system consisting of a protein poor supernatant phase and a protein rich coacervate phase.
Under certain conditions select ELP constructs are able to self assemble into micellar structures of nanometer scale when raised above their transition temperature. The micellar architecture consists of an inner hydrophobic core, with a composition like that of the protein rich coacervate phase, surrounded by hydrophilic head groups. For the use of ELP micelles as a drug delivery platform these particles should possess the ability to encapsulate solute molecules. In this study, solute solubility within the micelle core was investigated by measuring the partition coefficients of several solutes in five different ELP two-phase systems, then all data was fit to a linear free energy relationship (LFER) model to provide insight into the dominate interactions governing solute partitioning in ELP systems. From the LFER it is shown that the cavity formation energy, solute size, and the solvents hydrogen bond acidity are important parameters governing solute partitioning in the ELP solvents investigated. Additionally, the partition coefficients provide a measurement of ELP phase hydrophobicity from which the development of future ELP constructs is possible.