|Name||Ms. Sara Tabandeh|
|Organization or Institution||University of Central Florida|
Polypeptide-based Complex Coacervates: Hydrophobicity Effect of Amino Acids
Sara Tabandeh , Dr. Lorraine Leon
University of Central Florida
Complex coacervates are made via the liquid-liquid phase separation of mixtures of oppositely charged polyelectrolytes in aqueous solution. This polymer rich phase initially forms spherical micron sized liquid droplets. Due to their extremely low interfacial tension with water, complex coacervates have good encapsulation properties leading to applications in the food and pharmaceutical industries. There are many factors that affect complex coacervation such as stoichiometry (charge mixing ratio), ionic strength, total polymer concentration, pH, chirality and temperature1. Here we intend to explore the effect that increased hydrophobicity has on complex formation by using oppositely charged polypeptides designed to have different hydrophobic content. It has been shown that polypeptide chirality controls the phase behavior of polyelectrolyte complexes, where homochiral polypeptides form hydrogen-bonded solid precipitates while racemic polypeptides form complex coacervates as their chirality pattern disrupts backbone hydrogen bonding2. For this reason, we have synthesized ionic polypeptides using solid phase synthesis with an alternating sequence of D-Lysine (D-Lys) and varying L-amino acids as polycations and D-Glutamic acids (D-Glu) and varying L-amino acids as polyanions. We have chosen to use Glycine (Gly), Alanine (Ala) and Leucine (Leu) due to their increasing hydrophobicity index respectively. Mass spectroscopy (MALDI-TOF), H NMR and circular dichroism (CD) were used to characterize and confirm the molecular structure and chiral pattern of polypeptides. To investigate the effect of ionic strength and to find out the critical salt concentration (which is the concentration at which complex formation is no longer observed), we measured turbidity of our samples. Optical microscopy was used to confirm the turbidity results and the physical state of the complexes (liquid coacervates or solid precipitates). Initially, the interaction of three different lysine based polycations made with glycine, alanine or leucine mixed with Poly-(D,L) Glutamic acid (PRE) was investigated and the formation of liquid coacervates was confirmed by optical microscopy. The critical salt concentration of the different complexes was determined, indicating an increase in critical salt concentration with increased hydrophobicity of the polypeptide. The lysine based polycations were also mixed with the glutamic acid based polyanions resulting in temperature sensitive complex formation likely due to the reduced charge density of both polyelectrolytes. Future work includes evaluating the rheological behavior of the different complexes and their ability to encapsulate hydrophobic molecules, in order to establish the capability of these materials to deliver hydrophobic drugs.
1.Dimitris Priftis, Matthew Tirrell, Soft Matter 2012, 8, 9396.
2.Sarah L. Perry, Lorraine Leon et al., Nat. Commun. 2015, 6, 6052.