Date of Award

2012

Degree Type

Thesis

Department

Chemical and Biomedical Engineering

First Advisor

Holland, Nolan

Subject Headings

Polypeptides, Elastin, Viscosity, Polymers

Abstract

Elastin-like polypeptides (ELPs) are a part of the family of responsive polymers. These polymers can be made to respond to a wide variety of stimuli, including temperature, pH, salt, concentration, light, and solvent. Elastin-like polypeptides are soluble in water at low temperatures but they become hydrophobic and insoluble above their transition temperature. Elastin-like polypeptides, (GVGVP)40-foldon and (GVGVP)60-foldon, were expressed in bacterial system. These ELPs above their transition temperature, Tt, at low salt (< 45mM) and high pH (> pH 10) assemble into micelles where the hydrophobic tails phase separate in the interior of the micelle as an immiscible coacervate phase. The oligomerization domain termed as foldon, has a net negative charge and behaves as a hydrophilic group to stabilize the aggregates formed by the ELP chains above their transition temperature. The coacervate, which makes up interior of micelles, contains 37 protein and 63 water when it is in a bulk state. The aim of my research was to find out the density of protein in the micelle by using capillary viscometry. We used Ubbelohde capillary viscometer to calculate the relative viscosity of ELPs which was used to calculate the intrinsic viscosities using Kraemer and Huggins equations. The micelles at low salt concentration and high pH are spherical therefore we use equivalent sphere model to calculate the density of protein per micelle from intrinsic viscosity. Using this model we calculated the density of protein per micelle to be 0.26 g/ ml. Using our micelle model and data from light scattering, we calculated the density of protein in the coacervate to be 40 and rest water. There were two limitations in this project. First, specific viscosities at low concentrations were small with large errors. The second limitation was controlling the pH of the polymer solutions during the experiments. The pH of polymer solution could not easily be monitored once the sample was loaded in the viscometer

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