Investigating the hydrophobic collapse and secondary structure formation of model polypeptides in aqueous salts solutions

Open Access
Author:
Lee, Seung-yi
Graduate Program:
Chemistry
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
February 05, 2015
Committee Members:
  • Paul S Cremer, Thesis Advisor
Keywords:
  • hydrophobic
  • collpase
  • pepdide
  • salt
Abstract:
The first part of this thesis discusses the unique hydration of model polymers in H2O and D2O in order to expand the understanding of the relationship between hydrophobic hydration and solvent hydrogen bonding strength. Two model polymers, poly(dimethyl acrylamide) (PDMA) and poly(diethyl acrylamide) (PDEA), were compared. The uncollapsed state of PDMA was found to be more stable in H2O, while PDEA was more stable in D2O. To examine the origin of these phenomena, the effects of pH, solvent transfer, and ion-specificity on polymer collapse were investigated. Experiments were conducted utilizing light scattering, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), and Raman with multivariate curve resolution (MCR). Among the variables tested, the dominant effects were found to be highly dependent on the nature of the model polymer and its interaction with the solvent. PDMA was found to be less hydrophobically hydrated than PDEA and real proteins. The second part of this thesis describes the specific effects of calcium ions on the secondary structure of elastin-like polypeptides (ELPs). Two ELPs, V-120 and V5A2G3-120, were employed in this study. The phase transition temperatures of these ELPs were measured by light scattering measurements and correlated with spectroscopic signatures from circular dichroism (CD). At molar concentrations of calcium chloride, the amount of β-turn structure was found to increase more for V5A2G3 than V-120. This may be due to the fact that V5A2G3 has a fewer number of valine residues in its polypeptide sequence. These molecular level results may contribute to the understanding of the formation of bones in the body and may also aid in the development of the medical and bioengineer materials.