Date on Master's Thesis/Doctoral Dissertation

8-2021

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Degree Program

Chemistry, PhD

Committee Chair

Wittebort, Richard J.

Committee Member

Maurer, Muriel C.

Committee Member

Mueller, Eugene G.

Committee Member

Nantz, Michael H.

Committee Member

Lee, Donghan

Author's Keywords

Hydrophobic effect; backbone ordering; polyethylene glycol; hofmeister ions; double quantum nuclear magnetic resonance; thermomechanics

Abstract

Elastin is one of the most hydrophobic proteins, and it is extremely flexible when hydrated. The driving force for recoil is the decrease in entropy of the protein and/or the hydrating solvent. This dissertation is a study of both mechanisms. Following an introduction (Chapter 1), Chapters 2 and 3 investigate the recoil mechanism on the molecular level in the hydrating solvent and in the protein, respectively. Chapter 4 examines macroscopic properties of recoil by thermomechanics. Conclusions are discussed in Chapter 5. Using double quantum NMR, the deuterated water ordering at the elastin surface was studied quantitatively as a function of stretch and in the presence of solutes known to modulate the hydrophobic effect: polyethylene glycol (PEG), sulfate ion, a kosmotrope, and perchlorate ion, a chaotrope. When the purified elastin is stretched, a nearly one order of magnitude increase in the ordering of water is observed, and this is due to the increase in water exposed to the hydrophobic surface. When PEG and sulfate ions are added to the solvent, ordering of the water is significantly decreased due to a more compact protein with reduced solvent exposed surface area. At concentrations below 0.3 mol/kg perchlorate ion, only minor changes in the magnitude of the ordered water signal are observed because perchlorate interacts with peptide bonds and does not decrease exposed hydrophobic surface area. Ordering of elastin was studied using static 13C NMR to assess the amplitude of backbone motions in the mature elastic material. It was found that the residual shielding anisotropy is small, 1 – 3 ppm and within the experimental resolution of this experiment, no stretch induced ordering was observed. Thus, cross-linked elastin is dynamically disordered much like soluble minielastins. The thermomechanical experiments show that elastin is stiffer in the presence of PEG, sulfate and high perchlorate concentrations. These solutes do not interact with the protein and decrease the volume and the length of the fiber, confirming the increase in compaction. Also, they decrease the heat liberated, the change in entropy and the internal energy with stretch. Thus, the hydrophobic effect is the major player in elastin recoil.

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