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 Title: Conformational and Orientational Dynamics of Semi-Rigid Macromolecules in Shear Flow Author(s): Immaneni, Aravind Doctoral Committee Chair(s): McHugh, A.J. Department / Program: Chemical Engineering Discipline: Chemical Engineering Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Engineering, Chemical Abstract: The third study involves the conformational and phase stability of aqueous Poly-L-Lysine solutions in shear flow. Poly-L-lysine exists as an $\alpha$-helix at high pH and a random coil at neutral pH. When the $\alpha$-helix is heated above 27$\sp\circ$C, the macromolecule undergoes a conformational transition to a $\beta$-sheet. In this study, the stability of the secondary structure of poly-L-lysine in solutions subjected to shear flow, at temperatures below the $\alpha$-helix to $\beta$-sheet transition temperature, were examined using Raman spectroscopy and circular dichroism (CD). Solutions initially in the $\alpha$-helical state showed time-dependent increases in viscosity with shearing, rising to values as much as an order of magnitude. Visual observation and turbidity measurements showed the formation of a gel like phase under flow. Laser Raman measurements demonstrated the presence of small amounts of $\beta$-sheet structure evidenced by the amide I band at 1666 cm$\sp{-1}$. CD measurements indicated that solutions of predominantly $\alpha$-helical conformation at 20$\sp\circ$C transformed into 85% $\alpha$-helix and 15% $\beta$-sheet after being sheared for 20 minutes. However, on continued shearing the content of $\beta$-sheet conformation decreased. The observed phenomena were explained in terms of a "zipping up" molecular model based on flow enhanced hydrophobic interactions similar to that observed in gel-forming flexible polymers. (Abstract shortened by UMI.). Issue Date: 1997 Type: Text Language: English Description: 140 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1997. URI: http://hdl.handle.net/2142/82443 Other Identifier(s): (MiAaPQ)AAI9812639 Date Available in IDEALS: 2015-09-25 Date Deposited: 1997
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