Conformational and Orientational Dynamics of Semi-Rigid Macromolecules in Shear Flow
Immaneni, Aravind
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https://hdl.handle.net/2142/82443
Description
Title
Conformational and Orientational Dynamics of Semi-Rigid Macromolecules in Shear Flow
Author(s)
Immaneni, Aravind
Issue Date
1997
Doctoral Committee Chair(s)
McHugh, A.J.
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Language
eng
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.)."
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