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Flow‐induced conformational changes and phase behavior of aqueous poly‐ L ‐lysine solutions
Author(s) -
Immaneni A.,
McHugh A. J.
Publication year - 1998
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/(sici)1097-0282(199803)45:3<239::aid-bip6>3.0.co;2-s
Subject(s) - chemistry , shearing (physics) , random coil , raman spectroscopy , aqueous solution , helix (gastropod) , crystallography , phase transition , polymer , beta sheet , circular dichroism , protein structure , thermodynamics , organic chemistry , biology , snail , optics , ecology , biochemistry , physics
Poly‐ L ‐lysine exists as an α‐helix at high pH and a random coil at neutral pH. When the α‐helix is heated above 27°C, the macromolecule undergoes a conformational transition to a β‐sheet. In this study, the stability of the secondary structure of poly‐ L ‐lysine in solutions subjected to shear flow, at temperatures below the α‐helix to β‐sheet transition temperature, were examined using Raman spectroscopy and CD. Solutions initially in the α‐helical state showed time‐dependent increases in viscosity with shearing, rising 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 β‐sheet structure evidenced by the amide I band at 1666 cm −1 . CD measurements indicated that solutions of predominantly α‐helical conformation at 20°C transformed into 85% α‐helix and 15% β‐sheet after being sheared for 20 min. However, on continued shearing the content of β‐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. © 1998 John Wiley & Sons, Inc. Biopoly 45: 239–246, 1998