Flow-induced conformational changes and phase behavior of aqueous poly-L-lysine solutions

✍ Scribed by A. Immaneni; A. J. McHugh

• Publisher: Wiley (John Wiley & Sons)
• Year: 1998
• Tongue: English
• Weight: 152 KB
• Volume: 45
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/(sici)1097-0282(199803)45:3<239::aid-bip6>3.0.co;2-s

✦ Synopsis

Poly-L-lysine exists as an a-helix at high pH and a random coil at neutral pH. When the a-helix is heated above 27ЊC, the macromolecule undergoes a conformational transition to a b-sheet. In this study, the stability of the secondary structure of poly-L-lysine in solutions subjected to shear flow, at temperatures below the a-helix to b-sheet transition temperature, were examined using Raman spectroscopy and CD. Solutions initially in the a-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 b-sheet structure evidenced by the amide I band at 1666 cm 01 . CD measurements indicated that solutions of predominantly a-helical conformation at 20ЊC transformed into 85% a-helix and 15% b-sheet after being sheared for 20 min. However, on continued shearing the content of b-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.