Issue 1, 2011

α-Helix unfolding in simple shear flow

Abstract

The unfolding dynamics of the α-helical poly-L-lysine (α-PLL) in Couette flow is reported. Real-time circular dichroism measurements for a range of molecular weights and shear rates have been made. The PLL molecules show a time- and shear rate-dependent unfolding in simple shear flow with a critical strain ([small gamma, Greek, dot above]tc) value of ∼105. This strain value is found to be independent of the chain-length of the α-helices. The extent of unfolding is less pronounced with increasing molecular weight (M) for a given strain, showing a linear dependence of the remaining helix, α, on M: αM. Furthermore, the helix content, α, is found to show a power law dependence with strain: α ≈ ([small gamma, Greek, dot above]t)−1/2. A shear-induced rapid unfolding of short chain α-PLL molecules in the flow field occurs. The shear-stability of the larger molecular weights is due to the cohesive forces stabilizing the helix, combined with the associated hydrodynamic screening of helical segments from the full effect of the drag in the flow field. The data are compared with recent molecular dynamics simulations of the dynamics of dilute polymer solutions in shear flow and scaling arguments are used to interpret the trends in the data.

Graphical abstract: α-Helix unfolding in simple shear flow

Supplementary files

Article information

Article type
Paper
Submitted
20 Jul 2010
Accepted
16 Sep 2010
First published
13 Oct 2010

Soft Matter, 2011,7, 203-210

α-Helix unfolding in simple shear flow

I. B. Bekard, K. J. Barnham, L. R. White and D. E. Dunstan, Soft Matter, 2011, 7, 203 DOI: 10.1039/C0SM00692K

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