F Oesterhelt et al 1999 New J. Phys. 1 6 doi:10.1088/1367-2630/1/1/006
Single molecule force spectroscopy by AFM indicates helical structure of poly(ethylene-glycol) in water
F Oesterhelt, M Rief and H E Gaub
Show affiliationsWe elongated individual poly(ethylene-glycol) (PEG) molecules tethered at one end to an AFM cantilever. We observed the resistive force as a function of elongation in different solvents. In all cases the molecular response was found to be fully reversible and thus in thermodynamic equilibrium. In hexadecane the stretched PEG acts like an ideal entropy spring and can be well described as a freely jointed chain. In water we observed marked deviations in the transition region from entropic to enthalpic elasticity, indicating the deformation of a supra-structure within the polymer. An analysis based on elastically coupled Markovian two-level systems agrees well with recent ab initio calculations predicting that PEG in water forms a non-planar supra-structure which is stabilized by water bridges. We obtained a binding free energy of 3.0±0.3 kT.
- PACS
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61.25.H- Macromolecular and polymers solutions; polymer melts
- Subjects
- Dates
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Issue 1 (March 1999)
Received 10 November 1998
Published 24 March 1999
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Single molecule force spectroscopy by AFM indicates helical structure of poly(ethylene-glycol) in water
F Oesterhelt et al 1999 New J. Phys. 1 6
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