Viscoelastic properties of single poly(ethylene glycol) molecules.
The viscoelastic properties of single poly(ethylene glycol) (PEG) molecules were measured by analysis of thermally and magnetically driven oscillations of an atomic force microscope (AFM) cantilever/molecule system. The molecular and monomer stiffness and friction of the PEG polymer were derived using a simple harmonic oscillator (SHO) model. Excellent agreement between the values of these two parameters obtained by the two approaches indicates the validity of the SHO model under the experimental regimes and the excellent reproducibility of the techniques. A sharp minimum in the monomeric friction is seen at around 180 pN applied force which we propose is due to a force induced change in the shape of the energy landscape describing the conformational transition of PEG from a helical to a planar state, which in turn affects the timescale of the transition and therefore modifies the measured internal friction. A knowledge of the viscoelastic response of PEG monomers is particularly important since PEG is widely used as a linker molecule for tethering groups of interest to the AFM tip in force spectroscopy experiments, and we show here that care must be exercised because of the force-dependent viscoelastic properties of these linkers.
Kawakami
Masaru
M
Institute of Molecular Biophysics and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom.
Byrne
Katherine
K
Khatri
Bhavin S
BS
McLeish
Tom C B
TC
Smith
D Alastair
DA
D001703:Biophysics / Q000379:methods; D002627:Chemistry, Physical / Q000379:methods; D004548:Elasticity; D007700:Kinetics; D018625:Microscopy, Atomic Force; D015233:Models, Statistical; D008968:Molecular Conformation; D009991:Oscillometry; D011092:Polyethylene Glycols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry; D011312:Pressure; D013314:Stress, Mechanical; D013696:Temperature; D013816:Thermodynamics
D011108:Polymers; D011092:Polyethylene Glycols