Static and Dynamical Properties of Single Poly(Ethylene Glycol) Molecules Investigated by Force Spectroscopy
Abstract
Molecular recognition force spectroscopy was employed to probe the mechanical and dynamical features poly(ethylene glycol) (PEG). His6 was covalently coupled to AFM tips via PEG for the specific recognition of NTA on the surface. Force-extension profiles of single molecules obtained in force-distance cycles were fitted with an extended Worm Like Chain (WLC) model with a quality of the fit σdata-fit/σdata of 1.3. The fit revealed a persistence length LP of 3.8 ± 0.02 Å and an enthalpic correction term K0 of 1561 ± 33 pN. Amplitude-distance cycles were recorded with dynamical force microscopy. Fitting with the damped linear oscillator model, using values for the persistence length and the nonlinear spring constant from force-distance cycles, yielded a fit quality σdata-fit/σdata of 1.5. Force-distance cycles calculated from amplitude-distance cycles by integration nicely agreed with simultaneously measured force-distance cycles, and even yielded an improved signal to noise ratio. This shows that no dissipative and irreversible processes occur and that the force extension profile of PEG is determined by purely elastic behavior.
