title: Mechanically induced silyl ester cleavage under acidic conditions investigated by AFM-based single-molecule force spectroscopy in the force-ramp mode.
abstract: AFM-based dynamic single-molecule force spectroscopy was used to stretch carboxymethylated amylose (CMA) polymers, which have been covalently tethered between a silanized glass substrate and a silanized AFM tip via acid-catalyzed ester condensation at pH 2.0. Rupture forces were measured as a function of temperature and force loading rate in the force-ramp mode. The data exhibit significant statistical scattering, which is fitted with a maximum likelihood estimation (MLE) algorithm. Bond rupture is described with a Morse potential based Arrhenius kinetics model. The fit yields a bond dissociation energy De = 35 kJ mol(-1) and an Arrhenius pre-factor A = 6.6 × 10(4) s(-1). The bond dissociation energy is consistent with previous experiments under identical conditions, where the force-clamp mode was employed. However, the bi-exponential decay kinetics, which the force-clamp results unambiguously revealed, are not evident in the force-ramp data. While it is possible to fit the force-ramp data with a bi-exponential model, the fit parameters differ from the force-clamp experiments. Overall, single-molecule force spectroscopy in the force-ramp mode yields data whose information content is more limited than force-clamp data. It may, however, still be necessary and advantageous to perform force-ramp experiments. The number of successful events is often higher in the force-ramp mode, and competing reaction pathways may make force-clamp experiments impossible.
authors.affiliation: Munich University of Applied Sciences, Department of Applied Natural Sciences and Mechatronics, Lothstr. 34, 80335 Munich, Germany. clausen-schaumann@hm.edu alfred.kersch@hm.edu.
authors.forename: Sebastian W
authors.initials: SW
authors.lastname: Schmidt
authors.forename: Michael F
authors.initials: MF
authors.lastname: Pill
authors.forename: Alfred
authors.initials: A
authors.lastname: Kersch
authors.forename: Hauke
authors.initials: H
authors.lastname: Clausen-Schaumann
authors.forename: Martin K
authors.initials: MK
authors.lastname: Beyer