Volume 111, Issue 6, Pages 1163-1172 (September 2016) Can Dissipative Properties of Single Molecules Be Extracted from a Force Spectroscopy Experiment?  Fabrizio Benedetti, Yulia Gazizova, Andrzej J. Kulik, Piotr E. Marszalek, Dmitry V. Klinov, Giovanni Dietler, Sergey K. Sekatskii  Biophysical Journal  Volume 111, Issue 6, Pages 1163-1172 (September 2016) DOI: 10.1016/j.bpj.2016.08.018 Copyright © 2016 Biophysical Society Terms and Conditions

Figure 1 Schematic of the experimental setup. Bottom: a typical example of static force (black, lower curve), amplitude (red, middle curve), and phase (blue, upper curve) signals for the case of avidin-BBSA protein pairs, previously obtained at a dithering frequency of a few kilohertz (see (16,17) for details). The phase data, which look quite typical for this type of experiment (cf. (8,10)) have not been presented before because their interpretation was not clear for us. The Nanoscope IV Picoforce AFM was used in our new setup. Biophysical Journal 2016 111, 1163-1172DOI: (10.1016/j.bpj.2016.08.018) Copyright © 2016 Biophysical Society Terms and Conditions

Figure 2 (A–D) Examples of experimental data corresponding to the stretching of a single titin I27 molecule. The static force signal is presented in black, and X and Y channels (volts; for clarity of presentation, the signals are shifted vertically from each other) are shown in green and blue, respectively. (B) For illustration, we also present amplitude and phase curves that were calculated (restored) from X and Y signals using Eqs. 15–18. The pulling speed is equal to 25 nm/s and the dithering frequency is equal to 140 Hz. Biophysical Journal 2016 111, 1163-1172DOI: (10.1016/j.bpj.2016.08.018) Copyright © 2016 Biophysical Society Terms and Conditions

Figure 3 Amplitude (red) and phase (blue) channels of a single stretched dextran molecule obtained with dithering at a frequency of 240 Hz. The pulling speed is equal to 25 nm/s. In green we present an inverse of the properly shifted phase signal, which is hardly distinguishable from the amplitude signal. For clarity of presentation, the graphs are shifted vertically from each other. Biophysical Journal 2016 111, 1163-1172DOI: (10.1016/j.bpj.2016.08.018) Copyright © 2016 Biophysical Society Terms and Conditions

Figure 4 Example of experimental data corresponding to the stretching of a single dextran molecule. The static force signal is presented in black, and amplitude and phase signals (volts) are shown in red and blue, respectively. The pulling speed is equal to 25 nm/s and the dithering frequency is equal to 240 Hz. In this figure, a chair-boat transition of dextran that occurs at a force of ∼600 nN (215 nm) is barely discerned in the static force signal but is very well seen in the amplitude-related signal. The same transition is also shown in Fig. 3 (∼660 nm). Biophysical Journal 2016 111, 1163-1172DOI: (10.1016/j.bpj.2016.08.018) Copyright © 2016 Biophysical Society Terms and Conditions