Figure 3: (A) Probability density functions. The red curve represents a typical pdf of the unbinding forces measured on a DMPC bilayer with embedded calix[6]arenes at constant pulling velocity (600 nm/s). The binding probability was 23.0 %. The same experiment was repeated with the very same tip on a lipid bilayer consisting of pure DMPC (blue line). Here the probability dropped to 3.5 % reflecting non-specific interactions. (B) Loading rate dependence of the unbinding force. Squares represent the most probable unbinding force at each pulling velocity (respectively at each loading rate). From the linear semi-logarithmical fit xβ and koff are calculated according to Evans theory. The kinetic off rate for the cytochrome c – Calix[6]arene complex is 1.14±0.59 s-1 and xβ is 3.98±0.63 Å. The same measurements with a poly-T linker ended with a primary amine groups (B, inset) result in a koff value of 2.74±0.66 s-1 and xβ is 5.91±2.55 Å.