Chemistry Reference
In-Depth Information
Both the control polymer (9) and the modular polymer having multiple loops (8)
were subjected to single molecule force-extension studies using atomic force
microscopy (AFM). The single molecule nanomechanical properties for many biopo-
lymers including proteins (Kellermayer et al. 1997; Rief, Gautel, et al. 1997;
Marszalek et al. 1999; Li et al. 2000), polysaccharides (Rief, Oesterhelt, et al.
1997), DNAs, (Smith et al. 1999), and synthetic polymers (Ortiz and
Hadziioannou 1999) have been studied using AFM. We followed similar protocols
reported previously (Rief, Gautel, et al. 1997; Ortiz and Hadziioannou 1999;
Smith et al. 1999; Li et al. 2002) for single chain studies of our polymers using
AFM (Guan et al. 2003; Roland et al. 2003). Either the modular polymer 8 or the
control polymer 9 was allowed to be adsorbed from a dilute solution (10
25
-10
27
M) onto a freshly coated gold surface. The sample was probed in our custom-built
liquid cell using toluene as the solvent. We tried both physisorption and chemisorp-
tion with thiol ether terminally functionalized polymers, and both protocols gave
comparable results. When the tip was retracted, extension curves like the ones
shown in Figure 10.3 were recorded.
The single chain force-extension curves for both the control polymer (9) and the
modular polymer (8) are shown in Figure 10.3 (Guan et al. 2004). For control
Figure 10.3 AFM single chain force-extension data. (a) An overlay of representative force-
extension curves for modular polymer 8. Sawtooth patterned curves were consistently obtained.
(b) One representative single chain force-extension curve for control polymer 9, in which only
one peak was observed. (c) A single chain force-extension curve for modular polymer 8 shows
the characteristic sawtooth pattern with three peaks. In Figure 10.2b and c, all scattered dots
represent experimental data and the solid lines are results from WLC fitting. Adapted from
Guan et al. (2004). Copyright 2004 American Chemical Society.
