Covalent bond force profile and cleavage in a single polymer chain

We present here the measurement of the single-polymer entropic elasticity a nd the single covalent bond force profile, probed with two types of atomic force microscopes (AFM) on a synthetic polymer molecule: polymethacrylic ac id in water. The conventional AFM allowed us to distinguish two types of in teractions present in this system when doing force spectroscopic measuremen ts: the first interaction is associated with adsorption sites of the polyme r chains onto a bare gold surface, the second interaction is directly corre lated to the rupture process of a single covalent bond. All these bridging interactions allowed us to stretch the single polymer chain and to determin e the various factors playing a role in the elasticity of these molecules. To obtain a closer insight into the bond rupture process, we moved to a for ce sensor stable in position when measuring attractive forces. By optimizin g the polymer length so as to fulfill the elastic stability conditions, we were able for the first time to map out the entire force profile associated with the cleavage of a single covalent bond. Experimental data coupled wit h molecular quantum mechanical calculations strongly suggest that the break ing bond is located at one end of the polymer chain. (C) 2000 American Inst itute of Physics. [S0021-9606(00)50530-3].