Mechanically induced cis-to-trans isomerization of carbon–carbon double bonds using atomic force microscopy

Abstract

Cis-to-trans isomerization of carbon-carbon double bonds can be induced by the application of mechanical force. Using single molecule force spectroscopy by means of atomic force microscopy (AFM) we pulled polymer molecules which contained cis double bonds in the backbone. In the force versus extension profiles of these polymers, a sudden extension increase is observed which is due to the conversion of shorter cis isomers into longer trans isomers. The added length to the polymer results in relaxation in probed force. We find that the isomerization occurs at forces of 800 ± 60 pN, independent of AFM tip and solid substrate chemistries. Investigation of similar polymers which exclusively contained single bonds in the backbone showed no evidence of a similar transition.

Characterization of Single Polymer Molecules

“…Mechanically induced isomerization of cis carbon-carbon double bonds to trans conformation in polymer P1 is shown in Figure 8 [37]. Experiments were realized by adsorbing polymer chains from a solution with concentration 100 mg/L dissolved in dimethyl sulfoxide (DMSO).…”

“…Chemical structure of a triblock copolymer of poly(exo-N-(2-aminoethyl)-5-norbornene-2,3-dicarboximide) and poly(exo-N-hexyl-5-norbornene-2,3-dicarboximide) (P1)[37], poly(2-vinyl pyridine) (P2VP), poly(ethylene glycol) (PEG), poly(styrene) (PS), and poly(ethylene) (PE). The side blocks of P1 are about 11 monomers long (m ≈ 11) and the middle block 544 monomers long (n ≈ 544).…”

Quantitative Nano-characterization of Polymers Using Atomic Force Microscopy

“…[27] As will be discussed below, isomerization of carbon-carbon double bonds can be activated mechanically at a force of about 800 pN. [28] Let us now illustrate these notions with specific examples. The structures of polymers used in the experiments are summarized in Fig.…”

“…Analysis of the single molecule isomerization events results in an isomerization force F ct = 800±60 nN. [28] The isomerization force is lower than the force of breaking of covalent bonds and rings, 1-2 nN, which have higher activation energies. [40,41] Conclusion AFM has revolutionized our analytical capabilities of polymers and enabled high resolution and nanoscale description of individual molecules.…”

“…This is done by repeating the experiments on a more dilute polymer layer, or on surfaces that are chemically different. [28] The freely jointed chain (FJC) model can describe the force versus extension profiles of single molecules: [38] x = L coth…”