Understanding the Conformational Interconversions of a Polymer Chain in a Liquid Environment at the Single-molecule Level

The conformational interconversions of polymer chains have been of great interest as a basic scientific issue.Single-molecule force spectroscopy(SMFS)is a powerful tool for molecular manipulation,which enables experimental studies on the single-chain behaviors of polymers.The SMFS results show that an individual polymer chain in a liquid environment may have similar properties to an ideal chain,which contradicts the traditional theoretical view.Herein,by taking into account the collisions of solvent molecules,the conformational interconversions of a single polymer chain in a liquid environment have been analyzed.The conformational interconversion frequency of a carbon-carbon bond of an alkane chain can be estimated by establishing the relationship between the internal rotation barriers of small molecules(monomers)and the corresponding macromolecules.Since the time scale of conformational interconversions of the polymer backbone is much shorter than that of SMFS experiments,most polymers with C-C backbones behave as ideal chains in liquid environments.

Effect of chain length on the conformation and friction behaviour of DNA

Four double-stranded DNA films with different chain lengths were prepared on 3-aminopropyltriethoxysilane(APS)-modified mica surfaces in the NaCl solution with concentration ranging from 0.001 to 0.1 M.By using an atomic force microscope,the force-distance curves and friction behaviour of each DNA film were studied in the NaCl solution that was used in the sample preparation.When adsorbed on mica as films in salt solution,the conformation of DNA molecules would be a combination of loops and"train-like".As the chain length increased from 50 to 20000 bp,the extension rate of DNA film increased from 7.1to 11.5 in 0.001 mol/L NaCl solution,which suggested that the DNA molecule with long chain likely resulted in more extended conformation.In addition,under low normal load,low NaCl concentration could increase the friction of DNA film and the chain length revealed insignificant effect on the friction force of DNA film.Therefore,long chain DNA with low salt concentration is more conducive to the nanopore sequencing process,since extended conformation can make DNA molecules easier to reach into nanopore and the high friction can reduce the translocation speed.These results may benefit the development of the third-generation sequencing technique based on nanopore.