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.

Facile interconversions of topology and aromaticity of expanded porphyrin in solution

The dynamic transformations of conformations and aromatic properties of [32]octaphyrins（1.0.1.0.1.0.1.0） through rotating the pyrrolic ring of the macrocycles are demonstrated by theoretical simulations in CH2Cl2 solution. Facile multistep isomeriza- tions involving antiaromatic-Htickel and aromatic-Mobius topologies were also predicted by density functional theory （DFT）. The understanding of changes in topologies and aromaticities of free-base expanded porphrins may provide useful information to build new macrocycles with unique properties.