Liquid Phase TEM Observation for Conformational Dynamics of Single Polymer Chains

다국어 초록 (Multilingual Abstract)

Macromolecules have a chain structure made up of repeating building blocks and they are naturally flexible in solutions. In many solution systems of biological and synthetic polymers, macromolecules exist in a range of distinct conformations and undergo dynamic transitions between them, responsible for their specific functions and physicochemical properties, and determining a pathway to construct high-level structures. For example, intrinsically disordered proteins, which account for one-third of the proteins in the human proteome, do not adopt a standardized three-dimensional structure and their spontaneous interconversion between unfolded states are crucial in dynamic biological processes. In addition, highly regulated by complex molecular interactions and resulting conformational changes, various synthetic polymers form a wide range of high-order structures by self-structuring of individual molecules. Thus, it is important to understand the intrinsic structural diversity and dynamic behaviors of individual macromolecules at the single-chain level. Liquid-phase transmission electron microscopy (LPTEM) has recently enabled in situ observations of polymers, such as polystyrene sulfonate and poly(ethylene oxide) in aqueous solutions. It provides nanometer resolution in tracking individual molecules in solutions. Advancing LPTEM, here we achieve high-resolution tracking of dendronized polymer chains in graphene liquid cell TEM and elucidate a distinct individual chain architecture and conformational fluctuations of a single linear semi-flexible polymer in a theta solvent. Investigation of the single-chain dynamics combined with molecular dynamic (MD) simulations directly reveals that the degree of intra-chain interactions induces dynamic structural fluctuations between the coiled and elongated conformations of semi-flexible polymers. Additionally, we observe non-equilibrium single chain motions, showing that single-chain trajectories can be highly affected by the locally heterogeneous environment.