Solvent Dependent Folding of an Amphiphilic Polyaramid.

A series of synthetic alternating and amphiphilic aromatic amide polymers were synthesized by a step growth polymerization. Alternating meta- and para-linkages were introduced to force the polymer chain into a helical shape in the highly polar solvent water. The polymers were analyzed by 1H NMR spectroscopy and SEC in polar aprotic solvents such as DMSO and DMF. However, the polymers also showed good solubility in water. 1H NMR spectroscopy, small-angle X-ray scattering, and dynamic light scattering provided clear evidence of polymer folding in water but not DMF. We employed parallel tempering metadynamics in the well-tempered ensemble (PTMetaD-WTE) to simulate the free energy surfaces of an analogous model polymer in DMF and water. The simulations gave a molecular model of an unfolded structure in DMF and a helically folded tubular structure in water.

Supramolecular design of CO2-responsive lipid nanomaterials.

HYPOTHESIS: Stimuli-responsive materials can innovate in various fields, including food and pharmaceutical sciences. Their response to a specific stimulus can be utilized to release loaded bioactive molecules or sense their presence. The biocompatibility and abundance of CO2 in the environment make it an exciting stimulus for such applications. We hypothesize the formation of CO2-responsive self-assemblies of oleyl-amidine in water. Their integration into glycerol-monooleate-based (GMO) dispersions is further thought to form CO2-switchable liquid crystalline nanoparticles. The switch from an non-charged acetamidine surfactant to its cationic amidinium form triggers curvature changes that ultimately induces phase transitions. EXPERIMENTS: The CO2-switchable lipid (E)-N,N-dimethyl-N-((Z)-octadec-9-en1-yl)acetimidamide (OAm) is synthesized and formulated into emulsions and dispersed liquid crystals with GMO. The supramolecular structure and its response to CO2 are characterized using small angle X-ray scattering, dynamic light scattering, ζ-potential measurements and cryogenic transmission electron microscopy. FINDINGS: Depending on the composition, OAm is discovered to self-assemble into a variety of CO2-responsive lyotropic liquid crystalline structures that can be dispersed in excess water. CO2-triggered colloidal transformations from unstructured OAm-in-water emulsions to direct micelles; dispersed inverse hexagonal phase to direct rod-like micelles, and sponge phase to vesicles are discovered. These structural changes are driven by the reaction of OAm's amidine headgroup with CO2. The results provide a fundamental understanding of CO2-triggered functional nanomaterials and may guide their future design into delivery platforms and biosensors.