Supramolecular design of CO2-responsive lipid nanomaterials

Hypothesis: Stimuli-responsive materials can innovate in various fields, including food and pharmaceu-tical 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 excit-ing 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 aceta-midine 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 supramolec-ular structure and its response to CO2 are characterized using small angle X-ray scattering, dynamic light scattering, f-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 col-loidal 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 funda-mental understanding of CO2-triggered functional nanomaterials and may guide their future design into delivery platforms and biosensors.(c) 2023 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

This study hypothesizes the formation of CO2-responsive self-assemblies of oleyl-amidine in water and their integration into glycerol-monooleate-based (GMO) dispersions to form CO2-switchable liquid crystalline nanoparticles. The experiments involve synthesizing and formulating CO2-switchable lipids and characterizing their supramolecular structure and response to CO2. The findings reveal the self-assembly of CO2-responsive lyotropic liquid crystalline structures and the colloid transformations triggered by CO2, providing insights for the design of functional nanomaterials.