pH as a Design Tool for Low-Molecular-Weight Hydrogelators: Triggers, Structural Control, and Orthogonal Assembly

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Polymer Science

Background:

• Low-molecular-weight gelators (LMWGs) offer tunable alternatives to traditional thickeners.
• pH is an attractive stimulus for LMWGs due to its biological relevance.
• Recent advancements focus on novel pH-responsive LMWG categories.

Purpose of the Study:

• To review recent progress in three underexplored categories of pH-responsive LMWGs.
• To highlight N-oxide-type hydrogelators, phenylboronic acid-based LMWGs, and orthogonal self-assembly systems.
• To provide perspectives on designing next-generation stimuli-responsive soft materials.

Main Methods:

• Literature review of N-oxide-type hydrogelators, focusing on amide amine oxide surfactants and pyridine-N-oxide frameworks.
• Analysis of recent advances in phenylboronic acid-based LMWGs, particularly 3-isobutoxyphenylboronic acid.
• Review of pH-responsive orthogonal self-assembly systems, including hybrid hydrogels and multicomponent systems.

Main Results:

• N-oxide LMWGs demonstrate pH and temperature responsiveness through modulated hydrogen bonding.
• Phenylboronic acid-based LMWGs show gelation driven by hydrogen bonding, with pH triggering disruption.
• Orthogonal self-assembly systems showcase controlled drug release and self-sorting capabilities.

Conclusions:

• Emerging pH-responsive LMWGs offer significant potential for stimuli-responsive soft materials.
• N-oxide, phenylboronic acid, and orthogonal systems represent key areas of advancement.
• Further research is needed to overcome limitations and fully exploit these materials.