Chiral Supramolecular Assemblies: Controllable Construction and Biological Activity

A Unique Temperature-Induced Reverse Supramolecular Chirality-Assisted Gel-to-Gel Transition

Supramolecular hydrogels typically undergo a gel-to-sol transition with heat, as intermolecular interactions within the gel weaken. Although gel-to-gel transitions during heating are rare, they may occur due to minor rearrangements caused by thermal forces in the supramolecular self-assembled structure. Here, an unprecedented temperature-induced gel-to-gel transition assisted by supramolecular chiral inversion in a hydrogel system is presented. The transition results from a left-handed M-type helix to a right-handed P-type helix, attributed to the π-system-conjugated amino acid, l-Tyrosine (Fm- l-Tyr). Upon solvent dilution, Fm-l-Tyr induces translucent hydrogel formed by entangled fibers with a kinetically stable left-handed M-type supramolecular helix. At 70 °C, hydrogel transforms into an opaque gel with a reverse supramolecular chirality yielding a thermodynamically stable right-handed P-type helix. Supramolecular chiral inversion is substantiated by two chiroptical methods. This unique gel-to-gel transition, accompanied by chiral inversion, is anticipated to attract attention, especially for applications sensitive to chirality.

Chiral nanomaterials in tissue engineering

Addressing significant medical challenges arising from tissue damage and organ failure, the field of tissue engineering has evolved to provide revolutionary approaches for regenerating functional tissues and organs. This involves employing various techniques, including the development and application of novel nanomaterials. Among them, chiral nanomaterials comprising non-superimposable nanostructures with their mirror images have recently emerged as innovative biomaterial candidates to guide tissue regeneration due to their unique characteristics. Chiral nanomaterials including chiral fibre supramolecular hydrogels, polymer-based chiral materials, self-assembling peptides, chiral-patterned surfaces, and the recently developed intrinsically chiroptical nanoparticles have demonstrated remarkable ability to regulate biological processes through routes such as enantioselective catalysis and enhanced antibacterial activity. Despite several recent reviews on chiral nanomaterials, limited attention has been given to the specific potential of these materials in facilitating tissue regeneration processes. Thus, this timely review aims to fill this gap by exploring the fundamental characteristics of chiral nanomaterials, including their chiroptical activities and analytical techniques. Also, the recent advancements in incorporating these materials in tissue engineering applications are highlighted. The review concludes by critically discussing the outlook of utilizing chiral nanomaterials in guiding future strategies for tissue engineering design.

Preparation and temperature-controlled morphology of helical microrods composed of supramolecular α-cyclodextrin assemblies

Significant efforts have been devoted so far to artificially fabricate supramolecular helical nano- and microstructures through the regulated assembly of biological and synthetic building blocks. However, the preparation of supramolecular helical structures with a regulated morphology remains challenging. Here, helical microrods composed of supramolecular α-cyclodextrin (α-CD) assemblies were fabricated by allowing an α-CD/1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)/2-pentanol mixture to stand at 30-60 °C under high humidity conditions. The morphology could be controlled by temperature to produce helical microrods with a regulated pitch and length. These helical rods can be applied as optical devices, chiral separation devices and asymmetric catalysts.