Fine Tuning of Tyrosine-Derived Amphiphilic and Bolaamphiphilic Gelators for the Formation of pH-Responsive Supramolecular Gels

Low-molecular-weight gelators (LMWGs) are small organic
molecules
that self-assemble through noncovalent interactions into fibrous networks
capable of immobilizing solvents to create supramolecular gels that
can be used in biomedical applications and other fields. Unlike robust
polymeric gels, LMWGs offer tunability, stimuli-responsiveness, and
easy degradation. Designing effective LMWGs requires a delicate balance
of their weak, noncovalent interactions to form fibers instead of
crystals. We investigated the critical molecular features required
for the formation of a stimuli-responsive supramolecular gel derived
from O-benzyl tyrosine. The amino moiety of the amino
acid was coupled with six different fatty acids, yielding a series
of compounds. Our screening revealed that Adi-[Tyr(Bn)]2 and Aze-[Tyr(Bn)]2 emerged as successful gelators, forming
robust and responsive gels, while the other homologues formed less
stable gels or precipitates, often yielding crystalline materials.
The viscoelastic and self-assembly properties of the gels were comprehensively
analyzed by rheology, electronic circular dichroism (ECD), and scanning
electron microscopy (SEM), while single-crystal x-ray diffraction
(SC-XRD) was used to confirm and elucidate their structural features.
Interestingly, the ECD profile of Aze-[Tyr(Bn)]2 was reminiscent
of collagen-mimetic assemblies, which are of interest for applications
in tissue engineering and the design of biomaterials.