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.