Amine-Derivatized l -Phenylalanine and l -Tyrosine as Versatile Self-Assembled Platforms of Diverse Supramolecular Architectures: From Mesocrystals to Organogels

Abstract

Amino-acid-based systems have been specially investigated as potential functional biological or bioinspired materials. In this work, we show the remarkable ability of two small molecules based on the aryl amino acids l-tyrosine and l-phenylalanine to deliver different self-assembled structures, ranging from crystalline materials, such as single crystals and mesocrystals, to organogels. These compounds were obtained through the reaction of the amino acid with the aldehyde piperonal, resulting in not so explored derivatized systems, which conserve the carboxylic and secondary amine groups. The obtaining of each architecture is modulated by the environmental conditions, such as solvent, concentration, pH, temperature, and/or ionic strength, variables easy to control. We study the self-assembly process and features of the resultant materials using a combination of X-ray diffraction, density functional theory, small-angle X-ray scattering, and spectroscopic data. Both, in an organic solution or crystalline state, the self-assembly is governed by ionic intermolecular interactions assisted by H-bonds and, also, with the contribution of contacts involving the π-systems. As observed in related biological systems, we find that the OH function in the l-tyrosine moiety also exerts a tremendous impact over the supramolecular chemistry. In comparison with the free amino acids, the nonpolar moiety and additional short contacts provided by derivatization clearly offer new options and potential applications for more diverse environments. As a clear example, the gelation capability is tested in a crude oil sample, demonstrating a possible use in oil spill recovery.