Study of the morphology and orientation of mesostructured systems based on amino acids derivatives building blocks

JUAN MANUEL REY; FEDERICO MOVILLA; HUCK-IRIART, CRISTIÁN; , FLORENCIA DI SALVO

Campinas

Congreso; 29th RAU/Anual Users Meeting LNLS/CNPEM; 2019

lABORATORIO NACIONAL DE LUZ DE SINCROTRON

Recent studies show that small molecules based on amino acid derivatives are able to assemble into ordered superstructures, also called mesocrystals [1], when they are subjected to certain crystallisation conditions. The control over experimental parameters as pH, supersaturation level, ionic force and the use of additives, are some of the most popular approaches [2, 3] to obtain this new kind of material. Besides, due to its rich supramolecular chemistry, self-assembly strategies applied to some low-molecular weight building blocks can conduct to other kinds of solid materials, such as supramolecular gels. In this case, their properties can be modulated by variation of temperature or solvent, since these changes directly affect the strength of the non-covalent interactions within the gel network [4]. The development of a spanning network that can immobilize solvents or the self-assembly between the building blocks, are both governed by the presence of non-covalent interactions. Thus, there is a delicate balance for a low-weight molecule to behave as a gelator or, as a crystal building block.In the present work we analysed the physiochemical factors implied in the obtaining of different self-assembled structures such as gels and mesocrystals, in a new family of quiral small molecules based on the aryl amino acids L-Tyrosine and L-Phenylalanine. The resultant supramolecular structures and their physicochemical properties were studied by different spectroscopic techniques, X-ray diffraction (XRD), small angle X-ray scattering (SAXS), polarized light microscopy (PLM) and scanning electron microscopy (SEM). Moreover, we studied the preferential crystalline orientation within a single polycrystalline aggregate (mesocrystal) obtained under different synthesis conditions. These measurements were possible due to the advantages offered by the large area detector and the high-intensity collimated beam of the MX2 beamline at the LNLS. Diffraction patterns were collected under this experimental set up, which allowed the study of the characteristic systematic absences of the material. Powder-like diffractograms were obtained applying a radial integration of the data in the azimuthal angle using GSAS-II software. Based on the fact that, as mesocrystal orientation respect to beam is changed, systematic absences are also altered, we were able to study the structuration of the material along with their different morphologies. As expected, when a spherical-like mesocrystal was analysed, no systematic absences were observed. On the other hand, depending on the orientation of a rod-like aggregate, systematic absences were detected. These valuable results are a direct characterization of the hierarchy of the structuration of the material and together with the information derived from other techniques, allowed us to elucidate putative mechanisms of the self-assembly based on the crystallization conditions