Loading of the Model Amino Acid Leucine in UiO-66 and UiO-66-NH2: Optimization of Metal-Organic Framework Carriers and Evaluation of Host-Guest Interactions

Two metal-organic frameworks (MOFs), UiO-66 and UiO-66-NH2, were considered as containers for bioactive chemicals. We provide a synthesis technique, which allowed the production of these materials suitable for biomedical applications. Both MOFs were characterized as single-phase porous materials composed of nanoparticles (30-65 nm) with a zeta-potential of more than 40 mV in water suspension. D,L-Leucine was applied as a model molecule, which allowed us to trace the mechanism of the loading process. We showed that after synthesis, amino groups of UiO-66-NH2 are coordinated with solvent residuals. It results in a similar route of leucine loading in UiO-66 and UiO-66-NH2 samples. Using joint data of thermogravimetric analysis and calorimetry, infrared spectroscopy, and nitrogen adsorption, we revealed that methyl groups of leucine molecules are responsible for bonding of an MOF matrix. We proposed the formation of bonds between CH3 groups and benzene rings of linkers via CH-pi interaction. We also assessed the toxicity of the synthesized MOFs toward HeLa cells at 50 mu g/mL after 24 h incubation and revealed no negative effects on the viability of the cells, prompting further biomedical research in the areas of small-molecule delivery and cell signaling and metabolism modulation.

Automated summary

The synthesis technique allowed for the production of bioactive chemical containers UiO-66 and UiO-66-NH2 suitable for biomedical applications. By using D,L-Leucine as a model molecule, the loading process was traced, showing the coordination between amino groups of UiO-66-NH2 and solvent residuals, resulting in a similar route of leucine loading in both samples. Bond formation between methyl groups of leucine molecules and an MOF matrix was proposed, indicating potential applications in small-molecule delivery and cell signaling and metabolism modulation.