Crystalline Curcumin bioMOF Obtained by Precipitation in Supercritical CO₂ and Structural Determination by Electron Diffraction Tomography

This article analyzes the use of supercritical CO₂ green technology in the reactive crystallization processes involved in the formation of a bioMOF that contains curcumin and Zn^II metal centers. A new phase with a [Zn­(curcumin)]_n composition, termed sc-CCMOF-1, is presented. The developed scCO₂ protocol allows high yields of the small-sized crystalline material, which was characterized by the use of the recently developed electron diffraction tomography method applied to the resolution of submicrometric crystals. A remarkable 3D macrostructure with a complex morphology was obtained. To analyze the crystallization mechanism, multiple identical runs were performed under similar experimental conditions to study in each time period the crystal growth progress ex situ by X-ray diffraction and scanning electron microscopy. These experiments indicated that the process to achieve the sc-CCMOF-1 in a crystalline form involves the formation of amorphous or semicrystalline metastable phases that derived into hierarchical stable and crystalline nanoflower aggregates. In addition, a potential therapeutic application of the bioMOF has been tested by studying the released of the curcumin molecule at neutral pH.