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

Abstract

This article analyzes the use of supercritical CO 2 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 scCO 2 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.

Hierarchical Metal–Organic Frameworks with Macroporosity: Synthesis, Achievements, and Challenges

“…Compressed or supercritical carbon dioxide has been widely applied to a range of MOF processing steps including crystallisation [100][101][102], impregnation [103], dispersion [104], drying [105], and activation [106,107]. Formation of highly porous materials will generally benefit from the use of supercritical drying (typically scCO 2 ), with the low viscosity and high diffusivity of supercritical fluids being recognised as being especially vital for activation of large pores, to avoid pore collapse in MOFs during solvent removal [108].…”

Kinetics and Mechanisms of ZnO to ZIF‐8 Transformations in Supercritical CO2Revealed by In Situ X‐ray Diffraction

“…At the outset of this work, the use of scCO 2 in MOF processing has been mainly limited to postsynthetic activation where undesired molecular guest are cleansed from the framework . Possibly stemming from the low solubility of traditional MOF precursors, the synthesis of MOFs in scCO 2 has been challenging; successes include the synthesis of several low‐dimensional coordination polymers in pure scCO 2 , select MOFs in CO 2 ‐expanded solvents, and a novel bioMOF in a scCO 2 /EtOH mixture . The latter being characterized and imaged at different intervals over several reactions to gain insights into the growth of a 3D macrostructure.…”

Structure analysis of materials at the order–disorder borderline using three-dimensional electron diffraction

“…Still, it is the only technique able to deliver 3D structural data from single crystals or domains of few tens of nanometres. Nowadays, structure determination by 3D ED can be considered a standard option for inorganic compounds (Jiang et al, 2011;Samuha et al, 2014;Guo et al, 2015;Rozhdestvenskaya et al, 2017), and at least a reliable protocol for organic and metalorganic ones (Gorelik et al, 2012a;van Genderen et al, 2016;Wang et al, 2017;Gruene et al, 2018;Hynek et al, 2018;Jones et al, 2018;Portolé s-Gil et al, 2018;Yuan et al, 2018). ED has also been successfully applied to incommensurate materials (Palatinus et al, 2011;Steciuk et al, 2016), and to macromolecules (Shi et al, 2013;Yonekura et al, 2015;Clabbers et al, 2017;de la Cruz et al, 2017;Xu et al, 2018;Lanza et al, 2019) and other structures of biological relevance (Rodriguez et al, 2015;Zee et al, 2019).…”