Eun-Young Choi

Free radicals produced during metabolism induce effects, such as cell damage and cancer, because of their high reactivity. Although antioxidants in food products can eliminate free radicals, they are expelled within a relatively short period of time after serving their function. In this study, we investigated the possibility of using metal-organic frameworks (MOFs) with antioxidants as their ligands. Metal-organic frameworks are crystalline polymers with repetitively coordinated ligands and metal centers. We assume that once antioxidant-based MOFs are ingested, ligands are released on a long-term basis during the process of chemical and physical disintegration. To evaluate their eligibility, we established criteria for biocompatibility, particle size, and long-term antioxidant effects. For biocompatibility, we treated cells with various concentrations of MOFs and their precursors followed by a water-soluble tetrazolium 8 (WST-8) assay. The particle size distribution was analyzed using TEM and ImageJ software, and the antioxidant release was quantified using UV-vis spectroscopy. We concluded that Fe-based FeTHQ with the antioxidant tetrahydroxy-1,4-benzoquinone (THQ) as its ligand is the most effective long-term antioxidant with its effect lasting up to 7 days. Furthermore, microwave synthesis of FeTHQ was conducted to produce more suitable particles for in vivo antioxidant applications.

Enhancing the stability and durability of metal-organic frameworks (MOFs) is vital for practical applications because many promising MOF materials suffer from phase transitions and/or structural decompositions with humidity being a particularly damaging condition. In mechanical engineering, the frame of buildings and furniture can be stabilized significantly by installing a truss beam. Employing the same principle, we functionalized the organic component of MOF-5 to contain a carbazole moiety that can act as a molecular truss beam by reaching across the corner and forming a stable π–π interaction with a phenyl group on the edge position of the MOF-skeleton. This structural support enhanced the stability of the MOF substantially, allowing the designed MOF to maintain compositional integrity under steam conditions at 90 °C for ~5 days. The unmodified MOF-5 shows clear signs of structural collapse after ~1 h.

Ionothermal synthesis employs ionic liquids for synthesis of metal organic frameworks (MOFs) as solvent and template. The cations and anions of ionic liquids may be finely adjusted to produce a great variety of reaction environments and thus frameworks. Organisation of the structures synthesised from related ionic liquid combinations give rise to provocative chemical trends that may be used to predict future outcomes. Further analysis of their structures is possible by reducing the complex framework to its underlying topology, which by itself brings more precision to prediction. Through reduction, many seemingly different, but related classes of structures may be merged into larger groups and provide better understanding of the nanoscopic structures and synthesis conditions that gave rise to them. Ionothermal synthesis has promised to enable us to effectively plan the synthesis ahead for a given purpose. However, for its promise to be kept, several difficult limitations must be overcome, including the inseparable cations from the solvent that reside in the framework pore.

The framework of [RMI]₂[Co₂(BTC)₂(H₂O)₂] (RMI = 1-alkyl-3-methylimidazolium, alkyl; ethyl (EMI); propyl (PMI); butyl (BMI)), which has uniquely occurred in ionothermal reactions of metal salts and H₃BTC (1,3,5-benzenetricarboxylic acid), an organic ligand, reappeared in this work. Ionothermal reaction of cobalt acetate and H₃BTC with [BMI]Br ionic liquid as the reaction medium yielded the novel coordination polymer [BMI]₂[Co₂(BTC)₂(H₂O)₂] (compound B2). Similar ionothermal reactions with different [EMI]Br and [PMI]Br as the reaction media have been previously reported to produce [EMI]₂[Co₃(BTC)₂(OAc)₂] (compound A1) and [PMI]₂[Co₂(BTC)₂(H₂O)₂] (compound B1), respectively. In contrast with the trinuclear secondary building unit of A1, the framework structure of B1 and B2 consists of dinuclear secondary building units in common, but with subtle distinction posed by the different size of the incorporated cations. These structural differences amidst the frameworks showed interesting aspects, including guest and void volume, and were used to explain the chemical trend observed in the system. Moreover, the physicochemical properties of the newly synthesized compound have been briefly discussed.