Metal-organic frameworks (MOFs) are porous materials connected by metal ions or metal ion clusters and organic ligands through coordination bonds. They have a stable structure, high specific surface area, and very regular and adjustable pore structure. In the past 30 years, the development of MOF materials has been amazing. Their applications in chemical, pharmaceutical, energy, biological and electronic fields have shown tremendous growth and have shown excellent development prospects. Since the 1990s, rapid progress has been made in the synthesis, application and characterization of MOF materials, which has driven the exploration of fields related to this material. At present, the research on MOF materials is still in a hot stage, and more properties are still being discovered. According to the theory of coordination chemistry, metal-organic framework compounds are composed of lone pairs of electrons provided by organic ligands and empty orbitals provided by metal ions to form one-dimensional, two-dimensional or three-dimensional coordination polymer structures. The empty orbitals provided by metal ions and the number of teeth provided by organic ligands jointly determine the structural composition of this type of coordination polymer. Due to the wide variety of metal ions and organic ligands and their different coordination forms, the number of MOF materials reported in the Cambridge Structural Database in 2020 has reached tens of thousands, and there are great differences in performance between them. Therefore, MOF materials have attracted widespread attention in a short period of time and have become one of the new materials with the most application potential. Since MOFs have adjustable porosity, controllable particle size and structure, and surface modification, they have become one of the hottest materials in the field of biomaterials, and drug delivery systems based on MOFs also have great development potential.

Figure 1. Synthesis and crystal structure of KAUST-7 and KAUST-8. (Tchalala MR, et al.; 2019)

MOFs have advantages that traditional nanomaterials such as liposomes, polymers, and quantum dots do not have. Drug delivery systems based on MOFs have made significant progress in the past decade: the huge specific surface area has significantly increased the drug loading capacity of MOFs; through selection Appropriate organic ligands and metal ions can change the porosity and composition of MOFs; surface modification gives MOFs more functional properties; since coordination bonds are weak interactions, MOFs are easily degraded in biological matrices and have high biodegradability and biocompatibility.

KAUST-7 (NbOFFIVE-1-Ni) is an ultra-microporous MOF material whose chemical name is Cr-MIL-101-SO₃H. KAUST-7 was reported in Science by scientists at King Abdullah University of Science and Technology. KAUST-7 is composed of Ni²⁺ and pyrazine coordinated to form a square grid layer, and then the (NbOF₅)^2- inorganic pillar center supports the interlayer to form a three-dimensional structure. The flexible pore size is 3.0-4.8 Å. KAUST-7 has good high-temperature stability and chemical stability. It only undergoes structural decomposition when heated above 300°C. It maintains structural stability under 5%-95% humidity, and its adsorption is still guaranteed after being soaked in water for 6 months. As a unique MOF material, KAUST-7 can serve as a drug carrier. Similar to other MOFs materials, KAUST-7 also has a large specific surface area and pore size. This structure can effectively adsorb and encapsulate drug molecules. As a drug carrier, KAUST-7 has the ability to load large doses of drug molecules, adjustable drug release, and better stability and biocompatibility.

Alternate Names:
NbOFFIVE-1-Ni

References:
1. Tchalala MR, et al.; Fluorinated MOF platform for selective removal and sensing of SO2 from flue gas and air. Nat Commun. 2019, 10(1):1328.

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