Synthesis and potential applications of cyclodextrin-based metal-organic frameworks: a review

Abstract

Metal-organic frameworks are porous polymeric materials formed by linking metal ions with organic bridging ligands. Metal-organic frameworks are used as sensors, catalysts for organic transformations, biomass conversion, photovoltaics, electrochemical applications, gas storage and separation, and photocatalysis. Nonetheless, many actual metal-organic frameworks present limitations such as toxicity of preparation reagents and components, which make frameworks unusable for food and pharmaceutical applications. Here, we review the structure, synthesis and properties of cyclodextrin-based metal-organic frameworks that could be used in bioapplications. Synthetic methods include vapor diffusion, microwave-assisted, hydro/solvothermal, and ultrasound techniques. The vapor diffusion method can produce cyclodextrin-based metal-organic framework crystals with particle sizes ranging from 200 nm to 400 μm. Applications comprise food packaging, drug delivery, sensors, adsorbents, gas separation, and membranes. Cyclodextrin-based metal-organic frameworks showed loading efficacy of the bioactive compounds ranging from 3.29 to 97.80%.

Keywords: Cyclodextrin; Cyclodextrin-based metal–organic framework applications; Metal–organic frameworks; Synthesis methods.

Fig. 1

Potential applications of metal–organic frameworks. Metal–organic frameworks can be used in photovoltaic applications. Metal–organic frameworks can be used for electrochemical applications through energy storage and electrocatalysis. Metal–organic frameworks can be used to store and separate the gas. Metal–organic frameworks can be used in biomedical applications such as drug delivery, cancer treatment, and medical imaging. Metal–organic frameworks can be used as catalysis for organic transformations. MOFs refers to metal–organic frameworks. Kreno et al. ; Guo et al. ; Kaur et al. ; Li et al. ; Dhakshinamoorthy et al.

Fig. 2

The use of metal–organic frameworks in bioapplications faces some limitations, e.g., the high toxicity of synthetic components, the high toxicity of chemical reagents, and the unrecyclable preparation materials of metal–organic frameworks. In the most fundamental sense, metal–organic frameworks are porous polymeric materials formed by linking metal ions with organic bridging ligands. By constructing metal–organic frameworks from cyclodextrin and biocompatible metal ions, the limitations of metal–organic frameworks in bioapplications can be overcome. Methods for producing cyclodextrin-based metal–organic frameworks include vapor diffusion, microwave-assisted, hydro/solvothermal, and ultrasound-assisted. Food, anticritical, drug delivery, sensors, adsorbents, gas separation, and membranes are some of the applications for cyclodextrin-based metal–organic frameworks. MOFs refers to metal–organic frameworks, and CD-MOFs refers to cyclodextrin-based metal–organic frameworks

Fig. 3

(I) General structure of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin, (II) Tridimensional structure of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin with different sizes, (III) Digital structure of cyclodextrins, (IV) Digital representation of inclusion complex formation (Rajkumar et al. ; Crini 2014). Cyclodextrins have three types, including α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin. Cyclodextrin contains two faces, e.g., primary face and secondary face, two hydroxyl groups, a hydrophilic outer surface, and a hydrophobic cavity. Cyclodextrin has different sizes of hydrophobic inner cavities based on cyclodextrin type, including 0.57 nm for α-cyclodextrin, 0.78 nm for β-cyclodextrin, and 0.95 nm for γ-cyclodextrin. γ-cyclodextrin has a big hydrophobic inner cavity; thus, γ-cyclodextrin can encapsulate a high amount of bioactive agents. Cyclodextrins can be used as host–guest delivery systems

Fig. 4

Solubility of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin in water under different temperatures including 25, 45, and 60 °C (Poulson et al. 2022). Cyclodextrins can be dissolved in water. α-cyclodextrin can be dissolved in water by 12.8, 29.0, and 66.2 mg/100 mL at 25, 45, and 60 °C, respectively. β-cyclodextrin can be dissolved in water by 1.8, 4.5, and 9.1 mg/100 mL at 25, 45, and 60 °C, respectively. γ-cyclodextrin can be dissolved in water by 25.6, 58.5, and 129.2 mg/100 mL at 25, 45, and 60 °C, respectively. γ-cyclodextrin has a higher water solubility among the three cyclodextrin types. α-CD refers to α-cyclodextrin, β-CD refers to β-cyclodextrin, and γ-CD refers to γ-cyclodextrin

Fig. 5

(a) Basic structure of metal–organic frameworks and (b) the cubic structure of metal–organic framework-5. Metal–organic frameworks are produced via self-assembly of metal ions or clusters and organic linkers or struts. Metal–organic framework-5 contains zinc, oxygen, hydrogen, and carbon. Metal–organic framework-5 has a zinc-oxygen cage with a 7.16 Å diameter. Metal–organic framework-5 has a phenylene ring and carboxylate moiety. The diameter of metal–organic framework-5 is 25.85 Å

Fig. 6

(A) Crystal transformation of dense potassium acetate-γ-cyclodextrin-based metal–organic framework to porous potassium acetate-γ-cyclodextrin-based metal–organic framework (Ding et al. 2019), (B) The conformations of 18β-glycyrrhetinic acid@nano-γ-cyclodextrin-based metal–organic framework, and (C) Graph of pharmacodynamic graph of the treatment of pulmonary fibrosis by 18β-glycyrrhetinic acid (Liu et al. 2022). Copyright, 2022, Elsevier. CD-MOF refers to a cyclodextrin-based metal–organic framework, GA refers to 18β-glycyrrhetinic acid, CD refers to cyclodextrin, GA@nano-CD-MOF refers to 18β-glycyrrhetinic acid@nano-γ-cyclodextrin-based metal–organic framework

Fig. 7

Scanning electron microscopy images of the as-fabricated potassium cations-β-cyclodextrin-based metal–organic framework by acetone, acetonitrile, and methanol (Volkova et al. 2020) and scanning electron microscopy of the as-fabricated γ-cyclodextrin-based metal–organic framework with different methanol ratios (Liu et al. 2017a). Copyright, 2022, ACS

Fig. 8

Fabrication of cyclodextrin-based metal–organic framework@Ru(bpy)₃²⁺ nano-sensor for the cytokeratin 19 fragments antigen 21–1 detection. The process involves cyclodextrin-based metal–organic frameworks