Supramolecules usually refer to organized aggregates formed by two or more molecules that are binding together by intermolecular interaction. Supramolecular host materials are a class of functional materials, which have clear microstructure and macroscopic properties. Common supramolecular host materials are DNA, crown ether, cyclodextrin, calixarene, calixpyrrole, calixcarbazole, cucurbituril, columnar aromatic hydrocarbons, etc.
Supramolecular host materials have a wide range of applications in surface chemistry, biomedicine, and environmental governance.
- Surface chemistry: The gourd vein is formed by polycondensation of glycyrrhizin and polyformaldehyde under acid catalysis, and it is a kind of cyclic compound formed by the gan vein through methylene-based bridge. Gourd glands can be fixed on the surface in different ways, either by non-covalent bonds or covalent bonds. The large number of shell bases of the gourd gland port makes the electron cloud density at the port very large, so the gourd gland can be fixed to the surface of the substrate with positive charges or metal ions through ion-dipole action. Fixing the gourd vein on the surface of the substrate can greatly improve the performance of the gourd gland and the substrate, making it have important application value in the field of surface chemistry.
- Biomedicine: Supramolecular hydrogel materials mainly refer to biological materials bound together by non-covalent interactions between small molecules. Supramolecular hydrogel materials form supermolecules with ordered structure through self-assembly of molecules, and are increasingly used in biomedicine. In addition to supramolecular hydrogels, cyclodextrin is also a supramolecular host material which plays an important role in biomedicine. Cyclodextrin is a cyclic oligomer composed of glucoside. Because the cyclodextrin contains a hydrophilic outer wall and a hydrophobic cavity, it can form a stable host-guest complex with the hydrophobic guest in water. The main driving force is the hydrophobic and van der Waals forces between the inner surface of the cyclodextrin and the hydrophobic site on the guest interaction. Cyclodextrin has been approved by the US Food and Drug Administration and is widely used in pharmaceutical preparations. Cyclodextrin molecules have good water solubility and exhibit excellent host-guest properties. In recent years, cyclodextrin has been widely used in biomedicine and other fields due to its good biocompatibility. Cyclodextrin-based host-guest recognition can be used as a link to construct a variety of supramolecular assemblies with rich stimuli responsiveness, which makes the controlled release of loaded drugs / prodrugs possible in tumors. In the fields of biomedicine such as surgery and tissue repair, there is an increasing demand for adhesives that have high viscosity in water and can be repeatedly pasted and torn off. People often use supramolecular materials extracted from organisms such as spiders and silkworms to prepare waterproof adhesives.
Figure 1. Supramolecular hydrogel
- Environmental treatment: Chitosan, as a typical biomass adsorption material, is an inexpensive and environmentally friendly supramolecular substance during the selection and preparation of adsorbent materials. Chitosan molecules contain a large number of amino groups and hydroxyl groups, which can adsorb pollutants in water bodies through ion exchange, complexation, electrostatic attraction, etc., thus attracting widespread attention in the field of dye wastewater and heavy metal wastewater treatment. Hyperbranched polymers with branched structure and easy grafting modification have higher surface area than conventional macromolecules. Supramolecular adsorbents prepared by combining chitosan and hyperbranched polymers can provide a larger active contact area, which is beneficial to introduce dye ions into the adsorption and binding sites of chitosan in a large capacity. Therefore, such supramolecular adsorbents have extremely high application value in the field of environmental governance.
Figure 2. Supramolecular adsorbent CCMD
- Other fields: In addition to the above fields, supramolecular host materials are also widely used in other fields. For example, in the field of daily life, the addition of many chemical preservatives poses a potential safety risk to the human body and is constantly restricted by regulations. Plant essential oil supramolecules have good biodegradability, high LD50 value and other characteristics, providing a strong guarantee for their safe use. Therefore, plant essential oil supramolecules are often used as preservatives in oral care cleaning products. In addition, supramolecular assemblies, such as MOF, have a uniform cavity structure, a large specific surface area, and good thermodynamic stability, so they are widely used in the field of organic catalysis.
Figure 3. Organic reactions catalyzed by supramolecular host material MOF
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