Macrocycles refer to a class of compounds that contain macrocyclic structures in their molecular structure. Macrocycles can be two-dimensional or three-dimensional. They exist in organisms and nature, but also can be artificially synthesized. Macrocycles that exist in nature include blood proteins, chlorophyll porphyrin rings, vitamin B12 porphyrin and so on.
Macrocycles have a wide range of applications in many fields such as analytical chemistry, biomedicine, organic catalysis, and adsorption separation due to their advantages such as special structure and rich variety.
- Analytical chemistry: The macrocycles produced by calixarene and its analogs have the advantages of adjustable cavities, variable conformations, and easy modification, and are known as "third-generation supramolecules". It can identify guest molecules with the help of non-covalent bonds such as hydrogen bonding, static electricity, molecular forces, and stacking, so it has a very wide range of roles in analytical chemistry. For example, calixpyrrole compounds are a special class of calixarene, which has the ability to recognize anions and neutral molecules. It can selectively bind to a given receptor and show specificity during the binding process. In the process of calixpyrrole recognition, it often causes changes in the electrical, optical properties and conformation of the system, and even chemical changes. In the field of analytical chemistry, calixpyrrole macrocyclic compounds are often used to identify anions such as F-, H2PO4- and Cl-.
Figure 1. Structural formula of calixpyrrole and its derivatives
- Organic catalysis: Macrocycles are mainly used as catalysts in the field of organic catalysis. For example, 1,3-diethynylbenzene and excess 4-iodobenzyl alcohol are used as reaction raw materials, and a four-step organic reaction is used to construct a urea bond-containing macrocyclic molecule 1. The macrocycle has a large cavity, the two urea groups inside the molecule are in an antiparallel state, and the distance reaches 18 Ǻ. In spite of the interaction of hydrogen bonds between urea groups, macrocyclic molecules can self-assemble to form cylindrical nanomolecular tubes. Using the macrocyclic molecule 1 as a catalyst, the bimolecular coumarin can undergo a photodimerization reaction under ultraviolet light conditions and obtain a highly selective trans product, and the reaction has a high yield.
Figure 2. Synthesis of macrocycle 1 containing biurea group
- Biomedicine: Photodynamic therapy (PDT) is a method that relies on oxygen and produces therapeutic effects through photosensitizer-mediated and light interaction. Porphyrin is an achiral macrocyclic conjugated system with 24 centers and 26 electrons. It is a photosensitizer with excellent properties. Nanoporous materials prepared with porphyrin and silica have high photosensitizer loading rate, low cytotoxicity, excellent targeting, high singlet oxygen yield and efficient photodynamic efficiency after folic acid modification. The material can be used for targeted kinetic therapy of HeLa cells, thereby exerting its application in clinical therapy. Tetraimine Schiff base-type macrocycles, especially heterocyclic-containing Schiff base-type macrocycles have biological activities such as anti-cancer, anti-virus, and sterilization, and can be used as pharmaceutical ingredients.
- Adsorption separation: With the advancement of science and technology, dyes are widely used in manufacturing industries such as printing, leather, textiles and cosmetics. However, it cannot be ignored that with the extensive use of dyes in various fields, the ecological environment and human health have been greatly threatened. Among many dye treatment technologies, the adsorption method shows unique advantages in the treatment of difficult-to-degrade dyes. The choice of adsorbent in the adsorption method is particularly important. Since the macrocycle has the advantages of being easy to modify and easy to contain, it has great application prospect in the adsorption and removal of dyes. For example, macrocycles such as crown ethers and cyclodextrins have been the mainstay of supramolecular chemistry research. Their large ring cavity can provide host-guest chemistry, and are often used as fuel adsorbents. Macrocycles are used as dye adsorbents, which can successfully achieve efficient and fast dye adsorption, and effectively promote the recycling of industrial wastewater. In addition, macrocycles have many applications in gas adsorption. For example, the γ-cyclodextrin metal organic framework with reactive hydroxyl groups can perform highly selective chemical adsorption of CO2 by reversible carbon fixation at room temperature and low pressure.
Figure 3. The first generation of macrocycles-crown ether
- Ariane Borges. (2019). "Biological applications of amide and amino acid containing synthetic macrocycles." Supramolecular Chemistry 20, 575-596.
- Abdelraheem Eman M M. (2018), "Macrocycles: MCR synthesis and applications in drug discovery.." Acta crystallographica 008, 11-17.
- Ermert Philipp;. (2017), "Design, Properties and Recent Application of Macrocycles in Medicinal Chemistry." Chimia 21, 678-702.