Progress in host–guest macrocycle/pesticide research: Recognition, detection, release and application

Macrocyclic compounds are formed via a series of cyclic oligomers possessing repeating units, and classical examples include cyclodextrins, calix[n]arenes, cucurbit[n]urils and pillar[n]arenes (n represents the number of repeat units). Given their unique host–guest binding ability, macrocycles are often developed as hosts for specific guest molecular assembly systems, adsorption materials, drug delivery carriers, catalysts, and molecular recognition systems. For example, macrocyclic host molecules are widely used to encapsulate hydrophobic drug molecules to improve both the solubility and utilization efficiency of the drug. One type of potential host molecule that has seen increased agricultural use in recent years are pesticides. This includes herbicides, insecticides, and fungicides, and given the increased use, there is need to develop systems that can rapidly and effectively identify and detect such pesticides. In this review, we will discuss the use of cucurbit[n]urils, pillar[n]arenes, calix[n]arenes, cyclodextrins in this area, and their ability to form host–guest species with herbicides, insecticides and fungicides. Particular emphasis is given to the ability of such systems to improve the toxicity and release of the pesticide and the potential for practical application.