Cryptands are a type of molecular structure that can encapsulate other molecules or ions within their cavity. They are often composed of a three-dimensional arrangement of atoms, typically involving a central core surrounded by a network of linkers. This unique design allows cryptands to selectively bind specific guest molecules, making them useful in various applications, including drug delivery and sensing. The term "cryptand" is derived from the Greek word "kryptos," meaning hidden, reflecting their ability to hide or encapsulate guest species. These structures are part of a broader category known as supramolecular chemistry, which studies interactions between molecules that are not covalently bonded. Cryptands can be compared to crown ethers and spherands, which also serve to encapsulate ions and molecules.