makrotsükli

Macrocycle (makrotsükli in Estonian) is a large cyclic molecule in chemistry, typically containing 12 or more atoms in its ring. The cyclic structure often preorganizes functional groups, creating a defined cavity that can bind ions or small molecules. Macrocycles can be composed entirely of carbon or include heteroatoms such as oxygen, nitrogen, or sulfur. They are distinguished from smaller rings by ring size and the resulting conformational rigidity, which enhances selective binding and recognition.

Common families of macrocycles include crown ethers, which coordinate alkali and alkaline-earth metals; porphyrins and related macrocycles that host metals in biological systems; cyclodextrins, calixarenes, and cucurbiturils, which function as supramolecular hosts for guest molecules; and macrocyclic lactones and peptides that occur in natural products. The size and shape of the cavity, as well as the presence of pendant groups, determine binding selectivity and reactivity.

Synthesis and design of macrocycles often involve macrocyclization under dilute conditions or the use of templates that guide ring formation. Modern methods include ring-closing metathesis and macrolactamization, as well as templated cyclizations that improve yields. Computational and analytical tools assist in predicting cavity size and binding properties.

Applications of macrocycles span host–guest chemistry, catalysis, drug delivery and imaging, sensing, and materials science. Their ability to stabilize specific metal ions or small molecules and to recognize particular guests makes them central to supramolecular chemistry and related fields.