Topoisomer

Topoisomers or topological isomers are molecules with the same chemical formula and stereochemical bond connectivities but different topologies. Examples of molecules for which there exist topoisomers include DNA, which can form knots, and catenanes. DNA topoisomers can be interchanged by enzymes called topoisomerases.

Also see

 * Mechanically-interlocked molecular architectures
 * Catenane
 * Rotaxanes
 * Molecular knot
 * Molecular Borromean rings