Receptors are proteins that bind small ligands. Nuclear receptors are multifunctional proteins that transduce signals of their cognate ligands. Complexes with multiple bidentate ligands have geometric isomers. Xanthates bind to transition metal cations as bidentate ligands. Transmembrane receptors are activated by chemicals called ligands. Metallointercalators are complexes of a metal cation with polycyclic aromatic ligands. All of the metabolites of domperidone are inactive as D receptor ligands. The tartrate tetraanions serve as bidentate alkoxide ligands. RyRs form docking platforms for a multitude of proteins and small molecule ligands. Gallium(I) forms complexes with arene ligands such as hexamethylbenzene. Metal complexes containing only nitrosyl ligands are called isoleptic nitrosyls. Complexes of polydentate ligands are called "chelate" complexes. Chiral Schiff bases were one of the first ligands used for asymmetric catalysis. Some of the carbonyl ligands are highly labile. They have some of the characteristics of true steroids as receptor ligands.