Ligand

In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from covalent to ionic. Furthermore, the metal-ligand bond order can range from one to three. Ligands are viewed as Lewis bases, although rare cases are known to involve Lewis acidic "ligand."

Metals and metalloids are bound to ligands in virtually all circumstances, although gaseous "naked" metal ions can be generated in high vacuum. Ligands in a complex dictate the reactivity of the central atom, including ligand substitution rates, the reactivity of the ligands themselves, and redox. Ligand selection is a critical consideration in many practical areas, including bioinorganic and medicinal chemistry, homogeneous catalysis, and environmental chemistry.

Ligands are classified in many ways, including: charge, size (bulk), the identity of the coordinating atom(s), and the number of electrons donated to the metal (denticity or hapticity). The size of a ligand is indicated by its cone angle.

Ligand (disambiguation)

Ligand may refer to:

Ligand (biochemistry)

In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In protein-ligand binding, the ligand is usually a signal-triggering molecule binding to a site on a target protein. The binding typically results in a change of conformation of the target protein. In DNA-ligand binding studies, the ligand can be a small molecule, ion, or protein which binds to the DNA double helix.

The binding occurs by intermolecular forces, such as ionic bonds, hydrogen bonds and van der Waals forces. The association of docking is usually reversible through dissociation. Measurable irreversible covalent bonding between a ligand and target molecule is rare in biological systems. In contrast to the definition of ligand in metalorganic and inorganic chemistry, it is ambiguous whether the ligand typically binds at a metal site, as is the case in hemoglobin.

Ligand binding to a receptor (receptor protein) alters the chemical conformation (three-dimensional shape). The conformational state of a receptor protein determines the functional state. Ligands include substrates, inhibitors, activators, and neurotransmitters. The tendency or strength of binding is called affinity. Binding affinity is determined not only by host-guest interactions, but also by solvent effects that can play a dominant steric role in driving non-covalent binding in solution.