Molecular binding is an attractive interaction between two molecule

Molecule

A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

s which results in a stable association in which the molecules are in close proximity to each other. The result of molecular binding is formation of a molecular complex.

Types

Molecular binding can be classified into the following types:

• non-covalent
  Noncovalent bonding
  A noncovalent bond is a type of chemical bond, typically between macromolecules, that does not involve the sharing of pairs of electrons, but rather involves more dispersed variations of electromagnetic interactions. The noncovalent bond is the dominant type of bond between supermolecules in...
  
   – no chemical bonds are formed between the two interacting molecules hence the association is fully reversible
• reversible covalent
  Covalent bond
  A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
  
   – a chemical bond is formed, however the free energy
  Gibbs free energy
  In thermodynamics, the Gibbs free energy is a thermodynamic potential that measures the "useful" or process-initiating work obtainable from a thermodynamic system at a constant temperature and pressure...
  
   difference separating the non-bonded reactants from bonded product is near equilibrium
  Chemical equilibrium
  In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...
  
   and the activation barrier
  Activation energy
  In chemistry, activation energy is a term introduced in 1889 by the Swedish scientist Svante Arrhenius that is defined as the energy that must be overcome in order for a chemical reaction to occur. Activation energy may also be defined as the minimum energy required to start a chemical reaction...
  
   is relatively low such that the reverse reaction which cleaves the chemical bond easily occurs
• irreversible covalent – a chemical bond is formed in which the product is thermodynamically
  Thermodynamics
  Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
  
   much more stable than the reactants such that the reverse reaction does not take place.

Examples

Molecules that can participate in molecular binding include proteins, nucleic acids, carbohydrates, lipids, and small organic molecules such as drugs

DRUGS

Destroy Rebuild Until God Shows are an American post-hardcore band formed in 2010. They released their debut self-titled album on February 22, 2011.- Formation :...

. Hence the types of complexes that form as a result of molecular binding include:

• protein – protein
• protein – DNA
  DNA
  Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
  
  
• protein – hormone
  Hormone
  A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
  
  
• protein – drug

Proteins that form stable complexes with other molecules are often referred to as receptors

Receptor (biochemistry)

In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...

 while their binding partners are called ligand

Ligand (biochemistry)

In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In a narrower sense, it is a signal triggering molecule, binding to a site on a target protein.The binding occurs by intermolecular forces, such as ionic bonds, hydrogen...

s.