Nonkovalent

Nonkovalent interactions, more commonly written noncovalent or non-covalent, are intermolecular forces that do not involve the sharing or transfer of electrons to form covalent bonds. They govern the association, recognition, and assembly of molecules under normal conditions and are central to chemistry, biology, and materials science.

The main families include hydrogen bonds, electrostatic or ionic interactions, van der Waals forces (including London dispersion), dipole-dipole and dipole-induced dipole interactions, hydrophobic effects, and specific pi-related interactions such as pi-stacking and cation-π interactions. These forces vary in strength and directionality; hydrogen bonds and ionic interactions are relatively directional, while van der Waals forces are weaker per contact but can be cumulative.

Compared with covalent bonds, noncovalent interactions are weaker on a per-contact basis, typically ranging from a few kilojoules per mole to a few tens of kilojoules per mole. However, collectively they can yield substantial stabilization in complexes and assemblies. Their strength and specificity depend on the environment; solvent, temperature, and ionic strength can modulate them. In water, electrostatic contacts may be screened, while hydrophobic effects can drive assembly.

In biological systems, noncovalent interactions underlie DNA base pairing, protein folding, and receptor–ligand recognition, enabling reversible binding essential for signaling and metabolism. In chemistry and materials science, they drive self-assembly, supramolecular architectures, catalysis, and the design of drugs and nanomaterials.

Techniques such as X-ray crystallography, NMR spectroscopy, calorimetry, and computational modeling are used to study noncovalent interactions, supporting understanding of molecular recognition, allostery, and the behavior of complex macromolecules.