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Noncovalent bonding refers to a variety of interactions, that are not covalent in nature, between molecules or parts of molecules that provide force to hold the molecules or parts of molecules together usually in a specific orientation or conformation. These non-covalent interactions include: ionic bonds, hydrophobic interactions, hydrogen bonds, Van der Waals forces (aka London dispersion forces), Dipole-dipole bonds.
"Noncovalent bonding", "Noncovalent interactions" and "Noncovalent forces" all refer to these forces as a whole without specifying or distinguishing which specific forces are involved because noncovalent interactions often involve several of these forces working in concert. Noncovalent bonds are weak by nature and must therefore work together to have a significant effect. In addition, the combined bond strength is greater than the sum of the individual bonds. This is because the free energy of multiple bonds between two molecules is greater than the sum of the enthalpies of each bond due to entropic effects.
Examples
Protein Structure
Main article: Protein structureIntramolecular noncolvalent interactions are largely responsible for the secondary and tertiary structure of proteins and therefore the protein's function in the mechanisms of life. Intermolecular noncovalent interactions are responsible for protein complexes (quaternary structure) where two or more proteins function in a coherent mechanism.
Pharmaceuticals
Most drugs work through interacting with biomolecules, such as proteins or RNA, noncovalently. Relatively few drugs actually form covalent bonds with the biomolecules they interact with. Instead they interfere with or activate some biological mechanism through noncovalently interacting in very specific locations on specific biomolecules which present the perfect combination of noncovalent binding partners in just the right geometry.See also
"Noncovalent bonding"