Hydrogen Bonds

The phenomenon of hydrogen bonding (H‐bonding) has been recognized for almost a century in chemistry and biochemistry to explain weak, directional, attractive forces between electronegative atoms or groups mediated by a hydrogen atom.

Hydrogen bonds have played an incredibly important role in the history of structural biology. Both the structure of DNA and of protein α-helices and β-sheets were predicted based largely on the hydrogen bonds these structures form.

It is a type of weak force that results in the formation of dipole-dipole interaction between a hydrogen atom and an electronegative atom that is strongly bonded to another electronegative atom. The bond or bonds are mostly strong in comparison to normal dipole-dipole and dispersion forces.

Hydrogen bonds are formed when an electronegative atom approaches a hydrogen atom bound to another electro-negative atom. The most common electro negative atoms in biochemical systems are oxygen (3.44) and nitrogen (3.04) while carbon (2.55) and hydrogen (2.22) are relatively electropositive (the electronegativity values are given on the Pauling scale, and don’t have a direct physical meaning).

Of all known chemical bonds and forces, only hydrogen bonds are able to mediate the directional interactions of lower energy that are needed for the operation of genetic and catalytic tasks. For this reason and because of the unique quantum properties of hydrogen bonding, the functional molecules involved in life processes are predicted to have extensive hydrogen-bonding capabilities. A molecular medium generating a hydrogen-bond network is probably essential to support the activity of the functional molecules.

The hydrogen bond plays the most significant role in determining the structure and properties of molecular systems of importance to chemistry and biology.
Hydrogen Bonds