1920

Hydrogen Bonding

Worth Huff Rodebush (1887–1959), Wendell Mitchell Latimer (1893–1955), Maurice Loyal Huggins (1897–1981)

hydrogen bonds are the secret adhesive of the living world. They hold together the strands of DNA, help to determine the shapes of proteins, and occur in every kind of carbohydrate molecule. The active sites of receptors and enzymes, for example, almost invariably feature key hydrogen bonds in the protein’s own structure and with the substrate molecules that bind there.

American chemist Maurice Loyal Huggins was the first to suggest the concept of hydrogen bonds, and his work inspired his colleagues Wendell Mitchell Latimer and Worth Huff Rodebush to publish a 1920 paper that used hydrogen bonds to explain properties of certain liquids. Almost one hundred years of work since then have still not revealed all their secrets, though.

So what’s a hydrogen bond? That’s not such an easy question to answer. Even the best minds (such as American chemist Linus Pauling) have found plenty to occupy them here. Hydrogen bonding is partly just the attraction between a positively charged hydrogen atom and a negatively charged atom, such as nitrogen or oxygen, on a nearby molecule. These don’t have to be full charges. Oxygen and nitrogen atoms usually have extra electron density, making them clumps of partial negative charge. But this isn’t just an ionic bond, because hydrogen bonds are directional—if they’re not pointed in the right way, the attraction mostly disappears. It’s like a ghostly form of a standard single bond, and it’s strongest when the hydrogen itself is attached to an electron-rich atom like oxygen as well. Such oxygen-hydrogen and nitrogen-hydrogen compounds are found over a huge range of chemistry, and they’re especially crucial in the behavior of many biomolecules.

Water is the best example, with two hydrogen atoms attached to a single oxygen. Water molecules are very good hydrogen bond donors and acceptors at the same time, which is what makes it such a weird substance. It has a much higher boiling point than such a tiny molecule should, and it freezes into a hydrogen-bonded crystal lattice that’s actually less dense than the liquid. (Most liquids don’t have ice that floats.)

SEE ALSO Hydrogen Sulfide (1700), Hydrogen (1766), The Nature of the Chemical Bond (1939), Alpha-Helix and Beta-Sheet (1951), DNA’s Structure (1953), Polywater (1966), Computational Chemistry (1970), Polymerase Chain Reaction (1983), Recrystallization and Polymorphs (1998)

Hydrogen bonding is essential to the properties of water, which are essential to life on Earth.