The Name is Bond – Hydrogen Bond !

Well, what’s a hydrogen bond I hear you ask – who cares is probably what most people are secretly muttering under their breath. But yet again, it’s a fundamental chemical phenomenon that allows life on Earth as we know it – no hydrogen bonds, no liquid water, need I go on! Firstly let’s look at the definition and diagram of a hydrogen bond – a hydrogen bond is the electrostatic attraction between polar groups that occurs when a hydrogen (H) atom bound to a highly electronegative atom such as nitrogen (N), oxygen (O) or fluorine (F) experiences attraction to some other nearby highly electronegative atom.

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Nowadays it seems like an obvious phenomenon when we look at the higher than predicted boiling points for certain hydrides but the acceptance of their presence seems to have been a slow process for the chemical community. Initial investigations seem to have taken place in the Lewis (that’s G N Lewis who defined an acid as an electron pair acceptor) research group and first publication by Latimer and Rodebush dates back to 1920. Of interest it was believed that Lewis had tried to encourage the scientists in his team to take the section on this hydrogen bond out of the paper before publication. I found an excellent paper about the history of the acceptance of the term hydrogen bond which ran for over twenty years and have put the link below. By the end of the 1930’s Linus Pauling mentioned the hydrogen bond in his seminal book ‘The Nature of the Chemical Bond’ and so began the journey identifying hydrogen bonds as the important interactions that give us the three dimensional biological molecules that are the building blocks of life.

History of Hydrogen Bond
Proof that these bonds exist has been confirmed by crystallographic studies and it was Pauling who was at the forefront of this work. Crystallography uses x-rays to study the structure of molecules and how atoms are bonded together. In 1948 Pauling was studying the three dimensional structure of proteins and he identified hydrogen bonds as holding the polypeptide chains in an alpha helix. This discovery was considered the dawn of molecular biology and is thought to have contributed to Watson and Crick’s discovery of the structure of DNA.

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So where do we find hydrogen bonds? DNA, proteins, water, ethanol, polymers and the list goes on! And this week an entirely new class of hydrogen bond that forms between a boron–hydrogen group and the aromatic, π-electron system of a benzene ring has been reported. Interestingly this work has been completed by both theoretical and synthetic chemists and may have applications in boron based drugs. Recent publications show that we are still identifying the presence of traditional hydrogen bonds in molecule interactions and also discovering new types such as that just reported. The humble hydrogen bond is the glue that gives us Nature’s building blocks – it’s much more than just a chemical bond !

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