“Chemical structure” is a phrase that is not often heard unless one is in a chemistry class. Yet, it is the specific arrangement of atoms in a molecule, its “structure,” that governs its properties. Most people have heard of benzene, a natural constituent of crude oil and a known carcinogen. (Benzine, a mixture of hydrocarbon molecules like gasoline is a different substance). Benzene has six carbon atoms bound in a hexagonal arrangement, each linked to a hydrogen atom. It is like a hexagonal plate with spikes. Benzene is a liquid, but insert one oxygen atom in between one of the carbons and the hydrogen and you create phenol, a completely different molecule. Phenol is a solid, has disinfectant properties and is a present as an odour component (30 ppm) in a certain scotch whiskey. In the late 1800s, it was used in dilute form in the operating room and eventually led to germ-free techniques during surgery. Sadly, it was used by the Nazis in World War II as an extermination agent when injected in gram quantities.
The point here is that simply adding one atom of oxygen to benzene in a specific location in the molecule, dramatically alters its physical and biological properties. The pharmaceutical industry endlessly produces drug candidates by carefully changing the chemical structure of compounds that have potential medical properties. Changing the length of a carbon atom chain is one kind of subtle alteration that leads to altered physical and biological properties.
The giant molecule of hemoglobin, transporter of oxygen in the body, is made of several thousand atoms in a very specific arrangement. A small change in one corner of this molecule, the elimination of a couple of carbon atoms and an oxygen, signals a genetic blood disorder called sickle cell anemia. This subtle change causes the blood cell containing the altered hemoglobin to stick to a neighbor, impairing blood flow. It is amazing that such a devastating disease can be caused by a small change in chemical structure, caused in turn by a mutation in the hemoglobin gene.
So when you hear a discussion where the phrase “chemical structure” crops up, it is likely to be concerned with an important topic, not just with some esoteric phenomenon. Indeed, our very lives depend on the exact ways in which atoms are joined together.
By Dr. David Harpp
McGill University