2012: Advent Chemistry: Penicillin

by on December 13, 2012

We’re halfway through the month, and today is the day for looking at medical breakthoughs. There’s no actual reason for this, it just seems like a good idea.

This is penicillin:

The structure of penicillin, including the letter 'R' instead of an atom at one end.

Penicillin is, famously, produced by some kinds of mould as a form of self-protection, weeding out the competition. It’s a fantastic antibiotic. It kills the germs so that they can’t kill you, which is really rather handy. It was discovered by Alexander Fleming. It may also have been discovered by some other people, but they didn’t make it into the patent books.

Penicillin is a major part of the comfortable Western lifestyle I enjoy. I’m actually allergic to it, which isn’t all that uncommon, but penicillin was the first antibiotic manufactured in enough quantity to be available to everyone. It gave people hope, because they knew that antibiotics of that quality could and did exist and actually worked and saved lots of lives, so other antibiotics were invented, based upon the penicillin structure. In my life, it’s antibiotic-resistant bacteria that are frightening. A century ago, bacteria didn’t need to be resistant because there were no medicines to kill them.

Once again, the diagram needs a little explanation. Most people reading this are probably not particularly familiar with the more obscure elements and their symbols, so you’ll just have to trust me when I say that ‘R’ is not an element symbol. There is no ‘R’ in the Periodic Table. H is hydrogen and C is carbon and W is tungsten (blame the Germans) but R isn’t an element.

‘R’ is a catch-all symbol used in organic chemistry (which is the part of chemistry penicillin belongs to) to mean “Some kind of organic group”. Organic chemistry deals with all the molecules that are built from carbon skeletons and covalent bonds. R can be a huge number of things and is used for two purposes.

1. “I can’t be bothered to draw the rest of this molecule out because it isn’t relevant to what I’m talking about.”

2. “You can attach a variety of things to this point in the molecule and what I’m talking about will still apply.”

The ‘R’ in penicillin is used in sense 2. The active part of penicillin, the bit that kills bacteria, is shown. The other part can be a variety of things. I don’t know exactly which things will work and which won’t, but that R tells me that penicillin isn’t a specific molecule. It’s a class, a kind of molecule, and all penicillins possess that backbone shown above.

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