A sweet crystal structure


What is it?

glucose molecule

You’ve probably heard quite a number of scientific names for sugar?  For instance sucrose which makes up the sugar cubes we see on our table, and lactose which is found in milk.  But arguably glucose may be the most important. Glucose is a ‘monosaccharide’ and as such one of the three building blocks of all edible sugars, along with fructose and galactose.  

Both lactose and sucrose are actually made up of two sugars molecules attached together. For instance sucrose is made from a glucose and fructose ring. During digestion we break down these molecule into their simpler parts, like glucose, which gets absorbed into our blood. There it is used by our bodies proteins such as the glucose transport protein.   

Where did the structure come from?

Glucose is a great example of a molecular structure.  When crystallography was first established as a technique it was very unclear how useful it would be for molecular materials. These are often complicated molecules, made of light elements like carbon, hydrogen and oxygen, that do not scatter very well from x-rays.  

But in 1929 Kathleen Lonsdale, a scientist working in London, answered a very long standing problem with x-ray diffraction.  Up to that point there had been lots of debate about the weather a fundamental arrangement of 6 carbon atoms (known as a benzene ring) would be bent or not. It sounds very simple now, but it was a puzzle to the greatest minds of the day, great scientists like W.L. Bragg and Pauling pondered this.

Working with hexachlorobenzene (which formed crystals at room temperature, unlike pure benzene which melts at 5°C) Kathleen Lonsdale used x-ray diffraction to show the benzene molecule was flat.

benzene molecule

Along with showing how this fundamental part of organic chemistry, the benzene ring, was put together, Lonsdale also paved the way for the field of molecular crystallography. This is now a huge field of study, answering questions from how drugs interact with the cells of our body to how we could capture carbon dioxide from the atmosphere.


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