The very interesting web of connections

The Royal Institution has made a rather lovely film about William and Lawrence Bragg, the father and son Nobel laureates who came up the method of structural analysis by X-ray crystallography around 100 years ago. The film is constructed around an interview with Lawrence Bragg’s daughter Patience, a delightful lady who has very fond memories of her father and some wonderful stories about him.

I’m in there too, talking about the nuts and bolts of crystallography. You will see that I am sitting beside a model of lysozyme, one of the first protein molecules to be analysed by crystallography, a feat performed under the watchful eye of Lawrence Bragg at the Royal Institution in the latter years of his life. It’s nice to be sharing the screen with Patience, who has such a deep personal connection to the founders of my field. Unfortunately Patience and I didn’t have any scenes together but I was very glad to meet her and make a connection when she attended my lecture on crystallography at the RI last month.

It is odd to think that I would never have been involved in that film or given that lecture if I hadn’t started blogging about science just over five years ago. Through blogging I have made many interesting and unexpected connections with people and ideas. Meeting Lawrence Bragg’s daughter in October was just the latest in a long line.

Patience ThomsonPatience. Still from the RI film.

Until this week, that is, because another fascinating connection has snapped together on Tuesday with the publication of a paper on a new method in crystallography. I’ve already written about this paper and was keen to do so because it reports such a clever technical development, but I have realised that my account missed a trick.

Standard X-ray crystallography, as pioneered by the Braggs, relies on the ability of crystals to scatter or diffract X-rays. Diffraction is a quintessentially wave phenomenon; as a beam of X-rays passes through the crystal, every atom within is stimulated to radiate waves of X-rays in all directions. But re-radiated X-ray waves only emerge from the crystals in very distinct directions, giving rise to a pattern of diffraction spots that can be interpreted to figure out the molecular structure within the crystal. The spotted form of diffraction is due to the particular ways that the waves of X-rays radiated from each atom in the structure interfere — or add up — with one another as their crests and troughs criss-cross through space and time.

The new paper by Gonen and colleagues uses beams of electrons instead of X-rays to do crystallography, which at first sight seems an odd switch to make since electrons are particles, not waves. Their particulate nature was shown by their discoverer, JJ Thomson, an achievement for which he was awarded the Nobel prize for physics in 1906. But in a nice twist of family history, Thomson’s son George subsequently found that beams of electrons can also behave as waves and showed this elegantly by passing a beam of electrons through gold crystals (in gold foil) and recording the diffraction pattern. This was one of the powerful demonstrations of wave-particle duality that is at the heart of quantum mechanics. In his turn, George was awarded the Nobel prize for physics in 1937.

The marriage of the work of the Thomsons and the Braggs comes to new fruition in the work reported this week which has shown that electron diffraction can be now also be used to determine the structures of protein molecules from the tiniest of crystals. Rather nicely, Gonen’s team determined the structure of lysozyme again to show off the power of the method. I am sure that this new result will delight Bragg’s daughter, Patience; doubly so because she is married to David, the son of George Thomson.


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