I always like to check out a few sessions at ACS meetings that fall outside my usual beat. This time, I noticed a few interesting sounding sessions on ‘Visualizing chemistry’, so I went along to one this morning. It was fascinating stuff. A positive smorgasbord of imaging techniques awaited me, ranging from mass spectrometry (yes, you can use it to make pictures) to X-ray photoelectron spectromicroscopy. Oh, and there were lots of acronyms.
One thing I wasn’t aware of were how many techniques are available to work out the elemental distribution in a sample. For example, Richard Leapman gave a great talk about the use of STEM–EELS (Scanning transmission electron microscopy-electron energy loss spectroscopy) to generate three-dimensional images of cellular components. In this way, he has produced some great pictures of ribosomes that show exactly where the phosphorus can be found.
Completely different is the aforementioned X-ray photoelectron method. David Surman (he doesn’t have a personal web page, as he works in industry) described the latest imaging innovations in this technology, which produces elemental maps of surfaces. He described an example in which the method was used to study some medical-grade stainless steel samples (used for bone implants and so on), which were found to be prone to corrosion after laser ablation. He discovered that the laser-zapping led to a build-up of chromium at the edges of the ablated region. This build-up was the source of the corrosion problem.
But my favourite talk was from Martin Kessel, representing the High Resolution Electron Microscopy group at the National Cancer Institute, USA. They used 3D electron microscopy to image the ‘spikes’ that stud the surface of HIV. These spikes don’t form a regular pattern on the surface, which makes it difficult to get a reliable image using traditional electron microscopy. But by using a technique that generates an average image from thousands of pictures of individual spikes, a high-resolution structure has been produced. Crystal structures of parts of the proteins that make up the spikes have previously been obtained, and these dock beautifully into the microscope images, thus validating the crystal structures. Furthermore, the microscope has caught an image of the spike in complex with a CD4 receptor on a cell, revealing the changes in protein conformation that occur when HIV invades a luckless cell. It’s really great stuff, with fantastic pictures – Nature subscribers can read the paper itself at this link.
Great stuff, but sadly not terribly well attended, perhaps because the meeting room was tucked away in a obscure part of the building. It’s a real shame, because I’m sure that these talks would have been of great interest to many people.
Andrew Mitchinson (Senior Editor, Nature)