Getting the Drift
One of the things I’ve been looking forward to the most at The University of Melbourne is working on a brand new research project. The past few years I worked in the Agapie Group at Caltech in inorganic chemistry. I absolutely loved my project and learned more than I could have imagined. My hope was that while I am here I can jump into an entirely different kind of chemistry. And once again, I got exactly what I wished for. After reading 26 pages worth of project descriptions for the Research Project class I’m enrolled in, I picked my top four labs and submitted all my paperwork. I was assigned to work under Evan Bieske, whose research mainly focuses on using laser spectroscopy to investigate the properties of charged molecules, complexes, clusters, and nanoparticles in the gas phase. That means there’s lots of lasers in his lab, and no bubbling reactions or beakers or Erlenmeyer flasks full of the colorful and dangerous chemicals people usually associate with chemistry. Coming straight out that kind of lab, this was a really big and definitely exciting change. Here I am in my new lab next to the laser I’ll be working with.
My project is on Laser Induced Mobility Modification (LIMM) – a new form of ion spectroscopy. Let me break it down a bit. There’s something called Ion Mobility Spectrometry (IMS). The idea is that if you have an ion, it will drift across a voltage gradient (something negative flows toward a more positive area, or vice versa), so you have this channel down through ions are flowing. On top of that, you have a gas flowing in the direction opposite the ion flow. The gas will slow down the ions as it drifts through the path (like swimming against a current). How much the ions slow down depends on their size and shape (consider when jumping out of a plane, you’re gonna move much slower once your parachute opens) and also their electronic properties (my fellow chemists will kindly remember potential energy curves from Ch 21). You can compare the drift times of different ions, that is, the time it takes for the ions to get from one end of the voltage gradient to the other, and consider what that says about their shape.
Good? Okay. So that’s all been done before. And it’s a very well studied and understood technique. What we want to do is add a new twist to it by throwing a laser into the mix. You see, there’s certain kinds of molecules that photoisomerize, that is they change shape when you shine a certain light on them. Some good examples of these are the photoreceptor proteins in your eyes. You’ll probably know them as rods and cones. When these are hit by light, they absorb the energy and change shape. The new idea is that as these ions are moving down the drift channel, we can shine a laser on them, causing them to change shape, and that will cause them speed them up or down so we can measure their new drift time. Is that cool or what?
