Monday, July 8, 2013

Doing chemistry on a gondola!? (Parting thoughts on #TellurideSciencestyle)

Practically every TSRC Workshop lecture starts with some quip about how the landscapes of the terrain inspires us to think about our science. In my case, the landscapes are reminiscent of the potential energy surface that governs a chemical reaction. Molecules, like people, look for the shortest path traversing the lowest point on the ridge between the reactant valley and the product valley. Sometimes, the path isn't traversable because there is still snow along it or some other obstacle blocks the way. Or maybe there's something along the path that can accelerate the journey (such as the gondola giving you a lift and sidestepping 1000 feet or so of the vertical rise). Both of these events also occur in chemistry (or biochemistry). You can have steric clashes with other parts of the reacting molecule or the solvent which slows the reaction down, and you can have catalysts (or enzymes) or solvent fluctuations that speed it up. 

More specifically, one of the current debates in chemical reaction rate theory concerns whether transition state theory is sufficiently accurate (or at least, correctable) to make it useful for quantitative description. This debate maps directly to the question of how to compute the rate of crossing from one  valley to another across a torturous mountain range. The mountaineers will likely spend a lot of time discussing whether there is a single col (and which one) affords the best passage. Similarly, chemists debate whether there is a single "transition state" which describes the reaction. Some, including me, argue that accessibility to the transitions state (or col) and the ease to move through it is equally important. That is, it's not just a single point which determines the passage, but also the shape of the surface around it. The debate doesn't stop here because we can start to kibitz about whether or not there exists a second (or more) transition state that is important to describe the passage between the valleys (of the reactants and products). Or perhaps there exist a gondola which takes you over them even faster? While this latter event doesn't actually occur in the chemical context unless you add additional (shuttling) molecules to the system, the analogies between Telluride's landscapes and the energy landscapes over which chemistry takes place are clearly richer than they may appear at first sight. Thus, while this is my last post on Telluride until my next trip there, it will most certainly continue to inspire me.

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