LiCN taking a dip in an Ar bath

We all know that it’s easier to move through air than water. Changing the environment to molasses means that you’ll move even slower. Thus it’s natural to think that the thicker (denser) the solvent (bath), the slower a particle will swim through it. More precisely, what matters is not the density but the degree to which the moving particle interacts with the solvent, and this can be described through the friction between the particle and the fluid. Chemical reactions have long known to be increasingly slower with increasing friction. The problem with this seemingly simple concept is that Kramers showed long ago that there exists a regime (when the surrounding fluid is very weakly interacting with the particle) in which the reactions actually speed up with increasing friction. This crazy regime arises because reactants need energy to surmount the barriers leading to products, and they are unable to get this energy from the solvent if their interaction is very weak. A small increase of this weak interaction facilitates the energy transfer, and voila the reaction rate increases. What Kramers didn’t find is a chemical reaction which actually exhibits this behavior, and the hunt for such a reaction has long been on…

A few years ago, my collaborators in Madrid and I found a reaction that seems to exhibit a rise and fall in chemical rates with increasing friction. (I wrote about one of my visits to my collaborators in Madrid in a previous post.) It involves the isomerization reaction from LiCN to CNLi where the lithium is initially bonded to the carbon, crosses a barrier and finally bonds to the nitrogen on the other side. We placed it inside an argon bath and used molecular dynamics to observe the rate. Our initial work fixed the CN bond length because that made the simulation much faster and we figured that the CN vibrational motion wouldn’t matter much. But the nagging concern that the CN motion might affect the results remained. So we went ahead and redid the calculations releasing the constraint on the CN motion. I’m happy to report that the rise and fall persisted. As such the LiCN isomerization reaction rate is fastest when the density of the Argon bath is neither too small nor too large, but rather when it is just right.

The article with my collaborators, Pablo Garcia Muller, Rosa Benito and Florentino Borondo was just published in the Journal of Chemical Physics 141, 074312 (2014), and may be found at this doi hyperlink. This work was funded by the NSF on the American side of the collaboration, by Ministry of Economy and Competiveness-Spain and ICMAT Severo Ochoa on the Spanish side, and by the EU’s Seventh Framework People Exchange programme.

Power of analogies in science

If you know how a basketball spins on each of its axes, then it turns out that you also know how a classical methane molecule spins. Such analogical pairings are useful because they allow you to better understand the less familiar of the pair through what you know of the other. The trouble, of course, is that analogies are often imperfect. Not every property is directly connected between the pair. So you have to be careful to assign which are mappable. For example, you certainly won't be able to play basketball with methane despite the analogy with respect to rotations.

Meanwhile, mapping a problem to one that is even more difficult to solve sounds like a bad idea. But if the more difficult problem solves itself them you just might win out after all. Toshiyuki Nakagaki and his colleagues at Hokkaido University did just this, twice. First, they showed that they could map simple mazes onto a board in which mold could grow. It turns out that after a while, the mold grows best along the shortest path between the ends. It would be very difficult to simulate the mold growth, and yet the analogy allows the mold to solve a complicated optimization problem for us. It turns out that you can replace the maze with a real problem related to finding the best possible train network connecting some number of cities over a selected terrain. Now the mold can be used to find the optimal rail network. For each of these two analogies, Toshiyuki Nakagakii received ig Nobel awards. I mention him, in particular, because I got a chance to meet him while I was in Japan. And now, I wonder if I might be able to map the solution of a chemical reaction pathway to his mold growths?!

In detail, the dates and prizes of the teams recognized by ig Nobels for mold growths mentioned above are:

2008 ig nobel in Cognitive science: Toshiyuki Nakagaki, Hiroyasu Yamada, Ryo Kobayashi, Atsushi Tero, Akio Ishiguro, and Ágota Tóth, for discovering that slime molds can solve puzzles.

2010 ig nobel in Transportation Planning: Toshiyuki Nakagaki, Atsushi Tero, Seiji Takagi, Tetsu Saigusa, Kentaro Ito, Kenji Yumiki, Ryo Kobayashi of Japan, and Dan Bebber, Mark Fricker of the UK, for using slime mold to determine the optimal routes for railroad tracks.

Traveling through Japan

Cars drive on the left side of the road, but power outlets are 110V (generally close enough to 120V for most U.S. products to work) using ungrounded (2-pin) North American plugs. Hotels generally don't have fitness rooms, and if they do, they are aimed at leisure travelers opening well after your business meeting will start. Hotel breakfasts are awesome, often including a mix of western and Japanese items (without missing any from either cuisine.) Only downside is that it makes you miss the fitness room even more. Traveling through Japan is relatively easy because most locations are labeled in latin script. Bus and rail ticket vending machines always offer an English option. Nevertheless, there are invariably surprises. The good news is that service providers really do want to help. Indeed, the level of politeness is like white noise. It feels wrong only when it's not there. Surprisingly, everyone takes it for granted, rarely acknowledging the bows and the various statements of "domo origami gozaimasu" offered multiple times any time you go near (let alone interact with) a service person. Whenever possible, just say "domo." It means please and/or thank you. Most importantly, it conveys an acknowledgment that you are ready to treat the person in front of you like a human being.

I was lucky to have local hosts to make many of the steps work without having to fumble through them. I suppose that part of traveling like a scientist is that you have scientific friends wherever you go. The other part of traveling like a scientist is that you use the scientific method in figuring out how to use some common appliance or in facing whatever obstacle you encounter. For example, when I was setting up the projector for my talk, I was faced with a remote control whose buttons were entirely in Japanese. There had to be a button that turned it on and another that would switch the mode to the VGA input. The former was easy: it was the big red button. The latter was trickier but limited to a few likely candidates based on pattern recognition with US remotes. A little trial-and-error and, voila, my presentation was ready to start. I guess I could have waited for my hosts to do this, but after all their kindness, I wanted to give them one less thing to do. We could then move sooner into the purpose of my visit: discussing our latest scientific results, and using them to enable each other's next scientific advance.

Emergence and Campai

I was asked to make the final remarks at the end of the banquet of the recent 14th RIES-Hokudai Symposium.* Quite an honor, but also a lot of pressure. One thing I've learned over the years is that humor rarely translates, and it's easy to accidentally offend in a foreign language. My only saving grace was that the expectations were low. The symposium theme is "mou" —meaning networks— and that presumably had to be weaved in too.  So what to say?

I started by saying "Minasan Konichiwa." That got a round of applause. Proof that the expectations really were low. But here's the kicker: I asked Professors Tsuda, Nakagaki and Ohta, in turn, to say "campai." Each did so but at a sound level that was barely audible. I then asked all three to say "campai." The volume of sound was not the sum of the three earlier statements which would have remained barely audible. Rather, it was loud enough for all to hear easily. This little experiment involving a social network with sound as the observable is indicative of a non-additive (nonlinear) emergent phenomenon. I did not tell my three participants that I planned to ask them to do this. So I really got lucky that the experiment worked as planned. In so doing, though, I was able to provide an example of emergent function arising from collective (network) behavior in a way that most of the audience was able to appreciate and toast to. It also served as a basis for the seminar I delivered the following day on the emergence of structure from Janus and striped particles. Campai!

*Check out my recent post on the 14th RIES-Hokudai Symposium here. RIES is the Research Institute for Electronic Science at Hokkaido University.

The chemistry within networks

On December 11 and 12, my friend, Tamiki Komatsuzaki, organized the 14th RIES-Hokudai Symposium in Sapporo, Japan. I was lucky to be invited to present our work. I would argue that all the speakers were similarly lucky. The symposium was a gathering of representatives from disparate fields and several countries. While there, I learned that "Hokudai" itself is a fusion of Hokkaido and Daigatsu (university in Japanese).

At the RIES-Hodukai Symposium, we were brought together under the unifying theme of networks (mou in Japanese.) Network theory is fast growing into its own independent field, but it also serves as an interdisplinary glue connecting mathematics and computing to nearly everything. As such, the speakers spoke about transportation, nanoparticles, organic synthesis, cells, et cetera. The theme is also a double entendre. One intent of the workshop is to create a stronger human network between its diverse participants. This resonates with Prof. Kohei Tamo, the current President of the Chemical Society of Japan: “I often advise young researchers to make 100 friends at the expense of one paper." Of course, the network doesn't help if you don't have the papers (and the results they represent.)

It was exciting to see and participate in this effort urging us all to think about science broadly and across international lines. Hats off to Japan for supporting this!