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DBL%20Hendrix%20small.png College chemistry, 1983

Derek Lowe The 2002 Model

Dbl%20new%20portrait%20B%26W.png After 10 years of blogging. . .

Derek Lowe, an Arkansan by birth, got his BA from Hendrix College and his PhD in organic chemistry from Duke before spending time in Germany on a Humboldt Fellowship on his post-doc. He's worked for several major pharmaceutical companies since 1989 on drug discovery projects against schizophrenia, Alzheimer's, diabetes, osteoporosis and other diseases. To contact Derek email him directly: Twitter: Dereklowe

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May 4, 2009

Writing With Triazoles

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Posted by Derek

I’ve written before about the copper-catalyzed triazole formation (often referred to as “click chemistry”). It’s turned into a very useful way to stick all sorts of molecules and structures together, and is showing up in materials science, biochemistry, organic synthesis and other fields.

Now Fraser Stoddart’s lab has a new variation on the technique, using atomic force microscopy (AFM) equipment. If you’re not familiar with that machinery (invented in the 1980s), it’s rather startling. An AFM rig uses a very fine metal tip (fine, as in “down to one atom or so at the end” fine), which is brought down very close to a solid surface. And that’s close as in “within the size of a molecule or so” close. Once you’re ranged in, you can run these tips around in any direction you choose, and a lot ingenious measurements can be obtained. Both modern surface and solid-state chemistry live off this family instruments, with good reason.

One thing you can imagine doing is lowering some sort of active catalyst down near the surface and doing chemical reactions. If you want to tear up the surface below in some controlled fashion, that’s a bit easier, through straight oxidation or reduction. Forming bonds is a bit trickier, but that’s been achieved with some palladium reactions. Now Stoddart’s group has gotten it to work with the triazole chemistry, and in very straightforward fashion.

If you take an azide-functionalized silicon wafer (and these are well known), you can then dissolve some acetylene compound up in ethanol and put a drop of it on the surface. And lowering an AFM tip which has simply been coated with copper metal down to the surface is enough to initiate the reaction. As the tip moves, it “writes” a path of triazoles. The conditions are very mild, the resolution of the lines is very high (down to about 50 nanometers wide), and it turns out that the reaction is so fast that the tip can be moved at relatively high speed.

This opens up a potential way to stick all sorts of molecules to solid surfaces. There are a lot of ways known to do that, of course, but this one could have some real advantages. The selectivity and high resolution seen here could allow for very dense and complicated arrays of complex molecules to be laid down. Since the triazole reaction is compatible with all sort of biomolecules, this could provide a way to produce functionalized chips that would currently be rather hard (or nearly impossible) to make. And now that we can make them, we can start thinking up unusual things to do with them.

Comments (8) + TrackBacks (0) | Category: Chemical News


1. excimer on May 4, 2009 9:44 AM writes...

That paper was so cool. AFM (and to an even greater extent, STM) is one of those "gee whiz" techniques that, when you first learn about it, swear that it doesn't work. But it does!

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2. Rhenium on May 4, 2009 10:05 AM writes...

Holy selective catalysis! I wonder if you could user a palladium AFM tip to selectively catalyze parts of the surface....
To the patent office Batman!

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3. Wavefunction on May 4, 2009 10:12 AM writes...

The magic of quantum mechanics...gee whiz

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4. Anonymous on May 4, 2009 10:39 AM writes...

Woahh easy tigers - I hate to throw a spanner in the works but I spent 3 longs years of a PhD wrestling and cursing my AFM. I can count the number of times I got it to work properly on one hand...!

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5. Sili on May 4, 2009 1:08 PM writes...

Presumably JF is using this to tether his 'nanocomputers' to chips.

One of my old tutors post docced in JF's lab before returning and taking over the lab of his supervisor who retired early after (mild) heart attack.

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6. Mr. Zarch on May 4, 2009 4:14 PM writes...

Just a nitpick -- AFM tips are more likely to be made out of micromachined or etched silicon than out of metal, and they're more likely to be used in contact mode (dragged across the surface) or tapping mode (exactly what it sounds like) than in non-contact mode. You may be thinking of an STM tip.

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7. Grad on May 4, 2009 9:02 PM writes...

There are commercial sales of Pt and other metal coated tips for EFM, kelvin probe, cAFM, etc. As well as tips with ferromagnetic materials for MFM. Yes the vast majority of AFM is done as you've indicated, but you can buy Pt tips, so that ought to be a good place to start if you wanted to try this experiment.

Derek's description of the tip does sounds a lot more like a STM though.

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8. retappevyarcart on November 24, 2009 5:05 AM writes...

...please where can I buy a unicorn?

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