May 12, 2005

Supramolecular Structures 

A subject that is receiving a lot of attention nowadays is supramolecular chemistry, in which whole molecules are used as building blocks for bigger complex structures. This is closely related to the enticing subject of nanotechnology too. But the scope and proceedings of nanotech are often misunderstood: nanomachines will eventually be a reality (with all the risks and benefits of the case), but for the moment nanotechnology and supramolecular chemistry deal with organizing matter on a molecular scale, or just a bit bigger - nanometers, indeed.

Why are we interested in such things? Besides the irrepressible curiosity of humans (at least some), there are interesting practical applications: if you can control the structure of matter at molecular level, you can produce materials with exceptional properties. Very strong and/or very light materials; semiconductors; optical materials which are not only propagation means but can also perform operations onto photons (opening the way to optical computers); intelligent materials that can react to stimuli and change properties accordingly; and finally gain knowledge and even mimic biological systems.

Recently, I attended a couple of seminars on the argument: one dealt with the sophisticated novel spectroscopy techniques used to examine the intermolecular interactions. That is pretty advanced stuff, and I won't even begin and try to explain it. Let's just say that it's important in order to understand the fine details and thermodynamics (energy variations, basically) of how molecules interact with each other.

The other seminar was about much less intricated processes, and basically showed how certain molecules can self-assemble in particular architectures by simply adding metal ions. Self-assembly is the key here: those scientists did not force molecules together, but synthetized ones that simply will form certain structures because they can't do anything else, and because the thermodynamics are favourable. A cool one is a molecule that can go from linear (well, curved) shape to a helix one, shortening itself of a factor 7 simply adding Pb2+ ions - that may be useful as a micro-actuator, or as a basis for "artificial muscles". Self-assembly is also what biological systems do all the time, and very well.

On a slightly more philosophical note, in my opinion the self-assembly demonstrates that there is no need for a superior force to create everything down to the smallest details: once mulecules reach a certain degree of complexity - that isn't even so high - they will spontaneously self-assemble in more complex structures.


What I want to know is can we build the space elevator. I’ve read that the carbon-carbon bond , the strongest in chemical bonds, the one that creates diamonds, is not strong enough to create a cable into space that can support its own weight.

I never gave much thought to the Space Elevator concept, actually.

I should dust off a general chemistry book, but I think the carbon-carbon bond is not the strongest, as a matter of bonding energy. Of course carbon is the most practical to turn into fibers.

But this is not exactly the problem with the Space Elevator.
The real difficulties are more subtle, but no less hard to surmount. Steven Den Beste wrote about it a while ago, explaining the problem.

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