Scientists Find Molecular Complexes Can Store Binary Information

In a now classic 1959 lecture to the American Physical Society, Richard Feynman tantalized the audience by posing the question, "What are the possibilities of small but movable machines?"

"They may or may not be useful," Feynman said, "but they surely would be fun to make."

In this talk, Feynman anticipated the field of nanotechnology—then still decades away—by envisioning the potential for scaling machines down to the size of molecular assemblies. At this scale, Feynman knew, the field would be wide-open, which prompted him to title his talk, "There's Plenty of Room at the Bottom."

Today, a tiny amount of that room has been filled—420 cubic angstroms of it, in fact. To give an idea of scale, comparing 420 cubic angstroms to one liter of water is like comparing a thimble full of seawater to all the world's oceans (based on the crude estimated ocean volume of 1.34 billion cubic kilometers).

In the recent issue of the journal Angewandte Chemie, Professor and Director of the Skaggs Institute for Chemical Biology at The Scripps Research Institute (TSRI) Julius Rebek and Research Associate Alexaner Shivanyuk report that they have designed a reversibly assembled molecular encapsulation complex, which is like a tiny molecular "box" in which small molecules can be contained. The box is held together by weak intermolocular forces and can contain inside a constellation of up to three smaller molecules.

Significantly, Rebek and Shivanyuk report the ability to store and retrieve information from these encapsulation complexes by virtue of what they refer to as constellation isomerism—the arrangement of several molecules in space.

Isomers in chemistry are traditionally defined as molecules that have the same number of atoms of the same elements but which differ in structure. Constellation isomers are different in that they represent an emergent property of the system—isomerism by collaboration—rather than isomerism related to the individual molecules themselves.

The situation is analogous to having tennis ball cans that can hold up to three balls each. If the balls are both green and yellow, then there could be one of several combinations—green-green-green, green-yellow-green, yellow-yellow green, etc.—in each can. Two cans with equal numbers of green and yellow balls but in different orders (e.g., green-yellow-green and green-green-yellow) would be isometric.

Rebek and Shivanyuk formed their constellation isomers using their box-like encapsulation complexes and a mixture of two smaller molecules, chloroform and isopropylchloride. So in their experiments, they were able to form constellation isomers such as chloroform-chloroform-isopropylchloride and chloroform-isopropylchloride-chloroform.

From the point of view of storing information, the most interesting breakthrough was that they were able to use nuclear magnetic resonance (NMR) spectroscopy to detect differences between the different constellation isomers and distinguish one from the other. This allowed them to distinguish the chemically identical chloroform-chloroform-isopropylchloride from the chloroform-isopropylchloride-chloroform, for instance, by virtue of the sequence of encapsulated molecules—essentially providing them with a basic binary code.

Because the encapsulation complex shells can temporarily store a set of two different molecules in a particular arrangement that can be read, Rebek and Shivanyuk can assign a code to the particular order of molecules that can be stored and later retrieved.

This is the basis of information storage, and since they have done it at the molecular level, they could potentially store information in a much more compact form than is currently possible.

Though computers today are not the vacuum tube and wire monstrosities that they were in Feynman's day, they still rely on the engineering of silicon chips with integrated logic elements, which cannot get much smaller than they currently are because of physical limitations. Rebek estimates the diameter of his encapsulation complexes is 50 times shorter than the smallest possible integrated circuits.

To read the article, "Isomeric Constellations of Encapsulation Complexes Store Information on the Nanometer Scale" by Alexander Shivanyuk and Julius Rebek, Jr., please see http://www3.interscience.wiley.com/cgi-bin/abstract/102529761/START.

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