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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