X-Message-Number: 14370
From: "Gary Tripp" <>
Subject: self-assembly of nanocomputers
Date: Fri, 25 Aug 2000 17:57:45 -0400

A team of UCLA chemists reports significant progress toward the creation of
molecular computers with the first demonstration of a reconfigurable
molecular switch that works in a solid state at room temperature - a
breakthrough that solves one of the obstacles toward the creation of
molecular computers that could be much cheaper, smaller and more efficient
than today's silicon-based computers.
In the Aug. 18 issue of the journal Science, the UCLA chemists resolve the
challenge of a reconfigurable molecular switch that they presented last year
in a paper on molecular computers. The earlier paper, published in the July
16, 1999, issue of Science, received worldwide attention.

"Last year's paper was the first experimental step toward molecular
computers," said James R. Heath, professor of chemistry at UCLA. "This is
the second experimental step, and the steps are no longer a slow walk, but a
fast jog."

The team is led by Heath; J. Fraser Stoddart, who is UCLA's Saul Winstein
Professor of Organic Chemistry; and Pat Collier, a postdoctoral scholar in
Heath's laboratory.

"This molecular approach could have failed early on in many places, and it's
not failing," Heath said. "These are still early days, but right now, it
seems that everything is beginning to work together well and that many
avenues are opening up. That means that if our next set of experiments
doesn't work, we will have a number of other options to pursue. We're
getting there. Overall, the progress is faster than any of us expected."

Stoddart agreed, saying, "When I joined UCLA's faculty three years ago, if
someone had asked me how far off molecular computing was, I would have said
on a scale of a quarter-of-a-century. Things I was only dreaming of are
suddenly becoming a reality in Jim's lab."

In last year's Science paper, the researchers could switch the molecules
only once; now they have done so hundreds of times.

"Last year, we published an architectural demonstration with molecules and
demonstrated that it is possible to do simple mathematical operations,"
Heath said. "However, the switches used in that work switched only once, and
this limited their relevance to any serious technology. Now we have taken
another class of Fraser's molecules and demonstrated that they may be
repeatedly switched on and off over reasonably long periods of time in a
solid-state device under normal laboratory conditions. For the first time,
we are able to turn the molecular switches on and off repeatedly."

Closing in on molecular RAM Developing molecular RAM (random access memory)
was one of the major challenges the researchers cited last year, and now
they are close to reaching it.

"With this paper, we have achieved a critical step on the way to molecular
RAM at room temperature - which is required if this is to be a viable
technology," Heath said. "From here, molecular RAM may well be just a matter
of time. While there are many pitfalls between the demonstration of a
technology and the actual invention, at the moment, we can't see how any of
those pitfalls could prove fatal."

The research team gives much of the credit to the unique molecules that
Stoddart and his team develop. Stoddart has been working for more than a
decade on interlocking molecules with recognition sites.

"Not only do the molecular components in these interlocked molecules
communicate efficiently with one another but the molecules also interrelate
to one another in the solid-state device," Stoddart said. "It's significant
that we have moved from the incoherence we had in the solution state, and
have progressed from molecules that behaved like pedestrians walking in a
shopping mall to molecules that march like a united, well-trained army.
Where molecules were previously swimming around incoherently in solution,
now we see coherent molecular motion in a solid-state device. The molecules
have the ability to recognize one another and line up in an efficient

Stoddart's molecules, called catenanes, consist of two tiny mechanically
interlocked rings made up of atoms linked in a circle. To interlock the ring
components, Stoddart and his research team build chemical groups that
recognize one another into the components' precursors so that, when the
appropriate pieces are brought together in solution, they self-assemble to
form a pair of interlocked rings. In catenanes containing the right two
rings, one ring can be stimulated to move between two different states with
respect to the other reference ring, giving the catenane molecule its
bistability. It is the switching motion, which can be induced by taking away
and giving back an electron that is the molecular basis for the present
device. In last year's Science paper, the chemists used another kind of
interlocked molecule synthesized in the Stoddart labs. Called a rotaxane, it
has a dumbbell-shaped component that is encircled by a ring component after
the style of an abacus. Rotaxanes can also be made to switch their molecular

The catenanes reported in the new Science paper work much better than last
year's rotaxanes, said the chemists, who added that they are already working
with a new class of molecules that lead to significantly better switching
performance than the catenanes. In fact, the chemists are working with more
than a half-dozen different kinds of molecular switches, each with its own
unique characteristics.

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