Foresight Update 28 (page 4)
A publication of the Foresight Institute
Recent Progress (continued from previous
page)
Catalytic Structures
One of the natural applications of complex structures is catalysis. The
3D placement of active sites is important in the effective control of chemical
reactions. In addition to its importance as an application area, this is
important to nanotechnology as a source of new component parts, which may
be applied in either parallel or sequential techniques for constructing
new structures. The following three papers describe advances in the application
and analysis of catalytic structures.
Synthesis of porphyrins by multi-enzyme,
cell-free reactors
In the first paper, G. L. Verdine, writing in [Nature (supp) 384:11-13
7Nov96] describes the prospects for natural product chemistry in modern
drug design. Amongst other developments, he describes the operation of a
substantial enzyme cascade, writing: "The ease with which such in vitro
biosynthetic reactions assemble complex organic molecules can be truly remarkable:
in one case, a cocktail of 12 enzymes converted 5-aminolevulinic acid to
hydrogenobyrininc acid, an advanced intermediate along the vitamin B12 biosynthetic
pathway, giving a 20% overall yield. In a matter of hours, this bioreactor
was able to catalyse a 17-step conversion with an average stepwise yield
of 90%. ... As recently as ten years ago, the notion of overproducing a
dozen enzymes would have been greeted with derision, but recent advances
in polymerase chain reaction-assisted overproduction systems and affinity
tagging technology have greatly reduced the investment of time and labor
necessary to obtain pure proteins in quantity." This particular pathway
is important to nanotechnologists because porphyrins such as B12 are rigid,
fused, ring systems, potentially valuable as machine components. This application
of an enzyme system in a cell-free reactor also allows a wider variety of
potential substrates than in vivo techniques, including substrates, intermediates,
and products that would be toxic to intact cells. The single vessel, multistep
reactor is also analogous to the mill systems described in Nanosystems,
albeit with diffusive transport.
X-ray diffraction pictures of molecular
motions
In the second paper, V. Srajer et. al., writing in [Science 274:1726-1729
6Dec96], describe nanosecond x-ray diffraction analysis of structural changes
during photolysis of the CO complex of myoglobin. They were able to measure
shifts as small as an "iron displacement of 0.32 Å from the heme
plane". They are currently able to measure events as early as 4 nanoseconds
after the laser dissociates the CO, but anticipate that the "time resolution
can be extended to the 100-ps domain if shorter laser pulses are used."
At this point the length of the x-ray pulses, which are currently 150 ps
long, will set the temporal resolution.
This technique will be very helpful in probing the sequence of conformations
important in the operation of molecular machines, particularly when high
flexibility may make unexpected structures accessible, as in biopolymer
systems. One feature detected in the present study is a "transient
docking site for the photodissociated CO". In an analogous system designed
for high speed operation, this might represent a detection of an unexpected
speed limiting temporary trap, which is only visible in these transient
structures. While this technique sees intermediate structures in a reaction,
it is not generally fast enough to probe the potential energy surface in
the neighborhood of unstable transition states themselves, where timescales
are typically 0.1 ps. Those time scales are accessible to purely optical
techniques, however this x-ray technique provides much more spatial information.
One limitation of this paper's technique is that it sees an average of the
structures produced by a reaction, so too many accessible reaction pathways
can average away useful information.
For further information, see: http://www.ucmc.uchicago.edu/news/1996/molecular.movie.html
Catalytic DNA and combinatorial chemistry
In the third paper, R. Rawls, writing in [C&EN 75:33-35
3Feb97], describes work by a number of labs on catalytic DNA. Rawls writes
that "DNA is an ideal molecule to investigate using combinational chemistry"
and all of the labs involved have used combinational techniques to select
their catalysts. The reactions catalyzed have included RNA cleavage, DNA
cleavage, DNA ligation, and metal insertion into porphyrins. The DNA catalysts
have been much smaller than comparable protein catalysts. For example, D.
Sen's DNA for porphyrin metallation "has a molecular weight of roughly
8,000" while a mammalian protein that catalyzes the same reaction has
a weight of around 42,000. Since these catalysts are DNA, they may be relatively
simple to incorporate into 3D DNA frameworks, such as those
that N. Seeman has developed, allowing 3D placement of several catalytic
sites. In addition, the small size of the DNA catalysts may allow the same
function to be contained in a smaller volume than would be required for
protein catalysts.
Table of Contents - Foresight
Update 28
Mechanochemistry
One technique that is expected to become important in nanotechnology is
mechanochemistry, the process of directing chemical reactions by mechanical
forces on the reactants. The following paper describes experimental work
in this area.
An AFM experiment by S. P. Jarvis et. al [Nature 384: 247-249
21Nov96] succeeded in tracing the force curve of an Si/Si tip/substrate
pair smoothly through the negative stiffness regime. They augmented the
force feedback of their lever with a magnetic feedback loop to increase
the effective d.c. stiffness to 37 N/m. They measured the force curve by
slightly perturbing the force at a frequency above the response of the feedback
loop but below the free resonance frequency of their AFM lever, measuring
the displacement (and hence the effective stiffness of the tip/sample interaction).
They integrated the stiffness to yield the force curve, and integrated the
force curve to yield the effective potential, finding "the energy point
of inflection is at 2.5 eV, and that the maximum (tensile) force is just
under 0.3 nN, not impossibly far from the expected ~1.5 nN for a single
Si-Si bond, and rather larger than expected for a purely Van der Waals bond."
They found almost no hysteresis in their force curve with feedback turned
on, "observing a conservative potential interaction." This is
experimental evidence for thermodynamically reversible mechanochemistry,
in a silicon analog of the sp3 carbon bond cleavage case analyzed
in section 8.5.3 of Drexler's Nanosystems.
Jeffrey Soreff is a researcher at IBM with an interest in nanotechnology
Table of Contents - Foresight
Update 28
Media Watch
General circulation media have given much attention to the prospects of
nanotechnology in recent months, mostly favorably and accurately. The principal
exception is a publication that usually does better, the New York
Times.
Newsweek Magazine's January
27, 1997, cover story took a peek into the next millennium, and found nanotechnology
a likely part of the future. In the section devoted to science, "Uncovering
Secrets, Big and Small," science writer Sharon Begley started by describing
DNA-related advances such as "gene pharming" that seem "certain
to occur." She then turned immediately to the prospects of nanotechnology:
"Wilder forecasts have stiffer odds. Will the 21st century
see nano-assemblers? These microrobots would break down the chemical bonds
of cheap ingredients - grass and water, say-- and reassemble the carbon,
nitrogen, hydrogen and other molecules into, for instance, a sirloin steak.
You scoff? It is not much more incredible than a cow's ability to do the
same. And scanning tunneling microscopes can already manipulate single atoms,
which is what the assemblers would do."
Concluding the three-page article, Begley returns to the promise of nanotechnology:
"Dudley
Herschbach of Harvard University foresees making molecules that self-assemble
and self-replicate, sometime in the next 35 years. Biochemists are close
to doing it. And they have a good idea of what to do with those creations:
make those grass-into-sirloin nano-assemblers. In 1997 that seems like so
much science fiction, while genetic discoveries, for instance, seem like
sure bets. But sometimes, in science, the dark horse comes in before the
favorite."
The Philadelphia
Inquirer published one of the best discussions of nanotechnology
we've seen in the general press. Staff Writer Reid Kanaley captured the
theoretical basis of nanotechnology, its promise, and its possible economic
implications. Kanaley drew upon interviews with leaders in the field, including
Rice University Nobel Laureate Richard
Smalley, computational nanotechnologist Ralph
Merkle of Xerox PARC, chemist Nadrian
C. Seeman of New York University (winner
of Foresight's 1995 Feynman Prize), Al
Globus of NASA (co-chair with Merkle of the upcoming
Foresight Nanotechnology Conference), Foresight Institute's Chris Peterson,
and others. Kanaley accurately communicated the concept of "utility
fog", described how it could create skyscrapers, and carefully
discriminated between molecular nanotechnology and unrelated "top down"
efforts at miniaturization.
"Nanotechnologists drawing on advances in engineering, biotechnology
and computer science want to use individual atoms as if they were Tinkertoys
to create new materials and products that in some cases-- like those fictional
self-constructed buildings-- could mimic living organisms, reproduce, and
even assemble still other objects when turned loose by the trillions,"
Kanaley wrote.
Smalley is quoted as describing molecular nanotechnology as "a very
broad field and in many ways, the ultimate playground." Futurist Arthur
Shostak of Drexel University is quoted discussing the major social and economic
upheaval if nanotechnology succeeds in extending life span or in replicating
raw materials, or food. "Nano threatens the entire production infrastructure
that you and I take for granted," he said.
Merkle is quoted on the notion of self-replication
as the basis for nanotechnology. "Potatoes don't cost very much, even
though they are miracles of biology with tens of thousands of genes and
proteins. The reason they are inexpensive is that a potato can make more
potatoes," he said.
Technical Review, a publication
of the Massachusetts Institute of Technology, featured a major article by
Ralph Merkle, "It's
a Small, Small, Small, Small World," in which he laid out the concepts
of nanotechnology and the current state of the field. "Natural diamond
is expensive, we can't make it in the shapes we want, and it shatters. Nanotechnology
will let us inexpensively make shatterproof diamond (with a structure that
might resemble diamond fibers) in exactly the shapes we want. This would
let us make a Boeing 747 that would weight one-fiftieth of today's version
without any sacrifice in strength," Merkle wrote. Merkle has placed
an expanded
version of his article on his Web site.
Scientific American's February
1997 issue included a half-page article under the heading "Nanotechnology:
Scoring with Buckyballs." Writer Erica Garcia discussed Dr.
Smalley's use of fullerene tubes into scanning-force microscope (SFM) probes,
noting their durability against "crashes" because of inherent
flexibility. The same article pictured and discussed a molecular-sized
abacus created at IBM Zurich Research Laboratory by Dr. James Gimzewski
(a scheduled speaker at this fall's Foresight
Conference on Molecular Nanotechnology). His prototype calculator lines
up buckyballs on a grooved copper plate, allowing abacus-like manipulation
of the molecular "beads" with a scanning tunneling microscope
(STM). He's quoted as noting that this is the scale equivalent of "operating
a standard abacus with the Eiffel Tower," but the story notes that
"by showing what is possible, buckyballs are starting to score big
in the small field of nanotechnology."
Muddled identity permeated a New York
Times article in January that not only mistakenly identified micro-electromechanical
systems (MEMS) as the equivalent of nanotechnology, but also misidentified
the creator of the concept as "Eric Drexel", and wrongly asserted
that "the field of nanotechnology, practically speaking, has not done
much since the late physicist Richard
Feynman laid out its plans." Eh? Didn't the Times cover
Smalley's Nobel Prize
for work in nanotechnology? The article is more a discussion about science
fiction (Gibson's Idoru and Stephenson's Diamond Age) than
science. It's definitely not worth searching out.
Man clones sheep. Man clones monkeys. What's
next, an army of super-warriors? The near-hysterical reactions within media
and government circles to these developments offers one potential scenario
for considering the reverberations that could occur when nanotechnology
is realized. Self-proclaimed experts weighed in with lofty opinions, many
of which misrepresented the science, the ethical issues, or both. The
Economist summarized the media reaction well:
"The news of Dolly hit the headlines with a sickening thud--
the sound of a sheep that had been launched at full speed at the world's
pundits. And the pundits did not disappoint. Their responses were dismissive,
scared, funny, outrageous, wise and stupid by turns. The important thing,
it seemed, was to think of something to say, and say it first. Journalists,
hungry for copy, swallowed their quotes and spread them on the page, in
between invoking Aldous Huxley's 'Brave New World' and Ira Levin's 'The
Boys from Brazil'-- apparently the only literary references to cloning anyone
could remember....President Clinton, meanwhile, had only to say that there
were 'serious ethical questions' to generate gravitas. One of the advantages
of being president is that no one has the termerity to ask you too closely
what the questions are."
Newsweek's Sharon Begley (see above)
also offered a thoughtful discussion of the ethical and science issues,
but concluded with a blunt assessment:
"If Dolly's creation offers any lessons, it is these. First,
that which is not absolutely prohibited by the laws of nature is possible.
Second, science, for better or worse, almost always wins; ethical qualms
may throw some roadblocks in its path, or affect how widespread a technique
becomes, but rarely is moral queasiness a match for the onslaught of science."
One positive aspect of the debate over human cloning is that it creates
yet another difficult mixture of science and ethics that will give society
practice in dealing with such fusions prior to having to come to grips with
the potentially controversial applications of nanotechnology.
Table of Contents - Foresight
Update 28
Foresight Update 28 was originally published 30
March 1997.
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