New tools are catalysts for proactive chemistry
                       New research tools are catalysts for
                   chemists' proactive approach

By Alexandra Witze / Science Writer of The
                                Dallas Morning News
            Memories of high school chemistry conjure
            up images of test tubes, flasks and other
             laboratory glassware. But many of today's
           chemists haven't touched a beaker in
These days, you're more likely find
supercomputers and lasers in a chemistry
lab. Scientists are using these powerful
new technologies to scrutinize how atoms
and molecules fit together. And as
researchers develop these tools, they're
learning that they aren't limited to a
passive science of observation.
Once, people were at the mercy of the
molecules: Scientists had to wait for
chemical reactions to occur, then do their
best to understand what had happened.
Chemists today still use this traditional
approach of wait-and-watch, and it helps
them learn the detailed mechanics of
chemical reactions.
But some scientists are trying to go
beyond this: They are controlling how
chemistry happens. By moving atoms around,
or manipulating the outcome of chemical
reactions, researchers are discovering how
to drive chemistry. Instead of being
observers on the sidelines, chemists are
now out on the playing field.

 "We can use chemistry for more than just
  making molecules interact with each
 other," said Harvard University chemist
George Whitesides.
This new, active science is on display
this week in Dallas, where some 10,000
chemists are gathered for the annual
meeting of the world's largest scientific
society, the American Chemical Society.
From making better plastics to
understanding how molecules in the body
interact, the latest discoveries rely on
the proactive approach to chemistry.
                    * The quest to understand and drive
                                chemistry begins at the science's smallest
   level - the atom.

                                Researchers are now able to manipulate
                                atoms one at a time. In 1990, a group from
                                IBM's Almaden Research Center in San Jose,
                                Calif., described the world's smallest
                                advertisement - the letters "IBM" spelled
                                out in xenon atoms.

                                By using a special tool called a scanning
                                tunneling microscope, the scientists had
                                figured out how to nudge atoms around.
                                From the metallic tip of the microscope
                                flows a small electric current that
                                repulses atoms, allowing the scientists to
                                push the atoms exactly where they want.
                                The experiment has to be done in a
                                near-perfect vacuum, at very low
                                temperatures to keep the atoms from
                                wiggling around with heat.

                                "Otherwise they won't stand still to have
                                their picture taken," said IBM team leader
                                Donald Eigler.

                                The research group has since drawn more
                                elaborate patterns of atoms on surfaces,
                                including the Japanese kanji characters
                                for "atom." They've devised "quantum
                                corrals," in which a ring of atoms traps
                                electrons on a surface. And they figured
                                out how to attach another atom to the tip
                                of the microscope and drag it across the

                                Such work might one day help chemists
                                build novel structures, designed atom by

                                "We've never built molecules this way
                                before, so let's try," said Dr. Eigler.

                                * Occasionally the scientists can trigger
                                chemical reactions by placing two atoms
                                close enough to each other. Sometimes the
                                researchers have to zap the two atoms with
                                heat, electrons, or particles of light to
                                make the reaction happen, Dr. Eigler
                                reported recently in Philadelphia at a
                                meeting of the American Association for
                                the Advancement of Science.

                                In 1991, his group built a tiny atomic
                                "switch": The microscope tugged a single
                                xenon atom off a nickel surface, then
                                dropped it again, to represent "on" and
                                "off" positions. Expanding on this idea,
                                other researchers have found ways to
                                control single molecules as they rotate on
                                a surface.

                                Wilson Ho of Cornell University and
                                colleagues have sent an electric current
                                through the tip of a scanning tunneling
                                microscope to change how an oxygen
                                molecule spins above a platinum surface.
                                The idea is to learn more about what it
                                takes to rotate a molecule from one
                                position to another; after all,
                                researchers won't be able to build tiny
                                machines out of single molecules, as they
                                dream, if they can't control the
                                molecules' orientation.

                                Dr. Ho's team found that the oxygen
                                molecule would flip its position as they
                                varied the voltage and current coming from
                                the microscope's tip. The molecule's
                                rotation was apparently caused by the
                                motion of low-energy electrons within it,
                                the researchers reported this month in

                                Such studies, they wrote, add to the
                                growing knowledge of what it takes to
                                control individual molecules in different

                                * More insight into the control problem
                                comes from lasers, which can help
                                scientists see what happens when atoms and
                                molecules combine and recombine.

                                For example, chemist Ahmed Zewail of the
                                California Institute of Technology uses
                                very fast lasers to take snapshots of
                                chemical reactions as they occur. Atoms
                                separate and rejoin as molecules on the
                                timescale of "femtoseconds," or
                                quadrillionths of a second. So in order to
                                watch the reactions happening, Dr.
                                Zewail's group has to flash laser light
                                every few femtoseconds, like a strobe
                                light blinking in a disco.

                                In such rapid flashes, "any molecule will
                                look to you as if it is frozen," said Dr.

                                Over the past few years, his group has
                                gone from "freezing" simple reactions
                                between inorganic molecules to much more
                                complex interactions involving organic
                                molecules. For instance, his group is
                                currently studying the structure of DNA
                                and how it is affected by electrons moving
                                through it.

                                "We want to see the architecture of the
                                molecule itself changing over time," said
                                Dr. Zewail.

                                Other groups are studying a protein known
                                as bacteriorhodopsin, which is involved in
                                sight. A twist of this protein in the eye
                                triggers vision. By studying
                                bacteriorhodopsin with very fast laser
                                pulses, chemists have found that it takes
                                about 200 femtoseconds for the protein to
                                twist when light strikes the eye. One day,
                                scientists might be able to use
                                femtosecond laser pulses to drive chemical

                                This month in Science, chemist Richard
                                Zare of Stanford University also described
                                molecular control.

                                "We may actively intervene during the
                                course of the reaction," wrote Dr. Zare -
                                meaning that scientists could drive the
                                reactants to follow a chosen path out of
                                many different reaction possibilities.

                                Scientists had already known they could
                                send a chemical reaction somewhat in the
                                direction they wanted - by changing the
                                temperature or pressure at which the
                                reaction happened, for instance, or by
                                adding different catalysts to trigger the
                                reaction. Lasers, however, come in handy
                                when chemists want to set up the right
                                reaction, or even guide it as it occurs.

                                By carefully pumping the right kind of
                                laser light into a mixture of chemicals,
                                researchers can nudge molecules to be in
                                specific orientations or energy states. In
                                turn, that makes some molecules react in
                                different ways with others.

                                For example, scientists have slammed
                                charged particles, or ions, of nitric
                                oxide into a crystal of silver to produce
                                oxygen ions (formed when the bonds between
                                nitrogen and oxygen atoms break in the
                                nitric oxide). In 1995, chemists reported
                                that they got many more oxygen ions if
                                they used laser pulses to force the nitric
                                oxide to collide end-on, rather than
                                side-on, with the silver.

                                Another way to influence reactions is to
                                continually flash laser light into a
                                mixture of chemicals while the reaction is
                                going on. So far, only a few experimental
                                groups have been able to demonstrate this
                                type of control in the laboratory.

                                One scientific team recently used a laser
                                to alter the way in which an iodine
                                molecule absorbed energy. The regular
                                flashes of light struck the iodine at just
                                the right intervals to change the
                                molecule's energy states.

                                Chemists are just beginning to learn how
                                well they can control reactions by using
                                lasers. Any practical applications in
                                industry or other areas lie decades away,
                                said Dr. Zewail.

                                "Nevertheless, the real gain in pursuing
                                laser-based collision control is likely to
                                be the increased understanding of how
                                chemical reactions occur, which in time
                                will no doubt lead to important
                                applications," Dr. Zare wrote in the
                                Science article.


                                Yet even when scientists think they are
                                beginning to understand some chemical
                                processes, they discover behaviors that
                                are completely surprising.

                                For example, Stanford University
                                researchers have found that identical
                                polymer molecules can act completely
                                differently when asked to flow through a

                                Polymers, which are long, chainlike
                                molecules made up of repeating groups of
                                atoms, can actually help push fluid
                                through pipes when they're dissolved in
                                very small amounts. (Firetrucks use
                                polymers to force water out of their hoses
                                faster.) Nobel-laureate physicist Steven
                                Chu and colleagues have been studying how
                                long strands of the polymer DNA uncoil in
                                tiny currents.

                                Each strand of DNA is made up of similar
                                repeating sets of chemicals, so
                                theoretically the strands should behave
                                alike. But Dr. Chu's team has found that
                                the DNA molecules suffer from stubborn

                                The researchers stained the DNA strands
                                with fluorescent dye, then photographed
                                the strands unraveling within a flow. They
                                found that some of the DNA strands
                                remained coiled within the current like
                                little snakes. Others untangled into long,
                                straight strands with knots at each end,
                                like dumbbells. Still others folded in
                                half, or they remained kinked in the
                                middle, like knotted pieces of string.

                                Even though the strands were otherwise
                                identical, they behaved very differently
                                from each other - something that couldn't
                                have been learned by studying millions of
                                polymer molecules at the same time, Dr.
                                Chu reported at the Philadelphia meeting.

                                "It's amazing that you can find this very
                                diverse behavior by studying single
                                molecules," he said.

                                The experiments show how unpredictable
                                single molecules can be. Trying to learn
                                about them by studying their behavior in a
                                crowd is like trying to figure out what
                                kinds of animals a zoo contains by
                                studying only a creature made of a blend
                                of all the giraffes, snakes and bears in
                                the place, Dr. Chu said.

                                Scientists are finally figuring out ways
                                to peer into matter at its most basic
                                levels, as single molecules or even atoms.
                                Such new methods are unprecedented in the
                                history of chemistry. If the American
                                Chemical Society meets in Dallas in the
                                future, one prediction is certain:
                                Chemists will have gone even smaller in
                                their quest, and there probably still
                                won't be many test tubes in sight.


                      © 1998 The Dallas Morning News