X-Message-Number: 13083
Date: Thu, 13 Jan 2000 16:35:11 -0500
From: Jan Coetzee <>
Subject: smallest piece of ice

UNC-CH scientists create world's smallest pieces of

    CHAPEL HILL -- Using liquid helium, chemists at the University of
North Carolina at
    Chapel Hill have succeeded in artificially creating the world's
smallest pieces of ice.

    Don't look for them anytime soon clinking in your tea glass,
however. The pieces they
    made consist only of six molecules of water in flat hexagonal rings,
just as ice exists in

    The unusual achievement could go a long way toward boosting
knowledge of water,
    that unique and fascinating substance without which no life could
exist, the scientists
    say. A report on the research appears in the Jan. 13 issue of
Science. Chemistry
    graduate student Klaas Nauta and Dr. Roger E. Miller, professor of
chemistry, carried
    out the work and wrote the report.

    "Despite the fact that water is so important to us, we still don't
have a really good
    molecular level understanding of it," Miller said. "We can do pretty
well with some
    other systems, but water does interesting things that make it unique
and also make it
    somewhat difficult to understand."

    For example, a property of water that is bizarre -- yet taken for
granted -- is that unlike
    almost all other substances, it becomes less dense as it freezes,
Miller said. As a
    result, ice floats instead of sinking. The more normal behavior is
for solids to sink in
    their own liquid phases.

    "We know that when it freezes, water forms a unique hexagonal ring
structure, which
    accounts for its low density and the fact that it floats in water,"
Miller said.
    "Understanding the hydrogen bonding forces that align the water
molecules in this way
    is our goal."

    Doing this in bulk ice and water is complicated by the fact that
there are so many
    molecules to keep track of, he said.

    "After all, a single drop of water contains about
100,000,000,000,000,000,000 water
    molecules," the chemist said. "When we're trying to understand water
at a detailed
    level, having so many molecules is a real problem."

    The approach he and other scientists have taken over the past decade
or so has been to
    make small clusters of water molecules. They take three or four
molecules at a time
    and study them in pieces, applying what they learn to water in bulk.

    "The difficulty has been that every time people took six water
molecules and tried to
    make this hexagonal ring structure characteristic of ice, they ended
up with a
    high-density, collapsed cage structure, which is not what ice does,"
Miller said. "The
    difference is that bulk ice has a three-dimensional structure that
holds the molecules in
    position like a scaffold. The six water molecule lacks this
scaffolding, and the water
    molecules collapse into a non-ice-like arrangement."

    The new work involved developing methods that would allow
researchers to force
    individual ice molecules into shapes they wouldn't normally assume
on their own.

    "We used a liquid helium method that tricks nature into selectively
making ice rings,"
    he said. "Basically, by growing ice at very low temperatures, we
starve the molecules
    of the energy they need to rearrange themselves from the hexagonal
shape we want and
    into the collapsed cage shape we don't want."

    The basic premise of the work is to try to understand hydrogen
bonding in its most
    fundamental form, namely water, the chemist said.

    "Pharmaceutical companies have literally spent hundreds of millions
of dollars on
    molecular modeling simulations," he said. "They are trying to use
modeling to aid in
    the development of new and interesting chemical systems, including
new drugs. An
    important part of modern drug design is trying to predict the
properties of new drugs on
    a computer. That approach is only as good as our understanding of
the basic
    interactions between molecules, the very subject we are addressing
with our research."

    The work potentially could have a huge impact on the pharmaceutical
industry, for
    example, he said.

    Miller and his graduate students now are developing new ways of
studying water's
    interacting hydrogen bonds, which control much of biochemistry, he
said. The next step
    will be to introduce small biological molecules into the system to
learn how water
    interacts with them.


    Note: Miller and Nauta can be reached at (919) 962-0528. For a
    image of the ice molecule, go to
www.unc.edu/news/newsserv/pics/smallice.jpg. .

    Contact: David Williamson, (919) 962-8596.

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