Crystal copy

Coral craft. scientists have u (Credit: S Clark)BRITISH scientists claim to have unravelled the mystery that enables corals, sea
urchins and other marine invertebrates
to build complicated crystalline structures from calcium carbonate dissolved
in sea water, and are now using the trick
to develop their own weirdly shaped
crystals. The researchers say that this
could be a boon for industrial material
scientists - particularly those dealing
with computer discs and cassette tapes
- as crystals with different shapes and
sizes have different properties (New Scientist, Vol 146, No 1981).

In trying to imitate the marine
invertebrates, Stephen Mann, Jon
Didymus, and Stephen Sims of the
University of Bath are crystallising solutions of salts containing various addi
tives, in a bid to create their own crystals
of more exotic shapes.

The University of Bath team first
discovered that adding tiny amounts of
lithium ions to their solutions enabled
the calcium carbonate to form hexagonal structures similar to those formed
by oysters and other seashells.

Taking a cue from these organisms
which use not only simple ions but also
proteins rich in aspartic acid (an aminoacid) to control crystal growth, the
researchers turned to a polymer consisting of a chain of aspartic acid molecules.

When they added a small amount of this
polyaspartate to a solution of calcium
carbonate, they discovered that the crystals formed strange shapes with spiralling protuberances.

The researchers believe that the
polymer combines with calcium carbonate in solution to form a gel, which
they suspect coats the growing crystals,
blunting their sharp edges and preventing calcium carbonate from being
deposited regularly. The result is a crystal with smooth surface that looks similar to those produced by marine invertebrates.
Though they cannot, as yet, control
the shape of growing crystals precisely,
the scientists believe that this should not
be a problem because it might be possible to grow the crystals in molecules
containing cavities that would act as
templates. The sea organisms, in fact,
use such molecular containers to grow
and control the shape of crystals. "In the
long run, we hope to grow inorganic
crystals with tailored organic shapes," claims Mann.