VT College of Science Magazine Summer 2008 | Page 11

9
C o l l e g e

For chemists, therefore, it is often vital to determine
which hand of a molecule they are using. In other
words, when you have a sample of chiral molecules,

Crawford’s research applies the theory of quantum mechanics to devise computational methods in order to
eliminate having to create a synthetic molecule. “The
hope is that this will allow us to calculate things like
optical rotation very accurately,” he said. “So when an
organic chemist has a molecule and doesn’t know if it
is left- or right-handed, we can calculate that directly
on the computer.”
Crawford said the ultimate goal in his research is to be
able to provide organic chemists with computational
tools to determine the handedness of a particular molecule with which they are working. He said that such
tools could speed up the drug development process
by years.

Issue No. 5 suMMeR 2008

“Most drugs have this handedness property,” Crawford
said, “and for many of these drugs, even though both
hands can cause a reaction, it is a situation where one
hand does a good thing and one does a bad thing.” He
used thalidomide as an example. A mixture of both
hands of the drug was used in the late 1950s and early
1960s to treat morning sickness in pregnant women.
Later studies revealed that, while one of the two hands
acted as the desired sedative, the other hand was
found to cause significant birth defects. Thalidomide
was never approved by the FDA in the United States
and was eventually taken off the market in Europe.

M a g a z i n e

New research, led by a Virginia Tech chemist, may some- how do you distinguish between the left and right hand?
day help natural-products chemists decrease by years
This is where a technique called polarimetry comes
the amount of time it takes to develop certain types of
into play. By shooting plane-polarized light through a
medicinal drugs. The research by T. Daniel Crawford, assample of one hand, the chiral molecules in question
sociate professor of chemistry, involves computations
will rotate to a characteristic angle either clockwise
of optical rotation angles on chiral molecules. The reor counterclockwise, and the two hands of chiral molsearch, titled The Current State of ‘Ab Initio’ Calculations
ecules produce opposite rotations.
of Optical Rotation and Electronic Circular Dichroism
Spectra, appeared recently as the cover article in The “So if we figure out the direction and rotation of the
light of each hand, we have a frame of reference for
Journal of Physical Chemistry A.
determining whether we have the left or right hand of
Many chiral molecules are important for medical treata molecule,” Crawford said.
ment for illnesses ranging from acid reflux to cancer.
The term “chiral” means that two mirror images of a The problem with this method is that synthesizing the
molecule cannot be superimposed onto each other. two hands of chiral molecules is often extremely timeIn other words, some are “left-handed” and some are consuming. “It can take anywhere from weeks to years,”
Crawford said.
“right-handed.”

S C i e n C e

reSearCh yieldS ProMiSing reSultS in CoMPutational
QuantuM CheMiCal MethodS for drug develoPMent

o f

T. Daniel Crawford (left)
uses computational
methods to analyze
complex molecules.