Anna Gudmundsdottir |
In
Anna Gudmundsdottir’s laboratory at the University of Cincinnati,
dedicated researchers endeavor to tame the extremely reactive chemicals
known as radicals.
Highly
reactive radicals are atoms, molecules or ions frantically trying to
become something else. Their lifetimes are measured in fractions of
seconds and typically occur in the middle of a chain of chemical
reactions. They are also known as reactive intermediates. Much of
Gudmundsdottir’s work has focused on a family of radicals known as
triplet nitrenes.
“Triplet
nitrenes are reactive intermediates with high spin,” Gudmundsdottir
said. “You have a nitrogen molecule that has two unpaired electrons on
it. We discovered they were actually very stable for intermediates. They
live for milliseconds and that’s when we got into this idea can we make
them stable enough for various investigations.”
The
potential uses of relatively stable radicals have excited interest from
industry. The high spin Gudmundsdottir describes suggests that triplet
nitrenes, for example, might be ideal candidates for creating organic
magnets that are lighter, more flexible and energy-intensive than
conventional metal or ceramic magnets. Gudmundsdottir’s research
suggests that radicals, including triplet nitrenes, may show a pathway
to materials with many magnetic, electrical and optical properties.
“I
talk a lot about radicals,” Gudmundsdottir said. “Nitrenes are
radicals. We study the excited state of the precursors to the nitrenes.
We are looking at how you use the excited state of molecules to form
specific radicals.”
One
line of inquiry, presented by Gudmundsdottir to a recent Gordon
Research Conference, described how her team used radicals to create a
specific trap for a fragrance, which is then slowly released when
exposed to light.
“The
question was, can you actually tether a fragrance to something so that
it will release slowly?” Gudmundsdottir said. “It turned out that a
precursor similar to the ones we used to form the nitrenes could be used
it as a photoremovable protecting group.”
The
“photoprotectant” acts as a sort of cap, containing the fragrance until
the cap is pried off by a photon of light. For this particular purpose,
Gudmundsdottir said it was important to design a photoprotectant “cap”
that was somewhat difficult to pry off. For household products, such as a
scented cleaning fluid, consumers want fragrance to be released slowly
over a long period of time. That requires what is known as a low
“quantum yield.” In other words, how much fragrance gets released by how
many photons.
The
difficulty, Gudmundsdottir said, is that different applications need
different rates of release. For medical uses, doctors might want a
higher quantum yield, by which a little bit of light releases a lot of
medicine.
“There
are all kinds of applications for photoreactions,” she said, “from
household goods, perfumes, sun-protection, drug delivery and a variety
of biologically reactive molecules. So we just decided, OK, we are very
fundamental chemists, we’ll design different systems and see if we can
manipulate the rate of release.”
Gudmundsdottir’s
research group studies the release mechanism, locates where there are
limitations, and tries to determine what controls the rate. They also
consider environmental factors, including how the delivery systems react
with oxygen.
“We
do very fundamental work to get the knowledge here before can take it
into specific directions,” she said. “If we don’t understand it, we
can’t design where to take it next.”
Much
of this understanding develops from watching how radicals form and
decay. Gudmundsdottir’s group uses a laser flash photolysis system to
fire a laser into a sample and to track the spectrum of radiated light
as the radicals decay.
“What
I like about transient spectroscopy is actually seeing the
intermediates we work with on nanosecond, microsecond and millisecond
timescales,” she said.
The
team also uses computer modeling, but the chemical operations of these
short-lived and rapidly reacting chemicals are difficult to model, so
Gudmundsdottir has tapped into the resources of the Ohio Supercomputer
Center.
“Calculating
excited states takes up quite a bit of computer resources and that’s
why we use the supercomputer,” she said. “That’s a really nice resource
to have available. I can sit anywhere or my students can sit anywhere
and we can do the calculations to model reactions.”
Gudmundsdottir
said the questions raised by applications leads to helpful fundamental
questions that can be tackled through basic research.
“Going
forward, we probably want to do more applied study with our photo
protective groups, to collaborate with someone to see them in some other
applications,” she said. “I’m interested in how they act inside cells.”
Gudmundsdottir’s
team has received research support from the National Science
Foundation, the American Chemical Society-Petroleum Research Fund, UC’s
University Research Council, Ohio Supercomputer Center and the English
Speaking Union.