University
of Utah chemists
developed a method to design and test new catalysts. By using the new method,
the chemists also made a discovery that will make it easier to design future
catalysts.
The discovery: the sizes and electronic properties of
catalysts interact to affect how well a catalyst performs, and are not
independent factors as was thought previously. Chemistry Professor Matt Sigman
and doctoral student Kaid Harper, report their findings in Science.
“It opens our eyes to how to design new catalysts that we
wouldn’t necessarily think about designing, for a broad range of reactions,”
Sigman says. “We’re pretty excited.”
Sigman believes the new technique for designing and testing
catalysts “is going to be picked up pretty fast,” first by academic and then by
industrial chemists, who “will see it’s a simple way to rapidly design better
catalysts.”
‘Catalysts make the
world go ’round’
Catalysts speed chemical reactions without being consumed by those
reactions. Their importance to society and the economy is tough to overstate.
Products made with catalysts include medicines, fuels, foods, and fertilizers.
Ninety percent of U.S. chemical manufacturing
processes involve catalysts, which also are used to make more than one-fifth of
all industrial products. Those processes consume much energy, so making
catalytic reactions more efficient would both save energy and reduce emissions
of climate-warming carbon dioxide gas.
“Catalysts make the world go ’round,'” says Sigman. “Catalysts are how we make molecules more efficiently and, more important, make
molecules that can’t be made using any other method.”
The Utah
researchers developed a new method for rapidly identifying and designing what
are known as “asymmetric catalysts,” which are catalyst molecules that are
considered either left-handed or right-handed because they are physically
asymmetrical. In chemistry, this property of handedness is known as chirality.
Chemists want new asymmetric catalysts because they impart
handedness or chirality to the molecules they are used to make. For example,
when a left-handed or right-handed catalyst is used to speed a chemical
reaction, the chemical that results from that reaction can be either
left-handed or right-handed.
“Handedness is an essential component of a drug’s
effectiveness,” Sigman says.
Drugs generally work by latching onto proteins involved in a
disease-causing process. The drug is like a key that fits into a protein lock,
and chirality “is the direction the key goes” to fit properly and open the
lock, says Sigman.
“However, developing asymmetric catalysts [to produce
asymmetric drug molecules] can be a time-consuming and sometimes unsuccessful
undertaking” because it usually is done by trial and error, he adds.
Sigman says the new study “is a step toward developing
faster methods to identify optimal catalysts and insight into how to design
them.”
A mathematical
approach to catalyst design
Harper and Sigman combined principles of data analysis with principles of
catalyst design to create a “library” of nine related catalysts that they
hypothesized would effectively catalyze a given reaction—one that could be
useful for making new pharmaceuticals. Essentially, they used math to find the
optimal size and electronic properties of the candidate catalysts.
Then the chemists tested the nine catalysts—known as “quinoline proline ligands”—to determine how well their degree of handedness
would be passed on to the chemical reaction products the catalysts were used to
produce.
Sigman and Harper depicted results of the reactions using
the different catalysts as a 3D mathematical surface that bulges upward. The
highest part of the bulge represents those among the nine catalysts that had
the greatest degree of handedness.
This technique was used—and can be used in the future—to
identify the optimal catalysts among a number of candidates. But it also
revealed the unexpected link between the size and electronic properties of
catalysts in determining their effectiveness in speeding reactions.
“This study shows quantitatively that the two factors are
related,” and knowing that will make it easier to design many future catalysts,
Sigman says.
