Medical Design Briefs - November 2022 - 29

Tubing Coated with Light-Powered Catalysts Aids
Drug Manufacturing
The catalysts could act
on chemicals, helping to
synthesize drugs.
MIT, Cambridge, MA
Chemical reactions that are driven by
light offer a powerful tool for chemists
who are designing new ways to manufacture
pharmaceuticals and other useful
compounds. Harnessing this light energy
requires photoredox catalysts, which
can absorb light and transfer the energy
to a chemical reaction.
MIT chemists have now designed a
new type of photoredox catalyst that
could make it easier to incorporate
light-driven reactions into manufacturing
processes. Unlike most existing photoredox
catalysts, the new class of materials
is insoluble, so it can be used over
and over again. Such catalysts could be
used to coat tubing and perform chemical
transformations on reactants as they
flow through the tube.
" Being able to recycle the catalyst is
one of the biggest challenges to overcome
in terms of being able to use photoredox
catalysis in manufacturing. We
hope that by being able to do flow chemistry
with an immobilized catalyst, we can
provide a new way to do photoredox catalysis
on larger scales, " says Richard Liu,
an MIT postdoc and the joint lead author
of the new study.
The new catalysts, which can be
tuned to perform many different types
of reactions, could also be incorporated
into other materials including textiles
or particles.
Timothy Swager, the John D. MacArthur
Professor of Chemistry at MIT, is the senior
author of the paper, which appears in
Nature Communications. Sheng Guo, an
MIT research scientist, and Shao-Xiong
Lennon Luo, an MIT graduate student,
are also authors of the paper.
n Hybrid Materials
Photoredox catalysts work by absorbing
photons and then using that light
energy to power a chemical reaction,
analogous to how chlorophyll in plant
cells absorbs energy from the sun and
uses it to build sugar molecules.
Medical Design Briefs, November 2022
MIT chemists have designed a new type of photoredox catalyst that could make it easier to incorporate
light-driven reactions into continuous flow manufacturing processes. The polymer catalysts
could be used to coat tubing and perform chemical transformations on reactants as they flow
through the tube, as imagined in this digital artwork. (Credit: Richard Liu)
Chemists have developed two main
classes of photoredox catalysts, which
are known as homogeneous and heterogeneous
catalysts. Homogeneous catalysts
usually consist of organic dyes or
light-absorbing metal complexes. These
catalysts are easy to tune to perform a
specific reaction, but the downside is
that they dissolve in the solution where
the reaction takes place. This means they
can't be easily removed and used again.
Heterogeneous catalysts, on the other
hand, are solid minerals or crystalline
materials that form sheets or 3D structures.
These materials do not dissolve, so
they can be used more than once. However,
these catalysts are more difficult to
tune to achieve a desired reaction.
To combine the benefits of both of
these types of catalysts, the researchers
decided to embed the dyes that make up
homogeneous catalysts into a solid polymer.
For this application, the researchers
adapted a plastic-like polymer with
tiny pores that they had previously developed
for performing gas separations. In
this study, the researchers demonstrated
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that they could incorporate about a dozen
different homogeneous catalysts into
their new hybrid material, but they believe
it could work more many more.
" These hybrid catalysts have the recyclability
and durability of heterogeneous
catalysts, but also the precise tunability
of homogeneous catalysts, " Liu says.
" You can incorporate the dye without
losing its chemical activity, so, you can
more or less pick from the tens of thousands
of photoredox reactions that are
already known and get an insoluble
equivalent of the catalyst you need. "
The researchers found that incorporating
the catalysts into polymers also helped
them to become more efficient. One reason
is that reactant molecules can be held
in the polymer's pores, ready to react. Additionally,
light energy can easily travel
along the polymer to find the waiting
reactants.
" The new polymers bind molecules
from solution and effectively preconcentrate
them for reaction, " Swager says.
" Also, the excited states can rapidly migrate
throughout the polymer. The com29

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Medical Design Briefs - November 2022

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