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Polymer Chemist Julia Kalow Studies the Superpowers of Light

Julia Kalow
Julia Kalow, Ph.D. Photo by Jim Prisching.

In the realm of organic chemistry, there are “molecule people” and “reaction people.” Julia Kalow is the latter.

“There are people who like thinking about the structure of molecules and designing them,” says Kalow, an organic, polymer chemist and assistant professor at Northwestern University. “I think more about reactions; how a reaction works, how to make it faster, how to make it more selective.”

Specifically, the AAAS Member focuses on reactions involving light: she investigates how to use light to make new materials, as well as using different wavelengths to control and change a material’s properties, for example, making it change from being elastic like a rubber band, to more viscous, like silly putty. She also seeks to design new reactions controlled by light. Her innovative approach has been honored with one of the 2021 Marion Milligan Mason Awards from AAAS recognizing women early in their chemical science careers.

Over the past few years, Kalow and her colleagues have developed a hydrogel they can control with light, which they are now using as a platform for cell studies. Cells can be grown inside the hydrogel, making it particularly useful for biomedical experiments. “When you grow cells on a stiff flat petri dish, they actually behave very differently from when they are grown in a more relevant environment like tissue, which is soft and wet,” Kalow says.

To make the hydrogel, they took a common polymer material and inserted chemical light switches. When light is shone on the gel, the consistency of the material changes, becoming softer or stiffer. Notably, the changes are reversible, allowing the researchers to switch back and forth as needed. The reversible hydrogel avoids the need for any harsh reagents, simply relying on an external light source to initiate reactions, enabling the researchers to investigate questions about cellular movement and behavior without disturbing the cells.

Kalow is also investigating how to use light to instigate reactions and create new molecules with desired properties, such as absorbing specific wavelengths to maximize solar panel efficiencies or creating new light-emitting diodes (LEDs) and sensors. While other chemists are turning to machine learning to screen huge libraries of compounds and identify potential combinations with the desired property, Kalow is taking her cues from nature.

“We're trying to develop reactions that can behave like directed evolution,” she says.

Organisms with certain features survive certain selective pressures, such as when bacteria evolve to resist antibiotics; likewise, Kalow wonders if exposing a wide variety of molecules to specific light wavelengths will reveal molecules that react in useful ways. For example, finding organic molecules that can absorb infrared or near-infrared light could help develop organic electronic materials that are more abundant, lightweight, and flexible than commonly-used inorganic materials, such as silicon, germanium, and mercury cadmium telluride. 

While potential applications help guide her research, Kalow is primarily motivated to understand how things work at the fundamental level. “I always really like understanding why,” the Massachusetts native says. “It's always fun to discover something new that doesn't work the way you expected.”

Kalow specialized in small-molecule fluorination reactions for her Ph.D. from Princeton University. She branched out into polymer chemistry and materials science during a postdoc at the Massachusetts Institute of Technology, finding it satisfying to play with and further understand the compounds she synthesized.

When she launched her own lab at Northwestern University in 2016, she continued to combine these interests in polymer chemistry, synthesis and organic materials science. While COVID-19 has made the past year challenging, she is pleased with her group’s progress on the reversible hydrogels and molecule screening process. “We're at a very exciting point where a lot of the things that I dreamed about doing my first year are actually coming to fruition,” she says.

Kalow notes the Marion Milligan Mason Award will help advance these efforts further by providing support for experiments and, eventually, travel to conferences. She was honored to receive the award and delighted to see other respected colleagues on the recipient list. In particular, she has enjoyed networking with awardees across year groups, saying it was valuable to bounce ideas off of each other, even with those who are peers or only a few years ahead. She encourages other female scientists to do the same.

“You can find mentors anywhere,” she says. “It doesn't necessarily need to be someone a lot more established than you, which can be hard to find depending on where you are.” 

These days, Kalow is increasingly in the mentor role herself. She is teaching, writing, planning experiments, and working with her graduate students, who carry out most of the lab work. She finds it particularly gratifying to see students grow as researchers, from figuring out a tricky analysis or mastering a challenging technique, to giving good scientific talks.  

“Seeing my students become experts in something to the point where they know more about it than me,” she says, “that's really cool.”



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