Georgetown College. Georgetown University.

Katrina Heyrana hopes to pursue a M.D./Ph.D. after graduating from Georgetown. (Photo: Roland Dimaya)

By Theodora Danylevich

Katrina Heyrana, a senior in Dr. Jennifer Swift’s lab, currently specializes in the use of surfaces for growing crystals. A Chemistry major and a Music minor, Heyrana has twice published her labwork for the pharmacology department of the Georgetown University Medical Center.

Heyrana’s goal is to obtain an M.D./Ph.D. and work in the biomedical research field developing treatments for infectious diseases. She chose to work with Dr. Swift because she found the experiments in Dr. Swift’s lab to be the most innovative and exciting. An ambitious and discerning student, Heyrana’s work in the lab earned her a GUROP research grant this summer, and she has subsequently presented her work at conferences at Georgetown and the University of Maryland at Baltimore County.

A distinctive feature of the crystals that Heyrana’s work focuses on is that the same compound can take on a variety of shapes and molecular arrangements when it grows into a crystal, depending on the surrounding molecules or the surface that it grows on or adheres to. This is knows as crystal polymorphism.

“Polymorphs can have vastly different physical properties, varying in such aspects as melting point, color, and bioavailability. The last characteristic is especially important to the pharmaceutical industry because it is possible that one polymorph of a compound can work as a drug while a different polymorph of the same compound can be completely ineffective or even have deleterious effects,” explains Heyrana.

Heyrana's work seeks to isolate and analyze the various polymorphs that a given compound can crystallize into. The way that she goes about achieving this is twofold: First, she creates synthetic surfaces, known as “template surfaces” or self-assembled monolayers (SAMs), which are composed of specific molecules arranged in a way to encourage crystals to adhere to the surface and grow on it. Second, Heyrana immerses the different surfaces in a variety of compound solutions from which she analyzes the crystals that grown on the template surfaces. She and her lab partners then record functional features, such as which face of the crystal adheres to the template surface, which functional groups of the compound interact with the surface, whether the spacing of the molecules in the template surface and crystal lattice match up, and how the individual molecules of a crystal pack into a unit cell of the template surface.

“This helps us determine how the presence of template surfaces affects crystal growth out of solution,” she says.

The use of template surfaces for growing crystals is an innovative technique, key to efficiently controlling the growth of and analyzing specific polymorphs that come out of a given compound solution.

“When crystals grow out of solution without a template surface—which is the conventional way that crystals are produced—you have less control over the seeding and subsequent growth of the crystals. As a result, different polymorphs can grow concomitantly (they literally grow on top of one another) and it can be nearly impossible to separate them,” explains Heyrana.

Heyrana's specific focus is in crystallizing compounds that are derivative of urea. Heyrana and her lab-mates manipulate and modify the urea molecule to encourage the compound to crystallize in different ways.

“This is interesting to us because there's a lot of opportunity for rotation around the bonds between the nitrogen and the carbon of the phenyl rings of the molecules, so these compounds can adopt many different packing conformations,” explains Heyrana.

Ultimately, Heyrana seeks to find the most ideal combinations of SAMs and crystallization solvents to template the growth of only one polymorph in a given phenyl urea system at a time. After they find combinations that work, they try to figure out how and why they work so well, examining the various properties of each resultant polymorph.

“I've learned that things don't always go the way that you plan. But you have to be able to adapt and explain why these new things occur,” says Heyrana. Despite the time commitment involved, she likes the independence of having her own project and being accountable for her results.

“I really enjoy the implications of my work for medicine and industry. The ability to grow one polymorph and only one polymorph every time you need a crystal would help streamline production of pharmaceuticals, dyes, and even energetic supplies (and those are only a few of the industries that could use this technology). It would really be wonderful to be able to grow exactly what you want when you want it, which is not always the case with crystal growth. SAMs also help us understand molecular interactions as well as the thermodynamics of crystal growth,” she says.

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