Organic chemistry students synthesize new molecules that really shine in the spotlight
The funny thing about chemistry research is how often major breakthroughs result from deviations from the original plan. This was certainly the case at Ohio Northern University this year, where a casual observation changed the direction and scope of a Department of Chemistry and Biochemistry research project, and led to the creation of something the world had never seen.
Dr. Jake Zimmerman, associate professor of chemistry, is no stranger to synthesizing new molecules. As an organic chemist, it’s what he does. In just the past four years, his research group has published four papers involving new molecules created right here at ONU.
But it’s his group’s latest research that really draws the eye.
Over the past nine months, Zimmerman, along with three students — seniors Olivia Johntony and Daniel Steigerwald and junior Cody Criss — have synthesized more than 50 new molecules that share one dramatic characteristic: They glow.
More precisely, they fluoresce under ultraviolet light. Fluorescence is the property of a substance that allows it to produce visible light as it is being exposed to radiant energy like ultraviolet light. One type of ultraviolet light, the type that is used to make these molecules fluoresce, is more commonly known as “black light,” so if you went to college in the ’90s, visited a haunted house or have gone “cosmic bowling,” you’ve probably seen the phenomenon of fluorescence at work.
There are two principal factors to fluorescence. The first is how efficiently the molecule transforms radiant energy into visible light. To the naked eye, this translates to intensity or brightness. To chemists, it’s the result of the molecules quantum yield, or amount of photons released by the molecule. The best quantum yield is 1.0 (100 percent).
The second factor is color. Not every color of the visible spectrum can be produced using the method that Zimmerman’s team used. However, the researchers were able to produce the color blue, which is generally regarded as a difficult color to achieve. Even more impressive is that the group’s blue molecule has the highest quantum yield (.85) of all the molecules they created.
“Our goal last summer was to get good quantum yields in a range of colors,” says Zimmerman. “Our blue is very high, we’ve produced blue/green between .7 and .75, and green between .7 and .75.”
The research project uses an inverse demand hetero-Diels-Alder reaction, something that has never been used to create fluorescent chromone-based molecules. In fact, Zimmerman and his team didn’t even set out to create fluorescent molecules. Their primary area of interest lies in medicinal chemistry, and the original scope of the project was to create a new molecule based on a chromone structure that is found in many medicinally relevant molecules.
“I wish I could say that I knew that the molecules were going to fluoresce, but that’s not true,” he says. “We were interested in synthesizing a molecule that would penetrate cells and kill bacteria or something like that. It was only after a colleague noticed that one of our compounds fluoresced when dissolved in solution, did we even think to explore it. So, we kind of stumbled upon it. But in chemistry, that happens a lot.”
The group steered the project towards finding out just how well they could build fluorescing molecules. The resulting research went so well that the team is submitting two manuscripts for publication, one pertaining to the synthesis of the molecules, and another pertaining to a potential application as a chemical sensor.
“I remember having trouble the first couple of weeks with getting the compounds to fluoresce,” says Criss. “As we did more and more research, we started to better understand the mechanism of why it was fluorescing, and towards the end of the summer we started producing a lot brighter fluorescing compounds.”
In fact, a friendly competition blossomed among the students as to which compound would produce a better quantum yield or which ones “Dr. Z” liked best. Having any idea at all as to which molecule might preform better is a testament to the students’ command of organic chemistry.
“There are different substituents on the various chromones we used throughout this research. For example, one chromone might just have hydrogen atoms all around it. Another might have a methyl group. Our method for synthesis places different groups of atoms on the chromone’s structure, thereby changing its properties and creating different molecules,” says Johntony.
After the molecule is synthesized, the students then used ONU’s nuclear magnetic resonance (NMR) instrument to analyze the compound to ensure that they actually made what they set out to make. The NMR uses a superconducting electromagnet to create a concentrated magnetic field around a molecule. The machine then bombards the molecule with radio frequencies, which causes the nuclei of the atoms, to absorb energy. Different atoms absorb different frequencies, so scientists are able to determine which atoms are which, thereby validating the composition of the molecule.
It is important to make clear that Johntony, Steigerwald and Criss are not research assistants on this project. They worked side-by-side with Zimmerman and co-investigators Dr. Brian Myers, associate professor of chemistry, and Dr. David Kinder, professor of medicinal chemistry. The students synthesized the molecules themselves, validated them with the NMR and analyzed the results. They even had keycard-access to the NMR, a $250,000 instrument, so they could use it anytime they needed to.
To be sure, these students are very bright and very capable. But they are not unique at all in terms of the trust given in regards to this research project. Their experience is replicated dozens of times each year with students across the five disciplines of chemistry at ONU. It’s part of the culture of the Department of Chemistry and Biochemistry and of academic departments across campus.
Johntony has worked with Zimmerman for three years. She already has one publication and will get another when this research is published later this year. She graduates this May and begins dental school in the fall. She credits her undergraduate research experience with helping her pursue her dream of becoming a dentist for patients with special needs, and also for putting her on the right path early in her ONU career.
“By the time I took Dr. Z’s medicinal chemistry course, I’d already had one semester of research. So that class, especially the lab component, was a lot easier for me. I felt like I had a big head start. Having experience in a lab doing research gave me a lot of confidence.”
Experience is very important, but so too are outcomes. While it is far too early to identify with any certainty applications for their molecules, Zimmerman is submitting another manuscript for publication on their use as a potential chemical sensor for the fluoride ion.
An interesting thing happens when one of the group’s new molecules comes into contact with fluoride — it stops fluorescing. The reaction is so sudden and complete that it’s almost like flipping off a light switch. That is why Zimmerman believes there is potential for application as part of a detection mechanism for fluoride.
One might wonder why anyone would need to detect fluoride. After all, humans ingest fluoride all the time due to its benefit to teeth and bones. But fluoride at high doses can be harmful to humans. The molecules also show promise as biological imaging agents as the research shows they are capable of excellent cell membrane permeability.
From its beginning as an attempt to create a new disease-fighting chromone derivative, to its redirection into the phenomenon of fluorescence, and now to a potential future as a chemical sensor, this ONU research project is a fascinating peek into the exciting and often unpredictable world of chemistry research.