Photo by Janet Sassi
If someone peers through a microscope, a synthetic molecule known as a dendrimer looks somewhat like a snowflake—branching, symmetrical, each one uniquely constructed.
But beauty, according to Amy Balija, Ph.D. is only part of its charm.
Balija, assistant professor of chemistry, has been working with dendrimers in her John Mulcahy Hall laboratory for the last four years. Creating them, she said, is not unlike following a recipe in the kitchen: someone mixes particular chemical compounds in a container, then applies—in varying degrees—several other factors such as heat, stirring, filtering, etc. When complete, the chemist said, hopefully the modern-day piece of alchemy will do what its chemical designers intended it to do, and do it well.
“Dendrimers already have many applications, but their future possibilities are limitless,” Balija said. “They can mimic enzymes, be applied in fingerprinting analysis, deliver drugs inside the body, entrap pollutants in our environment and even function inside solar panels to make electricity.”
One problem, said Balija, is that it takes a very long time to construct dendrimers in the lab; the chemistry is intricate and painstaking and often requires a time-consuming purification process. In fact, the process can be so lengthy that it can be difficult for chemistry students to finish synthesizing a dendrimer during the course of one academic year, Balija said.
“This is an issue we need to address,” she said, “because scientists want to work with something that’s quick and easy to prepare.”
Typically, dendrimers are put together much in the same way as Legos, with sections of atoms, or monomers, binding perfectly with other sections and a core to form the larger structure. Last year, Balija and her team of undergraduate students discovered a fast way to prepare a monomer that makes up a section of a new pollutant-eating dendrimer they are currently studying.
The team, that consisted of Balija, Meghan Kirrane (FCRH ’10) and Sarah Tomas (FCRH ’10) combined an acid containing two nitrogen atoms with benzaldehyde, an almond-scented molecule, in alcohol. The resulting monomer easily separated from the alcohol by settling to the bottom of the reaction flask. Through further examination, the team discovered that the monomer was pure and needed no additional purification.
“The separation and purification is normally something chemists have to do themselves,” Balija said. “So this has a big impact. It’s important. It is a simple experiment with a lot of big connotations.”
In essence, Balija and her team discovered a new and shorter synthetic path to creating a successful dendrimer. Their particular dendrimer, which consists of a core and three monomers (called a three-armed core model), can be created in less than a day, she said. The research also opens the door for other organic chemists creating dendrimers to try similar experiments.
Balija’s as-yet-unnamed dendrimer, referred to in the lab as the “entrapping pollutant” dendrimer, is designed to attract Polycyclic Aromatic Hydrocarbon (PAH) pollutants that populate sources of human drinking water.
“PAHs are everywhere,” Balija said. “They are in our streams, our rivers and our oceans, which are bad because they are toxic chemicals. Right now our water treatment systems are not able to efficiently extract PAHs from the water, so we are drinking these chemicals in our water supply. And more is coming from our factories, our soaps, our lotions and from other things we use on an everyday basis.”
Like PAHs, Balija’s “entrapping pollutant” dendrimer is a hydrophobic compound, which means that it is repelled by water. When both substances are suspended in H2O, they naturally seek each other out in a “like-attracts-like” model of chemical binding. Eventually, she said, chemists will work with manufacturers to create dendrimer-enhanced water filtration systems.
But first, Balija and her students are undertaking a new series of laboratory tests on their dendrimer to see if the strategic placement of oxygen, nitrogen or sulfur atoms at key junctions in the structure can enhance its pollutant-eating properties. They aim to create the most potent PAH-eating macromolecule possible.
“Each of these chemical atoms has a different shape, different properties,” Balija said, “and there are thousands of combinations of atoms to test. But what we are finding in preliminary research is that different combinations of these three atoms really do make a difference in how the dendrimer is encapsulating the pollutants.”
In the fall of 2009, Balija and her students presented their research at the annual meeting of the American Chemical Society in Washington, D.C.
Ironically, her interest in synthesizing molecules for use in biological and material science applications came about via a core course she teaches called “Chemistry of the Environment.” Inspired by an article on PAHs, Balija saw the potential for a PAH-eating dendrimer; she has been working on it for just over a year, she said.
“My research seeks to better understand the dendrimer as an entity, and to share what I learn with others,” she said.
