Creating Systems that Mimic Nature
Mary Beth Williams, Associate Professor of Chemistry
"Ultimately, we want to mimic biology's ability to do things," says Mary Beth Williams, associate professor of chemistry, about the work that won her the 2007 Young Investigator Award from The Society for Electroanalytical Chemistry. The award recognized her research in "electrochemistry at the interface of nanoscience, and for the development of novel materials."
One thing that biology does that might be of tremendous value if we could learn how to do it as well as nature, is to turn sunlight into chemical energy. Williams and a group of her students are working to unlock some of the mysteries of artificial photosynthesis. Using a technique called metal coordination chemistry, they create molecules that look like small chains of DNA, but instead of DNA's double strands linked by hydrogen atoms, these bonds are formed with metal atoms. The result is a material that is more rigid and stable, and can support electron transfer and catalysis. These structures can be used to transfer electrons down a chain to do work, or be coupled to nearby strands magnetically.
"In photosynthesis, biology harnesses light and moves energy and electrons over nanometers and funnels it to a reaction center to do a chemical reaction. That requires precise alignment of different groups to allow electrons to move over very long distances very efficiently. And we don't know how to do that," Williams says.
Williams and her graduate student CJ Thode examine
gold nanoparticles magnetically linked with iron particles.
Her soft materials group is also interested in mimicking biology's ability to spontaneously self-assemble into larger organized structures. One of their goals is to use self-assembly to build devices that can move electrons and energy over a distance to a focused area to do a reaction, possibly photosynthesis. Another is to build a molecular switch or gate that might be magnetically controlled. Using the ability of soft materials to self-assemble into functional architectures might be a way of approaching the unfulfilled promise of molecular electronics, she suggests.
Another group focuses on hard materials, specifically in making chemically functional magnetic structures and controlling their motion in solution. These magnetic nanomaterials are less than 20nm in diameter, some potentially small enough to cross the blood/brain barrier, which opens huge areas of application in drug delivery and MRI contrast agents. Much of this group's efforts go into creating a library of nanoparticles and developing ways of attaching chemical functionalities to the outside of the particle. With this knowledge, it will be possible to attach a particular drug to the particle in predictable ways. In addition to drug delivery, these functionalized particles could be used for separations - attaching to a particular type of molecule in a solution, for instance, to perform bioanalysis - and in high density magnetic storage.
Transmission electron micrograph (TEM) image
of Fe2O3 nanoparticles self-assembled into a
hexagonal array. Scale bars are (A) 100 and (B) 25 nm.
(C) Cartoon illustrating a sterically stabilized nanoparticle.
"We've been working with Jim Connor at Hershey Medical Center to put proteins on particles that target neuroblastomas. Jim's group is using MRI to better image brain tumors with our particles. Though the particles are not very toxic, still we're seeing if they are building up elsewhere in the animal model to determine long-term effects. The nice thing is that with these chemistries we've developed we can attach multiple species to a particle. In addition to the protein we have attached a platinum containing drug, so the hope is we can get enhanced effect," Williams says.
Her hard materials group has been building models of microfluidic chips and using magnetic fields to control where the particles go. Putting together these devices and tuning them to get the right separations at the right times requires knowledge of fluid dynamics and the modeling of electromagnetic fields that is outside her group's areas of expertise. "We know we can do it," says Williams, "but we don't have the theory on how these gradients set up or what the fluid dynamics are. When you couple all these things together in microfabrication of the device - moving particles and embedded magnets - there are a lot of things we don't know. We're looking for collaborators in those areas, possibly someone in math might be interested."
(A) ~10 nm CoFe2O4 nanoparticles dispersed in hexane.
(B) The identical sample of nanoparticles placed next to a
permanent magnet. (C) A concentrated solution of CoFe2O4
nanoparticles with a permanent magnet placed underneath
the solution illustrating the characteristic Rosensweig spike pattern.
Although her soft and hard materials groups work in different areas of chemistry, they share the same lab and interact on a daily basis, exchanging ideas and presenting formal seminars to each other twice a year, Williams explains. In the seminars, the rule is that if the other group doesn't understand what you're doing, you have to do your presentation again, she says. This means that both groups have to understand basic organic chemistry and basic inorganic chemistry.
"They have to be fairly independent and excited about learning in this group because we don't fall squarely into one area. That means they have to be able to learn about everything, from materials characterization by going out to the Nanofab and learning how to use the TEM and the other equipment out there, to going to the other side of campus and working with bioengineers. We're not easily pigeon-holed into any subfield of chemistry."
Like most experimental scientists, Williams hopes to see her research move out of the laboratory into the real world, where it will have a positive impact on society. With the hard nanomaterials, functional magnetic particles, Williams sees a real near-term role in bioanalysis, bioseparation, and biomedicine.
The soft materials research, on the other hand, is a long-term project which could have a high payoff in the future. "It would be great if you could use photons to create methane or some other fuel and do it efficiently," she says. "Nature knows how to do that. We think in making systems that mimic nature using synthetic, artificial means - soft nanostructures - we'll be able to do that. It will take a long time. Even if our systems can't do it, I think what we learn will be useful for systems that will."
Funding for Professor Williams' research is provided by the National Science Foundation. Contact her at Validate to view address - Send Email via form.
