Imagine having the power to make molecules that never existed before you drew up the plans, broke down and re-constituted bonds. And your ultimate goal is to have these molecules become self-assembling structures that will grow into a machine. Now that’s chemistry at The University of Texas at Dallas [UTD]!
At least it is according to Greg Hundt, a fourth-year doctoral candidate with one year left.
“We make large hoop-shaped structures [called Wurster’s Crowns] on a molecular scale in the Sibert lab. They can capture organic guests inside them. Essentially, if you had a straight rod threaded through a wheel, that is the sort of mental image of what I'm talking about. This aggregate is called a pseudorotaxane with the Wurster's Crown providing the wheel-type structure.
“The catenane would be two hoop structures linked together like links in a chain. And then you control how these assemble – you put both of them free into a solution and they will form aggregate structures all by themselves. We can actually control how they assemble using electrochemistry – when you put in or remove electrons from the system, you can induce movement in these molecules relative to one another.
“On the grand scheme the big idea is people want to take these kinds of structures and do things with them. One, they want to make, or they think they can be the basis for, molecular-level machines. People are really trying to do this kind of thing, you know, they’re nanotech or nano-scale machines. You can store binary information at the molecular level through these kinds of systems,” Greg said.
These guests are ionic and organic molecular materials, such as paraquat, he said.
Wait a minute! Did he just say molecular-level machines? Scenes from a science fiction movie pop into mind. Where did this guy come from?
“I was born in Dallas. I was an undergraduate at Austin College, in Sherman, Texas, about an hour north of here, and I did research and published a paper there as an undergraduate. And so it was very easy for me to just come down and check out the UTD campus. I guess that’s part of what helped me come here, was that it was so easy geographically for me to come down and look," he said.
Greg said he liked the industrial aspects of UTD's chemistry program.
“If you look, the ACS [American Chemical Society] says that most chemists end up working for industry, so I thought that this would afford me an opportunity to go work for companies and things before I got my degree. And that is, in fact, what I have done. I left the department for a year and went on an internship and worked for Dow Chemical for a year and came back. And so it’s that kind of experience that other chemistry programs can’t give that I thought was so attractive about UTD,” Greg said.
The Sibert lab
Greg is a research assistant in the laboratory of Assistant Professor John Sibert, Ph.D. Sibert’s research program centers on the synthesis and coordination chemistry of novel classes of macrocyclic receptors with applications that range from catalysis to medicine to materials science.
“I’ve been doing research in the Sibert lab since I began at UTD. Except for the time I was away for my internship, I’ve worked in there both for my master’s work and now for my Ph.D. work,” Greg said.
But enough of Greg’s background information. Let’s go back to the goals of the research.
“It’s synthetic chemistry. I make new molecules that haven’t been made before and then we study their properties.
“Specifically, we want to see whether we can sense guests captured by our molecules. They are sort of elaborate molecular sensors, in a way. We use electrochemistry — CV [cyclic voltammetry] — and UV-Vis [ultraviolet-visible] instrumentation to study the way these molecules capture other ions and molecules in solution,” Greg said.
Cyclic Voltammetry and UV-Vis spectroscopy
Ultraviolet-Visible Spectroscopy, an analytical tool to determine organic structures, irradiates a compound with light of a particular wavelength. If the compound absorbs the light, the detector will record the amount of absorbance. By contrast, cyclic voltammetry measures the transfer of electrons during an oxidation-reduction [redox] reaction. Both are tools Greg and members of the Sibert lab – manipulators of the Wurster crowns – depend on to do their work.
“These molecules are designed to capture things within them. We can examine that capture through a variety of different ways. And cyclic voltammetry tells us how easily or how difficult the compound is to oxidize, or to remove electrons from. Once we capture guests, they all turn out to be harder to oxidize or remove electrons from the system, until recently, when we experienced that sometimes the opposite may also happen. But we can study that by CV and that gives us information about how tightly the guest is captured and the affinity that our molecules have for their guests.
“So essentially, it allows us to see what type of light is absorbed by molecules over time,” Greg said. “It also allows us very quickly to see whether or not we’ve been successful in designing molecules because I take it all the way from paper – drawing out exactly what we want to make – and so, in that process, you have to just ask yourself, 'What kind of properties are desirable in the end' and 'What do I need the molecule to be like?' ”
Breaking the law?
Greg continued, “We take it all the way from its inception on paper, through making it and then studying final properties. It’s, in fact, pretty gratifying to know whether or not your initial idea way back a year ago actually turns out to be useful or bunk.”
“It’s the way you arrange the matter that’s important,” Greg said, matter-of-factly. “Of course, we can’t create atoms or entirely new material but we can organize it in different ways, and that’s really the job of a synthetic chemist, is to break and create bonds to organize pre-existing molecules into new shapes and forms," he said
Does anybody else’s mind drift off to the lab of Dr. Frankenstein? Although the first law of physics states that matter can neither be created nor destroyed, what Greg is doing seems to come pretty darn close.
“But, yeah, the molecules in our lab, to the best of our knowledge, have never existed before. Synthesis is a really cool thing. You know at the end of the day, you get to hold a flask that you know you are the first person in the world to have ever held that molecule and looked at it, so it’s really kind of cool,” Greg said with a genuine look of pride.
Speaking of pride, Greg has nothing but praise for Sibert, his principal investigator.
“I think it’s pretty unique to the department that all graduate students are on a very friendly, casual basis with Sibert. It’s not some sort of aloof professor and students. We’ll go, as a group, out to lunch and then hang out. That’s a very unique atmosphere.
“And I think that’s Sibert’s idea, actually. He has said so many times that he wants the lab to be relaxed and casual because the more at home you feel in the lab, the more you'll come to work. So we’re fortunate in the sense that we have that atmosphere.
“But it leads to us coming in, even late at night. I mean, I worked until 4:30 a.m. last night in the lab. And that’s not uncommon. And not even for Sibert. He’s actually in there until very late at night, 3 or 4 in the morning, a couple of times a week. It’s like we are working with him as, not equals but operating in that sense on a daily basis. To us, that’s actually a nice leadership method that he has to get us to work or be in the lab,” Greg said.
Greg spoke of a trip last summer, when Sibert chartered a boat out of Lake Jackson to fish the Gulf of Mexico. Students from Sibert's lab participated as well as chemists from Dow Chemical Co. Before catching their bounty of fish — red snapper, mackerel, mahi mahi and shark — Greg said that they spent three hours heading out to sea.
"That's the thing: When you get a bunch of chemists on a boat, and you are isolated from everybody else, the conversation naturally turns to chemistry. So we just sat around, from the time the boat leaves the dock and you go out to where you are going to fish and you just end up chatting about chemistry.
"I mean, whatever comes to your mind. So actually that was a nice time for the UTD people and the Dow people to get together and have candid conversation, 'Hey, this is working. Hey, this isn’t working. What do you think?' that sort of thing.
"Gosh! You learn almost as much in those sort of casual settings as you do at a professional conference because you get to ask very specifically what it is you want to know," Greg said.
- Updated: September 23, 2005