AEM faculty spotlight:
When an engineer creates a new bridge design, reference tables are consulted. AEM Professor Richard James seeks to create such a reference on a slightly smaller scale, that of atoms and molecules. James, a Distinguished McKnight and Russell J. Penrose Professor, has long been interested in developing unusual new materials. Recently, his work has shifted toward biomaterials, specifically bacteriophage T4. Viruses like T4 are built of components that he calls “objective structures.” To picture an objective structure, imagine a group of identical people sitting in chairs that are arranged in a perfect circle. Each person sees exactly the same environment. Professor James discusses these and more in the following Q&A.
What kinds of research interest you these days?
My work is about the discovery of new materials. In my lab we make alloys from elemental materials. Mostly this is guided by theoretical developments. My students and I develop theory to understand the behavior of materials. We take predictions from the theory and we go to the lab and make the materials. As you can imagine, it can be a incredibly exciting, as when we actually discover a new material with some unexpected properties, or deeply humbling, when we realize that we have left an important factor out of the theory.
I don’t know if I wish to expose the deeply humbling moments, but much of our work is on shape memory materials, where a very large change of shape is induced by changing the temperature. This behavior is caused by a phase transformation in the material, like the change from ice to water, but in shape memory alloys the transformation is between two solid phases. A few years ago, guided by theory, we realized that if a material would have one of these phase transformations, and would also be magnetic and satisfy some other conditions coming from the theory, one should be able to induce the phase transformation by applying a magnetic field. With the help of Professor Shield, these materials were then realized in my lab and, at about the same time, in several other labs around the world. They are now called ferromagnetic shape memory materials. In the low temperature phase, if one brings a bar magnet close to the piece of material, it undergoes a big change of shape. We are now thinking about other ways a phase transformation can be used to allow a material to have properties that would be impossible in a single phase material. A dream material, for instance, would have a ferroelectric phase and a ferromagnetic phase. There is some idea from theory that one could find materials like that.
How would you look for such a material?
For one thing we rely on collaborations with physicists who do so called “first principles calculations” to help identify good candidate materials for these kinds of phase transformations, particularly cases where we might expect interesting properties like ferromagnetism or ferroelectricity. Another extremely important aspect of these transforming materials is reversibility. Lots of materials have these phase transformations, but few are highly reversible like shape memory materials. Of course, it is much more interesting when we have this high degree of reversibility, as one can then go easily back and forth between the phases. One of the breakthroughs we had recently is a new understanding of reversibility, completely contrary to what is written in textbooks. It is a quantitative understanding, so we could go to the lab and systematically change composition to achieve these special conditions that theoretically give high reversibility. My recent Ph.D. student, Jerry Zhang, did this, and the results were amazing: in some cases he decreased the size of the hysteresis (a measure of reversibility) by a factor of 10. There are fascinating new families of shape memory alloys that are emerging from this work.
Tell me a bit about objective structures.
This is a new direction in my research, and, as usual, I am beginning with the development of mathematical theory. If you look at the way viruses are made, the structures are built in a certain way. Imagine a structure which is built of identical molecules and each molecule contains a certain number of atoms. Imagine you number the atoms, one to one hundred, say. Then, in the structure, imagine that you sit on the 27th atom of one of the molecules, and you look at your environment. Nearby, you see other atoms of the same molecule, and a bit further away, you see other atoms of the other molecules. Now you go to the 27th atom of a different molecule and, again, sit on that atom and look at your environment. If you orient yourself in just the right way, you see exactly the same environment, just as in the circle of chairs I mentioned earlier. If this happens for corresponding atoms in every molecule of the structure, then I call that an objective structure. Lots of the parts of viruses have these structures. But also, most of the structures adopted by elements in the Periodic Table are objective structures with one atom per molecule, including exotic things like buckyballs and carbon nanotubes.
What can we learn from such structures?
For one thing, these are the natural structures to search for special physical properties like ferromagnetism, ferroelectricity and even superconductivity. For instance, in the case of ferromagnetism, if one of the atoms wants to have unpaired spins, that is, to be magnetic, all of the atoms will also want to be magnetic, because of the way objective structures are built. People in biology take structures as they are given and study them: it is considered less interesting in biology if one violates any of the conditions that occur in vivo. But I like to think in more of an engineering way about this, and the first step is understanding how they’re put together. This is a bit more like the way of thinking in materials science, too. Also, mathematical theory is almost completely absent from the toolbox of biologists, and we have found it to be incredibly useful in our work on the discovery of materials. Objective structures offer a special window into quantitative building of molecular structures.
How would someone go about building something like a virus?
When someone builds a bridge, they go to engineering tables and find I-beams and look at cross-sections and, from stress analysis, they understand how to use these in a reliable, efficient structure. What I would like is to have that kind of quantitative information for molecules, so you could build structures out of molecules in the same way you build bridge structures or anything else in engineering. If you could do this you might be able to build a structure which has certain bonding sites, functional groups and so forth. You might be able to build a structure which would exactly match some part of a virus. By doing that you may be able to make it so the virus naturally binds the structure, thereby disabling the virus. You might be able to build a tubular structure whose molecules exactly match the inside of a carbon nanotube. Suitably functionalized, it could be a template for the large-scale growth of carbon nanotubes.
How do you find objective structures? Do they all look like carbon nanotubes or viruses?
No, there are many others! In fact, last year, together with Prof. Ryan Elliott and our postdoc Kaushik Dayal, we set ourselves the task of writing an explicit formula for every objective structure. I was on sabbatical at the Max-Planck-Institute for Mathematics in the Sciences in Germany, and I think one can only contemplate trying such a calculation on a sabbatical. I myself have more than 1000 man-hours invested in this one calculation. But, we succeeded in finding an explicit formula for every objective structure. This is a basis for a systematic study of their properties.
Last Modified: Thursday, 04-Oct-2007 11:09:10 CDT -- this is in International Standard Date and Time Notation