We can put a bipyridine in there, which has some really fantastic chemistry. You can introduce things that have very rich photochemistry, say, ruthenium tris-bipyridine, as an amino acid inside the middle of a protein. You can do that now. Some are commercially available. Say instead of having a phenylalanine, you can replace the aromatic ring with pyridine.
Pyridine's a great ligand.
And it's wonderful, you can have all kinds of really interesting spectroscopy associated with it. I mean the possibilities are endless. Well, that's the trick. If you want to code for it, what you're going to have to do is go the route that Peter Schultz does. So they generate a completely new amino acid.