1. Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093, USA
2. Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois 60607, USA
3. Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306, USA
4. Department of Pharmacology, University of California San Diego, La Jolla, California 92093, USA
5. Department of Bioengineering, University of California San Diego, La Jolla, California 92093, USA
6. Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, USA