1. Beckman Institute, California Institute of Technology, Pasadena, California 91125, United States
2. Institute of Analytical Chemistry, University of Copenhagen, 2100 Copenhagen, Denmark
3. Department of Chemistry, Washington State University, Pullman, Washington 99164-4630, United States
4. Department of Chemistry, Pomona College, Claremont, California 91711-6338, United States
5. Department of Immunology, The Weizmann Institute of Science, Rehovot 76100, Israel