[1] Univ Calif Santa Barbara, Dept Chem & Biochem, Santa Barbara, CA 93106 USA
[2] Univ Calif Santa Barbara, Biomol Sci & Engn Program, Santa Barbara, CA 93106 USA
[3] Univ Calif Santa Barbara, Dept Phys, Santa Barbara, CA 93106 USA
[4] Univ Calif San Diego, Dept Chem & Biochem, La Jolla, CA 92093 USA