1. Chemistry Department, Northern Arizona University, Flagstaff, Arizona 86011, Exxon Research and Engineering, Annandale, New Jersey 08801, Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, U.K., AgBiotech Center, Rutgers University, Cook College, New Brunswick, New Jersey 08903, and Stanford Synchrotron Radiation Laboratory, SLAC, Stanford, California 94309