1. Chemical & Materials Sciences Division, MS K2-01, Pacific Northwest National Laboratory, Richland, Washington 99352; Department of Chemistry, Indian Institute of Science Education and Research, Pune 411021, India; Institut für Mathematik, Freie Universität Berlin, Arnimallee 6, 14195 Berlin, Germany; and Center for Bioinformatics, University of Saarland, 66041 Saarbrücken, Germany