1. Department of Chemistry and Biochemistry and Department of Mechanical Engineering and Bioengineering Program, University of Maryland, College Park, Maryland 20742, Calibrant Biosystems, 910 Clopper Road, Suite 220N, Gaithersburg, Maryland 20878, and Molecular Pathogenesis Unit, Surgical Neurology Branch, National Institute of Neurological Disorders and Stroke, Bethesda, Maryland 20892