1. Department of Applied Physics and Applied Mathematics, Center for Electron Transport in Molecular Nanostructures, NanoMedicine Center for Mechanical Biology, Columbia University, 020 Schapiro CEPSR, 530 West 120th Street, New York, New York 10027, and Department of Biochemistry and Molecular Biophysics, Columbia University, 650 West 168th Street, Black Building Room 536, New York, New York 10032