1. Physical Chemistry Department and Center for Nanoscience and Nanotechnology, The Hebrew University, Jerusalem 91904, Israel, Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, 69978 Israel and Tel Aviv University Nanotechnology Center, and Centro S3, CNR Istituto di Nanoscienze, Via Campi 213/A, 41125 Modena, Italy