1. Department of Fundamental Chemistry; Federal University of Pernambuco; Recife PE 50740-560 Brazil
2. Department of Physical Chemistry; ETH-Hönggerberg; Zurich CH-8093 Switzerland
3. Center for Vaccine Research, University of Pittsburgh, 9052 BST3; Pittsburgh PA 15261
4. Aggeu Magalhães Research Center, Oswaldo Cruz Foundation; Recife PE 50670-420 Brazil