1. São Carlos Institute of Physics, University of São Paulo, Caixa Postal 369, São Carlos, SP CEP 13560-970, Brazil
2. Laboratório de Retrovirologia, Universidade Federal de São Paulo, São Paulo, Brazil
3. Department of Chemistry, University of Hull, Cottingham Road, Hull HU6 7RX, U.K.
4. Department of Chemistry, University College London, London WC1H 0AJ, U.K.