1. Instituto de Química Médica (CSIC), Juan de la Cierva, 3, 28006 Madrid (Spain)
2. Department of Chemistry, Youngstown State University, Youngstown, Ohio 44555 (USA)
3. Departamento de Química, C‐9, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid (Spain), Fax: (+34) 91‐497‐5238