1. Unilever Research Laboratory Vlaardingen, Olivier van Noortlaan 120, NL-3313AT Vlaardingen, The Netherlands, Organisch-Chemisches Institut, Universität Münster, 48149 Münster, Germany, and ICOA/Université d'Orléans, B.P. 6759, F-45067 Orléans Cedex 2, France