1. Centre de Recherche Paul Pascal CNRS, UPR 8641, 33 Avenue A. Schweitzer, 33600 Pessac, France, Supramolecular Chemistry Biomimetism and Nanosciences, UMR 5802, Université Bordeaux 1, 351 Cours de la Libération, 33405 Talence, France, and Thermo Electron Corporation, Dieselstrasse 4, D-76227 Karlsruhe, Germany