First Artificial Receptor for Caffeine-A New Concept for the Complexation of Alkylated Oxopurines This work was supported by the Fonds der Chemischen Industrie (Liebig fellowships for S.R.W. and C.A.S.) and the Deutsche Akademie der Naturforscher Leopoldina/BMBF (postdoctoral fellowship for C.A.S.).