title: Recognition of caffeine in aqueous solutions.
abstract: Binding of caffeine in aqueous solutions has been achieved for the first time by using water-soluble, tetracationic peptide-porphyrin conjugates Zn-1 as the receptor molecules. The association constant for caffeine with receptor Zn-1 is in some cases as high as 6000 M(-1), only 5-6 times lower than the highest binding constant reported for an artificial caffeine receptor in low polarity aprotic solvents. The binding mechanism has been studied by a combination of experimental techniques such as UV-visible and NMR spectroscopy and microcalorimetry. Recognition of caffeine involves both stacking with the porphyrin ring and metal coordination. Subtle variations of the receptor structure affect the complexation. Receptors Zn-1 have also been investigated for the recognition of molecules structurally related to caffeine, for example, 1-methylimidazole. Selectivity towards oxopurine derivatives (caffeine and theophylline) have been found.
authors.affiliation: Laboratory of Supramolecular Chemistry and Technology MESA+ Research Institute, University of Twente, 7500 AE Enschede, The Netherlands.
authors.forename: Roberto
authors.initials: R
authors.lastname: Fiammengo
authors.forename: Mercedes
authors.initials: M
authors.lastname: Crego-Calama
authors.forename: Peter
authors.initials: P
authors.lastname: Timmerman
authors.forename: David N
authors.initials: DN
authors.lastname: Reinhoudt
mesh_terms: D002110:Caffeine / Q000032:analysis / Q000737:chemistry*; D002151:Calorimetry / Q000379:methods; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D009942:Organometallic Compounds / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D011166:Porphyrins / Q000737:chemistry; D012996:Solutions; D013056:Spectrophotometry, Ultraviolet; D013379:Substrate Specificity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry / Q000378:metabolism
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D010455:Peptides; D011166:Porphyrins; D012996:Solutions; D014867:Water; D002110:Caffeine; D015032:Zinc