title: Interaction of caffeine with L-tryptophan: study by 1H nuclear magnetic resonance spectroscopy.
abstract: The interaction of caffeine with L-tryptophan was investigated in aqueous solution adjusted to an ionic strength of 0.20, at pH 6.2, by using 1H NMR spectroscopy. Caffeine interacted with L-tryptophan at a molar ratio of 1:1 by parallel stacking. The thermodynamic parameters obtained for the complexation were as follows: delta G degree = -1.70 kcal/mol at 25 degrees C (K = 17.6 M-1), delta H degree = -3.7 kcal/mol, delta S degree = -6.7 eu. It was found that the driving force for parallel stacking is a combination of electrostatic, polarization, and dispersion interactions, and the contribution of hydrophobic bonding is not large. A possible stacking mode is postulated based on the complexation shifts and pi-electron charge distributions of caffeine and L-tryptophan.
authors.affiliation: Kobe Women's College of Pharmacy, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Nishijo
authors.forename: I
authors.initials: I
authors.lastname: Yonetani
authors.forename: E
authors.initials: E
authors.lastname: Iwamoto
authors.forename: S
authors.initials: S
authors.lastname: Tokura
authors.forename: K
authors.initials: K
authors.lastname: Tagahara
authors.forename: M
authors.initials: M
authors.lastname: Sugiura
mesh_terms: D002110:Caffeine / Q000032:analysis*; D055598:Chemical Phenomena; D002621:Chemistry; D009682:Magnetic Resonance Spectroscopy; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D014364:Tryptophan / Q000032:analysis*
chemical_list: D002110:Caffeine; D014364:Tryptophan