Interaction of caffeine with L-tryptophan: study by 1H nuclear magnetic resonance spectroscopy.
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.
Nishijo
J
J
Kobe Women's College of Pharmacy, Japan.
Yonetani
I
I
Iwamoto
E
E
Tokura
S
S
Tagahara
K
K
Sugiura
M
M
D002110:Caffeine / Q000032:analysis*; D055598:Chemical Phenomena; D002621:Chemistry; D009682:Magnetic Resonance Spectroscopy; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D014364:Tryptophan / Q000032:analysis*
D002110:Caffeine; D014364:Tryptophan