INTERACTION OF CAFFEINE WITH L-TRYPTOPHAN - STUDY BY H-1 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: ΔGo = −1.70 kcal/mol at 25 oC(K = 17.6M−1), ΔHo = −3.7 kcal/mol, ΔSo = −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 π‐electron charge distributions of caffeine and L‐tryptophan. Copyright © 1990 Wiley‐Liss, Inc., A Wiley Company