Thermodynamics of the enantiomers of amino acid and monosaccharide binding to fullerenol used as an artificial sweet taste receptor model

Fullerenol was used as sweet taste receptor model to investigate the binding affinities of structurally related pairs of enantiomers by isothermal titration calorimetry (ITC). It reveals that amino acid binding with fullerenol are enthalpy-cost and entropically-driven processes, whereas enthalpy contributes to monosaccharide binding to fullerenol. Spontaneous binding of amino acids was found through two sequential steps in which the sweeter enantiomer displays larger binding constants. Association of the d-form of fructose and l-form galactose with fullerenol suggested that, the higher the perceived sweetness intensity of the enantiomer, the larger was the binding constant with respect to their antipodes. Further investigation by molecular dynamic simulation showed that the binding energy and the perceived sweetness intensity were well correlated. The preliminary results of this biomimetic research cover the lack of information about the thermodynamic basis of sweet sensation and the underlying principles of sweetness differences between the enantiomers of amino acids and monosaccharides.