The comparison of electrostatic surface potentials (ESPs) of aromatic rings in tryptophan, tyrosine, phenylalanine, and histidine suggests that electronic effects also play a role in the binding to glycans (see Figure 2). After normalizing the electron densities for surface area, the tryptophan still remains the most electron rich acceptor of  interactions, suggesting a possible reason for its 9-fold prevalence in carbohydrate binding pockets. Overall, the electrostatic potential maps follow the prevalence trend of .