Selective recognition of tryptophan through inhibition of intramolecular charge-transfer interactions in an aqueous medium.

[reaction: see text] A novel donor-acceptor conjugate 1 was synthesized, and its interactions with various amino acids have been investigated as compared to the model system 2. The conjugate 1 unusually forms an intramolecular charge-transfer complex in the aqueous medium and undergoes selective binding interactions with tryptophan. The uniqueness of this system is that it selectively recognizes tryptophan among all other amino acids and involves synergistic effects of pi-stacking, electrostatic, and donor-acceptor interactions.