Structure and reactivity of supramolecular systems acting as highly selective "chemo-logic" devices in the gas phase

The present kinetic and IRMPD spectroscopic study demonstrated that the chiral macrocycle Chirabite-A (M) behaves in the gas phase as a selective template for aromatic amino acids (G). In the presence of amines (A = 2-aminobutane or piperidine), its proton-bound diastereomeric [M:H:G]’ complexes (G = phenylglycine, phenylalanine, tryptophan, dopa, and naphthylalanine), undergo time-dependent monoexponential decays with formation of the corresponding substitutioe ([M-H-A]) product, sometimes accompanied by the addition ([M:H:-G-AT7 derivative. Depending upon the nature and the configuration of G and A, ibe kinetic curves exhibit a plateau revealing the presence of unreactive [M:H:GI structures. In them, the amino acid is accommodated inside the macrocycle cavity in the zwitterionic form by sharing its acidic hydrogen atoms with the pyridine nitrogen atoms of the host. The same interactions are structurally inaccessible to dipeptides or monofunctional amines, which then can be readily released from their complexes. When the amino acid interacts with the amidocarbonyl oxygen atoms pointing outside the Chirabite-A cavity, it saves the canonical structure and can be readily displaced by amine A. The occurrence of isomeric forms has beeg confirmed by variable wavelength IRMPD spectroscopy. The structural and kinetic properties of diastereomeric [M:H:G]' complexes (G = aromatic amino acid) confer to them the features of “chemo-logic” device in the gas phase. Depending on the relative configuration of the M/G pair and the nature of the amine A, the loss of the amino acid may occur ("Logic-gate"). Furthermore, the logic output of a given [M:H:G]° diastereomer may depend upon the specific reaction threshold chosen (multi-output “logic gate”).