Effect of the formation of capsules of tetra(propyl) pyrogallol[4]arene on the host-guest interaction with neurotransmitters

Reaction between pyrogallol and butyraldehyde resulted in the formation of C-tetra(propyl)pyrogallol[4]arene and dimeric capsules. The structures were determined using FT-IR, 1H NMR, 13C NMR, and mass spectrometry. The host-guest complex of C-tetra(propyl) pyrogallol[4]arene (1) and the capsule with neurotransmitters (choline, betaine, and carnitine) were examined in DMSO via dynamic NMR and in the gaseous phase via electrospray ionization-mass spectrometry (ESI-MS). Initially, in DMSO, the results showed that the evaluated neurotransmitters formed a complex with C-tetra(propyl)pyrogallol[4]arene and with the capsule, which is broken by the interaction with the organic cation. Our careful NMR analysis was based on the assignment of 1H NMR signals of the C-tetra(propyl)pyrogallol[4]arene in DMSO‑d6 after the addition of variable amounts of the respective neurotransmitter. With this solvent, it was possible to define stable cone conformational arrangements based on the signals shown in the spectra of all the experiments. Association constants (K) of pyrogallo[4]arene with the neurotransmitters were estimated, and the results showed that the betaine complex had the highest K value. In the gaseous phase study using ESI-MS, the results showed the formation of a 1:1 inclusion complex between the studied neurotransmitters and pyrogallo[4]arene. Therefore, the formation of the capsule does not limit the formation process of the complex.This research was conducted with the financial support of the División de Investigación y Extensión sede Bogotá (DIEB) Universidad Nacional de Colombia-Sede Bogotá (project code 42135). José Luis Casas-Hinestroza thanks the program Colciencias Doctorado Nacional No. 727 for financing his Ph.D studies.Peer reviewe