Encapsulation of monoamine neurotransmitters and trace amines by amphiphilic anionic calix[5]arene micelles

The interactions between hydrochloride salts of biologically relevant amines and micelles formed by a water-soluble p-tert-butylcalix[5]arene were investigated by 1H NMR spectroscopy, using a combination of NOESY and DOSY techniques. DOSY measurements were conveniently used to assess the micelle affinity towards the target guests (phenylethylamine ≈ histamine ≈ serotonin > tyramine > dopamine > norepinephrine), whereas NOESY studies revealed the approximate position of these cationic guests within the different micellar regions. In general, all the guests were located in the palisade region of the micelle, with the exception of phenethylamine and histamine, the former being bound to the micellar core as well as the palisade, the latter preferring the outer shell of the micelle.