Dodecylammonium-glutamate Schiff bases of retinal

Abstract

Dodecylammonium glutamate (4) has been prepared from dodecylamine (2) and l-glutamic acid (3) in ethanol and in aqueous ethanol. The obtained crystalline glutamic acid salt of dodecylamine (4) has been characterized by absorption, FTIR, 1H NMR, 13C NMR, and mass spectroscopy. Reaction of all-trans retinal (5) with the α-amino group of 4 gave a Schiff base (6), which was protonated by the α-COOH group of the glutamyl residue. However, the protonated Schiff base underwent acid-catalyzed hydrolysis to 2 + 3 + 5. Some of 5 reacted with 2 to give the corresponding Schiff base. The proposed structures have been substantiated by insitu absorption, FTIR, and 1H NMR spectroscopy. Keywords: retinal Schiff base, retinal, rhodopsin model, dodecylammonium glutamate, Schiff-base protonation.