Retinylidene Schiff bases in phosphatidylcholine reverse micelles: formation, protonation and stability

Abstract

All-trans-N-retinylidene-n-butylamine 3 has been formed in inverted micelles of phosphatidylcholine (PC)–hexane containing varying amounts of water ([H₂O]/[PC]= 0–3) and the formation, protonation and stability have been studied. The micelles have been found to catalyse the Schiff-base formation. The Schiff-base was found to be stable in the presence of structured water molecules bonded to the polar head groups of the micelles. A larger water-pool causes the decomposition of the Schiff-base. Schiff-base 3 intercalated in the inverted micelle was found to undergo protonation in the presence of 3-chloropropionic acid, the extent of which depended on the water-pool size. The results are discussed in terms of the formation, protonation and stability of retinylidene Schiff-base chromophores in rhodopsins.