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Monolayer and Bilayer Stability of Ammonium Amphiphiles Carrying an Azobenzene Unit – Effects of Substituents at the Azobenzene Unit
Author(s) -
Everaars Marcel D.,
Marcelis Antonius T. M.,
Sudhölter Ernst J. R.
Publication year - 1996
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.199719970106
Subject(s) - azobenzene , chemistry , bilayer , monolayer , crystallography , amphiphile , vesicle , photochemistry , organic chemistry , membrane , molecule , copolymer , polymer , biochemistry
Abstract Novel double‐chained ammonium amphiphiles carrying one azobenzene moiety ( I ) have been synthesized. The bilayer‐stabilizing effect of different azobenzenes (ABs) has been investigated by measuring the “gel‐to‐liquid crystalline” phase transition temperatures of the formed bilayers in water using differential scanning calorimetry. It is found that the stabilizing effect of the azobenzenes strongly depends on the substituents at the aromatic ring. The stabilizing effect increases in the sequence F < H < NO 2 < CN < OCH 3 < N=N–Ph, which cannot be correlated with the electron‐withdrawing or ‐donating properties of the substituents. It is concluded that dipole‐dipole interactions between the ABs are of minor importance for the overall stabilization of the bilayer. Instead, other factors determine the strength of the van der Waals interactions between the ABs. In the bilayers the ABs form H‐aggregates as is observed by the blue shift of the UV absorption maximum. This blue shift is not affected by the “gel‐to‐liquid crystalline” phase transition. Bilayers of I –N=N–Ph do not exchange monomers with vesicles of didodecyldimethylammonium bromide, whereas all other investigated bilayers do. Compound I –N=N–Ph forms monolayers at the water‐air interface, which are much more stable than the monolayers of the other investigated compounds.