ISSN:
0947-3440
Keywords:
Mesogenic unit
;
Monomer exchange
;
“Gel-to-liquid crystalline” phase transition
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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 〈 NO2 〈 CN 〈 OCH3 〈 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.
Additional Material:
1 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.199719970106
