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Ca 2+ – and Ba 2+ –Ligand Coordinated Unilamellar, Multilamellar, and Oligovesicular Vesicles
Author(s) -
Song Aixin,
Jia Xiangfeng,
Teng Minmin,
Hao Jingcheng
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200600352
Subject(s) - vesicle , crystallography , chemistry , bilayer , ligand (biochemistry) , metal , small angle x ray scattering , barium , lipid bilayer , membrane , stereochemistry , inorganic chemistry , scattering , organic chemistry , receptor , biochemistry , physics , optics
Ca 2+ ‐ and Ba 2+ ‐coordinated vesicle phases were prepared in mixed aqueous solutions of tetradecyldimethylamine oxide (C 14 DMAO) and calcium oleate (Ca(OA) 2 ) or barium oleate (Ba(OA) 2 ). At the right mixing ratios, metal–ligand coordination between Ca(OA) 2 or Ba(OA) 2 and C 14 DMAO results in the formation of molecular bilayers due to the reduction in area per head group. Ca 2+ and Ba 2+ tightly associate to the head groups of surfactants and in this system the bilayer membranes are not shielded by excess salts. The structures of the birefringent samples of the Ca(OA) 2 /C 14 DMAO/H 2 O and Ba(OA) 2 /C 14 DMAO/H 2 O systems were determined by freeze‐fracture transmission electron microscopy (FF‐TEM), small‐angle X‐ray scattering (SAXS), and rheological measurements to consist of unilamellar, multilamellar, and oligovesicular vesicles. The coordination between C 14 DMAO and Ba(OA) 2 or Ca(OA) 2 plays an important role in the formation of the vesicles, which was easily confirmed by studying the phase behavior of the KOA/C 14 DMAO/H 2 O system in which only the L 1 phase forms, due to the absence of coordination between KOA and C 14 DMAO. A mechanism is proposed that accounts for the formation of these new metal–ligand coordinated vesicles.