Interfacial Concentrations of Chloride and Bromide and Selectivity for Ion Exchange in Vesicles Prepared with Dioctadecyldimethylammonium Halides, Lipids, and Their Mixtures

Abstract

The local concentrations of chloride, Clb, and bromide, Brb, in the interface of vesicles prepared with dioctadecyldimethylammonium chloride, DODAC, or bromide, DODAB, dipalmitoylphosphatidylcholine, DPPC, dimyristoylphosphatidylcholine, DMPC, and mixtures of DMPC, DPPC, and DODAC were determined by chemical trapping by analyzing product yields from spontaneous dediazoniation of vesiclebound 2,6-dimethyl-4-hexadecylbenzenediazonium ion. The values of Cl b and Brb in DODAC and DODAB vesicles increase with vesicle size, in agreement with previous data showing that counterion dissociation decreases with vesicle size. Addition of tetramethylammonium chloride displaces bromide from the DODAB vesicular interface. The value for the selectivity constant for Br/Cl exchange at the DODAB vesicular interface obtained by chemical trapping was ∼2.0, well within values obtained for comparable amphiphiles. In vesicles of DPPC the values of Cl b were very sensitive to the nature of the cation and decreased in the order Ca 2+ > Mg 2+ > Li + > Na + > K + ) Cs + ) Rb + g TMA + . The effect of the cation becomes more important as temperature increases above the phase transition temperature, Tm, of the lipid. The values of Clb increased sigmoidally with the mol % of DODAC in vesicles prepared with DODAC/lipid mixtures. In sonicated vesicles prepared with DODAC and DMPC (or DPPC), the values of Clb reach local concentrations measured for the pure amphiphile at 80 mol % DODAC. These results represent the first extensive study of local concentration of ions determined directly by chemical trapping in vesicles prepared with lipids, synthetic amphiphiles, and their mixtures.

Do Amphiphile Aggregate Morphologies and Interfacial Compositions Depend Primarily on Interfacial Hydration and Ion-Specific Interactions? The Evidence from Chemical Trapping

“…88 Specific cation effects are greater above the phase transition temperature of zwitterionic vesicles. 89 Addition of 1-2 M NaCl to zwitterionic phosphatidylcholine vesicles speeds phospholipase A 2 , PLA2, catalyzed hydrolysis of the vesicles, probably because selective association of Clover Na + gives the interface region a net negative charge, which promotes the binding of the cationic active site region of PLA2 to the vesicle interface. 90 Finally, the interfacial Cl -and Brconcentrations in cationic vesicles are on the order of 1-2 M, their interfacial concentrations increase with vesicle size, and as with micelles, the vesicles are more selective toward Br -than Cl -.…”

SANS investigation of the microstructures in catanionic mixtures of SDS/DTAC and the effect of various added salts

“…This is a regrettable gap, for applications, mainly in the biological area where bromide is to be avoided, and from a fundamental point of view, as bromide and chloride, being ions with principal similarities [24], are, however, known to affect interfaces rather differently [25,26], as shown by Hofmeister long ago, chloride being much more efficient for salting out proteins [27], a result usually partly explained by a higher hydration number for Cl À . This is in agreement with previous findings that the condensation of bromide on DTA + micelles is higher than for chloride [28].…”

Mixed monolayers involving DPPC, DODAB and oleic acid and their interaction with nicotinic acid at the air–water interface

“…DODAB forms stable monolayers at the air-water interface (Gonçalves da and also forms bilayer structures or liposomes when dispersed in aqueous solution (Scarpa et al, 2002). The incorporation of additional charged materials in liposomes can provide electrostatic repulsive forces between the suspended liposomes, preventing fusion or aggregation.…”