TY - JOUR
T1 - Extensive surface studies help to analyse zeta potential data
T2 - The case of cationic emulsions
AU - Rabinovich-Guilatt, Laura
AU - Couvreur, Patrick
AU - Lambert, Gregory
AU - Goldstein, Danny
AU - Benita, Simon
AU - Dubernet, Catherine
PY - 2004/8
Y1 - 2004/8
N2 - The present study is aimed to characterize the electrostatic parameters of oil in water emulsion droplets composed of MCT (medium chain triglycerides), PL (phospholipids) and Poloxamer and containing increasing concentrations of the cationic lipid oleylamine (OA), in Hepes 20 mM pH 7.4. The initial ζ-potential data suggesting saturation of the droplet surface at high OA concentrations were completed by supplementary analysis: the distribution of the oleylamine within the droplet was determined by reacting the amino groups with the hydrophilic TNBS (trinitrobenzenesulfonic acid), the method being initially standardised with vesicles. In addition, surface potential and pH at the droplet surface were monitored by the pH-sensitive fluorophore 4-heptadecyl-7- hydroxycoumarin. Our results demonstrate that almost all the OA is localised and fully ionised at the droplet surface for all concentrations and that the observed plateau in the ζ-potential values obeys the Gouy-Chapman theory of ion condensation. It is also shown that the slipping plane separation as estimated by the Eversole-Boardman equation is higher that the expected values of 0.2 nm as a result of the relative position of the fluorophore and the outer boundary of the lipid interface thickness and the Poloxamer anchored at the interface only plays a minor role.
AB - The present study is aimed to characterize the electrostatic parameters of oil in water emulsion droplets composed of MCT (medium chain triglycerides), PL (phospholipids) and Poloxamer and containing increasing concentrations of the cationic lipid oleylamine (OA), in Hepes 20 mM pH 7.4. The initial ζ-potential data suggesting saturation of the droplet surface at high OA concentrations were completed by supplementary analysis: the distribution of the oleylamine within the droplet was determined by reacting the amino groups with the hydrophilic TNBS (trinitrobenzenesulfonic acid), the method being initially standardised with vesicles. In addition, surface potential and pH at the droplet surface were monitored by the pH-sensitive fluorophore 4-heptadecyl-7- hydroxycoumarin. Our results demonstrate that almost all the OA is localised and fully ionised at the droplet surface for all concentrations and that the observed plateau in the ζ-potential values obeys the Gouy-Chapman theory of ion condensation. It is also shown that the slipping plane separation as estimated by the Eversole-Boardman equation is higher that the expected values of 0.2 nm as a result of the relative position of the fluorophore and the outer boundary of the lipid interface thickness and the Poloxamer anchored at the interface only plays a minor role.
KW - Cationic emulsion
KW - Oleylamine
KW - Poloxamer
KW - Surface pH
KW - Surface potential
KW - ζ-Potential
UR - http://www.scopus.com/inward/record.url?scp=3042511580&partnerID=8YFLogxK
U2 - 10.1016/j.chemphyslip.2004.04.003
DO - 10.1016/j.chemphyslip.2004.04.003
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C2 - 15210360
AN - SCOPUS:3042511580
SN - 0009-3084
VL - 131
SP - 1
EP - 13
JO - Chemistry and Physics of Lipids
JF - Chemistry and Physics of Lipids
IS - 1
ER -