Interações entre bicamadas lipídicas e interfaces hidrofóbicas / Interactions between lipid bilayers and hydrophobic interfaces

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

Determinations of surface tension (γ) at the air--water interface, contact angles (Θ), and in and ex-situ ellipsometric mean thickness (d) were used to study the interaction between dioctadecyldimethylammonium bromide (DODAB) small vesicles and spin-coated polystyrene sulfate (PSS) films on silicon wafers. Upon the adition of NaCl (50 mM final concentration) to a 0.2 mM DODAB dispersion, adsorption from vesicles on PSS films immediatly yielded a DODAB layer 6.0 nm thick which remained stable as a function of time. However, in water, in situ DODAB adsorption monotonically increased reaching at most 1.6--1.8 nm as a function of time (from 15 mm of interaction), which were not values consistent with bilayer deposition. At early stages in pure water, DODAB adsorption linearly increased with the square root of time, indicating a vesicle difision controlled process with ca. 1.0 x 10-11 m2s-1 as the vesicle diffusion coeficient (D) in nice agreement with reported D for similar vesicles. In contrast, adding 50 mM salt, resulted in a very fast adsorption kinetics determined by the hydrophobic atraction between salt-induced defects on lhe bilayer and the film surface. Ex situ measurements of DODAB, DHP e PC adsorption were difficult because wetting/drying cycles of the polimeric fiIms increased its mean thickness. From 0.1 up to 1.0 mM DODAB, the adsorbed film in air was more hydrophobic (advancing contact angle, ΘA = 84 ± 3°) than the bare PSS film (ΘA = 71 ± 4°). No effect of DHP film on the wettability of PSA film could be observed, just a increase of rougness revealed by the change of ΔΘ from2° to 11°( table 3). Pure PSA films are hydrophobic, as revealed by the mean advancing angle ΘA = 86 ± 5°. After interaction with PC, the surfaces turn less hydrophobic with a mean ΘA = 75 ± 3°. Air-water surface tension for a DODAB dispersion in pure water rapidly decreased upon salt addition (7-50 mM NaCI), suggesting salt-induced vesicle fusion wilh the air--water interface occurred, in nice agreement with saIt-induced vesicle fusion at the hydrophobic polymer-water surface.The investigation of the interaction between DODA salts and polymeric particles from diameter and zeta- potential measurements, allowed us to detect bilayer deposition optimized by salt adition in low concentration(0.05-5.0 mM NaCl).

ASSUNTO(S)

tensão superficial surface tension interfaces hidrofóbicas fosfatidilcolina (pc) interação química contact angle diotadecyldimethylammonium bromide (dodab) elipsometry posphatidylcholine (pc) poliestireno sulfato (pss) hydrophobic interfaces potencial zeta Ângulo de contato elipsometria brometo de diactadecildimetilamônio (dodab) dihexadecilfosfato de sódio (dhp) polystyrene sulfate (pss) zeta-potencial

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