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| Author(s): |
Renata Rapuano
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2000-04-28 |
| Examining board members: |
Ana Maria Carmona Ribeiro;
Ligia Ferreira Gomes;
Denise Freitas Siqueira Petri
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| Advisor: | Ana Maria Carmona Ribeiro |
| Abstract | |
Adsorption isotherms of bilayer-forming synthetic amphiphiles or phospholipids from vesicles onto hydrophilic silica particles (AEROSIL 0X-50) are obtained over a range of experimental conditions. Phosphatidylcholine (PC), dipalmitoylphosphatidylcholine (DPPC), and dioctadecyldimethylammonium bromide (DODAB) dispersed in 10 mM of two different buffers (Tris or HEPES) at 3 different pH values as small unilamellar vesicles present affinities for silica following the sequence: DODAB > DPPC > PC. Deposition of phospholipid bilayers was favoured by the presence of Tris as buffer, pH≤ 7.4, and temperatures above the phase transition temperature (Tc) for the phospholipid bilayer. Interaction at 65 ºC for 1 h between DPPC vesicles and silica efficiently leads to bilayer deposition at maximal adsorption, if Tris is the buffer used. Consistently, wettability of SiO2 planar surfaces precisely under conditions of bilayer deposition (as depicted from the isotherms) in the presence of the lipidic vesicles yielded a large increase on surface hydrophobicity for DPPC at 65 ºC and DODAB at room temperature. Reduction of merocyanine 540 absorbance at 565 nm was used as a marker for bilayer deposition onto the silica particles. Upon interaction with the solid particle, absorbance at 565 nm displays a decrease with rime that corresponds to the percentage of dye that became sandwiched between the bilayer and the solid particle surface and thereby hidden from the incident light. For DPPC at 65 ºC and DODAB at room temperature, but not for PC, occurrence of bilayer deposition depicted from the adsorption isotherms is confirmed from the three techniques employed for detection. (AU) | |