| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 601210 | Colloids and Surfaces B: Biointerfaces | 2011 | 7 Pages |
Wetting properties of commercial Al2O3 plates contacted with dipalmitoylphosphatidylcholine (DPPC) or DPPC + enzyme (phospholipase PLA2) in NaCl solution were determined by thin layer wicking and with the help of Washburn equation. Van Oss et al.’s approach to interfacial free energy interactions was applied to determining the solid surface free energy components. Wicking experiments were performed both for bare and alumina plates precontacted overnight with the probe liquid saturated vapours, as well as the untreated and DPPC (or DPPC + PLA2) treated alumina plates. For this purpose the penetration rates of n-octane, water and formamide were measured. From these experiments it resulted that original alumina surface is strongly polar with electron–donor interactions originating from the surface hydroxyl groups. Adsorption of DPPC on Al2O3 plates slightly increased the hydrophobic character of the alumina surface (considerable decrease of the electron–donor, γs− parameter and γsAB component was visible) in such a way that the hydrocarbon chains were directed outwards and the polar part towards the alumina surface. However, after the enzyme action the products of DPPC hydrolysis by PLA2 (palmitic acid and lysophosphatidylcholine) increased again the hydrophilic character of Al2O3 surface (a minor increase in γsAB component and drastic increase of the electron-donor γs− parameter was noticeable).After treatment with DPPC or DPPC + enzyme PLA2 solution the changes of the total surface free energy of alumina and its Lifshits-van der Waals (γsLW) component were in the range 7–10 mJ/m2, but the most considerable and delivering more interesting information were the changes of the electron–donor (γs−) parameter ranging from 27 to 35 mJ/m2. Moreover, the changes of the alumina surface wettability were dependent on the time of the enzyme contacting with DPPC in NaCl solution. On the basis of the obtained results it seems that the thin layer wicking method can be an additional useful tool in investigations of the effect of phospholipid and PLA2 action on the hydrophilic–hydrophobic character of alumina surface.
Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Original alumina surface (aluminium oxide 60, Merck) is strongly polar with the electron–donor interactions originating from the surface hydroxyl groups. ► Adsorption of the DPPC on Al2O3 plates increases a bit the hydrophobic character of alumina surface in such a way that hydrocarbon chains are directed outwards and the polar part towards alumina surface. ► Radical decrease of the electron–donor, γs− parameter and the major decrease in acid–base interactions, γsAB is noticeable. ► After the enzyme action the products of DPPC hydrolysis by PLA2 (palmitic acid and lysophosphatidylcholine) increase again the hydrophilic character of Al2O3 surface. ► The changes of alumina surface wettability are dependent on the time of enzyme contacting with DPPC in NaCl solution.
