Dynamic Adsorption and Surface Tension of Aqueous Dilauroylphosphatidylcholine Dispersions under Physiological Conditions

Abstract

The dynamic surface tension and equilibrium adsorption behavior of DLPC dispersions in phosphate buffer saline at 37 and 25 degrees C was studied with tensiometry, infrared reflection--absorption spectroscopy (IRRAS), and ellipsometry. The results are compared with those in water (Pinazo et al. Langmuir 2002, 18, 8888). Even though the pH and salinity have no apparent effect on the equilibrium surface tension and the surface pressure--area isotherm, they affect the dynamic surface tension by decreasing the adsorption rate and increasing the dynamic tension minima at a pulsating area of 20 or 80 cycles per minute. Moreover, IRRAS and ellipsometry results show that the adsorbed layers and the spread monolayers have larger area per molecule, or looser packing, in buffer than in water. A new hypothesis is proposed to elucidate the effect of pH/salinity on this zwitterionic surfactant: there is some specific interaction or binding between the ions from the buffer saline with the polar headgroups of DLPC. This interaction induces stronger intermolecular repulsions of the surfactant layer in buffer than that in water, despite the expected electrostatic screening effect, and causes higher dynamic surface tensions. The results have implications in designing lung surfactant replacement formulations.

Expulsion of bovine serum albumin from the air/water interface by a sparingly soluble lecithin lipid

“…Since DLPC has a solubility of ca. 4 ppm in water, it adsorbs onto the surface by a molecular mechanism, as shown previously with IRRAS data [18,22]. Moreover, DLPC has a low toxicity, as evidenced by tests on animals [23] and by DLPC use as liposome carriers of inhaled asthma drugs on humans [24][25][26].…”

“…The effects of the pH/salinity on the dynamic surface tension of DLPC dispersions at 37 • C have been presented [22]. In short, the adsorption rate of DLPC in buffer is slower than that in water under the same conditions of sample preparation.…”

“…By contrast, in protocol 4, dispersions were shaken and then sonicated using a sonicator probe (Sonicator ultrasonic liquid processor, model W-370, Heat Systems-Ultrasonic Inc., Plainview, NY) until they appeared translucent. The temperature of the samples prepared using this protocol was maintained in the range of 25-35 • C. In this article, results with protocols 3 and 4 are primarily reported, because with these protocols the surface tension results are more favorable [22]. Results with other protocols will be reported elsewhere.…”

“…5 • C. Hence, it can readily form fluid liposomes and vesicles at 37 or 25 • C, unlike DPPC, which has T c of ca. 41 • C, and thus forms fluid liposomes above 41 • C and "frozen" liposomes below 41 • C. DLPC, in water or in buffer, can produce surface tensions of 10 mN/m or lower at the area minimum during area pulsation [18,21,22]. Since DLPC has a solubility of ca.…”

Polymer–lipid interactions: Biomimetic self-assembly behaviour and surface properties of poly(styrene-alt-maleic acid) with diacylphosphatidylcholines

“…They were compared with the values obtained from the mixture of PSMA with increasing amounts of DMPC. It is known that the equilibrium surface tensions of phosphatidylcholines are independent of pH [41]. However, it is also known that protein-lipid interactions at air-liquid interfaces are dependent on electrostatic charges, cations, anions, distribution of protons, and surface potential, which are influenced by pH changes [42].…”