Interaction of poly(ethylene-glycols) with air-water interfaces and lipid monolayers: investigations on surface pressure and surface potential

Abstract

We have characterized the surface activity of different-sized poly(ethylene-glycols) (PEG; M(r) 200-100,000 Da) in the presence or absence of lipid monolayers and over a wide range of bulk PEG concentrations (10(-8)-10% w/v). Measurements of the surface potential and surface pressure demonstrate that PEGs interact with the air-water and lipid-water interfaces. Without lipid, PEG added either to the subphase or to the air-water interface forms relatively stable monolayers. Except for very low molecular weight polymers (PEGs < 1000 Da), low concentrations of PEG in the subphase (between 10(-5) and 10(-4)% w/v) increase the surface potential from zero (with respect to the potential of a pure air-water interface) to a plateau value of approximately 440 mV. At much higher polymer concentrations, > 10(-1)% (w/v), depending on the molecular weight of the PEG and corresponding to the concentration at which the polymers in solution are likely to overlap, the surface potential decreases. High concentrations of PEG in the subphase cause a similar decrease in the surface potential of densely packed lipid monolayers spread from either diphytanoyl phosphatidylcholine (DPhPC), dipalmitoyl phosphatidylcholine (DPPC), or dioleoyl phosphatidylserine (DOPS). Adding PEG as a monolayer at the air-water interface also affects the surface activity of DPhPC or DPPC monolayers. At low lipid concentration, the surface pressure and potential are determined by the polymer. For intermediate lipid concentrations, the surface pressure-area and surface potential-area isotherms show that the effects due to lipid and PEG are not always additive and that the polymer's effect is distinct for the two lipids. When PEG-lipid-mixed monolayers are compressed to surface pressures greater than the collapse pressure for a PEG monolayer, the surface pressure-area and surface potential-area isotherms approach that of the lipid alone, suggesting that for this experimental condition PEG is expelled from the interface.

Discontinuities in hygroscopic growth below and above water saturation for laboratory surrogates of oligomers in organic atmospheric aerosols

“…There is evidence for decreases in surface tension with increasing PEG molecular mass (Rey and May, 2010;Winterhalter et al, 1995). Our results are also in agreement with previous studies that suggest that the presence of high molecular mass species (e.g., HULIS, polcycarboxylic acids) in atmospheric aerosol can contribute to decreases in surface tension (Facchini et al, 2000;Ziese et al, 2008).…”

“…Further, previous studies of PEG-AS particles (using optical and Raman microscopy) have shown that, at some RH values, such systems undergo LLPS in which a PEG shell fully engulfs an AS core (Ciobanu et al, 2009(Ciobanu et al, , 2010. Finally, PEG oligomers have been shown to have pure component surface tensions substantially lower than that of water (Wu, 1974;Winterhalter et al, 1995;Rey and May, 2010;Wu et al, 2011) and, thus, may impact water-uptake behavior by lowering the surface tension of the droplet-air interface.…”

“…Not accounting for non-ideal interactions between particle components (i.e., assuming equilibrium partitioning to an ideal solution under circumstances in which this assumption is not valid) can result in a 10-40 % overprediction of cloud droplet number, depending on aerosol loading (Nenes et al, 2001). On the other hand, the presence of surface-active organic components can contribute to enhancements in CCN activity by reducing the surface tension of the particle surface-air interface (Ma et al, 2013;Sareen et al, 2013;Woo et al, 2013). In addition, simultaneous condensation of semivolatile organic vapors and water onto aerosol particles may enhance water uptake by increasing the availability of soluble material (Topping and McFiggans, 2012;Topping et al, 2013).…”

Coupling Reaction and Properties of Poly(ethylene glycol)-linked Phospholipases A2

“…31) In this study, we extended the measurements of PEG's surface activity and measured the eŠects of the presence of the polymer in the subphase on the surface pressure at air-water interfaces. In agreement with previous reports, 31,32) the results of this work show that PEG derivatives have an important surface activity. It is interesting to note that, despite this surface activity, the covalent attachment of this polymer to PLA2s tends to reduce their interaction with lipid monolayers, especially at high surface pressures.…”

Polyethylene glycols interact with membrane glycerophospholipids: is this part of their mechanism for hypothermic graft protection?

“…So, in bilayers at neutral pH, DPPC, DPPS, and DPPE have shown a phasetransition temperature of, respectively, 41.4°C, 53°C, and 63°C while SOPC monounsaturated glycerophospholipids have shown a transition temperature of 5.6°C [28][29][30][31]. In addition, it has been demonstrated that PEG increases the phase-transition temperature of glycerophospholipids, possibly by changing the solvation property of water [32][33][34].…”