Effect of Monovalent Ions on the Monolayers Phase Behavior of the Charged Lipid DPPG

Abstract

Brewster angle microscopy (BAM) studies on dipalmitoyl phosphatidyl glycerol (DPPG, sodium salt) monolayers on water subphases containing different amounts of NaCl are presented. Inhomogeneities in the monolayer appear after spreading at large mean areas per lipid molecule and at electrolyte concentrations in the subphase lower than 0.15 M NaCl. It is assumed that (i) after spreading DPPG is completely hydrolyzed, (ii) dissociation of the resulting acid depends on the electrolyte concentration in the subphase, and (iii) nondissociated acid molecules form solidlike aggregates in the monolayer, while the dissociated part surrounds them. Image processing of the BAM images allows us to calculate the surface densities of the lipid in the coexisting states, and the dissociation constant of the lipid in the monolayer ( ). The electrostatic contribution to the surface pressure was estimated using the obtained value. Comparison with the experimental π/A isotherms shows satisfactory agreement, confirming the value of the determined dissociation constant. We concluded that the described procedure is useful for the determination of for monolayers of charged surfactant molecules.

Understanding the biocide action of poly(hexamethylene biguanide) using Langmuir monolayers of dipalmitoyl phosphatidylglycerol

“…The isotherms for neat DPPG are shifted to higher areas when water was replaced by Theorell buffer or phosphate buffer as subphase. There is also a plateau in the liquid-expanded region, similarly to what is observed for DPPG monolayers on subphases made of ionic solutions [26,27]. With PHMB in the subphase, DPPG monolayers were expanded, indicating that the polymer remained at the air-liquid interface even at high surface pressures (30-40 mN m −1 ); that is, it was not removed from the interface by compression.…”

Electrostatics of heterogeneous monolayers. Constitutive equations and mathematical models

“…Certainly, selecting the impact of the contact line, this model neglects the differences of the electric parameters (e s , u l s , j s ) of the co-existing (LC/LE) phases. Yet they play a significant role in respect of the heterogeneous monolayer behavior [8,10,13]. In particular, the surface permittivity difference (De s ) is crucial for the nucleation in the presence of charges.…”

“…[19]): (i) by specific adsorption of ions and (ii) by dissociation of the adsorbed molecules. In the case of heterogeneous interfaces, the various surface phases are charged differently [13]. So by analogy with DL in the bulk, close to the contact line, surface DL-s should be formed [14,15].…”

“…In the case of ionic monolayers, due to pure electrostatic and electrochemical effects, additional interesting effects occur. The importance of their electrostatic treatment has been highlighted in multiple recent studies [12][13][14][15].…”

Electrostatic field effects on membrane domain segregation and on lateral diffusion

“…In contrast, monovalent cations (Li + , Na + , K + ) usually lower the transition temperature and expand the membrane (Träuble and Hansjörg 1973;Lösche et al 1985;Sovago et al 2007;Vega Mercado et al 2011). This effect has been ascribed to changes of the degree of ionization (Lösche et al 1985;Grigoriev et al 1999;Miñones et al 2002;Benedini et al 2011) and to the disruption of the hydrogen bonding (Vega Mercado et al 2011;Wydro 2011), both caused by the presence of ions. Several examples of phase segregation induced by divalent cations (mainly Ca 2+ ) have been reported (Galla and Sackman 1975;Hartmann et al 1977;Haverstick and Glaser 1987;Gadella et al 1990;Flanagan et al 1997;Rodriguez et al 2007;Lamberson et al 2007;Hayden et al 2009;Vequi-Suplicy et al 2010;Shimokawa et al 2010;Vega Mercado et al 2011) (Fig.…”