The influence of salinity on surfactant miscibility in mixed dipalmitoylphosphatidylcholine – perfluorooctadecanoic acid monolayer films

Eftaiha, Ala’a F.; Paige, Matthew F.

doi:10.1016/j.jcis.2010.09.045

Cited by 18 publications

(15 citation statements)

References 36 publications

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“…A total expansion of the monolayer occurs on the 2.0 M NaCl solution, where a larger MMA relative to water occurs at all surface pressures. The phase behavior of DPPC on NaCl solutions has been studied extensively, and a shift to higher MMAs in the LE and LE-LC coexistence phases has also been previously observed for moderately concentrated (P0.1 M) solutions [15,[38][39][40][41][42][43]. The extent of the MMA shift seems concentration-dependent, as it increases by 3-6 Å 2 /molecule for concentrated solutions (P0.5 M) [15,40,41], and is shifted 1-2 Å 2 /molecule for 0.1 M solutions [38,39].…”

Section: Resultsmentioning

confidence: 81%

Effect of cation enrichment on dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface

Adams

Casper

Allen

2016

Journal of Colloid and Interface Science

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The effect of highly concentrated salt solutions of marine-relevant cations (Na(+), K(+), Mg(2+), and Ca(2+)) on Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC) was investigated by means of surface pressure-area isotherms, Brewster angle microscopy (BAM), and infrared reflection-absorption spectroscopy (IRRAS). It was found that monovalent cations and Mg(2+) have similar phase behavior, causing DPPC monolayers to expand, while Ca(2+) induces condensation. All cations disrupted the surface morphology at high cation concentration, resulting in decreased reflectivity from the monolayer. Monolayer refractive index was calculated from BAM image intensity in the liquid condensed phase and decreased with increasing cation concentration, which suggests that orientation of the alkyl chains change. Monovalent ions increase ordering of the alkyl chains, more than divalents, yet have little interaction with the DPPC headgroup. Mg(2+) induces gauche defects in the alkyl chain and increases headgroup hydration at low lipid coverage but increases chain ordering and dehydrates the headgroup at high lipid coverage. Ca(2+) orders alkyl chains and dehydrates the phosphate moiety, independent of lipid phase. At the highest salt concentration investigated, significant narrowing of the asymmetric PO2(-) vibrational mode occurs and is attributed to considerable dehydration of the DPPC headgroup.

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Section: Resultsmentioning

confidence: 81%

Effect of cation enrichment on dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface

Adams

Casper

Allen

2016

Journal of Colloid and Interface Science

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“…Isotherms for the pure components were consistent with those reported elsewhere in the literature, with the pure DPPC isotherm exhibiting characteristic gaseous, liquid-expanded (LE), and liquidcondensed (LC) phases, with coexistence regions and a collapse plateau of ∼66 mN/m, and the C18F isotherm exhibiting a single, smooth curve with collapse plateau of ∼64 mN/m. 11,27 Limiting molecular areas (A 0 ) for the pure components, estimated by extrapolating the pseudolinear portion of the liquid-condensed phase to the mean molecular area axis intercept, were ∼61 and ∼34 Å 2 ·molecule −1 for DPPC and C18F, respectively. As an aside, Nakahara and Shibata 24 have commented that perfluorocarboxylic acids from commercial sources can contain significant impurities (certified purity of C18F from Alfa Aesar used here was reported as ∼97%) and have suggested that these impurities can result in A 0 values that are unreasonably large in comparison with those estimated from the cross-section of a perfluorocarbon chain (∼28 Å 2 ).…”

Section: Resultsmentioning

confidence: 99%

Influence of Film Composition on the Morphology, Mechanical Properties, and Surfactant Recovery of Phase-Separated Phospholipid-Perfluorinated Fatty Acid Mixed Monolayers

2012

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Monolayer surfactant films composed of a mixture of phospholipids and perfluorinated (or partially fluorinated) surfactants are of potential utility for applications in pulmonary lung surfactant-based therapies. As a simple, minimal model of such a lung surfactant system, binary mixed monolayer films composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and perfluorooctadecanoic acid (C18F) prepared on a simplified lung fluid mimic subphase (pH 7.4, 150 mM NaCl) have been characterized in terms of mixing thermodynamics and compressibility (measured through π–A compression isotherms), film morphology (via atomic force, fluorescence, and Brewster angle microscopy), as well as spreading rate and hysteresis response to repeated expansion–contraction cycles for a variety of compositions of mixed films. Under all mixing conditions, films and their components were found to be completely immiscible and phase-separated, though there were significant changes in the aforementioned film properties as a function of composition. Of particular note was the existence of a maximum in the extent of immiscibility (characterized by ΔG(ex)(π) values) and enhanced surfactant recovery during hysteresis experiments at χ(C18F) ≥ 0.30. The latter was attributed to the relatively rapid respreading rate of the perfluorinated amphiphile in comparison with DPPC alone at the air–water interface, which enhances the performance of this mixture as a potential pulmonary lung surfactant. Further, monolayer film structure could be tracked dynamically as a function of compression at the air–water interface via Brewster angle microscopy, with the C18F component being preferentially squeezed out of the film with compression, but returning rapidly upon re-expansion. In general, addition of C18F to DPPC monolayers resulted in improvements to mechanical, structural, and respreading properties of the film, indicating the potential value of these compounds as additives to pulmonary lung surfactant formulations.

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“…The physicochemical characterization of native and reconstructed samples from the SSML on pure water and seawater has traditionally been done using standard monolayer techniques (surface pressure– and surface potential–area isotherms) as well as Brewster angle microscopy (BAM) and electrochemical and nonlinear spectroscopy methods. − However, to obtain a fundamental understanding of the surface properties including intermolecular interactions and molecular organization of the SSML, it has been customary to provide measurements of model compounds relevant to the SSML as comparison. One proven experimental approach is to use Langmuir monolayers of pure phospholipids like DPPC on pure water or on simple aqueous salt solutions as simplified model systems for the SSML and the organic layer of marine aerosols, on which environmental conditions can be easily varied. − For instance, the influence of a salt like NaCl on the alkyl chains ordering and orientation, headgroup orientation, phase behavior, compressibility, and domain morphology of DPPC monolayers has previously been extensively studied using surface pressure–area isotherms. − More recently, surface-sensitive vibrational sum frequency generation (VSFG) spectroscopy has provided further molecular details on the effect of Na + cation binding on the PC headgroup orientation . Yet, to the authors’ knowledge, there have been very few experimental studies examining the impact of Na + and other important cations found in the marine environment such as K + , Mg 2+ , and Ca 2+ , at moderate and high concentrations (>0.3 M). − …”

Section: Introductionmentioning

confidence: 99%

Surface Potential of DPPC Monolayers on Concentrated Aqueous Salt Solutions

et al. 2016

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The presence and exchange of electrical charges on the surfaces of marine aerosols influence their ability to act as cloud condensation nuclei and play a role in thundercloud electrification. Although interactions exist between surface-active inorganic ions and organic compounds, their role in surface charging of marine aerosols is not well understood. In this study, the surface potential of dipalmitoylphosphatidylcholine (DPPC) monolayers, a zwitterionic phospholipid found in the sea surface microlayer, is measured on concentrated (0.3-2.0 M) chloride salt solutions containing marine-relevant cations (Na(+), K(+), Mg(2+), Ca(2+)) to model and elucidate the electrical properties of organic-covered marine aerosols. Monovalent cations show only a weak effect on the surface potential of DPPC monolayers in the condensed phase compared to water. In contrast, Mg(2+) and Ca(2+) increase the surface potential, indicating different cation binding modes and affinities for the PC headgroup. Moreover, it is found that for divalent chloride salt solutions, the PC headgroup and interfacial water molecules make the largest dipolar contribution to the surface potential. This study shows that for equal charge concentrations, divalent cations impact surface potential of DPPC monolayers more strongly than monovalents likely through changes in the PC headgroup orientation induced by their complexation along with the lesser ordering of interfacial water molecules caused by phosphate group charge screening.

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The influence of salinity on surfactant miscibility in mixed dipalmitoylphosphatidylcholine – perfluorooctadecanoic acid monolayer films

Cited by 18 publications

References 36 publications

Effect of cation enrichment on dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface

Effect of cation enrichment on dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface

Influence of Film Composition on the Morphology, Mechanical Properties, and Surfactant Recovery of Phase-Separated Phospholipid-Perfluorinated Fatty Acid Mixed Monolayers

Surface Potential of DPPC Monolayers on Concentrated Aqueous Salt Solutions

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