Using diffusion-induced growth instabilities to measure line tension at liquid condensed-liquid expanded domain boundaries.

Temperature and compression rate independent domain shape in Langmuir monolayers of di- n-dodecyl hydrogen phosphate at the air–water interface

Surface phase behavior of di- n-tetradecyl hydrogen phosphate in Langmuir monolayers at the air–water interface

How many phases and phase transitions do exist in Gibbs adsorption layers at the air–water interface?

Effect of temperature on the surface phase behavior of n-hexadecyl dihydrogen phosphate in adsorption layers at the air–water interface

Differential Partitioning of Pulmonary Surfactant Protein SP-A into Regions of Monolayers of Dipalmitoylphosphatidylcholine and Dipalmitoylphosphatidylcholine/Dipalmitoylphosphatidylglycerol

Differential Effects of Surfactant Protein A on Regional Organization of Phospholipid Monolayers Containing Surfactant Protein B or C

Sphingomyelinase-Induced Domain Shape Relaxation Driven by Out-of-Equilibrium Changes of Composition

The monolayer behavior of two amphiphilic, diacetylenic units containing pyridine ligands at the air−water interface is studied by measuring the surface pressure−area isotherms and by Brewster angle microscopy (BAM). Both amphiphiles form stable monolayers at the air−water interface. The amphiphile containing an ester group shows a well-defined liquid-expanded (LE) to liquid-condensed (LC) phase transition, while the amphiphile with the amide group forms only a condensed monolayer film at 9.4 °C. For both amphiphiles, addition of CuCl2 to the subphase causes an increase of the surface pressure (Πc) at which the phase transition appears, suggesting the formation of a coordination complex at the air−water interface. Addition of Cu(ClO4)2 to the subphase instead of CuCl2 causes an even larger increase in Πc, indicating that more copper ions bind to the monolayer which results in a more charged monolayer. On a pure water subphase, Brewster angle microscopy of the monolayer of the ester-containing ligand shows the formation of spiral dendritic crystalline domains at the plateau in the isotherm near the solid state region. The formation of spiral crystalline domains indicates that the LC phase is L1‘. The amide-containing ligand, however, forms two-dimensional crystalline domains directly after spreading at the air−water interface, which are pushed together upon compression. No chiral crystalline domains were observed for this amphiphile indicating that the ester and amide amphiphile have a different LC phase. Both amphiphiles spread uniformly when the subphase contains CuCl2, and upon compression crystalline domains are formed which grow when the area per molecule is reduced further, until a condensed monolayer film is formed. The shape of the crystalline domains on a Cu(II) ion containing subphase changes by replacing the Cl- counterion by a ClO4- anion. The size of the crystalline nuclei decreases when the Cu(II) concentration increases.

The surface behavior of two zwitterionic phospholipids: 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1-palmitoyl-2-[16-fluoropalmitoyl-phosphatidylcholine] (F-DPPC), has been investigated at the air-water interface at the temperature range from 10 to 30 °C. Surface pressure-area isotherms, BAM images and thickness-time curves were obtained for monolayers made from these pure phospholipids and from their mixtures.The comparative study of the behavior of both phospholipid monolayers with temperature showed some differences as the disappearance of the liquid expanded (LE)-liquid condensed (LC) phase transition at low temperatures for the DPPC but not for F-DPPC, because the F-DPPC monolayer is more expanded and more resistant to changes of temperature. On the other hand, film elasticity (C(s)(-1)) values calculated for both phospholipids show that the film condensation diminishes when the temperature increases, in accordance with the results obtained from surface pressure measurements.BAM images for F-DPPC monolayers recorded at different surface pressures and temperatures show the existence of numerous ovoid-like domains when the LE-LC phase transition is reached. However, in the LE and LC phases, homogeneous images were obtained. Time evolution of relative thickness along the compression of F-DPPC and DPPC monolayers shows similar behavior of both phospholipids, except at low temperatures.For DPPC/F-DPPC mixed systems, the plots of the mean molecular area as a function of F-DPPC mole fraction (X(F-DPPC)) indicated that, whatever the surface pressure, the experimental results match the theoretical values calculated from the additivity rule, a typical behavior for ideal mixed monolayers made of miscible components. This conclusion is confirmed from the values calculated for the free energy of excess (ΔG(exc)) of this system, which are practically zero, whatever the composition of the mixtures and the surface pressure at which ΔG(exc) values were calculated.

The surface conformational states of the Gibbs monolayer of ethylene glycol mono-n-dodecyl ether (C(12)E(1)) at the air/water interface was studied using dynamic surface tension, external reflection-absorption FT-IR spectroscopy (ERA FT-IR), and two-dimensional infrared (2D IR) correlation methods at constant temperature. The dynamic surface tensions were measured at different bulk concentrations of C(12)E(1), and it was observed that a constant surface tension region appears at approximately 38.5 mN m(-1) in a dynamic surface tension profile at concentrations higher than 11 micromol kg(-1). This constant surface tension region corresponds to the surface phase transition from liquid expanded (LE) to liquid condensed (LC). Two sets of ERA FT-IR spectra were collected, one at different bulk concentrations but after equilibrium time (equilibrium measurements) and another at constant bulk concentration (m = 16 micromol kg(-1)) but at different times (dynamic measurements). The first set of these measurements show that the peak area increases in the range of 11 < m < or = 16 micromol kg(-1), which means the increase in the number of surfactant molecules at the air/water interface. Also, the wavenumber of antisymmetric CH(2) stretching decreases gradually from approximately 2923 cm(-1) (for 10 and 11 micromol kg(-1)) to approximately 2918 cm(-1) (for m > or = 16 micromol kg(-1)) with increasing concentration. The wavenumbers of 2923 and 2918 cm(-1) were assigned to LE and LC phases, respectively, and the decrease of wavenumber in the concentration range of 11 < m < or = 16 micromol kg(-1) were correlated to the surface phase transition (LE --> LC), or in other words, in the mentioned concentration range, two phases coexist. The dynamic ERA FT-IR measurements at 16 micromol kg(-1) also confirm the surface phase transition from LE to LC. The 2D IR correlation method was applied to the both equilibrium and dynamic IR spectra of the C(12)E(1) monolayer. The synchronous correlation maps show two strong autopeaks at approximately 2922 and approximately 2851 cm(-1) and also show a strong correlation (cross-peaks) between antisymmetric CH(2) stretching (nu(a)) and symmetric CH(2) stretching (nu(s)). The asynchronous correlation maps show that both observed bands of nu(a) and nu(s) in one-dimensional IR split into two components with the characteristic of overlapped bands, which reveals the coexistence of two phases (LE and LC) at the interface at 11 < m < or = 16 micromol kg(-1). The synchronous and asynchronous maps that were obtained from dynamic IR spectra closely resembled the equilibrium map.

Dipalmitoylphosphatidylcholine (DPPC) is the predominant lipid component in lung surfactant. In this study, the Langmuir monolayer of deuterated dipalmitoylphosphatidylcholine (DPPC-d62) in the liquid-expanded (LE) phase and the liquid-condensed (LC) phase has been investigated at the air-water interface with broad bandwidth sum frequency generation (BBSFG) spectroscopy combined with a Langmuir film balance. Four moieties of the DPPC molecule are probed by BBSFG: the terminal methyl (CD3) groups of the tails, the methylene (CD2) groups of the tails, the choline methyls (CH3) in the headgroup, and the phosphate in the headgroup. BBSFG spectra of the four DPPC moieties provide information about chain conformation, chain orientation, headgroup orientation, and headgroup hydration. These results provide a comprehensive picture of the DPPC phase behavior at the air-water interface. In the LE phase, the DPPC hydrocarbon chains are conformationally disordered with a significant number of gauche configurations. In the LC phase, the hydrocarbon chains are in an all-trans conformation and are tilted from the surface normal by 25 degrees. In addition, the orientations of the tail terminal methyl groups are found to remain nearly unchanged with the variation of surface area. Qualitative analysis of the BBSFG spectra of the choline methyl groups suggests that these methyl groups are tilted but lie somewhat parallel to the surface plane in both the LE and LC phases. The dehydration of the phosphate headgroup due to the LE-LC phase transition is observed through the frequency blue shift of the phosphate symmetric stretch in the fingerprint region. In addition, implications for lung surfactant function from this work are discussed.

Comparisons and correlations between the properties of lipid molecules in crystals, bilayer dispersions in water, and monolayers on a water surface

Interactions of Pluronic block copolymers with lipid monolayers studied by epi-fluorescence microscopy and by adsorption experiments

Phase diagram of Gibbs monolayers of mixtures containing n-hexadecyl phosphate (n-HDP) and L-arginine (L-arg) at a molar ratio of 1:2 has been constructed by measuring surface-pressure-time (pi-t) isotherms with film balance and by observing monolayer morphology with Brewster angle microscopy (BAM). This phase diagram shows a triple point for gas (G), liquid expanded (LE), and liquid condensed (LC) phases at around 6.7 degrees C. Above this triple point, a first-order G-LE phase transition occurring at 0 surface pressure is followed by another first-order LE-LC phase transition taking place at a certain higher surface pressure that depends upon temperature. The BAM observation supports these results. Below the triple point, the pi-t measurements show only one first-order phase transition that should be G-LC. All of these findings are in agreement with the general phase diagram of the spread monolayers. However, the BAM observation at a temperature below the triple point shows that the thermodynamically allowed G-LC phase transition is, in fact, a combination of the G-LE and LE-LC phase transitions. The latter two-phase transitions are separated by time and not by the surface pressure, indicating that the G-LC phase transition is kinetically separated into these two-phase transitions. The position of the LE phase below the triple point in the phase diagram is along the phase boundary between the G and LC phases.

A near-field microscopy study of submicron domain structure in a model lung surfactant monolayer