Pure Water Subphase Research Articles

Study of Adsorption and Penetration of E2(279−298) Peptide into Langmuir Phospholipid Monolayers

The peptide corresponding to the sequence (279-298) of the Hepatitis G virus (HGV/GBV-C) E2 protein was synthesized, and surface activity measurements, pi-A compression isotherms, and penetration of E2(279-298) into phospholipid monolayers spread at the air-water interface were carried out on water and phosphate buffer subphases. The results obtained indicated that the pure E2(279-298) Langmuir monolayer exhibited a looser packing on saline-buffered than on pure water subphase and suggest that the increase in subphase ionic strength stabilizes the peptide monolayer. To better understand the topography of the monolayer, Brewster angle microscopy (BAM) images of pure peptide monolayers were obtained. Penetration of the peptide into the pure lipid monolayers of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) and into mixtures of dimyristoylphosphatidylcholine/dimyristoylphosphatidylglycerol (DMPC/DMPG) at various initial surface pressures was investigated to determine the ability of these lipid monolayers to host the peptide. The higher penetration of peptide into phospholipids is attained when the monolayers are in the liquid expanded state, and the greater interaction is observed with DMPC. Furthermore, the penetration of the peptide dissolved in the subphase into these various lipid monolayers was investigated to understand the interactions between the peptide and the lipid at the air-water interface. The results obtained showed that the lipid acyl chain length is an important parameter to be taken into consideration in the study of peptide-lipid interactions.

Interactions of a Fungistatic Antibiotic, Griseofulvin, with Phospholipid Monolayers Used as Models of Biological Membranes

Griseofulvin (GF) is an oral antibiotic for widely occurring superficial mycosis in man and animals caused by dermaphyte fungi; it is also used in agriculture as a fungicide. The mechanism of the biological activity of GF is poorly understood. Here, the interactions of griseofulvin with lipid membranes were studied using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC), and 1,2-myristoyl-sn-glycero-3-phosphoethanolamine (DMPE) monolayers spread at the air/water interface. Surface pressure (Pi), electric surface potential (Delta V), grazing incidence X-ray diffraction (GIXD), and Brewster angle microscopy (BAM) were used for studying pure phospholipid monolayers spread on GF aqueous solutions, as well as mixed phospholipid/GF monolayers spread on pure water subphase. Moreover, phospholipase A2 (PLA2) activity toward DLPC monolayers and molecular modeling of the GF surface and lipophilic properties were used to get more insight into the mechanisms of GF-membrane interactions. The results obtained show that GF has a meaningful impact on the film properties; we propose that nonpolar interactions are by and large responsible for GF retention in the monolayers. The modification of membrane properties can be detected using both physicochemical and enzymatic methods. The results obtained may be relevant for elaborating GF preparations with increased bioavailability.

Colorimetric detection of WGA in carbohydrate-functionalized polydiacetylene Langmuir–Schaefer films

In this paper, carbohydrate-modified polydiacetylene (PDA) films prepared by Langmuir–Schaefer (LS) technique were used as biosensors for studying the interaction of wheat germ agglutinin (WGA) with the carbohydrate. Studies showed that the addition of WGA, specific to N-acetylglucosamine, induced the films to change their color from blue to red. UV–vis and Resonance Raman (RR) spectra confirmed the occurrence of molecular recognition. Surface pressure–area isotherms showed that glycolipid and polydiacetylene molecules had good miscibility on pure water subphase, which was significant for further applications as biosensor.

Charge transfer complex formation at the air–water interface “in situ” studied by means of UV–vis reflection spectroscopy

Positively ionized monolayers of a viologen derivative, namely 1,1′-dioctadecyl-4,4′-bipyridilium (C 18V 2+), were prepared onto aqueous solutions of a tetracyanoquinodimethanide salt, [ ( CH 3 – CH 2 ) 3 NH ] + ( TCNQ ) 2 - , where the tetracyanoquinodimethanide anions are in a mixed valence state. UV–vis reflection spectroscopy has been used for proving in situ the incorporation of tetracyanoquinodimethanide anions into the viologen monolayer. The UV–vis spectra clearly show the presence of a band in the 550–850 nm region that is not visible in viologen monolayers fabricated onto a pure water subphase. Moreover, a charge-transfer interaction between the two molecules occurs at the air–water interface. A simultaneous quantitative analysis of the two active molecules in the UV–vis region has facilitated the investigation of the viologen tetracyanoquinodimethanide hybrid monolayers. An organization model at the air–water interface consistent with the reflection spectroscopy data has been proposed where a parallel arrangement of the viologen dications and ( TCNQ ) 2 - anions is assumed. The ratio of the two materials in the monolayer was also determined and resulted to be C 18 V 2 + : 2 ( TCNQ ) 2 - , i.e. stoichiometry of charges. This ratio decreases after a noticeable kink in the π- A isotherm, and has been interpreted as a reorganization of the molecules in the monolayer leading to an ejection of some ( TCNQ ) 2 - ions from the interface to the subphase, probably due to steric hindrance.

Chain orientation and headgroup structure in Langmuir monolayers of stearic acid and metal stearate (Ag, Co, Zn, and Pb) studied by infrared reflection-absorption spectroscopy

The monolayers of stearic acid at the air-water interface on pure water and ion-containing subphases have been studied using infrared reflection-absorption spectroscopy. In the presence of Co(2+), Zn(2+), and Pb(2+), ordered hydrocarbon chains and hexagonal subcell structure remain almost unchanged in comparison with those for the monolayer on pure water at the surface pressure of 20 m/Nm. In the cases of Co(2+) and Zn(2+), the H-bonded monodentate and unsymmetric bidentate chelating structure within the headgroups were formed, and in the case of Pb(2+), three types of structures, bidentate chelating, unsymmetric chelating, and bidentate bridging coordinations, were formed. The hydrocarbon chains in the monolayers are uniaxially oriented at a tilt angle of approximately 0 degrees with respect to the surface normal in contrast to a tilt angle of approximately 20 degrees on pure water surface at 20 m/Nm by the computer simulation of theoretical calculation to experimental data. In the presence of Ag(+), multilayers were developed with the highly ordered hydrocarbon chains in a triclinic subcell structure and a bidentate bridging structure within the headgroups. The multilayers were composed of three monolayers and the hydrocarbon chains in each monolayer were oriented at an angle of approximately 30 degrees away from the surface normal with their C-C-C planes almost perpendicular to the water surface.

Peptidolipid as Binding Site of Acetylcholinesterase: Molecular Recognition of Paraoxon in Langmuir Films

Peptidolipid C18H35O (stearoyl)-Phe-Trp-Ser-His-Glu (peptidolipid A) was synthesized and spread at the air-water interface to study the interaction with an organophosphorus compound. Paraoxon, sodium dihydrogen phosphate, or 4-nitrophenyl phosphate disodium was added to the subphase, but only paraoxon changed the surface pressure-area (pi-A) isotherm of peptidolipid A. This indicated a specific interaction between paraoxon and peptidolipid A. To clarify which amino acid residue of peptidolipid A was responsible for the interaction, peptidolipid B, namely, C18H35O-Gly-His-Ser-Glu-Glu, was synthesized and studied as a Langmuir film. The difference between the pi-A isotherms of peptidolipid B in the absence and presence of paraoxon in the subphase was minimal; consequently, the presence of amino acids phenylalanine (Phe) and tryptophan (Trp) in peptidolipid A may explain the interaction between peptidolipid A and paraoxon. The compression-decompression cycles and kinetic studies of peptidolipid A showed that the Langmuir film was stable. The in situ optical properties of the peptidolipid A Langmuir film such as UV-vis and fluorescence spectroscopies were examined to elucidate the interaction between peptidolipid A and paraoxon. UV-vis absorption of peptidolipid A was investigated in the presence and absence of paraoxon in the subphase. The emission maximum of fluorescence of Trp in peptidolipid A was observed at 351 nm on pure water, and the band intensity decreased when the concentration of paraoxon increased in the subphase. This suggested that the Trp was involved in the molecular recognition process. Epifluorescence micrographs showed domains of peptidolipid A on the pure water subphase. In the presence of paraoxon in the subphase, the Langmuir film of peptidolipid A showed a homogeneity, which was another indication of the recognition between paraoxon and peptidolipid A.

Molecular Organization of an Amphiphilic Styryl Pyridinium Dye in Monolayers at the Air/Water Interface in the Presence of Various Anions

Amphiphilic 4-(3',4'-dimethoxystyryl)-N-octadecylpyridinium perchlorate and bromide form stable monolayers at the air/water interface. Small differences in the surface pressure-area and surface potential-area isotherms depending on the anion indicate interactions between the chromophore and the anions on the pure water subphase. The monolayer behavior is considerably modified on 10 mM aqueous solutions of KI, KClO4, KCl, and KF as revealed by isotherm measurements, reflection spectroscopy, and Brewster angle microscopy. The phase transition observed in the isotherms is shifted to higher surface pressure because of variation of the salt according to the Hofmeister series. Upon monolayer compression, the chromophores are increasingly tilted, and a shift of the band to longer wavelengths is attributed to the environment becoming less polar. However, in the case of KCl at small areas per molecule, relaxation is observed at constant area with the appearance of a new band shifted to shorter wavelengths. This band is assigned to small associates of about four chromophores (H aggregates). In the case of KI, a new band shifted to longer wavelengths is found. Theoretical calculations did not yield a transition in the observed range, even for large aggregates (J aggregates). Therefore, other interactions may be responsible for the appearance of this band.

Synthesis, Langmuir and Langmuir–Blodgett film behaviour of new dendritic amphiphiles

New amphiphilic compounds 1–9 that feature a construction with dendronized hydrophilic and hydrophobic segment groups connected to a specific aromatic or aliphatic spacer unit have been synthesized, following a modular building block strategy. The hydrophilic dendrons are typically branched elements with peripheral carboxylic groups, unlike the hydrophobic dendrons that contain peripheral alkyl chains as part of respective amide functions. The hydrophilic dendrons are in different generations of branching, while the hydrophobic dendrons are all in the first generation of branching (three terminal branching), but differ in the length of the alkyl chains, thus giving rise to designed structure and amphiphilic properties in the new compounds. The resulting surfactants are capable of forming well-defined Langmuir films of remarkable stability when spread from a solution onto an aqueous subphase. Nevertheless, specific packing behaviour and orientation of the amphiphilic molecules were found, depending on the molecular structure, as determined using analysis of the surface pressure–area (π–A) isotherms. Langmuir–Blodgett transfer of the first monolayer from a pure water subphase to a clean silicon wafer proved possible for the amphiphiles of peripheral alkyl chain length C12, while the amphiphiles with the longer alkyl chains failed, possibly due to the more rigid monolayers they form, impeding the transfer.

Polymerization of a Cysteinyl Peptidolipid Langmuir Film

The surface pressure-area isotherm of a cysteinyl peptidolipid on a pure water subphase (pH 5.8) was compared with that on a water subphase saturated with oxygen and buffered with ammonium bicarbonate (pH 7.8). A reduction of the limiting molecular area was observed for the isotherm measured on the subphase saturated with oxygen. Hysteresis in the compression-decompression cycles of the Langmuir film was also observed. Taking into consideration the chemical structure of the peptidolipid, we rationalized that the free sulfhydryl groups of the peptidolipid were oxidized in the presence of oxygen in the alkaline subphase to form intermolecular disulfide bonds at the air-water interface. The surface topography of the peptidolipid Langmuir film was observed by epi-fluorescence microscopy and the Langmuir-Blodgett film by environmental scanning electron microscopy (ESEM). The micrographs showed evidence of the polymerization of the cysteinyl peptidolipid at the air-water interface. Furthermore, the XPS spectra of the Langmuir-Blodgett films also proved the existence of disulfide bonds. The control peptidolipid C(18)-Ser-Gly-Ser-OH showed identical surface pressure-area isotherms in the presence or absence of an oxygen-saturated subphase.

Molecular recognition and removal properties of Langmuir–Blodgett films of nucleolipid amphiphiles bearing thymine headgroup

Three different types of nucleolipid amphiphiles bearing thymine moiety in the headgroup, N-octadecyl thymine-1-acetamide (OTA), octadecyl ammonium thymine-1-acetate (OATA) and N, N-didodecyl thymine-1-acetamide (DDTA) were synthesized, and the molecular recognition capabilities of the corresponding Langmuir (L) and Langmuir–Blodgett (LB) films for melamine (MELA), 2,4,6-triaminopyrimidine (TAP) and 2,6-diaminopyridine (DAP) were investigated. The π– A isotherm revealed that an L film of OTA requires two-dimensional expansion along with molecular recognition due to the tight packing nature of the headgroups of the film. However, such expansion was not observed in the case of OATA and DDTA, and this may be due to conformational relaxation based on ionic bonding between the headgroup and the alkyl chain in the OATA, and due to sufficient space around the headgoup of the DDTA. In addition, molecular recognition, removal and re-recognition properties were investigated for the LB films of the amphiphils. Although, any LB film deposited from a pure water subphase did not exhibit recognition ability at room temperature, the OTA LB film deposited from a guest molecule aqueous solution followed by removing the embedded guest molecule from the film was found to recognize the corresponding guest molecule. Therefore, it is reasonable to conclude that both sufficient space for migration and location of the guest molecules in the film and dynamic stability of the film versus the recognition and removal process should be required for fabricating a chemical sensing device based on reversible molecular recognition and removal.

Mixing characterization of perylene and merocyanine Langmuir–Blodgett films

Langmuir–Blodgett (LB) films of mixtures of 3,4,9,10-perylenetetracarboxylic diimide (PTCDI), merocyanine dye (DO) and arachidic acid (C 20) with different molecular ratios, were prepared on Cd 2+-containing and pure-water subphases. The characterization of mixed Langmuir and LB films were performed by using, respectively, surface pressure–molecular area isothermetry and UV–Vis–IR absorption spectroscopy. The analysis indicates that interaction between the two dyes modifies their arrangements and electronic states in their mixed Langmuir films spread upon the Cd 2+-containing subphase. However, the mixed LB films with the pure-water subphase are showed to be simple physical mixtures. The difference in the mixing effect observed for the Langmuir films upon the Cd-containing and pure-water subphases may be caused by the formation of metal chelation with the former subphase.

Fabrication of a composite nano-ultrathin film of poly-phenylene-vinylene and C 60 derivative

The monolayers of pure C 60 derivative (C60-COOH) are stable on the surface of pure water subphase and poly-phenylene-vinylene derivative (PPV) solution, respectively. The composite ultrathin film of PPV and C60-COOH was successively fabricated on the quartz and mica substrate by using Langmuir–Blodgett technique. X-ray photoelectron spectrometry (XPS) measurements show that the PPV is embedded into the film during the fabrication process. The surface morphologies of pure C60-COOH film and the composite film were investigated with atomic force microscopy (AFM), respectively. The phenomenon of electron transmission between PPV and C60-COOH in the composite film was confirmed by UV–vis spectra.

Development of a fluid functionalized lipidic matrix applied to direct in situ polynucleotide detection

This work presents a new approach for direct detection of polyelectrolytes at the air–water interface, based on the investigation of the interfacial properties of an active lipidic matrix especially designed for polynucleotide immobilization. A synthetic lipid with a cationic spermine headgroup, DiOctadecylamidoGlycylSpermine (DOGS), was spread at the interface to form a distortable film able to capture polynucleotides. The control of the organization state of this functionalized monolayer upon compression was achieved by recording surface pressure–area ( π– A) isotherm diagrams, presenting a specific shape with a typical liquid expanded–liquid condensed phase transition on a pure water subphase. In the presence of various dsDNA concentrations in the subphase, the isotherms were markedly modified in a time and concentration-dependent manner. The main modifications, corresponding to a large shift towards higher molecular areas and a clear fading of the phase transition, were corroborated by the fine analysis of the monolayer compressibility profile, thus suggesting a characteristic change in the monolayer fluidity as a function of both time and DNA concentration. Moreover, an ATR-Fourier transform infrared (ATR-FTIR) characterization showed evidences for the adsorption of DNA strands onto the lipidic matrix. The direct observation of the mixed monolayer morphology by Brewster angle microscopy (BAM) strongly suggests that DNA adsorption induces a reorganization of lipids at the interface, as evidenced by the change in the condensed lipidic domains morphology in the presence of DNA in the subphase. The immobilization of various polynucleotidic probes of 4000, 400 and 22 base length, confirmed by fluorescence microscopy, had similar effects on DOGS interfacial properties. Preliminary studies are finally presented to explore the possibility of using this system for the study of hybridization between complementary strands. Hence, this study demonstrates this functionalized matrix behaves as a fluid support where polynucleotide immobilization induces interfacial properties modifications, which could be further exploited through the experimental characterization of Faraday instabilities sensitive to visco-elasticity variations.

Gelation of Octadecyltrimethoxysilane at the Air/Water Interface: Effect of Perfluorotetradecanoic Acid and Divalent Cadmium Ions

The effect of an acidic surfactant, perfluorotetradecanoic acid (PFTDA), on the gelation of octadecyltrimethoxysilane (ODTMS) monolayers at the air/water interface was investigated using a Langmuir film balance, attenuated total reflection (ATR) infrared spectroscopy, and atomic force microscopy (AFM). The gelation of ODTMS was greatly accelerated by adding only 2 mol % PFTDA into the monolayer; in this case, the hydrolysis of ODTMS was completed within a few minutes, whereas otherwise it took 18 h. ATR-IR spectroscopy clearly demonstrated that the gelation of a 49:1 ODTMS/PFTDA monolayer proceeded on a pure water subphase mainly via hydrolysis followed by condensation. In the presence of PFTDA, the local acidity at specific sites is presumed to be very high, catalyzing the hydrolysis of ODTMS. The extremely fast rate is attributed not only to the lateral diffusion of PFTDA in the mixed monolayer but also to proton propagation where the proton(s) involved in the initial hydrolysis are transposed rapidly to the nearby methoxy groups for subsequent hydrolysis. The catalytic activity of PFTDA can be neutralized, however, simply by the addition of multivalent metallic ions such as Cd2+ to form saltlike complexes with PFTDA; the rate of 2-D sol-gel processes can thus be easily regulated by a minute amount of PFTDA and/or Cd2+ added into the reaction system.

Thermodynamic and mechanical properties of model mitochondrial membranes

Cardiolipin is a unique four-tailed, doubly negatively charged lipid found predominantly within the inner mitochondrial membrane, and is thought to be influential in determining membrane potential and permeability. To determine the role of cardiolipin in modulating the properties of membranes, this study investigates the thermodynamics of mixed cardiolipin and phosphatidylcholine monolayers and bilayers. Gibbs free energy analysis of mixed monolayers indicates that at low cardiolipin concentrations (5–10 mol%), there is a positive deviation from ideality on a pure water subphase, while at physiological salt concentrations a negative deviation from ideality is observed. The mechanical properties of bilayers containing cardiolipin were measured using micropipette aspiration. Both apparent area compressibility modulus, as well as lysis tension, decrease with increasing cardiolipin content. This destabilization indicates a decrease in the cohesive energy of the membrane. This interplay between interactions of lipids in monolayers and bilayers, suggests cardiolipin plays a dual role in modulating membrane properties. Cardiolipin enhances lateral interactions between lipids within monolayer leaflets, while simultaneously decreasing the cohesive energy of membranes at physiologically relevant concentrations. Taken together, these findings correlate with the decreased permeability and creation of folds in the inner mitochondrial membrane.

Detection of NH Stretching Signals from the Monolayers of Amino Acid Amphiphiles at the Air−Water Interface and Change of Hydrogen Bond Depending on Metal Ion in the Subphase: Infrared Reflection−Adsorption Spectroscopy

The monolayers of amino acid amphiphiles at the air−water interface on pure water and ion-containing subphases have been studied using infrared reflection−absorption spectroscopy. It is the first time that the NH stretching signals are detected from the monolayers at the air−water interface with this technique. In the presence of Ag+ and Pb2+ in the subphases, the covalent interaction between metals and carboxylate groups is predominant in the form of chelating and/or bridging bidentate coordination, and the intermolecular hydrogen-bonding interaction between the adjacent molecules through amide groups is increased in comparison with that in the case of pure water. In the presence of Ca2+ and Cu2+, the ionic interaction between metal ions and carboxylate groups is preferred, and the intramolecular hydrogen bond is developed. The hydrogen bond in the monolayers at the air−water interface undergoes an obvious change in type and strength depending on metal ion in the subphase.

Synthesis and Supramolecular Self-Assembly Study of a Novel Porphyrin Molecule in Langmuir and Langmuir−Blodgett Films

The self-assembly and supramolecular engineering of porphyrins into ordered arrays have recently attracted much interest because of their promising application potential in molecular and electronic devices, spintronics, energy harvesting and storage, catalysis, and sensor development. We herein report the synthesis and supramolecular self-assembly study of a novel porphyrin molecule, 2Por-TAZ, in Langmuir and Langmuir-Blodgett films. The 2Por-TAZ molecule contains two porphyrin macrocycles attached to a triaminotriazine headgroup. Triaminotriazines are known to form a highly ordered linear supramolecular self-assembly through complementary hydrogen bonding with barbituric acid molecules at the air-water interface. Surface pressure-area isotherm measurements and polarized UV-vis absorption spectroscopic studies indicate that the 2Por-TAZ molecules adopted an edge-on orientation at the air-water interface. Polarized UV-vis absorption study also revealed that the 2Por-TAZ molecules formed linear supramolecular networks on pure water and barbituric acid subphase with porphyrin flat planes facing toward the compression direction. The binding of barbituric acid with 2Por-TAZ molecules was observed from the expansion of the Langmuir monolayer film. Compared to the transferred LB film from pure water subphase, both the UV-vis absorbance and fluorescence emission intensity of the LB film transferred from barbituric acid subphase increased significantly.

Thermodynamic and mechanical properties of model mitochondrial membranes

Cardiolipin is a unique four-tailed, doubly negatively charged lipid found predominantly within the inner mitochondrial membrane, and is thought to be influential in determining membrane potential and permeability. To determine the role of cardiolipin in modulating the properties of membranes, this study investigates the thermodynamics of mixed cardiolipin and phosphatidylcholine monolayers and bilayers. Gibbs free energy analysis of mixed monolayers indicates that at low cardiolipin concentrations (5–10 mol%), there is a positive deviation from ideality on a pure water subphase, while at physiological salt concentrations a negative deviation from ideality is observed. The mechanical properties of bilayers containing cardiolipin were measured using micropipette aspiration. Both apparent area compressibility modulus, as well as lysis tension, decrease with increasing cardiolipin content. This destabilization indicates a decrease in the cohesive energy of the membrane. This interplay between interactions of lipids in monolayers and bilayers, suggests cardiolipin plays a dual role in modulating membrane properties. Cardiolipin enhances lateral interactions between lipids within monolayer leaflets, while simultaneously decreasing the cohesive energy of membranes at physiologically relevant concentrations. Taken together, these findings correlate with the decreased permeability and creation of folds in the inner mitochondrial membrane.

Fourier transform surface-enhanced Raman scattering of single-layer nucleolipid Langmuir–Blodgett films on silver island film substrates

Surface-enhanced Raman scattering (SERS) spectra of four amphiphilic nucleolipids in single-layer Langmuir–Blodgett (LB) films deposited on silver island film substrates from pure water and complementary nucleotide-containing subphase and corresponding powder normal Raman spectra were obtained. The analysis of these spectra indicates that the SERS effect is mainly caused by a charge-transfer mechanism, and only the nucleobase headgroup moieties and complementary bases combined with them through hydrogen bonds, which are directly in contact with the silver island film substrates, could be enhanced. For the amphiphilic nucleolipids with the identical nucleobase headgroups, the SERS spectra of the LB films are similar, implying that the orientations of these nucleobase moieties on the silver substrates are analogous. However, the nucleobase takes different orientations on the silver substrates before and after complementary binding. The nucleobases in the LB films deposited from pure water are nearly lying flat on the silver surface, while the complementary binding pairs transferred from the air/water interface tend to take an end-on orientation on the metal surface.

Memory effects on the interfacial characteristics of dioctadecyldimethylammonium bromide monolayers at the air–water interface

The structural and dynamic characteristics of dioctadecyldimethylammonium bromide (DODAB) monolayers on a pure water subphase were investigated by surface film balance, Brewster angle microscopy, and relaxation in area and surface pressure at constant surface pressure and area, respectively. The first compression–expansion cycle of the monolayer is not reversible and the second π– A compression isotherm deviates to larger molecular areas relative to the first one. At a microscopic level this hysteresis may be assigned to an irreversible hydration of the ammonium groups of DODAB. The morphology and reflectivity of DODAB monolayers during compression and expansion on the monolayer depend on the monolayer history. Bright domains randomly dispersed were observed during compression before collapse. Surprisingly, this random distribution of domains changes into a fractal-like structure during the monolayer expansion in a narrow range of surface pressures. This morphology does not form when the monolayer is previously compressed above the collapse surface pressure. 2D foam-like structure is often observed when the film is expanded at maximum area. Relaxation phenomena in DODAB monolayers are attributed to monolayer reorganization and nucleation of liquid-condensed domains from the liquid-expanded phase. These time-dependent processes are irreversible.