Oleg Konovalov - Academia.edu (original) (raw)

Papers by Oleg Konovalov

Spectrochimica Acta Part B: Atomic Spectroscopy, 2008

The x-ray standing wave method has been applied to study self-assembling processes in a protein-l... more The x-ray standing wave method has been applied to study self-assembling processes in a protein-lipid film formed by injecting the protein-lipid mixture of alkaline phosphatase and phosphatidylinositol under the phospholipid monolayer preliminarily deposited on the water subphase by Langmuir method. X-ray standing wave measurements allowed to determine the composition of the protein-lipid film and to locate ions position in the direction normal to the film surface. The presence of trace Ni contamination incorporated in the protein-lipid film from the water subphase has been established. Numerical analysis of the X-ray standing wave fluorescence data revealed that after injection under the phospholipid monolayer, the proteinlipid mixture separated in a self-assembled manner to layered structure, molecules of alkaline phosphatase arranged themselves into a pure protein layer containing no phospholipid molecules.

We describe a new cell for studies in environment of normal and supercritical gases in large pres... more We describe a new cell for studies in environment of normal and supercritical gases in large pressure and temperature range. This device is developed for various scientific applications. One of the first applications planned in collaboration with the LPEC (Laboratoire de Physique de l'Etat Condensé), is the in situ physi- and chemisorption of CO2 gas at the surface of large

Synthetic Metals, 2001

The drying of thick solutions of the conjugated polymer poly(octylthiophene) (POT) was followed i... more The drying of thick solutions of the conjugated polymer poly(octylthiophene) (POT) was followed in situ by grazing incidence diffraction of synchrotron X-rays from the solution surface, with the solvent evaporation rate being controlled by a¯ow of dry nitrogen gas. It was found that a solid, partially crystalline ®lm is formed on the upper surface while the interior is still¯uid. The initially formed ®lm is swollen and of restricted correlation length, but the swelling disappears gradually on further drying. A considerable fraction (>20%) of the polymer within the effective beam volume near the surface is transformed from the disordered to the ordered state only during the removal of the last 5% of the solvent.

The Journal of Physical Chemistry C, 2010

We propose a strategy to modulate the electronic structure of gallium arsenide (GaAs) semiconduct... more We propose a strategy to modulate the electronic structure of gallium arsenide (GaAs) semiconductors by the covalent deposition of uniform monolayers of helical peptides. After the optimization of coupling groups and reaction conditions, structures of peptide monolayers on GaAs were characterized by the combination of grazing incidence-X-ray scattering and Fourier transform infrared spectroscopy yielding the thickness, the area occupied by one peptide helix, and the tilt angle of helical axis with respect to the surface normal. The deposition of the same peptides on high electron mobility transistor (HEMT) devices resulted in a clear change in the carrier mobility depending on the length of peptide helices. The obtained results demonstrated that the macrodipole potential of oriented peptide helices can be utilized for flexible tuning of the electronic structure (band bending) of semiconductors, which can offer a unique alternative to the commonly used doping of charge carriers.

The Journal of Physical Chemistry B, 2007

In order to be used in versatile DNA delivery systems, novel cationic lipids were synthesized. Th... more In order to be used in versatile DNA delivery systems, novel cationic lipids were synthesized. The head groups of the new compounds represented by monoamines or oligoamines can be charged or uncharged depending on the environmental pH. Since their pK values are unknown, the protonation properties of these lipids have been studied in a wide pH range. In our experiments, the amphiphilic molecules were organized as a Langmuir monolayer at the air-water interface. Total reflection X-ray fluorescence (TRXF) was used to determine the 2D concentration of bromide counterions bound to a positively charged (protonated) Langmuir monolayer. The protonation rate of the novel cationic lipids was estimated by comparing the fluorescence intensity with that of dioctadecyldimethylammonium bromide monolayers as a reference. TRXF investigations were supplemented with results of film-balance measurements, grazing incidence X-ray diffraction, and X-ray reflectivity data. The results obtained display that the monolayers of all studied compounds are completely uncharged at pH values above 10. In the investigated pH region, the highest protonation rate of the monolayers is observed at pH 3. The influence of the monolayer packing density on the protonation properties is clearly shown.

The Journal of Physical Chemistry B, 2013

We have demonstrated that the complementary combination of grazing incidence X-ray fluorescence (... more We have demonstrated that the complementary combination of grazing incidence X-ray fluorescence (GIXF) with specular X-ray reflectivity (XRR) can be used to quantitatively determine the density profiles of Ni 2+ ions complexed with chelator headgroups as well as S atoms in recombinant proteins anchored to lipid monolayers at the air/water interface. First, we prepared phospholipid monolayers incorporating chelator lipid anchors at different molar fractions at the air/water interface. The finestructures perpendicular to the global plane of monolayers were characterized by XRR in the presence of Ni 2+ ions, yielding the thickness, roughness, and electron density of the stratified lipid monolayers. X-ray fluorescence intensities from Ni Kα core levels recorded at the incidence angles below and above the critical angle of total reflection allow for the determination of the position and lateral density of Ni 2+ ions associated with chelator headgroups with a high spatial accuracy (±5 Å). The coupling of histidine-tagged Xenopus cadherin 11 (Xcad-11) can also be identified by changes in the fines-structures using XRR. Although fluorescence intensities from S Kα level were much weaker than Ni Kα signals, we could detect the location of S atoms in recombinant Xcad-11 proteins.

The Journal of Physical Chemistry B, 2001

An investigation of bulk single crystals and crystalline monolayers at the air-water interface of... more An investigation of bulk single crystals and crystalline monolayers at the air-water interface of secondary alcohols bearing 16 and 17 carbons has been carried out in order to investigate their molecular packing. These "simple" chiral molecules can be seen as model systems; therefore, their study might provide broader knowledge of how chirality affects the molecular arrangement. The bulk racemic mixtures exhibit racemate organization, i.e., ordered mixtures of left and right enantiomers, with a head to head packing, whereas the pure enantiomers present a head to tail arrangement. The former type of motif has been reported for many amphiphilic molecules, whereas the latter is more rare. In two dimensions, all compounds, pure enantiomers, racemic mixtures, as well as other mixtures, present a hexagonal rotator phase with lattice parameters close to 5 Å. The rotational motion suggests the formation of a two-dimensional solid solution. However, upon heating, monolayers of 2-heptadecanol present a peculiar evolution. For mixtures of the two enantiomers with ratios between 1:1 and 2:1, the hexagonal phase transforms to a centered rectangular one, due to an inclination of molecules of about 10°with respect to the vertical. The loss of hexagonal symmetry is attributed to the formation of a racemate.

Soft Matter, 2008

Interactions of the antimicrobial peptide protegrin-1 (PG-1) with phospholipid monolayers have be... more Interactions of the antimicrobial peptide protegrin-1 (PG-1) with phospholipid monolayers have been investigated by using grazing incidence X-ray diffraction (GIXD) and specular X-ray reflectivity (XR). The structure of a PG-1 film at the air-aqueous interface was also investigated by XR for the first time. Lipid A, dipalmitoyl-phosphatidylglycerol (DPPG) and dipalmitoyl-phosphatidylcholine (DPPC) monolayers were formed at the air-aqueous interface to mimic the surface of the bacterial cell wall and the outer leaflet of the erythrocyte cell membrane, respectively. Experiments were carried out under constant area conditions where the pressure changes upon insertion of peptide into the monolayer. GIXD data suggest that the greatest monolayer disruption produced by PG-1 is seen with the DPPG system at 20 mN/m since the Bragg peaks completely disappear after introduction of PG-1 to the system. PG-1 shows greater insertion into the lipid A system compared to the DPPC system when both films are held at the same initial surface pressure of 20 mN/m. The degree of insertion lessens at 30 mN/m with both DPPC and DPPG monolayer systems. XR data further reveal that PG-1 inserts primarily in the head group region of lipid monolayers. However, only the XR data of the anionic lipids suggest the existence of an additional adsorbed peptide layer below the head group of the monolayer. Overall the data show that the extent of peptide/lipid interaction and lipid monolayer disruption depends not only on the lipid composition of the monolayer, but the packing density of the lipids in the monolayer prior to the introduction of peptide to the subphase.

Soft Matter, 2012

ABSTRACT To what extent is the ordering of fluids at interfaces governed by the bulk structure of... more ABSTRACT To what extent is the ordering of fluids at interfaces governed by the bulk structure of the fluid? In order to address this question, we have studied a dense, charge-stabilized colloidal suspension at the fluid–air interface and at two different solid–fluid interfaces using specular X-ray reflectivity. The experimental data are well described by a simple model of a stratified fluid, with the wall–particle potential mainly affecting the position of the first particle layer with respect to the interface. The decay of the fluid's density profile can for all the studied interfaces be described by a characteristic wavelength and a decay length, both of which are independently determined from the bulk phase using small-angle X-ray scattering. This latter finding is consistent with theoretical predictions and recent surface-force experiments.

Soft Matter, 2010

The growth mechanism of a protein monolayer at the air–water interface was investigated using dyn... more The growth mechanism of a protein monolayer at the air–water interface was investigated using dynamic surface tension, diffuse X-ray scattering and X-ray fluorescence techniques. To ensure the surface sensitivity, the grazing angle was kept smaller than the critical angle ...

Soft Matter, 2010

ABSTRACT Grazing incidence X-ray diffraction has been used to determine the structure of two-dime... more ABSTRACT Grazing incidence X-ray diffraction has been used to determine the structure of two-dimensional organic-inorganic crystals formed of a behenic acid monolayer spread over a Mn2+ or Mg2+ solution at high pH. Using a new method based on careful structure factor determination, building of molecular models and simulated annealing, the number and position of the divalent ions in the unit cell, the orientation of the chain backbone planes and carboxylic headgroups conformation defects could be determined. In agreement with their bulk solution properties, Mn2+ and Mg2+ behave very differently. Individual Mn2+ ions adsorb below the negatively charged films, whereas the superstructure includes hydrolysis products containing one or several Mg2+ ions in the case of magnesium. This difference is also reflected in the kinetics of structure formation.

Physical Review Letters, 2007

We have investigated the surface composition of alkali-halide aqueous solutions using grazing inc... more We have investigated the surface composition of alkali-halide aqueous solutions using grazing incidence x-ray fluorescence. Using mixtures of salts as a means to enhance the short-range effects, small differences in concentration over a few angstrom could be resolved, with, for example I ÿ or Br ÿ > Cl ÿ. In order to explain our data, we need to include an effective potential accounting for the short-range (Å) solvent mediated couplings, responsible for specific effects together with dispersion forces. This attractive potential (few k B T for halides) leads to concentration profiles which are in good agreement with recent numerical simulations.

Physica B: Condensed Matter, 2005

Peptide secretion by living organisms constitutes an integral response process exploited by natur... more Peptide secretion by living organisms constitutes an integral response process exploited by natural immune systems. In this work we present a model study and insight into this process reporting the thermodynamic and structural effects induced in phospholipid monolayers due to peptide insertion into the layer. Synchrotron X-ray radiation is combined with the Langmuir technique and exploited to form 'lipid-peptide' monolayers and probe the physical characteristics of the fundamental biological process of 'peptide secretion'. Our experiments show that the insertion of peptides in the phospholipid layer has adverse effects on the elastic properties of the layer manifested through the bending rigidity.

Langmuir, 2007

Interactions of native DNA with octadecylamine (ODA) and hexadecymdimethylammonium bromide (HTAB)... more Interactions of native DNA with octadecylamine (ODA) and hexadecymdimethylammonium bromide (HTAB) monolayers at the air/water interface were studied by π-A isotherms, ellipsometry, and X-ray reflectivity. We show that the microscopic structure of ODA-DNA complexes is definitely consistent with a single-stranded form for DNA. On the contrary, with HTAB, DNA complexes in its native form. The crucial difference in the behavior of these two fairly similar lipids is due to the presence of the amine group in ODA. These results should be relevant to applications such as DNA chips and sensors.

Langmuir, 2009

The behavior of mixed-ligand-coated gold nanoparticles at a liquid-liquid interface during compre... more The behavior of mixed-ligand-coated gold nanoparticles at a liquid-liquid interface during compression has been investigated. The system was characterized by measuring pressure-area isotherms and by simultaneously performing in situ X-ray studies. Additionally, Monte Carlo (MC) simulations were carried out in order to interpret the experimental findings. With this dual approach it was possible to characterize and identify the different stages of compression and understand what happens microscopically: first, a compression purely in-plane, and, second, the formation of a second layer when the in-plane pressure pushes the particles out of the plane. The first stage is accompanied by the emergence of an in-plane correlation peak in the scattering signal and a strong increase of the pressure in the isotherm. The second stage is characterized by the weakening of the correlation peak and a slower increase in pressure.

Journal of Colloid and Interface Science, 2011

The protein collagen is the major component of connective tissue and it is involved in many biolo... more The protein collagen is the major component of connective tissue and it is involved in many biological functions. Its degradation is at the basis of different pathological processes. The up-regulated expression of matrix metalloproteinases and the down-regulated expression of their inhibitors are the causes for such degradation. The aim of this work was to evaluate the possibility to fabricate collagen based containers for drug encapsulation and release by cellular demand by the action of matrix metalloproteinases. In present work collagen type I based microcapsules were fabricated by means of the layer-by-layer assembly of oppositely charged collagen and poly (stirene sulfonate) onto colloidal particles, followed by removal of the cores to obtain hollow microcapsules. The process of shell growth on planar supports was monitored by quartz crystal microbalance. X-ray reflectivity measurements were carried out at the solid/water interface to study the interaction of matrix metalloproteinase 1 with LbL films of collagen. The morphology of hollow capsules was characterized by scanning electron microscopy, and compared to that of capsules exposed to the matrix metalloproteinase 1. Finally the matrix metalloproteinase 1 mediated permeability of capsules variation was studied by Confocal Laser Scanning Microscopy. The results demonstrated the possibility to fabricate a drug delivery system where the release of the drug is dependent on the biochemistry of the pathological state.

Journal of Applied Crystallography, 2003

X-ray total external reflection fluorescence has been applied to detect an angular dependence of ... more X-ray total external reflection fluorescence has been applied to detect an angular dependence of fluorescence yield modulated by evanescent/X-ray standing wave pattern from metal-rich organic monolayer alone on water surface. Theoretical consideration reveals that electric field intensity in a molecular monolayer is completely determined by an area per one molecule value that can be obtained from pressure-area isotherm. This allows getting an ion position inside a monolayer from the corresponding fluorescence angular dependence. The possibilities of the technique have been used at the SR beamline ID10B (ESRF) to characterize Langmuir monolayers of phthalocyanines and cyclolinear polyorganosiloxanes formed on air/water interface.

Langmuir : the ACS journal of surfaces and colloids, Jan 4, 2008

In this Letter, we present a method for the decoration of layer-by-layer (LbL) structures by heav... more In this Letter, we present a method for the decoration of layer-by-layer (LbL) structures by heavy metal ions, which allows X-ray reflectivity (XRR) measurements at the solid/water interface. The improved contrast has allowed us to obtain well-structured X-ray reflectivity curves from samples at the liquid/solid interface that can be used for the film structure modeling. The developed technique was also used to follow the formation of complexes between DNA and the LbL multilayer. The XRR data are confirmed by independent null-ellipsometric measurements at the solid/liquid interface on the very same architectures.

The European Physical Journal Special Topics, 2007

Liposome suspensions comprising the synthetic cationic lipid DOTAP, the zwitterionic DPPC and the... more Liposome suspensions comprising the synthetic cationic lipid DOTAP, the zwitterionic DPPC and the anti-cancer agent Paclitaxel were deposited on solid substrates and investigated by X-ray and neutron reflectivity measurements at ESRF and ILL. Well ordered multilamellar drug/lipid membranes were obtained, such as indicated by the several orders of Bragg reflections in the diffraction pattern. With an excess of Paclitaxel, additional Bragg peaks from the drug crystalline phase could be observed. Changes of the molecular organization in the drug-lipid system were investigated as a function of relative humidity using a custom-built controlled humidity chamber. For DOTAP multilayers the effects of bilayer swelling were much more pronounced than for DPPC under similar conditions, while the crystalline peaks of the drug were not affected. The pronounced swelling of DOTAP multilayers might be related to the electrostatic repulsion between the charged lipid headgroups.

Journal de Physique IV (Proceedings), 2002

M-366 JOURNAL DE PHYSIQUE IV d' un fragment de C-cadhkrme plus court sur l a protkine entike La c... more M-366 JOURNAL DE PHYSIQUE IV d' un fragment de C-cadhkrme plus court sur l a protkine entike La compltmentarltd de nos rksultats avec ceux d' &udes blochlmlques devralt nous permettre d'avancer dans l a compr6hension des mCcanlsmes de I'adh&lon cellulawe 1.

Spectrochimica Acta Part B: Atomic Spectroscopy, 2008

The x-ray standing wave method has been applied to study self-assembling processes in a protein-l... more The x-ray standing wave method has been applied to study self-assembling processes in a protein-lipid film formed by injecting the protein-lipid mixture of alkaline phosphatase and phosphatidylinositol under the phospholipid monolayer preliminarily deposited on the water subphase by Langmuir method. X-ray standing wave measurements allowed to determine the composition of the protein-lipid film and to locate ions position in the direction normal to the film surface. The presence of trace Ni contamination incorporated in the protein-lipid film from the water subphase has been established. Numerical analysis of the X-ray standing wave fluorescence data revealed that after injection under the phospholipid monolayer, the proteinlipid mixture separated in a self-assembled manner to layered structure, molecules of alkaline phosphatase arranged themselves into a pure protein layer containing no phospholipid molecules.

We describe a new cell for studies in environment of normal and supercritical gases in large pres... more We describe a new cell for studies in environment of normal and supercritical gases in large pressure and temperature range. This device is developed for various scientific applications. One of the first applications planned in collaboration with the LPEC (Laboratoire de Physique de l'Etat Condensé), is the in situ physi- and chemisorption of CO2 gas at the surface of large

Synthetic Metals, 2001

The drying of thick solutions of the conjugated polymer poly(octylthiophene) (POT) was followed i... more The drying of thick solutions of the conjugated polymer poly(octylthiophene) (POT) was followed in situ by grazing incidence diffraction of synchrotron X-rays from the solution surface, with the solvent evaporation rate being controlled by a¯ow of dry nitrogen gas. It was found that a solid, partially crystalline ®lm is formed on the upper surface while the interior is still¯uid. The initially formed ®lm is swollen and of restricted correlation length, but the swelling disappears gradually on further drying. A considerable fraction (>20%) of the polymer within the effective beam volume near the surface is transformed from the disordered to the ordered state only during the removal of the last 5% of the solvent.

The Journal of Physical Chemistry C, 2010

We propose a strategy to modulate the electronic structure of gallium arsenide (GaAs) semiconduct... more We propose a strategy to modulate the electronic structure of gallium arsenide (GaAs) semiconductors by the covalent deposition of uniform monolayers of helical peptides. After the optimization of coupling groups and reaction conditions, structures of peptide monolayers on GaAs were characterized by the combination of grazing incidence-X-ray scattering and Fourier transform infrared spectroscopy yielding the thickness, the area occupied by one peptide helix, and the tilt angle of helical axis with respect to the surface normal. The deposition of the same peptides on high electron mobility transistor (HEMT) devices resulted in a clear change in the carrier mobility depending on the length of peptide helices. The obtained results demonstrated that the macrodipole potential of oriented peptide helices can be utilized for flexible tuning of the electronic structure (band bending) of semiconductors, which can offer a unique alternative to the commonly used doping of charge carriers.

The Journal of Physical Chemistry B, 2007

In order to be used in versatile DNA delivery systems, novel cationic lipids were synthesized. Th... more In order to be used in versatile DNA delivery systems, novel cationic lipids were synthesized. The head groups of the new compounds represented by monoamines or oligoamines can be charged or uncharged depending on the environmental pH. Since their pK values are unknown, the protonation properties of these lipids have been studied in a wide pH range. In our experiments, the amphiphilic molecules were organized as a Langmuir monolayer at the air-water interface. Total reflection X-ray fluorescence (TRXF) was used to determine the 2D concentration of bromide counterions bound to a positively charged (protonated) Langmuir monolayer. The protonation rate of the novel cationic lipids was estimated by comparing the fluorescence intensity with that of dioctadecyldimethylammonium bromide monolayers as a reference. TRXF investigations were supplemented with results of film-balance measurements, grazing incidence X-ray diffraction, and X-ray reflectivity data. The results obtained display that the monolayers of all studied compounds are completely uncharged at pH values above 10. In the investigated pH region, the highest protonation rate of the monolayers is observed at pH 3. The influence of the monolayer packing density on the protonation properties is clearly shown.

The Journal of Physical Chemistry B, 2013

We have demonstrated that the complementary combination of grazing incidence X-ray fluorescence (... more We have demonstrated that the complementary combination of grazing incidence X-ray fluorescence (GIXF) with specular X-ray reflectivity (XRR) can be used to quantitatively determine the density profiles of Ni 2+ ions complexed with chelator headgroups as well as S atoms in recombinant proteins anchored to lipid monolayers at the air/water interface. First, we prepared phospholipid monolayers incorporating chelator lipid anchors at different molar fractions at the air/water interface. The finestructures perpendicular to the global plane of monolayers were characterized by XRR in the presence of Ni 2+ ions, yielding the thickness, roughness, and electron density of the stratified lipid monolayers. X-ray fluorescence intensities from Ni Kα core levels recorded at the incidence angles below and above the critical angle of total reflection allow for the determination of the position and lateral density of Ni 2+ ions associated with chelator headgroups with a high spatial accuracy (±5 Å). The coupling of histidine-tagged Xenopus cadherin 11 (Xcad-11) can also be identified by changes in the fines-structures using XRR. Although fluorescence intensities from S Kα level were much weaker than Ni Kα signals, we could detect the location of S atoms in recombinant Xcad-11 proteins.

The Journal of Physical Chemistry B, 2001

An investigation of bulk single crystals and crystalline monolayers at the air-water interface of... more An investigation of bulk single crystals and crystalline monolayers at the air-water interface of secondary alcohols bearing 16 and 17 carbons has been carried out in order to investigate their molecular packing. These "simple" chiral molecules can be seen as model systems; therefore, their study might provide broader knowledge of how chirality affects the molecular arrangement. The bulk racemic mixtures exhibit racemate organization, i.e., ordered mixtures of left and right enantiomers, with a head to head packing, whereas the pure enantiomers present a head to tail arrangement. The former type of motif has been reported for many amphiphilic molecules, whereas the latter is more rare. In two dimensions, all compounds, pure enantiomers, racemic mixtures, as well as other mixtures, present a hexagonal rotator phase with lattice parameters close to 5 Å. The rotational motion suggests the formation of a two-dimensional solid solution. However, upon heating, monolayers of 2-heptadecanol present a peculiar evolution. For mixtures of the two enantiomers with ratios between 1:1 and 2:1, the hexagonal phase transforms to a centered rectangular one, due to an inclination of molecules of about 10°with respect to the vertical. The loss of hexagonal symmetry is attributed to the formation of a racemate.

Soft Matter, 2008

Interactions of the antimicrobial peptide protegrin-1 (PG-1) with phospholipid monolayers have be... more Interactions of the antimicrobial peptide protegrin-1 (PG-1) with phospholipid monolayers have been investigated by using grazing incidence X-ray diffraction (GIXD) and specular X-ray reflectivity (XR). The structure of a PG-1 film at the air-aqueous interface was also investigated by XR for the first time. Lipid A, dipalmitoyl-phosphatidylglycerol (DPPG) and dipalmitoyl-phosphatidylcholine (DPPC) monolayers were formed at the air-aqueous interface to mimic the surface of the bacterial cell wall and the outer leaflet of the erythrocyte cell membrane, respectively. Experiments were carried out under constant area conditions where the pressure changes upon insertion of peptide into the monolayer. GIXD data suggest that the greatest monolayer disruption produced by PG-1 is seen with the DPPG system at 20 mN/m since the Bragg peaks completely disappear after introduction of PG-1 to the system. PG-1 shows greater insertion into the lipid A system compared to the DPPC system when both films are held at the same initial surface pressure of 20 mN/m. The degree of insertion lessens at 30 mN/m with both DPPC and DPPG monolayer systems. XR data further reveal that PG-1 inserts primarily in the head group region of lipid monolayers. However, only the XR data of the anionic lipids suggest the existence of an additional adsorbed peptide layer below the head group of the monolayer. Overall the data show that the extent of peptide/lipid interaction and lipid monolayer disruption depends not only on the lipid composition of the monolayer, but the packing density of the lipids in the monolayer prior to the introduction of peptide to the subphase.

Soft Matter, 2012

ABSTRACT To what extent is the ordering of fluids at interfaces governed by the bulk structure of... more ABSTRACT To what extent is the ordering of fluids at interfaces governed by the bulk structure of the fluid? In order to address this question, we have studied a dense, charge-stabilized colloidal suspension at the fluid–air interface and at two different solid–fluid interfaces using specular X-ray reflectivity. The experimental data are well described by a simple model of a stratified fluid, with the wall–particle potential mainly affecting the position of the first particle layer with respect to the interface. The decay of the fluid's density profile can for all the studied interfaces be described by a characteristic wavelength and a decay length, both of which are independently determined from the bulk phase using small-angle X-ray scattering. This latter finding is consistent with theoretical predictions and recent surface-force experiments.

Soft Matter, 2010

The growth mechanism of a protein monolayer at the air–water interface was investigated using dyn... more The growth mechanism of a protein monolayer at the air–water interface was investigated using dynamic surface tension, diffuse X-ray scattering and X-ray fluorescence techniques. To ensure the surface sensitivity, the grazing angle was kept smaller than the critical angle ...

Soft Matter, 2010

ABSTRACT Grazing incidence X-ray diffraction has been used to determine the structure of two-dime... more ABSTRACT Grazing incidence X-ray diffraction has been used to determine the structure of two-dimensional organic-inorganic crystals formed of a behenic acid monolayer spread over a Mn2+ or Mg2+ solution at high pH. Using a new method based on careful structure factor determination, building of molecular models and simulated annealing, the number and position of the divalent ions in the unit cell, the orientation of the chain backbone planes and carboxylic headgroups conformation defects could be determined. In agreement with their bulk solution properties, Mn2+ and Mg2+ behave very differently. Individual Mn2+ ions adsorb below the negatively charged films, whereas the superstructure includes hydrolysis products containing one or several Mg2+ ions in the case of magnesium. This difference is also reflected in the kinetics of structure formation.

Physical Review Letters, 2007

We have investigated the surface composition of alkali-halide aqueous solutions using grazing inc... more We have investigated the surface composition of alkali-halide aqueous solutions using grazing incidence x-ray fluorescence. Using mixtures of salts as a means to enhance the short-range effects, small differences in concentration over a few angstrom could be resolved, with, for example I ÿ or Br ÿ > Cl ÿ. In order to explain our data, we need to include an effective potential accounting for the short-range (Å) solvent mediated couplings, responsible for specific effects together with dispersion forces. This attractive potential (few k B T for halides) leads to concentration profiles which are in good agreement with recent numerical simulations.

Physica B: Condensed Matter, 2005

Peptide secretion by living organisms constitutes an integral response process exploited by natur... more Peptide secretion by living organisms constitutes an integral response process exploited by natural immune systems. In this work we present a model study and insight into this process reporting the thermodynamic and structural effects induced in phospholipid monolayers due to peptide insertion into the layer. Synchrotron X-ray radiation is combined with the Langmuir technique and exploited to form 'lipid-peptide' monolayers and probe the physical characteristics of the fundamental biological process of 'peptide secretion'. Our experiments show that the insertion of peptides in the phospholipid layer has adverse effects on the elastic properties of the layer manifested through the bending rigidity.

Langmuir, 2007

Interactions of native DNA with octadecylamine (ODA) and hexadecymdimethylammonium bromide (HTAB)... more Interactions of native DNA with octadecylamine (ODA) and hexadecymdimethylammonium bromide (HTAB) monolayers at the air/water interface were studied by π-A isotherms, ellipsometry, and X-ray reflectivity. We show that the microscopic structure of ODA-DNA complexes is definitely consistent with a single-stranded form for DNA. On the contrary, with HTAB, DNA complexes in its native form. The crucial difference in the behavior of these two fairly similar lipids is due to the presence of the amine group in ODA. These results should be relevant to applications such as DNA chips and sensors.

Langmuir, 2009

The behavior of mixed-ligand-coated gold nanoparticles at a liquid-liquid interface during compre... more The behavior of mixed-ligand-coated gold nanoparticles at a liquid-liquid interface during compression has been investigated. The system was characterized by measuring pressure-area isotherms and by simultaneously performing in situ X-ray studies. Additionally, Monte Carlo (MC) simulations were carried out in order to interpret the experimental findings. With this dual approach it was possible to characterize and identify the different stages of compression and understand what happens microscopically: first, a compression purely in-plane, and, second, the formation of a second layer when the in-plane pressure pushes the particles out of the plane. The first stage is accompanied by the emergence of an in-plane correlation peak in the scattering signal and a strong increase of the pressure in the isotherm. The second stage is characterized by the weakening of the correlation peak and a slower increase in pressure.

Journal of Colloid and Interface Science, 2011

The protein collagen is the major component of connective tissue and it is involved in many biolo... more The protein collagen is the major component of connective tissue and it is involved in many biological functions. Its degradation is at the basis of different pathological processes. The up-regulated expression of matrix metalloproteinases and the down-regulated expression of their inhibitors are the causes for such degradation. The aim of this work was to evaluate the possibility to fabricate collagen based containers for drug encapsulation and release by cellular demand by the action of matrix metalloproteinases. In present work collagen type I based microcapsules were fabricated by means of the layer-by-layer assembly of oppositely charged collagen and poly (stirene sulfonate) onto colloidal particles, followed by removal of the cores to obtain hollow microcapsules. The process of shell growth on planar supports was monitored by quartz crystal microbalance. X-ray reflectivity measurements were carried out at the solid/water interface to study the interaction of matrix metalloproteinase 1 with LbL films of collagen. The morphology of hollow capsules was characterized by scanning electron microscopy, and compared to that of capsules exposed to the matrix metalloproteinase 1. Finally the matrix metalloproteinase 1 mediated permeability of capsules variation was studied by Confocal Laser Scanning Microscopy. The results demonstrated the possibility to fabricate a drug delivery system where the release of the drug is dependent on the biochemistry of the pathological state.

Journal of Applied Crystallography, 2003

X-ray total external reflection fluorescence has been applied to detect an angular dependence of ... more X-ray total external reflection fluorescence has been applied to detect an angular dependence of fluorescence yield modulated by evanescent/X-ray standing wave pattern from metal-rich organic monolayer alone on water surface. Theoretical consideration reveals that electric field intensity in a molecular monolayer is completely determined by an area per one molecule value that can be obtained from pressure-area isotherm. This allows getting an ion position inside a monolayer from the corresponding fluorescence angular dependence. The possibilities of the technique have been used at the SR beamline ID10B (ESRF) to characterize Langmuir monolayers of phthalocyanines and cyclolinear polyorganosiloxanes formed on air/water interface.

Langmuir : the ACS journal of surfaces and colloids, Jan 4, 2008

In this Letter, we present a method for the decoration of layer-by-layer (LbL) structures by heav... more In this Letter, we present a method for the decoration of layer-by-layer (LbL) structures by heavy metal ions, which allows X-ray reflectivity (XRR) measurements at the solid/water interface. The improved contrast has allowed us to obtain well-structured X-ray reflectivity curves from samples at the liquid/solid interface that can be used for the film structure modeling. The developed technique was also used to follow the formation of complexes between DNA and the LbL multilayer. The XRR data are confirmed by independent null-ellipsometric measurements at the solid/liquid interface on the very same architectures.

The European Physical Journal Special Topics, 2007

Liposome suspensions comprising the synthetic cationic lipid DOTAP, the zwitterionic DPPC and the... more Liposome suspensions comprising the synthetic cationic lipid DOTAP, the zwitterionic DPPC and the anti-cancer agent Paclitaxel were deposited on solid substrates and investigated by X-ray and neutron reflectivity measurements at ESRF and ILL. Well ordered multilamellar drug/lipid membranes were obtained, such as indicated by the several orders of Bragg reflections in the diffraction pattern. With an excess of Paclitaxel, additional Bragg peaks from the drug crystalline phase could be observed. Changes of the molecular organization in the drug-lipid system were investigated as a function of relative humidity using a custom-built controlled humidity chamber. For DOTAP multilayers the effects of bilayer swelling were much more pronounced than for DPPC under similar conditions, while the crystalline peaks of the drug were not affected. The pronounced swelling of DOTAP multilayers might be related to the electrostatic repulsion between the charged lipid headgroups.

Journal de Physique IV (Proceedings), 2002

M-366 JOURNAL DE PHYSIQUE IV d' un fragment de C-cadhkrme plus court sur l a protkine entike La c... more M-366 JOURNAL DE PHYSIQUE IV d' un fragment de C-cadhkrme plus court sur l a protkine entike La compltmentarltd de nos rksultats avec ceux d' &udes blochlmlques devralt nous permettre d'avancer dans l a compr6hension des mCcanlsmes de I'adh&lon cellulawe 1.