In situ determination of the structure and composition of Langmuir monolayers at the air/water interface by neutron and X-ray reflectivity and ellipsometry

Maestro, Armando; Gutfreund, Philipp

doi:10.1016/j.cis.2021.102434

Cited by 24 publications

(22 citation statements)

References 89 publications

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“…The samples studied here yielded laterally homogeneous interfaces on the length scale of the in-plane neutron coherence length, on the order of several microns 65 . This implies that the measured SNR can be correlated with the averaged SLD depth profile across the interface delimited by this coherence length and, therefore, the in situ structure of the microgels as a function of the distance from the interface z can be determined.…”

Section: Resultsmentioning

confidence: 99%

In-situ study of the impact of temperature and architecture on the interfacial structure of microgels

et al. 2022

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The structural characterization of microgels at interfaces is fundamental to understand both their 2D phase behavior and their role as stabilizers that enable emulsions to be broken on demand. However, this characterization is usually limited by available experimental techniques, which do not allow a direct investigation at interfaces. To overcome this difficulty, here we employ neutron reflectometry, which allows us to probe the structure and responsiveness of the microgels in-situ at the air-water interface. We investigate two types of microgels with different cross-link density, thus having different softness and deformability, both below and above their volume phase transition temperature, by combining experiments with computer simulations of in silico synthesized microgels. We find that temperature only affects the portion of microgels in water, while the strongest effect of the microgels softness is observed in their ability to protrude into the air. In particular, standard microgels have an apparent contact angle of few degrees, while ultra-low cross-linked microgels form a flat polymeric layer with zero contact angle. Altogether, this study provides an in-depth microscopic description of how different microgel architectures affect their arrangements at interfaces, and will be the foundation for a better understanding of their phase behavior and assembly.

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Section: Resultsmentioning

confidence: 99%

In-situ study of the impact of temperature and architecture on the interfacial structure of microgels

et al. 2022

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“…Three isotopic contrast data sets were recorded and analysed together: hydrogenous lipid mixture in buffered D2O and ACMW, and deuterated lipid mixture in buffered D2O (Figure 4A and D). Because of these samples yielded laterally homogeneous interfaces on the length scale of the in-plane neutron coherence length (on the order of ∼10 -30 μm 27 ) according to BAM (Figure 3A), the measured reflectivity curves can be correlated with an averaged SLD depth profile across the interface delimited by this coherence length. The out-of-plane structure of the lipid monolayers as a function of the distance from the interface z can be, therefore, determined.…”

Section: Figure S1mentioning

confidence: 99%

“…Previously, synthetic lipid monolayers, for example using DPPC (1,2-dipalmitoylsn-glycerol-3-phosphocholine) and POPC (1-palmitoyl-2-oleoyl-glycero-3-phosphocholine), or complex mixtures such as the so-called canonical mixture (containing POPC, sphingomyelin and cholesterol), were employed to mimic cellular membranes as well as lung surfactants [17][18][19][20][21][22][23][24][25][26] . Even though Langmuir monolayers are not well suited to address transmembrane processes, their versatility allows the investigation of lipid' structure and organisation of single membrane leaflets at the air/water interface, by exploiting a plethora of interfacial in situ techniques [27][28][29] , thus offering the possibility of untangling different questions of biophysical interest. Here, Langmuir monolayers composed of natural lipids were studied by surface pressure-area isotherms, Brewster angle microscopy (BAM) and neutron reflectometry (NR).…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, neutrons interact very differently with hydrogen and deuterium nuclei, therefore, through isotopic substitution, it is possible to highlight structural and chemical differences in specific regions of interest such as, for example, identifying the presence of water molecules and the position and orientation of hydrophobic tails and polar headgroups. 27 The combined experimental approach used in this work shed light on the interfacial structure of in vitro model systems of the plasma and ERGIC membranes, with emphasis on the structural effects associated with the incorporation of cholesterol in the membranes. Although natural lipids were previously used in the form of bi-and multilayers to mimic eukaryotic cell membranes, which were then characterized by neutron reflectometry 30,31 and diffraction 32,33 , to the best of our knowledge, this is the first report describing the use of natural lipids extracted from yeast and studied in the form of monolayers at the air/water interface, in order to mimic biological relevant membranes, and to provide direct structural evidences about the role of cholesterol.…”

Section: Introductionmentioning

confidence: 99%

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Investigation on the relationship between lipid composition and structure in model membranes composed of extracted natural phospholipids

Santamaria

Batchu

Fragneto

et al. 2022

Preprint

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Unravelling the structural diversity of cellular membranes is a paramount challenge in life sciences. In particular, lipid composition affects the membrane collective behaviour, and its interactions with other biological molecules. Here, the relationship between membrane composition and resultant structural features was investigated by surface pressure-area isotherms, Brewster angle microscopy and neutron reflectometry on in vitro membrane models of the mammalian plasma and endoplasmic-reticulum-Golgi intermediate compartment membranes in the form of Langmuir monolayers. Natural extracted yeast lipids were used because, unlike synthetic lipids, the acyl chain saturation pattern of yeast and mammalian lipids are similar. The structure of the model membranes, orthogonal to the plane of the membrane, as well as their lateral packing, was found to depend strongly on their specific composition, with cholesterol having a major influence on the in-plane morphology, yielding a coexistence of liquid-order and liquid-disorder phases.

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“…The latter consists in a mixture of D 2 O and H 2 O (8.92% v/v), which matches the scattering length density (SLD) of air (b air = 0 • 10 −4 nm −2 ), and therefore only the polymer contributes to the reflected signal of the curves in Figures 1a and b The samples studied here yielded laterally homogeneous interfaces on the length scale of the in-plane neutron coherence length, on the order of several microns. 65 This implies that the measured SNR can be correlated with the averaged SLD depth profile across the interface delimited by this coherence length and, therefore, the insitu structure of the microgels as a function of the distance from the interface z can be determined. This is done by fitting the reflectivity curves with a model consisting in different layers characterized by a thickness, d, a roughness, σ, and a SLD, b.…”

Section: Standard Microgels At the Interfacementioning

confidence: 99%

In-situ study of the impact of temperature and architecture on the interfacial structure of microgels

Bochenek,

Camerin,

Zaccarelli

et al. 2022

Preprint

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The structural characterization of microgels at interfaces is fundamental to understand both their 2D phase behavior and their role as stabilizers that enable emulsions to be broken on demand. However, this characterization is usually limited by available experimental techniques, which do not allow a direct investigation at interfaces. To overcome this difficulty, here we employ neutron reflectometry, which allows us to probe the structure and responsiveness of the microgels in-situ at the air-water interface. We investigate two types of microgels with different cross-link density, thus having different softness and deformability, both below and above their volume phase transition temperature, combining experiments with computer simulations of realistic in silico synthesized microgels. We find that temperature only affects the portion of microgels in water, while the strongest effect of the microgels softness is observed in their ability to protrude into the air. In particular, standard microgels have an apparent contact angle of few degrees, while ultra-low cross-linked microgels form a flat polymeric layer with zero contact angle. Altogether, this study provides an indepth microscopic description of how different microgel architectures affect their arrangements at interfaces, and will be the foundation for a better understanding of their phase behavior and assembly. This manuscript has been accepted for publication in Nature Communications (open access). The final version of the manuscript including the Supplementary Information will be available in the future.

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In situ determination of the structure and composition of Langmuir monolayers at the air/water interface by neutron and X-ray reflectivity and ellipsometry

Cited by 24 publications

References 89 publications

In-situ study of the impact of temperature and architecture on the interfacial structure of microgels

In-situ study of the impact of temperature and architecture on the interfacial structure of microgels

Investigation on the relationship between lipid composition and structure in model membranes composed of extracted natural phospholipids

In-situ study of the impact of temperature and architecture on the interfacial structure of microgels

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