Structural characterization of soft interfaces by standing-wave fluorescence with X-rays and neutrons

Schneck, Emanuel; Demé, Bruno

doi:10.1016/j.cocis.2015.06.001

Cited by 18 publications

(20 citation statements)

References 66 publications

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“…However, it is not always possible to deduce the relevant structural features from such "global" density profiles. In contrast, x-ray fluorescence allows determining element-specific density profiles across an interface [25]. The technique is based on the characteristic fluorescence induced by the illuminating x-rays via photoelectric ionization and has commonly been used to study element distributions at gas/liquid interfaces [26][27][28].…”

Section: Introductionmentioning

confidence: 99%

Element-specific density profiles in interacting biomembrane models

Schneck¹,

Rodriguez-Loureiro²,

Bertinetti³

et al. 2017

J. Phys. D: Appl. Phys.

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Surface interactions involving biomembranes, such as cell-cell interactions or membrane contacts inside cells play important roles in numerous biological processes. Structural insight into the interacting surfaces is a prerequisite to understand the interaction characteristics as well as the underlying physical mechanisms. Here, we work with simplified planar experimental models of membrane surfaces, composed of lipids and lipopolymers. Their interaction is quantified in terms of pressure-distance curves using ellipsometry at controlled dehydrating (interaction) pressures. For selected pressures, their internal structure is investigated by standing-wave x-ray fluorescence (SWXF). This technique yields specific density profiles of the chemical elements P and S belonging to lipid headgroups and polymer chains, as well as counter-ion profiles for charged surfaces.

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Section: Introductionmentioning

confidence: 99%

Element-specific density profiles in interacting biomembrane models

Schneck¹,

Rodriguez-Loureiro²,

Bertinetti³

et al. 2017

J. Phys. D: Appl. Phys.

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“…The latter is formed by interference of the incident and reflected waves and its shape depends on the angle of incidence of the X-ray beam with respect to the interface. The angle-dependent fluorescence intensity thus contains information on the interfacial element distribution (7). This principle has been exploited for the study of interfacial phenomena involving solid, liquid, and gas phases (8)(9)(10)(11)(12)(13)(14)(15)(16).…”

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confidence: 99%

“…However, such high-resolution studies have thus far dealt only with the fluorescence of comparatively heavy elements. Even models of biological surfaces have been labeled, in one way or another, with heavy elements that are not naturally abundant in biological matter (7). Light chemical elements have so far only investigated in a grazing-incidence configuration with low spatial resolution (15,16).…”

mentioning

confidence: 99%

Atom-scale depth localization of biologically important chemical elements in molecular layers

Schneck

Scoppola

Drnec

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers' global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces.surfaces | interfaces | lipid membranes | protein adsorption | X-ray scattering N anometric biomolecular layers in interfacial geometries are key components of biological matter. Biological membranes, for example, are 2D molecular structures composed mainly of lipids and proteins in an aqueous environment (1, 2). Interfacial biomolecular layers are also important from a biotechnological perspective, where surfaces are often designed to selectively promote or prevent the adsorption of bio(macro)molecules from solution (3). To investigate the diverse behavior of biomolecules at interfaces, well-defined planar model systems of biological and biotechnologically relevant interfaces have been established (4, 5). Processes involving biomolecules at interfaces are typically accompanied by a spatial reorganization of molecules, changes in molecular conformations, or the adsorption of molecules in a chemically heterogeneous environment (6). Structural insight on the nanometer scale is therefore of paramount importance.X-ray and neutron scattering are uniquely suited for the structural investigation of biomolecular systems. Specular reflectometry reveals matter density profiles perpendicular to a planar interface. However, it is generally difficult to elucidate molecular conformations and elemental distributions from such "global" density profiles. In contrast, standing-wave X-ray fluorescence (SWXF) allows determining element-specific density profiles across an interface. The SWXF technique is based on the elementcharacteristic fluorescence induced by a standing X-ray wave. The latter is formed by interference of the incident and reflected waves and its shape depends o...

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“…The shape of the reflectivity curve R(q z ) encodes the interfacial SLD profile, so that the latter can be reconstructed. [63,64] In summary, X-ray and neutron diffraction techniques allow for the comprehensive structural investigation of all sorts of interfaces with high spatial resolution. [48][49][50][51][52][53][54][55][56][57][58][59] In neutron reflectometry, selective deuteration is commonly used to enhance the SLD contrast between different chemical components and thus to better discriminate between their interfacial distributions.…”

Section: Structural Investigationsmentioning

confidence: 99%

“…Depending on the measurement configuration this approach is commonly referred to as grazing-incidence X-ray fluorescence (GIXF) [60][61][62] or standing wave X-ray fluorescence (SWXF). [63,64] In summary, X-ray and neutron diffraction techniques allow for the comprehensive structural investigation of all sorts of interfaces with high spatial resolution. Note however, that all these techniques unfold their full potential only for nearly perfectly planar interfaces with topographic roughness in the Å to nm range.…”

Section: Structural Investigationsmentioning

confidence: 99%

The Interaction between Soft Interfaces: Forces and Structural Aspects

Schneck

2016

Adv Materials Inter

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Soft interfaces constituted by two-dimensional molecular layers play important roles in numerous technological applications and are major components of all biological matter, for example in the form of biomembranes. The mutual interaction between such interfaces often crucially influences their function as well as the structural organization of the entities they form. The forces acting between two soft interfaces in liquids not only depend on their chemical properties, like charge density or hydrophilicity. They are often also closely connected to the structural response of the interfaces to their interaction, for instance in terms of molecular conformations or ion distributions. This interplay renders the description of the interaction between soft or chemically complex interfaces challenging. In the present article, various experimental and theoretical approaches to the study of interacting soft interfaces are reviewed with a focus on structural aspects

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Structural characterization of soft interfaces by standing-wave fluorescence with X-rays and neutrons

Cited by 18 publications

References 66 publications

Element-specific density profiles in interacting biomembrane models

Element-specific density profiles in interacting biomembrane models

Atom-scale depth localization of biologically important chemical elements in molecular layers

The Interaction between Soft Interfaces: Forces and Structural Aspects

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