Search results for "Superstructure"
showing 10 items of 45 documents
Investigation of the superstructure of native collagen by a combination of small angle X-ray scattering, electron microscopy and light diffraction
1978
It is shown that there exists a direct correlation between the light diffraction pattern of an electron-microscopical picture and the X-ray small angle scattering. By this means it can be proved for native collagen prepared by a special method that the density pattern of stained samples imaged in the electron microscopy is identical with the density pattern available from moist fibres. The reflex intensities of the small angle X-ray scattering are taken for calculating the density structure whereby the necessary phases are delivered by the electron microscopic examination combined with light diffraction.
Phase separation in superconducting and antiferromagneticRb0.8Fe1.6Se2probed by Mössbauer spectroscopy
2011
${}^{57}$Fe-M\"ossbauer studies of superconducting Rb${}_{0.8}$Fe${}_{1.6}$Se${}_{2.0}$ with ${T}_{C}$ $=$ 32.4 K were performed on single-crystalline and polycrystalline samples in the temperature range 4.2--295 K. They reveal the presence of 88% magnetic and 12% nonmagnetic Fe${}^{2+}$ species with the same polarization dependence of their hyperfine spectra. The magnetic species are attributed to the 16$i$ sites of the $\sqrt{5}\ifmmode\times\else\texttimes\fi{}\sqrt{5}\ifmmode\times\else\texttimes\fi{}1$ superstructure and the nonmagnetic Fe species to a nanosized phase observed in recent structural studies of superconducting K${}_{x}$Fe${}_{2\ensuremath{-}}$${}_{y}$Se${}_{2}$ systems ra…
Más allá de Marx: postobrerismo y posmarxismo. Una revisión de los fundamentos teóricos de la multitud y el pueblo
2018
The article is a synthetic essay that exposes the main theoretical lines of the postmarxist approach of Laclau and Mouffe, on the one hand, and the autonomist post-operaism of Negri, Hardt, Virno, etc., on the other hand. These theories are conceived as attempts to rationalize current political bets by various political sectors and social movements. It analyzes both argumentative strategies from «orthodox» Marxism and the structure / superstructure relationship; and the forms of constitution of new subjectivities. It compares the theoretical fundamentals of hegemonic articulations and counter-power experiences. It discusses, likewise, the scope and limitations of the categories of «people» …
Sustainable soy protein microsponges for efficient removal of lead (II) from aqueous environments
2023
Protein-based materials recently emerged as good candidates for water cleaning applications, due to the large availability of the constituent material, their biocompatibility and the ease of preparation. In this work, new adsorbent biomaterials were created from Soy Protein Isolate (SPI) in aqueous solution using a simple environmentally friendly procedure. Protein microsponge-like structures were produced and characterized by means of spectroscopy and fluorescence microscopy methods. The efficiency of these structures in removing Pb2+ ions from aqueous solutions was evaluated by investigating the adsorption mechanisms. The molecular structure and, consequently, the physico-chemical propert…
L-Tryptophan on Cu(111): engineering a molecular labyrinth driven by indole groups
2015
The present article investigates the adsorption and molecular orientation of L-Tryptophan, which is both an essential amino acid important for protein synthesis and of particular interest for the development of chiral molecular electronics and biocompatible processes and devices, on Cu(111) using scanning tunneling microscopy and spectroscopy at 55 K and at room temperature. The arrangement of chemisorbed L-Tryptophan on the copper surface varies with both temperature and surface coverage. At low coverage, small clusters form on the surface irrespective of temperature, while at high coverage an ordered chain structure emerges at room temperature, and a tightly packed structure forms a molec…
Tunable Superstructures of Dendronized Graphene Nanoribbons in Liquid Phase
2019
In this Communication, we report the first synthesis of structurally well-defined graphene nanoribbons (GNRs) functionalized with dendritic polymers. The resultant GNRs possess grafting ratios of 0.59-0.68 for the dendrons of different generations. Remarkably, the precise 3D branched conformation of the grafted dendrons affords the GNRs unprecedented 1D supramolecular self-assembly behavior in tetrahydrofuran (THF), yielding nanowires, helices and nanofibers depending on the dimension of the dendrons. The GNR superstructures in THF exhibit near-infrared absorption with maxima between 650 and 700 nm, yielding an optical bandgap of 1.2-1.3 eV. Ultrafast photoconductivity analyses unveil that …
Crystal‐Structure Studies of Mononuclear Iron(II) Complexes with Two‐Step Spin Crossover: [Fe{5‐NO 2 ‐sal‐N(1,4,7,10)}] Revisited
2013
In the region of the spin transition of spin-crossover (SCO) compounds there coexist molecules in both high-spin (HS) and low-spin (LS) states. In the case of two-step spin transition, theoretical predictions and computer simulations have shown that HS and LS complex molecules should be ordered in the plateau region. Several examples that support this hypothesis are already presented in the literature. Herein, we discuss a mononuclear complex of iron(II) with two-step spin transition in terms of long-range ordering of HS and LS molecules. In such compounds, spin transition is associated with the formation of a superstructure. However, previous studies of the [Fe{5-NO2-sal-N(1,4,7,10)}] [5-N…
Organic nanosheets with charged surface: two dimensional self-assembly of a non-symmetric bis-acylurea with pyridyl end group
2011
We present a novel non-symmetric bis-acylurea that self-assembles into two dimensional nanosheet superstructures. The bis-acylurea (PyrC8Bn) has a pyridyl and a benzyl end group divided by a spacer group [–NHCONHCO–(CH2)8–CONHCONH–, C8] with two hydrogen bonding sites. Upon cooling a hot solution in ethanol, the molecule self-assembles into multilayered nanosheet structures due to the intermolecular biaxial hydrogen bonding. The surface charge of the nanosheets could be switched between positive and neutral by adjusting the pH. The charged character of the nanosheets was utilized in immobilizing negatively charged gold nanoparticles. An attempt to regulate the self-assembly allowed us to fi…
Synthesis and Spectral and Structural Characterization of a New Series of Bis-Strapped Chiral Porphyrins Derived from L-Proline
2001
International audience; New chiral porphyrins were obtained in reasonable yields in three steps, starting from the áâáâ atropisomer of mesotetrakis(o-aminophenyl)porphyrin (TAPP). These potential catalysts for the enantioselective epoxidation of alkenes were obtained by the reaction of different linkers on the same Lprolinoyl-picket porphyrin. Their 1H NMR spectral characteristics, as well as the crystal structure of one of them, clearly indicate that the orientation of the proline cycle depends on the linker used to tether the two pickets on each side of the porphyrin. The same linker is employed for both sides of the porphyrin; hence the resulting D2-symmetric superstructure.
From ZIF-8@Al2O3Composites to Self-Supported ZIF-8 One-Dimensional Superstructures
2015
International audience; Efficient preparation of composite materials consisting of ZIF-8 nanocrystals embedded inside the channels of macroporous anodic aluminum oxide membranes is reported. 1-D self-supported ZIF-8 superstructures are recovered through matrix dissolution.