Small-angle X-ray Diffraction Methods Research Articles

Study of Kinetics of Solid Phase Transition in Tetracosane С24Н50 by High-Resolution Synchrotron X-Ray Powder Diffraction

Using the small-angle synchrotron X-ray diffraction method at the research facility “BELOK” of the Kurchatov synchrotron radiation source at the NRC Kurchatov Institute, it was shown that the first-order solid phase transition in tetracosane C24H50 passes according to a heterogeneous mechanism in a narrow temperature range ΔT ~ 1 K in accordance with the theory of diffuse phase transitions.

Influence of UV Radiation on Structure of Lyotropic Liquid Crystals

Molecular mechanisms of the impact of ultraviolet (UV) rays on biological systems can be divided into three categories: structural and functional changes of DNA, photoinactivation of proteins and structural damage of cell membranes. Though a large number of studies have explored the first two categories of UV ray impacts on biological systems and have proposed various feasible models for the pathways of these impacts, few studies have explored structural damage of cell membranes and the only proposed mechanisms for this UV impact is that of lipid, peroxide, and amino acid oxidation with the impact of various wave lengths of UV rays, A (400–320 nm), B (300–275 nm), and C (275–180 nm) being explained by these mechanisms. In the present work, we have studied the biological impact of UV rays on the phospholipid bilayer by using simultaneous small and large angle X-ray diffraction method.

Highly hydrothermally stable FePO4–SBA-15 synthesized using a novel one-pot hydrothermal method

The hydrothermal stability of FePO4–SBA-15 synthesized using a novel one-pot hydrothermal method (OP) was systematically investigated using two methods: treatment with pure steam at 800 °C or with boiling water at 100 °C. The structural changes in the samples were monitored using small angle X-ray diffraction and N2-physisorption methods. It was found that the hydrothermal stabilities of OP samples remained high and showed little difference over the FePO4-doping range 5–40 wt%. These results differ from previous reports that the loading of heterogeneous metal atoms significantly influences the hydrothermal stability of the host ordered mesoporous material. For comparison, the hydrothermal stabilities of FePO4–SBA-15 synthesized using an impregnation method (IMP) and commercially obtained SBA-15 were also studied. The order of the sample hydrothermal stabilities was OP > IMP >> SBA-15. The formed FePO4 protective layers helped to prevent mesostructure degradation during hydrothermal treatment, therefore modified samples showed superior hydrothermal stabilities compared with pure SBA-15. The superior performance of OP samples over IMP samples is mainly attributed to the formation of stable Si–O–Fe bonds and more micropores in OP samples.

Synthesis and characterization of thiourea- and urea-linked glycolipids as low-molecular-weight hydrogelators

Novel glycolipids with thiourea- and urea-linkers have been synthesized as low-molecular-weight gelators by reacting glycosyl aminoacetamides with alkyl isothiocyanates and isocyanates. The influence of the linker groups on their self-assembly properties has been studied. A gelation study of the obtained neoglycolipids in various solvents showed that they are good hydrogelators. Urea-linked glycolipids showed better hydrogelating ability as compared to thiourea linked glycolipids. The influence of sugar head group and alkyl chain length on the glycolipid’s self-assembly has also been studied. The fibrillar structures of the supramolecular hydrogels have been characterized by scanning electron microscopy (SEM). The thermal properties of the hydrogels formed by urea linked glycolipids have been studied by differential scanning calorimetry (DSC) and VT-NMR. Molecular packing has been studied by small angle (SAXS) and single crystal X-ray diffraction methods.

Effects of spatial ordering of quantum dot arrays from small-angle X-ray diffraction data under variation of growth parameters

The small angle X-ray diffraction method is applied to the system of germanium quantum dots in the silicon matrix prepared by molecular-beam epitaxy in self-organization mode using the Stranski-Krastanov technique. Depending on the growth mode, the specific distances between Ge quantum dots and deviations from their correlated distribution are determined. The results are in agreement with the scanning tunneling microscopy data.

CuO nanoclusters coated with mesoporous SiO2 as highly active and stable catalysts for olefin epoxidation

A one-pot solvothermal synthetic method to prepare uniform CuO colloidal nanocrystal clusters (CNCs) with sizes of approximately 60 nm was developed. To enhance their stabilities, the CuO CNCs were coated with mesoporous SiO2 shells to form CuO CNCs@meso-SiO2 nanocomposites. The CuO CNCs as well as the CuO CNCs@meso-SiO2 composite catalyst were characterized by transmission electron microscopy, small-angle X-ray diffraction and N2adsorption-desorption methods. These results indicate that the SiO2 shells have winding mesoporous channels with an average size of 3.7 nm, which are very favorable for mass transfer and catalytic reactions. This nanocomposite catalyst exhibited excellent activity and stability in olefin epoxidation reactions. The structure of the composite catalyst remained intact after eight consecutive runs, while pure CuO CNCs severely aggregated after only 1 run.

Synthesis and thermal properties of rigid oxa-bridged-containing dimers and tetramers

Several symmetrical, linear dimers and some star-like tetramers were prepared using easily accessible oxa-bridged derivatives as central rigid cores. In order to produce new liquid crystalline materials various mesogenic/promesogenic groups, containing biphenyl-4,4′-diol, 4,4′-(diazene-1,2-diyl)diphenol and cholesterol sub-moieties, were connected through oxy-ethylene linkers via an ester linkage, in the end-on fashion. Their thermal behaviour and mesomorphic properties were investigated by differential scanning calorimetry (DSC), polarized optical microscope (POM), and variable temperature small-angle X-ray diffraction (XRD) methods. While essentially all the biphenyl-4,4′-diol- and 4,4′-(diazene-1,2-diyl)-based dimeric derivatives exhibited smectic liquid crystalline mesophases, the nature of which are mesogenic groups dependent, none of the cholesterol-containing compounds and tetramers were mesomorphic.

Characteristic Shear-Flow Orientation in LC Block Copolymer Resulting from Compromise between Orientations of Microcylinder and LC Mesogen

The shear flow orientation in the diblock copolymers composed of polystyrene (PS) and side-chain liquid crystal polymer (LCP) was investigated by the wide and small-angle X-ray diffraction methods. Two diblock copolymers prepared by atom transfer radical polymerization have the weight fractions of the PS segment of 0.13 and 0.21, and form a well-defined microsegregation structure with PS cylinders hexagonally packed in a matrix of LCP which forms smectic A, nematic, and isotropic phases in order of increasing temperature. Two types of shear flow orientation have been observed, depending on the type of the phase in the LCP matrix. The shear flow at nematic temperatures orients well the PS microcylinders as well as the LC mesogens in the velocity direction. This parallel-b orientation is expectable from the general orientation of the microcylinders and the LC mesogens in shear flow. When the LCP matrix transforms to the smectic LC, the mesogens are aligned parallel to the velocity gradient direction entaili...

Synthesis of mesoporous calcium phosphate using hybrid templates

Mesostructured calcium phosphate was synthesized by means of the combination of a soluble metal salt with an aqueous phenylphosphonic acid solution containing sodium dodecyl sulfate (SDS). Phenylphosphonic acid (PhP) was selected as the template to pattern the materials with pores generated by the formation of a lamellar calcium PhP phase. SDS was introduced to improve the thermal stability of the pore structure. The resulting materials were characterized by means of X-ray diffraction (XRD), small-angle X-ray diffraction (SAXS), electron microscopes and BJH gas absorption method. With the aid of SDS, calcium phosphate materials with the surface area and pore volume as 72 m 2/g and 569 cm 3/g, respectively, were successfully developed at the SDS:PhP molar ratio of 0.3:1. It was found that the addition of SDS could effectively improve the thermal stability of the pore structure. A possible mechanism was proposed to interpret the formation procedure and the improved thermal stability of the mesoporous structure.

Lanthanide luminescent mesomorphic complexes with macrocycles derived from diaza-18-crown-6

Four tetracatenar (L1–L4) and one hexacatenar (L5) ligands, derived from the diaza-18-crown-6 framework, are synthesized and characterized. In these ligands, the amine functions are fitted with benzoyloxybenzyl linker groups, attached either with a carbonyl function (L1) or a methylene bridge (L2–L5) and bearing alkoxy chains, R, of various lengths: R = OCH3 for L2, OC10H21 for L3 and L5, OC12H25 for L1, and OC16H33 for L4. The non-mesomorphic ligands L1 and L3–L5 react with various lanthanide salts to give complexes forming thermotropic hexagonal columnar phases, as ascertained by thermal, optical and small-angle X-ray diffraction methods. The length of the alkoxy chains (L3 and L4) does not much influence the mesogenic behaviour, irrespective of the linker function, the number of alkoxy chains, the counterion or the lanthanide ion. The best systems proved to be the nitrato lanthanide complexes with L3, which present a Colh phase over 100 °C (up to 147 °C for La) with melting transition temperatures between 58 (La) and 86 (Tb) °C. In the case of [Eu(NO3)3L3], chosen as a representative example of all the complexes in this analysis, the inter-column separation of 29.2 A agrees well with the packing of cylindrical columns resulting from an alternated stacking of the molecules, in which the two mesogenic arms extend on the same side, i.e. stacking the molecules in a bent conformation. The liquid crystalline phases containing Eu and Tb display metal-centred emission, meaning that these complexes are interesting building blocks for the design of luminescent liquid crystalline materials.

Comparison of Mesomorphic Properties in Chiral and Achiral Homologous Series of High Tilted Ferroelectrics and Antiferroelectrics

Homologous series of chiral (S) 4-(1-methylheptyloxycarbonyl)-phenyl and achiral 4-(4-heptyloxycarbonylphenyl 4-(perfluoroalkanoyloxyhexyloxy)biphenylates or 4-(alkanoyloxyhexyloxy)biphenylates, chiral (S) and racemic (R,S) 4′-(1-methyl heptyloxycarbonyl)biphenyl-4-yl 4-(perfluoroalkanoyloxyhexyloxy)benzoates or 4 (alkanoyloxyhexyloxy)benzoates have been prepared and their phase transitions have been investigated by DSC and polarizing thermomicroscopic methods. Moreover the temperature dependence of interlayer spacing by a small angle X-ray diffraction method has been studied. The chiral and achiral members exhibit a SmC anti. phase, while racemic members only exhibit SmC phase. Fluorinated compounds have lower melting points, lower melting enthalpy and broader range of the SmC anti. phase than earlier prepared series with shorter spacer group (CH 2 ) m , m < 6. They are very useful components for the formulation of orthoconic (interlayer tilt 90°) antiferroelectric mixtures with temperature range from (−20°C) to 100°C.

The Effect of Lateral Long Hydrocarbon Chain on Mesomorphic Properties

A homologous series of 4-(4-CnH2n + 1O-phenoxycarbonyl)-phenyl 3-CmH2m + 1 O-4-cyanobenzoates and the bromo derivatives were synthesized (m = 2∼14, n = 2∼8). The LC properties are notably affected by m rather than n. The members with large m preferentially exhibit a smectic C phase. The layer structures of smectic A and C phases and the phase transition behavior were examined by a small angle X-ray diffraction method, and the results are discussed in terms of their molecular structures.

Stable cubic phases in codispersions of glucocerebroside and palmitoyloleoylphosphatidylethanolamine

The effect of glucocerebroside (GlcCer) on the structure and thermotropic phase behavior of aqueous dispersions of palmitoyloleoylphosphatidylethanolamine (POPE) has been examined using simultaneous small-angle and wide-angle X-ray diffraction methods. Binary mixtures of GlcCer:POPE in molar ratios of 2:100, 5:100, 10:100, 20:100, 30:100, and 40:100 were examined in the temperature range 20–90 °C. Cubic phase has been observed in binary mixtures comprised of molar ratios greater than 5:100 in the temperature range of 60–90 °C upon heating at a rate of 2 °C/min. The cubic phase is relatively stable and coexists with inverted hexagonal or lamellar phases. It persists in the codispersions throughout subsequent cooling scans to 30 °C. The space group of the cubic phase is determined to be Pn3 m or Pn3. The lattice constant of the Pn3 m cubic phase was found to be almost constant when it coexists with lamellar liquid-crystal phase. Marked temperature-dependent changes were observed when cubic phase coexists with hexagonal phase or lamellar-gel phases. This is the first report of cubic phases formed by codispersions of glycosphingolipids and phospholipids. The mechanism of cubic phase formation and the interaction between GlcCer and POPE is discussed in terms of the putative biological functions of glycolipids.

The Layer Structure in Smectic A Phases and the Phase Transition Behavior for Cyano- and Nitrofuran Compounds

Abstract The layer structure and phasetransition behavior of smectic A phases for 4-(4-alkoxyphenoxycarbonyl)phenyl 5-X-furan-2-carboxylates (X = CN, NO2) were examined by a small-angle X-ray diffraction method. The higher homologs of both compounds exhibit two kinds of smectic A (Sm A) phases and experience the Sm A-Sm A transition. One Sm A phase exhibited at a higher temperature region having a layer spacing of 1.5–1.9 times the calculated molecular length; and the layer spacing gradually increases with decreasing temperature. The other Sm A phase exhibited at a lower temperature region having a layer spacing of twice the calculated molecular length; also, the layer spacing is almost independent of the temperature. The Sm A–Sm A transition behavior is discussed.

Antioxidant activity of the monoamine oxidase B inhibitor lazabemide

Free radical-induced damage to lipid and protein constituents of neuronal membranes contributes to the pathophysiology of neurodegenerative diseases, including Alzheimer’s disease (AD). The development of an effective inhibitor of oxidative stress represents an important goal for the treatment of AD. In this study, the intrinsic antioxidant activity of lazabemide, a potent and reversible inhibitor of monoamine oxidase B (MAO-B), was tested in a membrane-based model of oxidative stress. Under physiologic-like conditions, lazabemide inhibited lipid peroxidation in a highly concentration-dependent manner. At low, pharmacologic levels of lazabemide (100.0 nM), there was a significant ( P < 0.001) and catalytic reduction in lipid peroxide formation, as compared with control samples. The antioxidant activity of lazabemide was significantly more effective than that of either vitamin E or the MAO-B inhibitor, selegiline. The ability of lazabemide to inhibit oxidative damage is attributed to physico-chemical interactions with the membrane lipid bilayer, as determined by small angle x-ray diffraction methods. By partitioning into the membrane hydrocarbon core, lazabemide can inhibit the propagation of free radicals by electron-donating and resonance-stabilization mechanisms. These findings indicate that lazabemide is a potent and concentration-dependent inhibitor of membrane oxy-radical damage as a result of inhibiting membrane lipid peroxidation, independent of MAO-B interactions.

POLYMERIC SURFACTANTS BASED ON OLEIC ACID III. Copolymerization of Sodium Acrylamidostearate and Oleic Acid in a Lamellar Liquid Crystal

ABSTRACT Copolymerization of sodium acrylamidostearate (NaAAS) and oleic acid was performed in the lamellar liquid crystal (LLC) formed by NaAAS, oleic acid and water, in the absence of N.N’-methylenebisacrylamide (MBAA) and in the presence of MBAA, respectively. In the absence of MBAA, after the polymerization the lamellar structure remained, and the disorder of the lamellar liquid crystal was, to some extent, enhanced. Surface tension, small-angle X-ray diffraction, viscosity, and fluorescence methods were used to study the properties of the linear copolymer. The linear polymeric surfactant behaves like

Effect of Oxidative Stress on Membrane Structure: Small-Angle X-Ray Diffraction Analysis

Free radical damage to cellular membranes appears to underlie alterations in function in aging and various pathological processes, including cardiovascular disease. The objective of this study was to directly characterize changes in the molecular structure of membrane lipid bilayers resulting from oxidative stress. Membrane samples reconstituted from either synthetic or cardiac phospholipids enriched with polyunsaturated fatty acids were examined at high resolution using small-angle x-ray diffraction methods. In this study, Fe 2+/ ascorbate-induced lipid peroxidation produced significant and dose-dependent alterations in the basic physical structure of the phospholipid bilayer. Electron density profiles (Å vs. electrons/Å 3) calculated from the x-ray diffraction data showed a marked reduction in the hydrocarbon core width of dilinoleoyl phosphatidylcholine (DLPC) bilayers from 36 Å to 32 Å, and a decrease in overall membrane width, including surface hydration, from 48.7 Å to 44.6 Å. In addition, a broad decrease in molecular volume was observed ±3–10 Å from the center of the membrane bilayer, along with interdigitation of the terminal methyl segments. Pronounced changes in the lipid bilayer structure following oxidative stress were also observed in membranes reconstituted from cardiac lipids, including a 4 Å reduction in hydrocarbon core width from 40 Å to 36 Å and interdigitation of the terminal methyl segments. These data provide direct evidence for changes in membrane hydrocarbon core width and molecular volume resulting from phospholipid peroxidation, which may contribute to perturbations in membrane structure/function relationships associated with aging and cardiovascular disease.

Construction and X-ray reflectivity study of self-assembled lysozyme/polyion multilayers

The process of multilayer assembly via layer-by-layer deposition of linear polyions and lysozyme have been studied. The films were fabricated on glass slides by alternate electrostatic adsorption of anionic poly(styrenesulfonate) (PSS), cationic poly(allylamine) (PAA) polyions and hen egg-white lysozyme. The multilayer build-up was monitored by the small-angle X-ray diffraction method. X-ray reflectivity curves from the films measured at different steps of the assembly reveal Kiessig fringes. From their periodicity the film thickness was calculated. The growth step for a PSS/PAA bilayer equals 37 Å. The thickness of the lysozyme layer equals 45 Å, which is close to dimensions of the lysozyme molecule determined by X-ray crystallography. An analysis of surface charges of the lysozyme molecule shows some preferentially positive charged regions, which are the most probable sites of interactions with negatively charged PSS.

Evolution of Structure, Phase Composition, and X-Ray Reflectivity of Multilayer Mirrors Mo–(B + C) after Annealing at 250–1100°C

Structural, phase, and chemical stabilities of x-ray multilayer mirrors Mo–(B + C) with periods in the range 8–11.5 nm were studied at temperatures of 250–1100°C by small-angle and large-angle x-ray diffraction and electron microscopy methods. Two amorphizations at ∼450 and ∼750°C and two crystallizations at ∼650 and ∼850°C of Mo-based layers were observed, which were due to the formation of the molybdenum carbides MoC (hex), γ-MoC, and Mo2C instead of the metal Mo, and to the formation of the molybdenum borides MoB2and Mo2B5instead of molybdenum carbides, respectively. Both amorphizations of Mo-based layers were accompanied by smoothing of interfaces and by an increase of the multilayer x-ray reflectivity at λ = 0.154 nm. Both crystallizations of Mo-based layers promoted the development of interface roughness and a decrease of multilayer x-ray reflectivity. The destruction of Mo–(B + C) multilayers at ∼1100°C was caused by the recrystallization of Mo2B5layers.

Evolution of Structure, Phase Composition, and X-Ray Reflectivity of Multilayer Mirrors Mo–(B + C) after Annealing at 250–1100°C

Structural, phase, and chemical stabilities of x-ray multilayer mirrors Mo-(B + C) with periods in the range 8-11.5 nm were studied at temperatures of 250-1100°C by small-angle and large-angle x-ray diffraction and electron microscopy methods. Two amorphizations at ~450 and ~750°C and two crystallizations at ~650 and ~850°C of Mo-based layers were observed, which were due to the formation of the molybdenum carbides MoC (hex), γ-MoC, and Mo2C instead of the metal Mo, and to the formation of the molybdenum borides MoB2 and Mo2B5 instead of molybdenum carbides, respectively. Both amorphizations of Mo-based layers were accompanied by smoothing of interfaces and by an increase of the multilayer x-ray reflectivity at λ = 0.154 nm. Both crystallizations of Mo-based layers promoted the development of interface roughness and a decrease of multilayer x-ray reflectivity. The destruction of Mo-(B + C) multilayers at ~ 1100°C was caused by the recrystallization of Mo2B5 layers.