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Micro-Raman spectroscopy and X-ray diffraction were used to study time-dependent structural changes in sputtered Ce 1-x Gd x O 2-x/2 films. The F 2 g peak position was measured at five well-defined film locations; X-ray diffraction assessed in-plane compressive strain and unit cell volume. For x = 0.05, at all locations monitored post-annealing, the F 2 g frequency continued to increase during two weeks and for x = 0.10, at 4 of 5 locations during six weeks. This time-dependent behavior is attributed to relaxation of local elastic dipolar strain fields. Raman spectroscopy can properly evaluate strain in thin films of these materials only when mechanical properties, defect structure, temporal and thermal history are considered. [ABSTRACT FROM AUTHOR]

There is continuing interest in determiningessential structuralfeatures of polymer gels, which display photoelectric and/or thermoelectricbehavior. One such gel is the blend, poly(4-vinylpyridine-co-butylmethacrylate)/poly(4-vinylpyridine), dissolved in liquid pyridine.Following extended aeration of a three-component mixture, which servesas a model for the gel side chain interactions, crystallization ofa new molecule, 4-isopropylpyridine hydroxide (IPPOH), occurs.X-ray diffraction, DFT modeling, and spectroscopy were used to determinethe structural, electronic, and luminescent properties of the crystal.The crystal structure reveals molecules forming head-to-tail, hydrogen-bondedchains without base stacking or marked interchain interaction. Themolecular chains are characterized by moderately long-lived, blue-violetluminescence excited in the near-UV. Because these photoluminescentproperties resemble those of the gel from which the crystals are derived,we may posit similar structural features in the gel for which directstructural analysis is not available. [ABSTRACT FROM AUTHOR]

Abstract: Pb1-x Cd x S films have been deposited by chemical bath deposition with particular attention paid to the formation of single phase films. Using a combination of citrate and ethylenediamine complexes, single phase films (verified by a combination of X-ray diffraction and chemical analysis) could be reproducibly formed up to a maximum of x =0.15, and irreproducibly up to 0.18. Attempts to increase the Cd content further resulted in formation of an initial layer of pure CdS but without any increase (in fact, a decrease often occurred) in the Cd content of the subsequent solid solution film. The effects of variation of the deposition parameters (pH, temperature, concentrations of various reactants) on the chemical and phase compositions of the films are described. [Copyright &y& Elsevier]

Fluid balance in the intervertebral disc under applied load is determined primarily by its swelling pressure, that is, the external pressure at which it neither loses nor gains water. This depends on the composition of the tissue, in particular on its proteoglycan concentration. Proteoglycans develop a high osmotic pressure due to their fixed negatively charged groups. Because of their size, proteoglycans are excluded from the collagen's intrafibrillar volume; hence their osmotic activity is determined only by the extrafibrillar water. Here, we show that in order to evaluate correctly the swelling pressure in the annuli fibrosi of human intervertebral disc, it is essential to evaluate its proportion of intrafibrillar water. We used low-angle X-ray scattering and osmotic stress techniques to determine the lateral packing of the collagen molecules in the fibrils of the annuli fibrosi (ages: 25-77). It was found that the lateral packing and, hence, the intrafibrillar water content depends on age, external osmotic pressure, and location in the tissue. Subtracting intrafibrillar water from total hydration yields the amount of extrafibrillar water, from which the true fixed charge density of the tissue could be estimated. From a force balance, it would appear that collagen tension plays only a minor role in the equilibrium of the human intervertebral disc under load, in contrast to articular cartilage, where collagen tension is important for load bearing. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [ABSTRACT FROM AUTHOR]

Experimental data that define conditions under which cholesterol crystallites form in cholesterol/phospholipid model membranes are reviewed. Structural features of the phospholipids that determine cholesterol crystallization include the length and degree of unsaturation of the acyl chains, the presence of charge on the headgroups and interheadgroup hydrogen bonds. [Copyright &y& Elsevier]

Abstract Solid-state drawing to high extension ratios of melt-extruded VGCF-iPP nanocomposite filaments results in remarkable increases in modulus and strength, which mask any contribution of nano-reinforcement or inter-particle confinement observed previously. Based on X-ray diffraction and thermal analyses it is shown that the drawing process involves crumpling of the original 'shish-kebab' structure, accompanied by lateral shrinkage of the 'kebabs', disappearance and reorientation of daughter lamellae and significant increases in the degree of crystallinity by solid-state recrystallization. The effects of the initial diameter of the as-extruded filaments and those of the nanofibers and the 'shish-kebab' structure are dominated by the drawing process, which produces a highly aligned fibrillar structure with superior mechanical properties. A cartoon model of the effect of solid-state drawing of extruded iPP and nanocomposite filaments on the transition from 'shish-kebab' to fibril morphology is presented. Graphical abstract Image Highlights • Drawing of VGCF-iPP nanocomposite filaments generates high mechanical properties. • Drawing induces solid-state recrystallization by crumpling of 'shish-kebab' structure. • Shrinkage of 'kebabs' and reorientation of daughter lamellae increase crystallinity. • Effects of confinement and nanoreinforcement are dominated by a fibrillar structure. [ABSTRACT FROM AUTHOR]

This paper presents the structural details of nylon 66 transcrystallinity induced by aramid (kevlar 29, 49 and 149) and carbon (pitch based) fibers, as determined by high spatial resolution X-ray diffraction. Using stepwise scanning, the orientation of the lamellae in the transcrystalline layer was measured as a function of distance from the fiber. The main observation is that this orientation is distinct for each system and almost independent of distance from the fiber. Of particular interest is the bi-layered transcrystallinity formed on a surface treated kevlar 49 fiber, in which the lamellar a* axis is nearly perpendicular and at an angle of ∼12° to the fiber in the outer and inner layer, respectively. The crystallographic analysis generates grids of oriented lamellae with respect to the fiber axis. [Copyright &y& Elsevier]

The dearth of high quality, three dimensional crystals of membrane proteins, suitable for X-ray diffraction analysis, constitutes a serious barrier to progress in structural biology. To address this challenge, we have developed a new crystallization medium that relies on the conjugation of surfactant micelles via base-pairing of complementary hydrophobic nucleosides. Base-pairs formed at the interface between micelles bring them into proximity with each other; and when the conjugated micelles contain a membrane protein, crystal nucleation centers can be stabilized, thereby promoting crystal growth. Accordingly, two hydrophobic nucleoside derivatives – deoxyguanosine (G) and deoxycytidine (C), each covalently bonded to a 10 carbon chain were synthesized and added to an aqueous solution containing octyl β - d -thioglucopyranoside micelles. These hydrophobic nucleosides induced the formation of oil-rich globules after 2 days incubation at 19 °C or after a few hours in the presence of ammonium sulfate; however, phase separation was inhibited by 100 mM GMP. The presence of the membrane protein bacteriorhodopsin in the conjugated – micellar dispersion resulted in the growth within the colorless globules of a variety of purple crystals, the color indicating a functional protein. On this basis, we suggest that conjugation of micelles via base-pair complementarity may provide significant assistance to the structural determination of integral membrane proteins. [ABSTRACT FROM AUTHOR]

We have studied the properties of mixtures of cholesterol with dioleoylphosphatidylcholine (DOPC), and with several other phospholipids, including 1-stearoyl-2-oleoylphosphatidylcholine (SOPC) and dioleoleoylphosphatidylserine (DOPS), as a function of cholesterol molar fraction and of temperature. Mixtures of DOPC with a cholesterol molar fraction of 0.4 or greater display polymorphic behavior. This polymorphism includes the formation of structures that give rise to isotropic peaks in 31P NMR at cholesterol molar fractions between 0.4 and 0.6, dependent on the thermal history of the sample. Cryo-electron microscopy studies demonstrate the formation of small globular aggregates that would contribute to a narrowing of the 31P NMR powder pattern. At molar fraction cholesterol 0.6 and higher and at temperatures above 70°C, the mixtures with DOPC convert to the hexagonal phase. Lipid polymorphism is accompanied by the phase separation of cholesterol crystals in the anhydrous form and/or the monohydrate form. The crystals that are formed have substantially altered kinetics of hydration and dehydration, compared with both pure cholesterol monohydrate crystals and with crystals formed in the presence of the other phospholipids that do not form the hexagonal phase in the presence of cholesterol. This fact demonstrates that these cholesterol crystals are in intimate contact with the DOPC phospholipid and are not present as morphologically separate structures. [Copyright &y& Elsevier]