Robust phase determination in complex solid solutions using diffuse multiple scattering.

A novel methodology is presented for identifying and distinguishing between structural phases in multi-phasic systems, such as piezoelectric materials like PMN-PT [Pb(Mg1/3Nb2/3)O3-PbTiO3], PIN-PMN-PT [Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3] and PZT [Pb(Zr,Ti)O3], using diffuse multiple scattering and Kossel line diffraction techniques. The method exploits the splitting of triple line intersections from special coplanar reflections combined with logical constraints to generate a splitting fingerprint for robust crystallographic phase determination and discrimination.

Rational redesign of the ferredoxin-NADP+-oxido-reductase/ferredoxin-interaction for photosynthesis-dependent H2-production.

Utilization of electrons from the photosynthetic water splitting reaction for the generation of biofuels, commodities as well as application in biotransformations requires a partial rerouting of the photosynthetic electron transport chain. Due to its rather negative redox potential and its bifurcational function, ferredoxin at the acceptor side of Photosystem 1 is one of the focal points for such an engineering. With hydrogen production as model system, we show here the impact and potential of redox partner design involving ferredoxin (Fd), ferredoxin-oxido-reductase (FNR) and [FeFe]­hydrogenase HydA1 on electron transport in a future cyanobacterial design cell of Synechocystis PCC 6803. X-ray-structure-based rational design and the allocation of specific interaction residues by NMR-analysis led to the construction of Fd- and FNR-mutants, which in appropriate combination enabled an about 18-fold enhanced electron flow from Fd to HydA1 (in competition with equimolar amounts of FNR) in in vitro assays. The negative impact of these mutations on the Fd-FNR electron transport which indirectly facilitates H2 production (with a contribution of ≤42% by FNR variants and ≤23% by Fd-variants) and the direct positive impact on the Fd-HydA1 electron transport (≤23% by Fd-mutants) provide an excellent basis for the construction of a hydrogen-producing design cell and the study of photosynthetic efficiency-optimization with cyanobacteria.

The interfacial nature of proximity-induced magnetism and the Dzyaloshinskii-Moriya interaction at the Pt/Co interface.

The Dzyaloshinskii-Moriya interaction has been shown to stabilise Nèel domain walls in magnetic thin films, allowing high domain wall velocities driven by spin current effects. The interfacial Dzyaloshinskii-Moriya interaction (IDMI) occurs at the interface between ferromagnetic and heavy metal layers with strong spin-orbit coupling, but details of the interaction remain to be understood and the role of proximity induced magnetism (PIM) in the heavy metal is unknown. Here IDMI and PIM are reported in Pt determined as a function of Au and Ir spacer layers in Pt/Co/Au,Ir/Pt. Both interactions are found to be sensitive to sub-nanometre changes in the spacer thickness, correlating over sub-monolayer spacer thicknesses, but not for thicker spacers where IDMI continues to change even after PIM is lost.

Si1-x Ge x /Si Interface Profiles Measured to Sub-Nanometer Precision Using uleSIMS Energy Sequencing.

The utility of energy sequencing for extracting an accurate matrix level interface profile using ultra-low energy SIMS (uleSIMS) is reported. Normally incident O2 (+) over an energy range of 0.25-2.5 keV were used to probe the interface between Si0.73Ge0.27/Si, which was also studied using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). All the SIMS profiles were linearized by taking the well understood matrix effects on ion yield and erosion rate into account. A method based on simultaneous fitting of the SIMS profiles measured at different energies is presented, which allows the intrinsic sample profile to be determined to sub-nanometer precision. Excellent agreement was found between the directly imaged HAADF-STEM interface and that derived from SIMS. Graphical Abstract ᅟ.

Long-range magnetic interactions and proximity effects in an amorphous exchange-spring magnet.

Low-dimensional magnetic heterostructures are a key element of spintronics, where magnetic interactions between different materials often define the functionality of devices. Although some interlayer exchange coupling mechanisms are by now well established, the possibility of direct exchange coupling via proximity-induced magnetization through non-magnetic layers is typically ignored due to the presumed short range of such proximity effects. Here we show that magnetic order can be induced throughout a 40-nm-thick amorphous paramagnetic layer through proximity to ferromagnets, mediating both exchange-spring magnet behaviour and exchange bias. Furthermore, Monte Carlo simulations show that nearest-neighbour magnetic interactions fall short in describing the observed effects and long-range magnetic interactions are needed to capture the extent of the induced magnetization. The results highlight the importance of considering the range of interactions in low-dimensional heterostructures and how magnetic proximity effects can be used to obtain new functionality.

Simultaneous dynamic electrical and structural measurements of functional materials.

A new materials characterization system developed at the XMaS beamline, located at the European Synchrotron Radiation Facility in France, is presented. We show that this new capability allows to measure the atomic structural evolution (crystallography) of piezoelectric materials whilst simultaneously measuring the overall strain characteristics and electrical response to dynamically (ac) applied external stimuli.

Focused-ion-beam induced interfacial intermixing of magnetic bilayers for nanoscale control of magnetic properties.

Modification of the magnetic properties in a thin-film ferromagnetic/non-magnetic bilayer system by low-dose focused ion-beam (FIB) induced intermixing is demonstrated. The highly localized capability of FIB may be used to locally control magnetic behaviour at the nanoscale. The magnetic, electronic and structural properties of NiFe/Au bilayers were investigated as a function of the interfacial structure that was actively modified using focused Ga(+) ion irradiation. Experimental work used MOKE, SQUID, XMCD as well as magnetoresistance measurements to determine the magnetic behavior and grazing incidence x-ray reflectivity to elucidate the interfacial structure. Interfacial intermixing, induced by low-dose irradiation, is shown to lead to complex changes in the magnetic behavior that are associated with monotonic structural evolution of the interface. This behavior may be explained by changes in the local atomic environment within the interface region resulting in a combination of processes including the loss of moment on Ni and Fe, an induced moment on Au and modifications to the spin-orbit coupling between Au and NiFe.

Depth-dependent magnetism in epitaxial MnSb thin films: effects of surface passivation and cleaning.

Depth-dependent magnetism in MnSb(0001) epitaxial films has been studied by combining experimental methods with different surface specificities: polarized neutron reflectivity, x-ray magnetic circular dichroism (XMCD), x-ray resonant magnetic scattering and spin-polarized low energy electron microscopy (SPLEEM). A native oxide ∼4.5 nm thick covers air-exposed samples which increases the film's coercivity. HCl etching efficiently removes this oxide and in situ surface treatment of etched samples enables surface magnetic contrast to be observed in SPLEEM. A thin Sb capping layer prevents oxidation and preserves ferromagnetism throughout the MnSb film. The interpretation of Mn L(3,2) edge XMCD data is discussed.

Strain dependent selection of spin-slip phases in sputter deposited thin-film epitaxial holmium.

We report the structural and magnetic characterization of sputter deposited epitaxial Ho. We present room temperature characterization by atomic force microscopy and x-ray diffraction and temperature dependent characterization by x-ray diffraction and neutron diffraction. The data show the onset and change of the magnetic state as a function of temperature. Films of different thickness, exhibiting signs of differing epitaxially induced strain, tend towards specific spin-slip phases in the low temperature regime. The more highly strained thinnest films tend towards values with a longer magnetic wavelength.

Identification of N-terminal regions of wheat leaf ferredoxin NADP+ oxidoreductase important for interactions with ferredoxin.

Wheat leaves contain two isoproteins of the photosynthetic ferredoxin:NADP(+) reductase (pFNRI and pFNRII). Truncated forms of both enzymes have been detected in vivo, but only pFNRII displays N-terminal length-dependent changes in activity. To investigate the impact of N-terminal truncation on interaction with ferredoxin (Fd), recombinant pFNRII proteins, differing by deletions of up to 25 amino acids, were generated. During purification of the isoproteins found in vivo, the longer forms of pFNRII bound more strongly to a Fd affinity column than did the shorter forms, pFNRII(ISKK) and pFNRII[N-2](KKQD). Further truncation of the N-termini resulted in a pFNRII protein which failed to bind to a Fd column. Similar k(cat) values (104-140 s(-1)) for cytochrome c reduction were measured for all but the most truncated pFNRII[N-5](DEGV), which had a k(cat) of 38 s(-1). Stopped-flow kinetic studies, examining the impact of truncation on electron flow between mutant pFNRII proteins and Fd, showed there was a variation in k(obs) from 76 to 265 s(-1) dependent on the pFNRII partner. To analyze the sites which contribute to Fd binding at the pFNRII N-terminal, three mutants were generated, in which a single or double lysine residue was changed to glutamine within the in vivo N-terminal truncation region. The mutations affected binding of pFNRII to the Fd column. Based on activity measurements, the double lysine residue change resulted in a pFNRII enzyme with decreased Fd affinity. The results highlight the importance of this flexible N-terminal region of the pFNRII protein in binding the Fd partner.

A screen for potential ferredoxin electron transfer partners uncovers new, redox dependent interactions.

Ferredoxin (Fd) is the primary soluble acceptor at the end of the photosynthetic electron transport chain, and is known to directly transfer electrons to a wide range of proteins for use in metabolism and regulatory processes. We have conducted a screen to identify new putative Fd interaction partners in the cyanobacteria Synechocystis sp. PCC 6803 using Fd-chromatography in combination with MALDI-TOF mass spectrometry. Many novel interactions were detected, including several redox enzymes, which are now candidates for further experiments to investigate electron transfer with Fd. In addition, some proteins with regulatory activity related to photosynthesis were identified. We cloned and expressed one such protein, known as RpaA, which is a specific regulator of energy transfer between phycobilisomes and PSI. Using the recombinant protein we confirmed direct interaction with Fd, and discovered that this was dependent on redox state. The screen for putative Fd-binding proteins was repeated, comparing oxidizing and reducing conditions, identifying many proteins whose interaction with Fd is redox dependent. These include several additional signaling molecules, among them the LexA repressor, Ycf53 and NII, which are all involved in interpreting the redox state of the cell.

RASOR: an advanced instrument for soft x-ray reflectivity and diffraction.

We report the design and construction of a novel soft x-ray diffractometer installed at Diamond Light Source. The beamline endstation RASOR is constructed for general users and designed primarily for the study of single crystal diffraction and thin film reflectivity. The instrument is comprised of a limited three circle (theta, 2theta, and chi) diffractometer with an additional removable rotation (phi) stage. It is equipped with a liquid helium cryostat, and post-scatter polarization analysis. Motorized motions are provided for the precise positioning of the sample onto the diffractometer center of rotation, and for positioning the center of rotation onto the x-ray beam. The functions of the instrument have been tested at Diamond Light Source, and initial test measurements are provided, demonstrating the potential of the instrument.

Expression of multiple forms of ferredoxin NADP+ oxidoreductase in wheat leaves.

In higher plants there are two forms of ferredoxin NADP(+) oxidoreductase (FNR), a photosynthetic pFNR primarily required for the photoreduction of NADP(+), and a heterotrophic hFNR which generates reduced ferredoxin by utilizing electrons from NADPH produced during carbohydrate oxidation. The aim of this study was to investigate the presence of multiple forms of FNR in wheat leaves and the capacity of FNR isoforms to respond to changes in reductant demand through varied expression and N-terminal processing. Two forms of pFNR mRNA (pFNRI and pFNRII) were expressed in a similar pattern along the 12 cm developing primary wheat leaf, with the highest levels observed in plants grown continuously in the dark in the presence (pFNRI) or absence (pFNRII) of nitrate respectively. pFNR protein increased from the leaf base to tip. hFNR mRNA and protein was in the basal part of the leaf in plants grown in the presence of nitrate. FNR activity in plants grown in a light/dark cycle without nitrate was mainly due to pFNR, whilst hFNR contributed significantly in nitrate-fed plants. The potential role of distinct forms of FNR in meeting the changing metabolic capacity and reductant demands along the linear gradient of developing cells of the leaf are discussed. Furthermore, evidence for alternative N-terminal cleavage sites of pFNR acting as a means of discriminating between ferredoxins and the implications of this in providing a more effective flow of electrons through a particular pathway in vivo is considered.

Saliva-promoted adhesion of Streptococcus mutans MT8148 associates with dental plaque and caries experience.

Colonization of enamel surfaces by Streptococcus mutans is thought to be initiated by the attachment of bacteria to a saliva-derived conditioning film (acquired pellicle). However, the clinical relevance of the contribution of saliva-promoted S. mutans adhesion in biofilm formation has not yet been fully elucidated. The aim of this study was to correlate saliva-promoted S. mutans adhesion with biofilm formation in humans. We correlated all measurements of salivary factors and dental plaque formation in 70 healthy subjects. Dental plaque development after thorough professional teeth cleaning correlated positively with S. mutans adhesion onto saliva-coated hydroxyapatite pellets and the glycoprotein content of either parotid or whole saliva. Saliva-promoted S. mutans adhesion and glycoprotein content were also positively correlated with each other in parotid and whole saliva. By contrast, neither salivary mutans streptococci, Lactobacillus nor Candida correlated with biofilm formation. Parotid saliva-mediated S. mutans adhesion was significantly higher in 12 caries-experienced (CE) subjects than in 9 caries-inexperienced (CI) subjects. Salivary S. mutans adhesion was significantly less (p < 0.01) in the CI group than in the CE group. In conclusion, the present findings suggest the initial S. mutans adhesion, modulated by salivary protein adsorption onto the enamel surface, as a possible correlate of susceptibility to dental plaque and caries.

Reduction of saliva-promoted adhesion of Streptococcus mutans MT8148 and dental biofilm development by tragacanth gum and yeast-derived phosphomannan.

The aim of this study was to investigate materials which reduce saliva-promoted adhesion of Streptococcus mutans onto enamel surfaces, and their potential in preventing dental biofilm development. The effects of hydroxyapatite (HA) surface pretreatment with hydrophilic polysaccharides on saliva-promoted S. mutans adhesion in vitro and de novo dental biofilm deposition in vivo were examined. Saliva-promoted adhesion of S. mutans MT8148 was significantly reduced by pretreatment of the HA surface with tragacanth gum (TG) and yeast-derived phosphoglycans. Extracellular phosphomannan (PM) from Pichia capsulata NRRL Y-1842 and TG reduced biofilm development on lower incisors in plaque-susceptible rats when administered via drinking water at concentrations of 0.5% and 0.01%, respectively. The inhibitory effect of TG on de novo dental biofilm formation was also demonstrated when administered via mouthwash in humans. It is concluded that TG and yeast-derived PM have the potential for use as anti-adherent agents and are effective in reducing de novo dental biofilm formation.

Expression of peroxisome proliferator-activated receptor-gamma in renal ischemia-reperfusion injury.

The pathogenesis of ischemia-reperfusion injury is known to involve cytokines and particularly surface adhesion molecules, the expression of which initiates the attachment of inflammatory cells. Peroxisome proliferator-activated receptor (PPAR)-gamma is considered an important immunomodulatory factor as well as a fatty acid regulator. In this study, we researched the expression of PPAR-gamma in renal ischemia-reperfusion injury of the rat. The right kidney was harvested and left renal artery and vein were clamped under laparotomy. The kidney was reperfused after 90 minutes of ischemia, and rats were sacrificed at 0, 1.5, 3, 5, 12, and 24 hours after reperfusion. PPAR-gamma expression was analyzed by immunohistochemical staining using monoclonal antibody. In normal kidney, PPAR-gamma staining was weak on endothelial cells, including mesangial cells. On the other hand, PPAR-gamma staining was weak on interstitial cells and strong on collecting ducts of medulla. From 1.5 to 5 hours after reperfusion, PPAR-gamma staining was strong on endothelial cells, moderate on interstitial cells, and strong on collecting ducts. Twelve hours after reperfusion, PPAR-gamma staining was weak on endothelial cells, moderate on interstitial cells, and strong on collecting ducts. PPAR-gamma is induced on collecting ducts, interstitial cells, and endothelial cells in a rat model having renal ischemia-reperfusion injury.

Human interleukin-10 transduced fetal liver stem cells prolong survival of mouse skin and heart allografts.

Interleukin (IL)-10 regulates immune responses, acting as a suppressive cytokine by inhibiting the synthesis of Th1 cytokines, such as IL-2 and interferon (IFN)-gamma. It also strongly down-regulates major histocompatibility complex (MHC) class II determinants on antigen presenting cells (APC). On the other hand, long-term tolerance is well correlated with the persistence of a peripheral microchimerism. In this study, we investigated the synergistic effect of human IL-10 (huIL-10) and hematopoietic microchimerism for the induction of long-term tolerance. Irradiated Balb/c mice (H-2d) were used as recipients (fetal liver stem cells [FLSC], skin and heart) and C57BL/6 (H-2b) mice were used as donors of FLSC, skin and heart. Recipients were simultaneously transplanted with the heart, the skin and with huIL-10 gene-transduced FLSC. Microchimerism was checked using fluorescent flow cytometry, huIL10 production using enzyme-linked immunosorbent assay (ELISA), and graft survival was evaluated by daily observation. Significant level of huIL10 (up to 900 pg/mL) was detected for more than 2 weeks in the serum of mice that underwent transplantation. Four weeks after the FLSC injection, microchimerism was identified in the recipient lymphoid organs (spleen, thymus, and bone marrow) by the presence of donor cells (H-2b). Finally, in the group of mice treated with huIL-10 gene-transduced FLSC, skin allografts survived for 18.9 +/- 1.8 days compared with 9.5 and 9.6 days in the groups of mice treated with nontransduced FLSC or huIL-10 alone, respectively. The same pattern for heart allograft survival was observed. HuIL-10 transduction of donor hematopoietic stem cells resulted in production of huIL-10, cell engraftment, and chimerism. Although full tolerance was not obtained, specific and highly significant (P < .001) prolongation of the survival of donor heart allografts with (more than 2-fold compared with nontreated groups) was observed. The infiltration of the transplanted heart and its late rejection demonstrate that stem cells transduced with huIL-10 gene induce "prope" tolerance in this model.

Study of cyclooxygenase-2 in renal ischemia-reperfusion injury.

The pathogenesis of ischemia-reperfusion (I/R) injury is known to involve cytokines and particularly surface adhesion molecules, the expression of which initiates the attachment of inflammatory cells. Cyclooxygenase (COX)-1 and COX-2 catalyze the initial key enzymatic steps in the metabolism of arachidonic acid. COX-1 is constitutively expressed in most tissues, whereas COX-2 is induced in response to proinflamamatory cytokines and stress. In this study we examined the expression of COX-1 and COX-2 in the rat after 90 minutes of warm-I/R injury. Rats were sacrificed at 0, 1.5, 3, 5, 12, and 24 hours after reperfusion. COX-2 expressions were analyzed by immunohistochemical staining, which was graded on a scale of 0 to 4. All results are presented as the mean values +/- SD. Data analyses used analysis of variance. COX-2 expression was most intense on endothelial cells at 3 and 5 hours after reperfusion. From 12 to 24 hours after reperfusion COX-2 expression on endothelial cells gradually became weaker. COX-2 expression scores were significantly higher at 1.5, 3, 5, 12, and 24 hours after reperfusion than at 0 hours. However, there were no differences in COX-1 expression after reperfusion. Several hours after the maximum of COX-2 expression the maximum renal I/R injury was observed. These results suggest a relationship between COX-2 expression and renal I/R injury.

Tenascin-C regulates proliferation and migration of cultured astrocytes in a scratch wound assay.

Tenascin-C (TNC), an extracellular matrix glycoprotein, is involved in tissue morphogenesis like embryogenesis, wound healing or tumorigenesis. Astrocytes are known to play major roles in wound healing in the CNS. To elucidate the roles of TNC in wound closure by astrocytes, we have examined the morphological changes of cultured astrocytes in a scratch wound assay and measured the content of soluble TNC released into the medium. We have also localized the expression of TNC mRNA, TNC, glial fibrillary acidic protein (GFAP), vimentin and integrin beta1. After wounding, glial cells rapidly released the largest TNC isoform and proliferated in the border zones. Subsequently, they became polarized with unidirectional processes and finally migrated toward the denuded area. The proliferating border zone cells and pre-migratory cells intensely expressed TNC mRNA, TNC-, vimentin-, GFAP- and integrin beta1-like immunoreactivity, while the migratory cells showed generally reduced expression except the front. Exogenous TNC enhanced cell proliferation and migration, while functional blocking with anti-TNC or anti-integrin beta1 antibody reduced both of them. These results suggest that mechanical injury induces boundary astrocytes to produce and release TNC that promotes cell proliferation and migration via integrin beta1 in an autocrine/paracrine fashion.

The relationship between interface structure, conformality and perpendicular anisotropy in CoPd multilayers.

The relationship between the interface structure and perpendicular anisotropy in sputtered Co/Pd multilayers has been investigated using grazing incidence x-ray scattering and vibrating sample magnetometry. Using fits to a self-affine fractal model of the interfaces, the variation in in-plane correlation length, fractal parameter and conformality has been determined as a function of the number of repeats in the Co/Pd bilayers. As the number of interfaces rises, the roughness becomes predominantly non-conformal and the in-plane length scale associated with the roughness increases as a power law with multilayer thickness. It is suggested that the loss of conformality, characterized by a relatively short out-of-plane correlation length, may be the cause of the reduction in anisotropy energy per interface observed for high numbers of bilayer repeats. There is a weak association between fractal parameter and interface anisotropy; a reduction in the fractal dimension of the interface appears to result in a higher surface anisotropy.