Apparent Structural Change Research Articles

Modulating Chemical Environments of Metal-Organic Framework-Supported Molybdenum(VI) Catalysts for Insights into the Structure-Activity Relationship in Cyclohexene Epoxidation.

Solid supports are crucial in heterogeneous catalysis due to their profound effects on catalytic activity and selectivity. However, elucidating the specific effects arising from such supports remains challenging. We selected a series of metal-organic frameworks (MOFs) with 8-connected Zr6 nodes as supports to deposit molybdenum(VI) onto to study the effects of pore environment and topology on the resulting Mo-supported catalysts. As characterized by X-ray absorption spectroscopy (XAS) and single-crystal X-ray diffraction (SCXRD), we modulated the chemical environments of the deposited Mo species. For Mo-NU-1000, the Mo species monodentately bound to the Zr6 nodes were anchored in the microporous c-pore, but for Mo-NU-1008 they were bound in the mesopore of Mo-NU-1008. Both monodentate and bidentate modes were found in the mesopore of Mo-NU-1200. Cyclohexene epoxidation with H2O2 was probed to evaluate the support effect on catalytic activity and to unveil the resulting structure-activity relationships. SCXRD and XAS studies demonstrated the atomically precise structural differences of the Mo binding motifs over the course of cyclohexene epoxidation. No apparent structural change was observed for Mo-NU-1000, whereas the monodentate mode of Mo species in Mo-NU-1008 and the monodentate and bidentate Mo species in Mo-NU-1200 evolved to a new bidentate mode bound between two adjacent oxygen atoms from the Zr6 node. This work demonstrates the great advantage of using MOF supports for constructing heterogeneous catalysts with modulated chemical environments of an active species and elucidating structure-activity relationships in the resulting reactions.

Dissipative Self-Assembly of Dynamic Multicompartmentalized Microsystems with Light-Responsive Behaviors

Summary Living cells are compartmentalized systems operating far from thermodynamic equilibrium and consume energy from the environment to carry out their functions. The construction of biomimetic synthetic compartments has both scientific and technological value. Despite many advances, the assembly of synthetic compartments that present nonequilibrium behaviors based on dissipative (or transient) self-assembly remains a grand challenge. Here, we describe the design and synthesis of multicompartmental systems with an active microstructure and complex behaviors. By including an artificial pathway for energy dissipation, we demonstrate the autonomous generation of active polymeric systems using a strategy based on polymerization-induced self-assembly (PISA), driven by chemical fuel. Remarkably, these self-organized synthetic systems exhibit a dynamic change in their multicompartmental structures when exposed to light. This work introduces a strategy toward the design and construction of synthetic compartments with a dynamic structure and also presents pathways to engineer materials with spatially controllable structures and functionalities.

Viscoelastic behavior corresponding to reptative relaxation times across the λ-transition for liquid elemental sulfur.

Continued interest regarding the rheometric measurements of molten sulfur has persisted due to the need for industrial-scale transportation and handling of the material in a liquid phase. This has allowed for extended research developments to attain a fundamental understanding of the fluid. This work reports novel high temperature modulus data over the λ-transition region for liquid elemental sulfur, measured through the use of a modified Anton-Paar Modular Compact Rheometer 302. From these measurements, further insight was gained on the viscoelastic behavior and reptative relaxation times for liquid elemental sulfur. The slow relaxation time, τs, related to reptative behavior, was found to be between 0.24 s and 0.28 s at 190 °C. Utilizing the Maxwell relation, this was determined to correspond to an estimated viscosity range from 72 000 × 10-3 Pa s to 95 000 × 10-3 Pa s, which is in agreement with previous viscosity studies on liquid sulfur. A Cole-Cole plot of the experimental data also displayed characteristics of Debye-like relaxation, suggesting that the slow relaxation process was related to local S-S bond scission and recombination in sulfur chains and was not a relaxation coinciding with a polymeric chain mode. Finally, consecutive heating and cooling of the sulfur sample gave replicate values up to 210 °C on the third heating cycle, where an apparent structural change took place possibly due to cycling over the secondary transition, producing a thermal history, or sulfur reactions with trace impurities. This 210 °C temperature was found to have some recurrence within the literature.

Interface modulation of twinned PtFe nanoplates branched 3D architecture for oxygen reduction catalysis

Highly-branched dendritic Pt-based nanocrystals possess great potential in catalyzing the oxygen reduction reaction (ORR), but encounter performance ceiling due to their poor thermal and electrochemical stability. Here, we present a novel PtFe nanodendrites (NDs) branched with two-dimensional (2D) twinned nanoplates rather than conventional 1D nanowires, which breaks the ORR performance ceiling of dendritic catalysts by inducing the unique Pt-skin configuration via rationally thermal treatment. By further hybridizing the Pt-skin PtFe NDs/C with amino-functionalized ionic liquids (ILs), we achieve an unprecedented mass activity of 3.15 A/mgPt at 0.9 V versus reversible hydrogen electrode (RHE) in the PtFe-based ORR electrocatalytic system. They also show excellent electrocatalytic durability for ORR with negligible activity decay and no apparent structural change after 20,000 cycles, in sharp contrast to the nanowires branched PtFe NDs counterpart. The remarkable catalytic performance is attributed to a combination of several structural features, including 2D morphology, twin boundary, partially ordered phase and strong coordination with amino group. This work highlights the significance of stabilizing electrocatalytic structures via morphology tuning, which thus enables further surface and interface modification for performance breakthrough in ORR electrocatalysis.

Backbone Chemical Composition and Monomer Sequence Effects on Phenylene Polymer Persistence Lengths.

Despite a vast body of the literature devoted to the use of phenylene polymers in the fabrication of graphene nanoribbons, the study of the physical properties of these precursors still poses open questions whose answers will certainly contribute to the design of more efficient/precise synthesis protocols. Particularly, persistence length measurements combined with size exclusion chromatography techniques assign both semiflexible to semirigid structures depending on the molecular weight of the precursor (NaritaNat. Chem.2014, 6, 126−13224451588). Peculiarly, these results suggest an apparent structural change upon increasing the length of the polymers. To address this puzzle, we use single-chain models to study the stiffness of polyphenylene precursors in a theta-like solvent as a function of chain composition and monomer sequence. Steric effects are isolated by considering random walk chains with segment length distributions and the position of monomers determined by the nature of the arene substitution along the backbone. Moreover, two homopolymer limiting cases are defined, that is, meta and para sequences, by associating two types of monomers to each possible substitution pattern. We consider, within these two limiting cases, chains with different compositions and monomer sequences. We compute persistence lengths, mean square end-to-end distances, and gyration and hydrodynamic radii. We find that distinct values of the persistence length for apparently the same chain chemistry are the result of different mixing ratios and the arrangement along the chain of the two positional isomers of the same monomer. Finally, we discuss the relation between two-dimensional density of the number of crossings and the length of polyphenylene segments as they would occur upon strong chain adsorption onto a substrate.

Cations mediating proton conductivity in an oxalate based microporous coordination polymer

Through cation substitution in a zirconium based coordination polymer, an isostructural framework 1@NH4+ has been prepared without any apparent structural change. The proton conductivity of 1@NH4+ is successfully improved. It exhibits high proton conductivity (1.39 × 10−2 S cm−1) at 98% relative humidity and 60 °C.

Monetary policy transmission in systemically important economies and China’s impact

This paper examinesthe monetary policy transmission mechanism in four systemically important economies. The impact of monetary policy is found to be broadly comparable for China, the US, the Eurozone, and Japan. Identifying a role for the financial sector is essential to unpacking various channels through which monetary policy operates. Global factors play a significant role and their impact is strongest for China and weakest for Japan. China’s impact is significant with the Eurozone displaying the most interdependence and Japan the least. Time-varying VARs suggest that contrasts in the responses to monetary policy shocks persist highlighting some of the remaining differences in the transmission mechanism. Finally, there is no apparent structural change in the estimated relationships around the time when the Fed intervened after 2008. It is conjectured that Quantitative Easing may well have prevented such a break.

Effects of FGFR2 kinase activation loop dynamics on catalytic activity.

The structural mechanisms by which receptor tyrosine kinases (RTKs) regulate catalytic activity are diverse and often based on subtle changes in conformational dynamics. The regulatory mechanism of one such RTK, fibroblast growth factor receptor 2 (FGFR2) kinase, is still unknown, as the numerous crystal structures of the unphosphorylated and phosphorylated forms of the kinase domains show no apparent structural change that could explain how phosphorylation could enable catalytic activity. In this study, we use several enhanced sampling molecular dynamics (MD) methods to elucidate the structural changes to the kinase’s activation loop that occur upon phosphorylation. We show that phosphorylation favors inward motion of Arg664, while simultaneously favoring outward motion of Leu665 and Pro666. The latter structural change enables the substrate to bind leading to its resultant phosphorylation. Inward motion of Arg664 allows it to interact with the γ-phosphate of ATP as well as the substrate tyrosine. We show that this stabilizes the tyrosine and primes it for the catalytic phosphotransfer, and it may lower the activation barrier of the phosphotransfer reaction. Our work demonstrates the value of including dynamic information gleaned from computer simulation in deciphering RTK regulatory function.

Transformative gender interventions

Purpose Translating the well-established theory of the gendered organization into strategic interventions that build more gender equitable organizations has proven to be difficult. The authors introduce the emergence of the “bifocal approach” and its subsequent development and examine the potential of the “bifocal approach” as a feminist intervention strategy and an alternative means of countering gender inequalities in organizations. While pre-existing transformative interventions focus on more immediately apparent structural change, the focus begins with the development of individuals. The paper aims to discuss these issues. Design/methodology/approach Developed through iterative cycling between theory and practice, the “bifocal approach” links the existing focus on women’s development with a focus on transformative organizational change. The bifocal approach deliberately begins with the organization’s current way of understanding gender in order to build towards frame-breaking transformative change. Findings The authors show how the bifocal is able to overcome some of the main difficulties of earlier transformative approaches, maintaining organizational access, partnership building, sustaining a gender focus and ultimately sustaining the change effort itself. The bifocal approach seeks structural change, however, the change effort rests with individuals. The development of individuals, as conceived within the bifocal approach was designed to create a “small wins” ripple effect, linking individual (agency) and organizational change (structure). Practical implications The bifocal approach offers a comprehensive re-modelling of traditional interventions for other scholars and practitioners to build on. Organizational interventions previously categorized as “fixing women” could be re-examined for their capacity to provide the foundation for transformative change. Originality/value The contribution of this paper lies in proposing and examining the bifocal approach as a feminist intervention strategy that overcomes the dualism between the existing frames of organizations and the transformative frame of scholars, in order to move practice and theory forward.

Fe ion doping effects on structure, magnetic and transport properties of La0.7Ca0.3Mn1−xFexO3 (0≤x≤0.10) thin films on Si substrates

The La0.7Ca0.3Mn1−xFexO3 (LCMFO: 0≤x≤0.10) thin films were synthesized by chemical solution deposition process on Si substrates. The structure, magnetic and transport properties have been investigated systematically. With the increase of Fe ion doping concentration, from x=0 to x=0.10, no apparent structural change was observed. While, the magnetization and Curie temperature were reduced dramatically, from 168emu/cm3 and 231K for x=0–18emu/cm3 and 81K for x=0.10, indicating that Fe ion suppressed the double-exchange mechanism and enhanced the anti-ferromagnetic ordering. Meanwhile, the resistance was very sensitive to Fe ion doping and an enhanced magnetoresistance (−94%) was observed in the sample of x=0.05.

Study on Raman Spectra of the Polyacrylonitrile Iron Complex Nanofibers

We have measured the Raman spectra of all samples in the process of preparing polyacrylonitrile (PAN) iron complex nanofibers, and compared their Raman spectral characteristics, and thus gained a preliminary result for the PAN nanofibers structural changes in the different stages. Through its Raman spectral analysis and comparison we can find that the cyano group (C N) of modified PAN nanofibers disappeared while the Raman bands of C = N group appeared. For the pre-oxidized PAN nanofiber, because the D and G bands of the C = C vibration appeared in the Raman spectra, it is concluded that the PAN nanofiber has an apparent structural change. Finally, it is also found that that Fe3+and O2-ions have formed coordination bonds in the further prepared PAN iron (Fe3+) complex nanofibers because the characteristic Raman band of Fe = O bond appears.

Neuromuscular ultrasound in polyneuropathies and motor neuron disease

Current standards for diagnosing polyneuropathies (PN) and motor neuron disease (MND) sometimes lack early sensitivity and result in delayed diagnosis and treatment. Neuromuscular ultrasound (NMUS), already established in the diagnosis of entrapment neuropathies, may offer another means of diagnosis and monitoring response to therapy. This review of current evidence discusses diffuse nerve hypertrophy in hereditary demyelinating neuropathies, multifocal nerve enlargement in acquired demyelinating PN and the lack of readily apparent structural change in axonal neuropathies. NMUS detection of fasciculations and muscular change in MND is also reviewed, along with the need for further research to better define the role of nerve imaging in patients with PN.

Toxicology and cytogenetic analysis of a Drosophila melanogaster mutant resistant to Imidacloprid and DDT

Resistance to all major insecticide classes has developed in numerous and diverse insect field populations. Imidacloprid, the worldwide most used neonicotinoid, has been extensively applied during the last decade for the control of different insect pests. Lately, cases of sporadic resistance also to neonicotinoids, including Imidacloprid, have been reported. Drosophila melanogaster is one of the most popular model organisms in biology and, although not a pest species, a promising model system for insecticide resistance research. In this study, we present a toxicological and karyotypic analysis of a Drosophila mutant (MiT[w-]3R2) resistant to Imidacloprid and cross-resistant to DDT. Karyotype analysis of polytene chromosome of MiT[w-]3R2 flies did not identify any apparent structural change of the polytene chromosome linked with the resistance phenotype.

Anti-tumor effect of a novel FAK inhibitor TAE226 against human oral squamous cell carcinoma

Focal adhesion kinase (FAK) overexpression is frequently found in invasive and metastatic cancers, but its role in oral squamous cell carcinoma is not yet well understood. In order to seek therapies targeting oral squamous cell carcinoma, we developed the novel FAK Tyr(397) inhibitor TAE226 and investigated its anti-tumor effects and mechanisms. Expression of phosphorylated FAK Tyr(397) was examined by immunohistochemical and immunoblot analysis. The effect of TAE226 on in vitro and in vivo studies were confirmed by proliferation, cell cycle, apoptosis and angiogenesis analysis. We found that phosphorylated FAK was highly expressed in human tongue oral squamous cell carcinoma in patients. Importantly, TAE226 greatly suppressed the proliferation, migration and invasion of human oral squamous cell carcinoma SAS cells with an apparent structural change of actin fiber and a loss of cell adhesion. In addition, TAE226 inhibited the expression of phospho-FAK Tyr(397) and phospho AKT Ser(473), resulting in caspase-mediated apoptosis. Furthermore, oral administration of TAE226 in mice suppressed the growth and angiogenesis of oral squamous cell carcinoma xenografts in vivo. Our results provide compelling evidence that FAK is critically involved in oral squamous cell carcinoma and that the FAK inhibitor TAE226 can potentially be effectively used for the treatment of oral squamous cell carcinoma.

Structural Disordering and Relaxation Process in an Amorphous Alloy

Structural change in an amorphous alloy was measured by applying a load below the global yield stregth at ambient temperatures. It was observed that the magnitude of the apparent structural change occuring in the amorphous alloy is determined by the compatative relationship between the stress-induced disordering process and the thermally-activated relaxation process. Structural disorder was observed to take place even at a stress well below the global yield, and the degree of the disorder was increased abruptly at the earlier stage of loading and saturated with time. In the mean time, unlike the previous belief, the relaxation process was observed to occur even at embient temperatures, and the degree of the relaxation was observed to increase linearly with time. The analytical equation predicting the structural change was proposed. (Received May 16, 2011)

Emission Properties from Induced Structural Degradation of a-C:H Thin Film

Hydrogenated amorphous carbon (a-C:H) films were deposited by plasma enhanced chemical vapor deposition on silicon substrates. a-C:H thin film was irradiated to a typical He-Cd laser to study its emitting properties. The photoluminescence (PL) intensity during the irradiation achieved a maximum value when 2,000 seconds elapsed. Fourier transform infrared measurement revealed a-C:H thin film suffered transformation from a polymer-like to graphite-like phase during laser irradiation. Thermal annealing was done at various temperatures, ranging from room temperature to <TEX>$400^{\circ}C$</TEX> in the atmosphere, to investigate structural changes in a-C:H film by heat generation during the emission. PL intensity of a-C:H thin film increased 1.5 times without apparent structural change, as annealing temperature increased up to <TEX>$200^{\circ}C$</TEX>. However, a-C:H film above <TEX>$200^{\circ}C$</TEX> exhibited significant decrease of PL accompanying dehydrogenation. This led to a red shift of the PL peak.

Fe-doping induced Griffiths-like phase in La0.7Ba0.3CoO3

The effect of Fe-doping on the magnetic properties of the ABO3-type perovskite cobaltites La0.7Ba0.3Co1–yFeyO3 (0 ≤ y ≤ 0.80) is reported. With no apparent structural change in any doped sample, the Curie temperature (TC) and the magnetization (M) are greatly suppressed for y ≤ 0.30 samples, while a distinct increase in TC for the y = 0.40 sample is observed. With the further increase of Fe concentration, TC increases monotonically. Griffiths-like phases in 0.40 ≤ y ≤ 0.60 samples are confirmed. The formation of the Griffiths-like phase is ascribed to B-site disordering induced isolation of ferromagnetic (FM) clusters above TC.

Discovery of Ferromagnetic-Half-Metal–to–Insulator Transition inK2Cr8O16

The hollandite chromium oxide K2Cr8O16 has been synthesized in both powder and single-crystal form under high pressure. Combining electrical resistivity, magnetic susceptibility, and x-ray diffraction, we found that K2Cr8O16 is a ferromagnetic metal (or half-metal) with T(C)=180 K and shows a transition to an insulator at 95 K without any apparent structural change but retaining ferromagnetism. K2Cr8O16 is quite unique in three aspects: It has a rare mixed valence of Cr3+ and Cr4+; it has a metal (or half-metal)-to-insulator transition in a ferromagnetic state; and the resulting low-temperature phase is a rare case of a ferromagnetic insulator. This discovery could open a new frontier on the relation of magnetism and conducting properties in strongly correlated electron systems.

Inelastic neutron scattering and Raman spectroscopic investigation of l-alanine alaninium nitrate, a homologue of a ferroelectric material

The 2 : 1 amino acid salt of L-alanine with nitric acid was crystallized and the vibrational spectrum measured at 25 K by incoherent inelastic neutron scattering (INS) spectroscopy. The spectrum was simulated using solid-state density functional theory based on a new 90 K structure determination. A feature observed at approximately 450 cm(-1) in the INS spectrum of L-alanine alaninium nitrate is noticeably absent in the calculation. Raman spectroscopy reveals spectral differences between the spectra at 77 and 293 K with a 450 cm(-1) feature appearing at low temperature. The nature of these spectral changes and the disagreement between the INS spectrum and its simulation are discussed in relation to an apparent structural change involving motion of a proton at low (<90 K) temperature.

Dual Tyrosine Kinase Inhibitor for Focal Adhesion Kinase and Insulin-like Growth Factor-I Receptor Exhibits Anticancer Effect in Esophageal Adenocarcinoma In vitro and In vivo

Focal adhesion kinase (FAK) regulates integrin and growth factor-mediated signaling pathways to enhance cell migration, proliferation, and survival, and its up-regulation correlates malignant grade and poor outcome in several types of cancer. In this study, we aimed to raise a potential therapeutic strategy using a FAK inhibitor for Barrett's esophageal adenocarcinoma. The expression status of FAK in clinical Barrett's esophageal adenocarcinoma tissues was determined by immunohistochemistry. Cultured esophageal adenocarcinoma cells were treated with TAE226, a specific FAK inhibitor with an additional effect of inhibiting insulin-like growth factor-I receptor (IGF-IR), to assess its anticancer effect in vitro. Western blot was carried out to explore a participating signaling pathway for TAE226-induced cell death. Furthermore, TAE226 was orally administered to s.c. xenograft animals to investigate its anticancer effect in vivo. Strong expression of FAK was found in 94.0% of Barrett's esophageal adenocarcinoma compared with 17.9% of Barrett's epithelia, suggesting that FAK might play a critical role in the progression of Barrett's esophageal adenocarcinoma. When esophageal adenocarcinoma cells were treated with TAE226, cell proliferation and migration were greatly inhibited with an apparent structural change of actin fiber and a loss of cell adhesion. The activities of FAK, IGF-IR, and AKT were suppressed by TAE226 and subsequent dephosphorylation of BAD at Ser(136) occurred, resulting in caspase-mediated apoptosis. In vivo tumor volume was significantly reduced by oral administration of TAE226. These results suggest that TAE226, a dual tyrosine kinase inhibitor for FAK and IGF-IR, could become a new remedy for Barrett's esophageal adenocarcinoma.