Search

Neutron reflectivities of phosphatidylcholine monolayers in the liquid condensed (LC) phase on ultrapure H(2)O and D(2)O subphases have been measured on a Langmuir film balance. Using a dedicated liquid surface reflectometer, reflectivities down to R = 10(-6) in the momentum transfer range Q(z) = 0-0.4 A(-1) were accessed.In a new approach, by refining neutron reflectivity data from chain-perdeuterated DPPC-d(62) in combination with x-ray measurements on the same monolayer under similar conditions it is shown that the two techniques mutually complement one another. This analysis leads to a detailed conception of the interface structure. It is found that in the LC phase (which is analogous to the L(beta), phase in vesicle dispersions) the head group is interpenetrated with subphase water (4 +/- 2.5 molecules per lipid) and the average tilt angle of the hydrophobic chains from the surface normal is 33 +/- 3 degrees.

Coherent X-ray imaging is an active field at synchrotron sources. The images rely on the available coherent flux over a limited field of view. At many synchrotron beamlines a double-crystal monochromator (DCM) is employed in a standard nondispersive arrangement. For coherent diffraction imaging it is advantageous to increase the available field of view by increasing the spatial coherence length (SCL) of a beam exiting such a DCM. Here, Talbot interferometry data together with ray-tracing simulations for a (+ - - +) four-reflection experimental arrangement are presented, wherein the first two reflections are in the DCM and the final fourth reflection is asymmetric at grazing exit. Analyses of the interferometry data combined with the simulations show that compared with the beam exiting the DCM a gain of 76% in the SCL was achieved, albeit with a factor of 20 reduction in flux density, which may not be a severe penalty at a synchrotron beamline. Previous efforts reported in the literature to increase the SCL that employed asymmetric crystal diffraction at grazing incidence are also discussed. A much reduced SCL is found presently in simulations wherein the same asymmetric crystal is set for grazing incidence instead of grazing exit. In addition, the present study is compared and contrasted with two other means of increasing the SCL. These are (i) focusing the beam onto an aperture to act as a secondary source, and (ii) allowing the beam to propagate in vacuum an additional distance along the beamline. [ABSTRACT FROM AUTHOR]

The six-coordinate ruthenium(II) porphyrin complexes (OEP)Ru(CO)(Q), (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrinato dianion; Q = quinoline, Qnl (2); quinine, QN (3)) have been prepared from (OEP)Ru(CO) (1) and characterized by MS, IR, UV–visible and 1H NMR spectroscopy. The X-ray crystal structure of 2 has been determined, which reveals quinoline coordination to Ru through the nitrogen atom. In the crystal packing of 2, the two Qnl groups of adjacent porphyrins are positioned relatively parallel to each other at a close distance of 3.30 Å, implying a relatively strong π-π interaction. The X-ray crystal structure of 1 was obtained, which revealed coordination of the water to the ruthenium center. By comparing the spectroscopic data for 1, 2 and 3, it was determined that the site of binding of QN to Ru is likely through the nitrogen atom of the quinoline moiety. The redox behavior of the complexes at a Pt working electrode studied in a CH2Cl2 solution with NBu4PF6 as support electrolyte by cyclic voltammetry revealed oxidations that are porphyrin-centered. [ABSTRACT FROM AUTHOR]

To fully exploit ultra-short X-ray pulse durations routinely available at X-ray free-electron lasers to follow out-of-equilibrium dynamics, inherent arrival time fluctuations of the X-ray pulse with an external perturbing laser pulse need to be measured. In this work, two methods of arrival time measurement were compared to measure the arrival time jitter of hard X-ray pulses. The methods were photoelectron streaking by a THz field and a transient refractive index change of a semiconductor. The methods were validated by shot-to-shot correction of a pump-probe transient reflectivity measurement. An ultimate shot-to-shot full width at half-maximum error between the devices of 19.2 ± 0.1 fs was measured. [ABSTRACT FROM AUTHOR]

The malaria parasite resides within erythrocytes during one stage of its life cycle. During this intraerythrocytic period, the parasite ingests the erythrocyte cytoplasm and digests approximately two-thirds of the host cell hemoglobin. This digestion occurs within a lysosome-like organelle called the digestive vacuole. Several proteases are localized to the digestive vacuole and these proteases sequentially breakdown hemoglobin into small peptides, dipeptides, and amino acids. The peptides are exported into the host cytoplasm via the chloroquine-resistance transporter and an amino acid transporter has also been identified on the digestive vacuole membrane. The environment of the digestive vacuole also provides appropriate conditions for the biocrystallization of toxic heme into non-toxic hemozoin by a poorly understood process. Hemozoin formation is an attribute of Plasmodium and Haemoproteus and is not exhibited by other intraerythrocytic protozoan parasites. The efficient degradation of hemoglobin and detoxification of heme likely plays a major role in the high level of replication exhibited by malaria parasites within erythrocytes. Unique features of the digestive vacuole and the critical importance of nutrient acquisition provide therapeutic targets for the treatment of malaria. [ABSTRACT FROM AUTHOR]

The SIRIUS beamline of Synchrotron SOLEIL is dedicated to X-ray scattering and spectroscopy of surfaces and interfaces, covering the tender to mid-hard X-ray range (1.1-13 keV). The beamline has hosted a wide range of experiments in the field of soft interfaces and beyond, providing various grazing-incidence techniques such as diffraction and wide-angle scattering (GIXD/GIWAXS), small-angle scattering (GISAXS) and X-ray fluorescence in total reflection (TXRF). SIRIUS also offers specific sample environments tailored for in situ complementary experiments on solid and liquid surfaces. Recently, the beamline has added compound refractive lenses associated with a transfocator, allowing for the X-ray beam to be focused down to 10 μm × 10 μm while maintaining a reasonable flux on the sample. This new feature opens up new possibilities for faster GIXD measurements at the liquid-air interface and for measurements on samples with narrow geometries. [ABSTRACT FROM AUTHOR]

The African Light Source (AfLS) project is now almost eight years old. This article assesses the history, current context and future of the project. There is by now considerable momentum in building the user community, including deep training, facilitating access to current facilities, growing the scientific output, scientific networks and growing the local laboratory-scale research infrastructure. The Conceptual Design Report for the AfLS is in its final editing stages. This document specifies the socio-economic and scientific rationales and the technical aspects amongst others. The AfLS is supported by many national and Pan-African scientific professional bodies and voluntary associates across many scientific disciplines, and there are stakeholders throughout the continent and beyond. The current roadmap phases have expanded to include national and Pan-African level conversations with policy makers through new Strategic Task Force groups. The document summarizes this progress and discusses the future of the project. [ABSTRACT FROM AUTHOR]

2D conjugated polymers (2DCPs) possess extended in-plane π-conjugated lattice and out-of-plane π-π stacking, which results in enhanced electronic performance and potentially unique band structures. These properties, along with predesignability, well-defined channels, easy postmodification, and order structure attract extensive attention from material science to organic electronics. In this review, the recent advance in the interfacial synthesis and conductivity tuning strategies of 2DCP thin films, as well as their application in organic electronics is summarized. Furthermore, it is shown that, by combining topology structure design and targeted conductivity adjustment, researchers have fabricated 2DCP thin films with predesigned active groups, highly ordered structures, and enhanced conductivity. These films exhibit great potential for various thin-film organic electronics, such as organic transistors, memristors, electrochromism, chemiresistors, and photodetectors. Finally, the future research directions and perspectives of 2DCPs are discussed in terms of the interfacial synthetic design and structure engineering for the fabrication of fully conjugated 2DCP thin films, as well as the functional manipulation of conductivity to advance their applications in future organic electronics., (© 2024 Wiley‐VCH GmbH.)

This model discussion focuses on links between the unique properties of relaxor ceramics and the basics of Critical Phenomena Physics and Glass Transition Physics. It indicates the significance of uniaxiality for the appearance of mean-field type features near the paraelectric-to-ferroelectric phase transition. Pretransitional fluctuations, that are increasing up to the size of a grain and leading to inter-grain, random, local electric fields are responsible for relaxor ceramics characteristics. Their impact yields the pseudospinodal behavior associated with "weakly discontinuous" local phase transitions. The emerging model redefines the meaning of the Burns temperature and polar nanoregions (PNRs). It offers a coherent explanation of "dielectric constant" changes with the "diffused maximum" near the paraelectric-to-ferroelectric transition, the sensitivity to moderate electric fields (tunability), and the "glassy" dynamics. These considerations are challenged by the experimental results of complex dielectric permittivity studies in a Ba0.65Sr0.35TiO3 relaxor ceramic, covering ca. 250 K, from the paraelectric to the "deep" ferroelectric phase. The distortion-sensitive and derivative-based analysis in the paraelectric phase and the surrounding paraelectric-to-ferroelectric transition reveal a preference for the exponential scaling pattern for ε(T) changes. This may suggest that Griffith-phase behavior is associated with mean-field criticality disturbed by random local impacts. The preference for the universalistic "critical & activated" evolution of the primary relaxation time is shown for dynamics. The discussion is supplemented by a coupled energy loss analysis. The electric field-related tunability studies lead to scaling relationships describing their temperature changes. [ABSTRACT FROM AUTHOR]

The present review places emphasis on a comprehensive survey of experimental techniques to probe the structural and morphological features at the nanoscale range in thin magnetic films, incorporating those available at in-house laboratories as well as those at state-of-the-art synchrotron radiation facilities. This elucidating the range of available techniques, and the information they can yield represents a step for advancing the understanding of and for unlocking new possibilities in the design and optimization of thin magnetic films across a wide range of applications. [ABSTRACT FROM AUTHOR]

A series of heterocyclic chloroquine hybrids, containing a chain of two carbon atoms at position four of the quinolinic chain and acting as a link between quinoline and several benzoyl groups, is synthesized and screened in vitro as an inhibitor of β-hematin formation and in vivo for its antimalarial activity against chloroquine-sensitive strains of Plasmodium berghei ANKA in this study. The compounds significantly reduced haeme crystallization, with IC50 values < 10 µM. The values were comparable to chloroquine's, with an IC50 of 1.50 ± 0.01 µM. The compounds 4c and 4e prolonged the average survival time of the infected mice to 16.7 ± 2.16 and 14.4 ± 1.20 days, respectively. We also studied the effect of the compounds 4b, 4c, and 4e on another important human parasite, Leishmania mexicana, which is responsible for cutaneous leishmaniasis, demonstrating a potential leishmanicidal effect against promasigotes, with an IC50 < 10 µM. Concerning the possible mechanism of action of these compounds on Lesihmania mexicana, we performed experiments demonstrating that these three compounds could induce the collapse of the parasite mitochondrial electrochemical membrane potential (Δφ). The in vitro cytotoxicity assays against mammalian cancerous and noncancerous human cell lines showed that the studied compounds exhibit low cytotoxic effects. The ADME/Tox analysis predicted moderate lipophilicity values, low unbound fraction values, and a poor distribution for these compounds. Therefore, moderate bioavailability was expected. We calculated other molecular descriptors, such as the topological polar surface area, according to Veber's rules, and except for 2 and 4i, the rest of the compounds violated this descriptor, demonstrating the low antimalarial activity of our compounds in vivo. [ABSTRACT FROM AUTHOR]

The commonly quoted bistable Higgs potential is not a proper description of the Higgs field because, among other technical reasons, one of its stable states acquires a negative expectation value in vacuum. We rely on formal catastrophe theory to derive the form of the Higgs potential that admits only one positive mean value in vacuum. No symmetry is broken during the ensuing phase transition that assigns mass to the Higgs field; only gauge redundancy is "broken" by the appearance of phase in the massive state, but this redundancy is not a true symmetry of the massless field. Furthermore, a secondary, certainly amusing conclusion, is that, in its high-energy state, the field oscillates about its potential minimum between positive and negative masses, but it is doubtful that such evanescent states can survive below the critical temperature of 159.5 GeV, where the known particles were actually created. [ABSTRACT FROM AUTHOR]

In this communication, we describe the application of Boltzmann kinetic equations for modeling massive electronic excitation in a silicon nanocrystal film after its irradiation with intense femtosecond hard X-ray pulses. This analysis was inspired by an experiment recently performed at the X-ray free-electron laser facility SACLA, which measured a significant reduction in atomic scattering factors triggered by an X-ray pulse of the intensity ∼ 10 19 W/cm 2 , occurring on a timescale comparable with the X-ray pulse duration (6 fs full width at half maximum). We show that a Boltzmann kinetic equation solver can accurately follow the details of the electronic excitation in silicon atoms caused by such a hard X-ray pulse, yielding predictions in very good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The advent of next-generation synchrotron radiation sources and X-ray freeelectron lasers calls for high-quality Bragg-diffraction crystal optics to preserve the X-ray beam coherence and wavefront. This requirement brings new challenges in characterizing crystals in Bragg diffraction in terms of Bragg-plane height errors and wavefront phase distortions. Here, a quantitative methodology to characterize crystal optics using a state-of-the-art at-wavelength wavefront sensing technique and statistical analysis is proposed. The method was tested at the 1-BM-B optics testing beamline at the Advanced Photon Source for measuring silicon and diamond crystals in a self-referencing single-crystal mode and an absolute double-crystal mode. The phase error sensitivity of the technique is demonstrated to be at the λ/100 level required by most applications, such as the characterization of diamond crystals for cavity-based X-ray freeelectron lasers. [ABSTRACT FROM AUTHOR]

Self-seeded hard X-ray pulses at PAL-XFEL were used to commission a resonant X-ray emission spectroscopy experiment with a von Hamos spectrometer. The self-seeded beam, generated through forward Bragg diffraction of the [202] peak in a 100 mm-thick diamond crystal, exhibited an average bandwidth of 0.54 eVat 11.223 keV. A coordinated scanning scheme of electron bunch energy, diamond crystal angle and silicon monochromator allowed us to map the Ir Lβ2 X-ray emission lines of IrO2 powder across the Ir L3-absorption edge, from 11.212 to 11.242 keV with an energy step of 0.3 eV. This work provides a reference for hard X-ray emission spectroscopy experiments utilizing self-seeded pulses with a narrow bandwidth, eventually applicable for pump--probe studies in solid-state and diluted systems. [ABSTRACT FROM AUTHOR]

X-ray free electron lasers deliver photon pulses that are bright enough to observe diffraction from extremely small crystals at a time scale that outruns their destruction. As crystals are continuously replaced, this technique is termed serial femtosecond crystallography (SFX). Due to its high pulse repetition rate, the European XFEL enables the collection of rich and extensive data sets, which are suited to study various scientific problems, including ultra-fast processes. The enormous data rate, data complexity, and the nature of the pixelized multimodular area detectors at the European XFEL pose severe challenges to users. To streamline the analysis of the SFX data, we developed the semiautomated pipeline EXtra-Xwiz around the established CrystFEL program suite, thereby processing diffraction patterns on detector frames into structure factors. Here we present EXtra-Xwiz, and we introduce its architecture and use by means of a tutorial. Future plans for its development and expansion are also discussed. [ABSTRACT FROM AUTHOR]

Water is one of the most essential substances for life on Earth and plays a vital role in both natural and technological processes. Recently, there has been growing interest in studying the behavior of water molecules in confined spaces, particularly in low‐dimensional materials and structures. Regardless of whether it is in the form of gas, liquid, or solid, water can interact and form interfaces with many low‐dimensional structures. Given the current controversial understanding of two‐dimensional (2D) ice and the increasing interplay between water/ice and 2D materials such as graphene and transition‐metal dichalcogenides, we provide a brief overview of recent progresses on the interfaces of 2D ice and 2D van der Waals layered materials. This review highlights their potential contributions to the breakthroughs in tribology, membrane technology, nanofluidic, and nanodevice applications. Of particular interest is the recent discovery of ultrahigh lubricity between 2D ice and 2D layered materials, as well as the ability to modulate the surface adhesion between layers. These findings have the potential to enable new technological advances in both electronics and various industries. Meanwhile, this rapidly evolving field presents its own challenges, and we also discuss future directions for exploiting the interactions between 2D ice and 2D layered materials. [ABSTRACT FROM AUTHOR]