s: The Dismissal of New Female CEOs: A Role Congruity Perspective By www.newswise.com Published On :: Wed, 13 Nov 2024 06:30:24 EST Full Article
s: Who Learns Fastest, Wins: Lean Startup and Discovery Driven Growth By www.newswise.com Published On :: Wed, 06 Nov 2024 09:55:44 EST Full Article
s: Religion in Family Firms: A Socioemotional Wealth Perspective on Top-Level Executives with Perceived Religiosity By www.newswise.com Published On :: Fri, 08 Nov 2024 09:10:54 EST Full Article
s: US: N. Korea Sent 10,000 Troops to Russia By world.kbs.co.kr Published On :: Tue, 29 Oct 2024 10:12:16 +0900 [Inter-Korea] : The U.S. Department of Defense said North Korea has sent around ten-thousand troops to Russia and some of them have already moved closer to Ukraine. Pentagon spokesperson Sabrina Singh told reporters on Monday that Washington believes the North has sent about ten-thousand troops to eastern Russia for ...[more...] Full Article Inter-Korea
s: NIS: Some N. Korean Troops May Be on Front Lines of Russia-Ukraine War By world.kbs.co.kr Published On :: Tue, 29 Oct 2024 14:33:34 +0900 [Inter-Korea] : South Korea’s intelligence agency believes some of the North Korean troops deployed to Russia in support of its military offensive in Ukraine may have been transported to the front lines, including high-ranking generals. According to senior members of the rival political parties on the parliamentary ...[more...] Full Article Inter-Korea
s: JCS: N. Korea Likely Fired ICBM at High Angle By world.kbs.co.kr Published On :: Thu, 31 Oct 2024 07:32:33 +0900 [Inter-Korea] : South Korea’s Joint Chiefs of Staff(JCS) suspects that North Korea fired an intercontinental ballistic missile(ICBM) toward the East Sea on Thursday morning. The JCS said it detected the launch from the Pyongyang area around 7:10 a.m., adding the missile was fired at a steep angle and flew about ...[more...] Full Article Inter-Korea
s: JCS: N. Korea May Have Fired New Solid-Fuel ICBM Using 12-Axle TEL By world.kbs.co.kr Published On :: Thu, 31 Oct 2024 14:57:14 +0900 [Inter-Korea] : The South Korean military said North Korea may have fired a new solid-fuel intercontinental ballistic missile(ICBM) on Thursday, using the recently unveiled 12-axle transporter erector launcher(TEL). At a press briefing, Joint Chiefs of Staff(JCS) spokesperson Lee Sung-joon shared the early-stage ...[more...] Full Article Inter-Korea
s: JCS: N. Korea Continues GPS Jamming Attacks on S. Korea for 2nd Day By world.kbs.co.kr Published On :: Sat, 09 Nov 2024 13:47:48 +0900 [Inter-Korea] : North Korea continues GPS jamming attacks against South Korea for the second day since Friday. According to Seoul's Joint Chiefs of Staff(JCS) on Saturday, the GPS jamming provocations from the North's Haeju and Gaeseong regions have disrupted the operations of dozens of South Korean vessels and civilian ...[more...] Full Article Inter-Korea
s: US Experts: Uranium Enrichment Facility Images Released by N. Korea Differs from that of 2010 By world.kbs.co.kr Published On :: Thu, 19 Sep 2024 17:55:20 +0900 [Science] : Two U.S. experts who inspected North Korea’s uranium enrichment facility at the Yongbyon nuclear complex in 2010 have analyzed recent images of a similar facility in the North and pointed out differences. Stanford University professor emeritus Siegfried Hecker and Robert Carlin, a scholar at the ...[more...] Full Article Science
s: Reuters: Trump Heading to Palm Beach Convention Center to Meet Supporters By world.kbs.co.kr Published On :: Wed, 06 Nov 2024 15:26:15 +0900 [International] : U.S. Republican presidential nominee Donald Trump is reportedly heading to the Palm Beach County Convention Center in Florida to address his supporters at an election night rally. That is according to Reuters on Wednesday, citing an unnamed official from the former president’s election camp. Trump, ...[more...] Full Article International
s: Reports: 50,000 Russian, N. Korean Troops Preparing to Attack By world.kbs.co.kr Published On :: Mon, 11 Nov 2024 09:57:14 +0900 [International] : The Russian military has reportedly assembled a force of 50-thousand soldiers, including North Korean troops, to carry out an assault with the goal of reclaiming territory in Russia’s Kursk region. Quoting a U.S. official on Sunday, CNN said Russia has amassed tens of thousands of troops to carry out ...[more...] Full Article International
s: Goldman Sachs: Trump Tariff Threat Looms Large By world.kbs.co.kr Published On :: Tue, 12 Nov 2024 11:50:28 +0900 [International] : The U.S. investment bank Goldman Sachs has projected higher tariffs as a result of Donald Trump’s U.S. election victory, not only for China but also for South Korea, Taiwan and other Asian countries. According to the U.S. broadcaster CBNC on Monday, Andrew Tilton, Goldman’s chief Asia-Pacific economist, ...[more...] Full Article International
s: Scallions vs. Green Onions: What's the Difference? By recipes.howstuffworks.com Published On :: Tue, 16 Jul 2024 11:45:18 -0400 You've probably seen people and recipes use the terms "scallions" and "green onions" interchangeably — and for once, the conflation is correct. When it comes to distinguishing scallions vs. green onions, these terms describe the same vegetable. Full Article
s: How to Get Sap Out of Clothes: Step-by-step Instructions By home.howstuffworks.com Published On :: Thu, 31 Oct 2024 10:05:02 -0400 Ah, tree sap: the ultimate sticky situation. Whether it's from a hike through the woods or after decorating a Christmas tree, tree sap can cling to your clothes like a magnet. Learning how to get sap out of clothes is essential, especially if you live or work near an area with a lot of trees. Full Article
s: What to Do With Old Computers: 3 Responsible Options By computer.howstuffworks.com Published On :: Wed, 12 Jun 2024 11:58:23 -0400 After years of hard work and loyalty, some computers must finally retire. But since they can't take a pension and move to Florida, where do old computers end up? Full Article
s: Top Private Search Engines: Comparing 5 Competitors By computer.howstuffworks.com Published On :: Tue, 16 Jul 2024 11:44:29 -0400 In the realm of online privacy, private search engines provide a shield against intrusive tracking and data collection. Let's explore five prominent options. Full Article
s: Google Easter Eggs: Sweet Treats Hidden in Plain Sight By computer.howstuffworks.com Published On :: Fri, 26 Jul 2024 10:10:02 -0400 Google is home to a ton of super fun hidden Easter eggs you can check out right from your browser. Go ahead, try a couple. You won't be disappointed. Full Article
s: Emotional Cancer Meets Free-Spirited Aquarius: Compatibility Breakdown By entertainment.howstuffworks.com Published On :: Fri, 08 Nov 2024 05:30:03 -0500 Discover the compatibility between Cancer and Aquarius in love, friendship, and relationships. Learn how their emotional and intellectual traits align or clash. Full Article
s: Aquarius Moon Traits: Understanding the Emotional Landscape By entertainment.howstuffworks.com Published On :: Sat, 09 Nov 2024 05:30:03 -0500 Explore the Aquarius Moon's traits, emotional depth, and how it influences relationships, creativity, and personal growth in astrology. Unlock its mysterious power. Full Article
s: Zodiac Signs Elements: Discover the Power Behind Each Element By entertainment.howstuffworks.com Published On :: Wed, 13 Nov 2024 05:30:03 -0500 Discover the unique traits of each zodiac element—fire, earth, air, and water. Uncover how these elements shape personalities and compatibility in astrology. Full Article
s: Moving stones: faults, slopes and sediments - British Geological Survey By news.google.com Published On :: Fri, 12 Jan 2024 08:00:00 GMT Moving stones: faults, slopes and sediments British Geological Survey Full Article
s: A contribution to the crystal chemistry and topology of organic thiosulfates: bis(1-methylpiperazinium)·S2O3·H2O versus 1-methylpiperazinediium·S2O3·3H2O By journals.iucr.org Published On :: Crystal structure and topology of two new thiosulfates formed with mono- and diprotonated species of 1-methylpiperazine is reported. Full Article text
s: Polymorph sampling with coupling to extended variables: enhanced sampling of polymorph energy landscapes and free energy perturbation of polymorph ensembles By journals.iucr.org Published On :: 2024-10-15 A novel approach to computationally enhance the sampling of molecular crystal structures is proposed and tested. This method is based on the use of extended variables coupled to a Monte Carlo based crystal polymorph generator. Inspired by the established technique of quasi-random sampling of polymorphs using the rigid molecule constraint, this approach represents molecular clusters as extended variables within a thermal reservoir. Polymorph unit-cell variables are generated using pseudo-random sampling. Within this framework, a harmonic coupling between the extended variables and polymorph configurations is established. The extended variables remain fixed during the inner loop dedicated to polymorph sampling, enforcing a stepwise propagation of the extended variables to maintain system exploration. The final processing step results in a polymorph energy landscape, where the raw structures sampled to create the extended variable trajectory are re-optimized without the thermal coupling term. The foundational principles of this approach are described and its effectiveness using both a Metropolis Monte Carlo type algorithm and modifications that incorporate replica exchange is demonstrated. A comparison is provided with pseudo-random sampling of polymorphs for the molecule coumarin. The choice to test a design of this algorithm as relevant for enhanced sampling of crystal structures was due to the obvious relation between molecular structure variables and corresponding crystal polymorphs as representative of the inherent vapor to crystal transitions that exist in nature. Additionally, it is shown that the trajectories of extended variables can be harnessed to extract fluctuation properties that can lead to valuable insights. A novel thermodynamic variable is introduced: the free energy difference between ensembles of Z' = 1 and Z' = 2 crystal polymorphs. Full Article text
s: Preparing research samples for safe arrival at centers and facilities: recipes for successful experiments By journals.iucr.org Published On :: 2024-07-11 Preparation of biomacromolecules for structural biology studies is a complex and time-consuming process. The goal is to produce a highly concentrated, highly pure product that is often shipped to large facilities with tools to prepare the samples for crystallization trials or for measurements at synchrotrons and cryoEM centers. The aim of this article is to provide guidance and to discuss general considerations for shipping biomacromolecular samples. Details are also provided about shipping samples for specific experiment types, including solution- and cryogenic-based techniques. These guidelines are provided with the hope that the time and energy invested in sample preparation is not lost due to shipping logistics. Full Article text
s: Towards expansion of the MATTS data bank with heavier elements: the influence of the wavefunction basis set on the multipole model derived from the wavefunction By journals.iucr.org Published On :: This study examines the quality of charge density obtained by fitting the multipole model to wavefunctions in different basis sets. The complex analysis reveals that changing the basis set quality from double- to triple-zeta can notably improve the charge density related properties of a multipole model. Full Article text
s: PyFaults: a Python tool for stacking fault screening By journals.iucr.org Published On :: Here, an open-source Python library for identifying and screening potential stacking fault models in crystalline materials with planar disorder is presented. Full Article text
s: Optimal operation guidelines for direct recovery of high-purity precursor from spent lithium-ion batteries: hybrid operation model of population balance equation and data-driven classifier By journals.iucr.org Published On :: This study proposes an operation optimization framework for impurity-free recycling of spent lithium-ion batteries. Using a hybrid population balance equation integrated with a data-driven condition classifier, the study firstly identifies the optimal batch and semi-batch operation conditions that significantly reduce the operation time with 100% purity of product; detailed guidelines are given for industrial applications. Full Article text
s: Stability of inorganic ionic structures: the uniformity approach By journals.iucr.org Published On :: 2024-10-14 The crystal structure uniformity is numerically estimated as the standard deviation of the crystal space quantizer 〈G3〉. This criterion has been applied to explore the uniformity of ionic sublattices in 21465 crystal structures of inorganic ionic compounds. In most cases, at least one kind of sublattice (whole ionic lattice, cationic or anionic sublattice) was found to be highly uniform with a small 〈G3〉 value. Non-uniform structures appeared to be either erroneous or essentially non-ionic. As a result, a set of uniformity criteria is proposed for the estimation of the stability of ionic crystal structures. Full Article text
s: DOMAS: a data management software framework for advanced light sources By journals.iucr.org Published On :: 2024-02-01 In recent years, China's advanced light sources have entered a period of rapid construction and development. As modern X-ray detectors and data acquisition technologies advance, these facilities are expected to generate massive volumes of data annually, presenting significant challenges in data management and utilization. These challenges encompass data storage, metadata handling, data transfer and user data access. In response, the Data Organization Management Access Software (DOMAS) has been designed as a framework to address these issues. DOMAS encapsulates four fundamental modules of data management software, including metadata catalogue, metadata acquisition, data transfer and data service. For light source facilities, building a data management system only requires parameter configuration and minimal code development within DOMAS. This paper firstly discusses the development of advanced light sources in China and the associated demands and challenges in data management, prompting a reconsideration of data management software framework design. It then outlines the architecture of the framework, detailing its components and functions. Lastly, it highlights the application progress and effectiveness of DOMAS when deployed for the High Energy Photon Source (HEPS) and Beijing Synchrotron Radiation Facility (BSRF). Full Article text
s: Ion beam figuring for X-ray mirrors: history, state-of-the-art and future prospects By journals.iucr.org Published On :: 2024-05-21 Synchrotron light sources require X-ray optics with extremely demanding accuracy for the surface profile, with less than 100 nrad slope errors and sub-nanometre height errors. Such errors are challenging to achieve for aspheres using traditional polishing methods. However, post-polishing error correction can be performed using techniques such as ion beam figuring (IBF) to improve optics to the desired quality. This work presents a brief overview of the history of IBF, introduces some of the challenges for obtaining such demanding figure errors, and highlights the work done at several in-house IBF facilities at synchrotron light sources worldwide to obtain state-of-the-art optical quality. Full Article text
s: StreamSAXS: a Python-based workflow platform for processing streaming SAXS/WAXS data By journals.iucr.org Published On :: 2024-07-15 StreamSAXS is a Python-based small- and wide-angle X-ray scattering (SAXS/WAXS) data analysis workflow platform with graphical user interface (GUI). It aims to provide an interactive and user-friendly tool for analysis of both batch data files and real-time data streams. Users can easily create customizable workflows through the GUI to meet their specific needs. One characteristic of StreamSAXS is its plug-in framework, which enables developers to extend the built-in workflow tasks. Another feature is the support for both already acquired and real-time data sources, allowing StreamSAXS to function as an offline analysis platform or be integrated into large-scale acquisition systems for end-to-end data management. This paper presents the core design of StreamSAXS and provides user cases demonstrating its utilization for SAXS/WAXS data analysis in offline and online scenarios. Full Article text
s: BEATS: BEAmline for synchrotron X-ray microTomography at SESAME By journals.iucr.org Published On :: 2024-07-15 The ID10 beamline of the SESAME (Synchrotron-light for Experimental Science and Applications in the Middle East) synchrotron light source in Jordan was inaugurated in June 2023 and is now open to scientific users. The beamline, which was designed and installed within the European Horizon 2020 project BEAmline for Tomography at SESAME (BEATS), provides full-field X-ray radiography and microtomography imaging with monochromatic or polychromatic X-rays up to photon energies of 100 keV. The photon source generated by a 2.9 T wavelength shifter with variable gap, and a double-multilayer monochromator system allow versatile application for experiments requiring either an X-ray beam with high intensity and flux, and/or a partially spatial coherent beam for phase-contrast applications. Sample manipulation and X-ray detection systems are designed to allow scanning samples with different size, weight and material, providing image voxel sizes from 13 µm down to 0.33 µm. A state-of-the-art computing infrastructure for data collection, three-dimensional (3D) image reconstruction and data analysis allows the visualization and exploration of results online within a few seconds from the completion of a scan. Insights from 3D X-ray imaging are key to the investigation of specimens from archaeology and cultural heritage, biology and health sciences, materials science and engineering, earth, environmental sciences and more. Microtomography scans and preliminary results obtained at the beamline demonstrate that the new beamline ID10-BEATS expands significantly the range of scientific applications that can be targeted at SESAME. Full Article text
s: Web-CONEXS: an inroad to theoretical X-ray absorption spectroscopy By journals.iucr.org Published On :: 2024-08-01 Accurate analysis of the rich information contained within X-ray spectra usually calls for detailed electronic structure theory simulations. However, density functional theory (DFT), time-dependent DFT and many-body perturbation theory calculations increasingly require the use of advanced codes running on high-performance computing (HPC) facilities. Consequently, many researchers who would like to augment their experimental work with such simulations are hampered by the compounding of nontrivial knowledge requirements, specialist training and significant time investment. To this end, we present Web-CONEXS, an intuitive graphical web application for democratizing electronic structure theory simulations. Web-CONEXS generates and submits simulation workflows for theoretical X-ray absorption and X-ray emission spectroscopy to a remote computing cluster. In the present form, Web-CONEXS interfaces with three software packages: ORCA, FDMNES and Quantum ESPRESSO, and an extensive materials database courtesy of the Materials Project API. These software packages have been selected to model diverse materials and properties. Web-CONEXS has been conceived with the novice user in mind; job submission is limited to a subset of simulation parameters. This ensures that much of the simulation complexity is lifted and preliminary theoretical results are generated faster. Web-CONEXS can be leveraged to support beam time proposals and serve as a platform for preliminary analysis of experimental data. Full Article text
s: RefXAS: an open access database of X-ray absorption spectra By journals.iucr.org Published On :: 2024-08-27 Under DAPHNE4NFDI, the X-ray absorption spectroscopy (XAS) reference database, RefXAS, has been set up. For this purpose, we developed a method to enable users to submit a raw dataset, with its associated metadata, via a dedicated website for inclusion in the database. Implementation of the database includes an upload of metadata to the scientific catalogue and an upload of files via object storage, with automated query capabilities through a web server and visualization of the data and files. Based on the mode of measurements, quality criteria have been formulated for the automated check of any uploaded data. In the present work, the significant metadata fields for reusability, as well as reproducibility of results (FAIR data principles), are discussed. Quality criteria for the data uploaded to the database have been formulated and assessed. Moreover, the usability and interoperability of available XAS data/file formats have been explored. The first version of the RefXAS database prototype is presented, which features a human verification procedure, currently being tested with a new user interface designed specifically for curators; a user-friendly landing page; a full list of datasets; advanced search capabilities; a streamlined upload process; and, finally, a server-side automatic authentication and (meta-) data storage via MongoDB, PostgreSQL and (data-) files via relevant APIs. Full Article text
s: α-d-2'-Deoxyadenosine, an irradiation product of canonical DNA and a component of anomeric nucleic acids: crystal structure, packing and Hirshfeld surface analysis By journals.iucr.org Published On :: 2024-01-22 α-d-2'-Deoxyribonucleosides are products of the γ-irradiation of DNA under oxygen-free conditions and are constituents of anomeric DNA. They are not found as natural building blocks of canonical DNA. Reports on their conformational properties are limited. Herein, the single-crystal X-ray structure of α-d-2'-deoxyadenosine (α-dA), C10H13N5O3, and its conformational parameters were determined. In the crystalline state, α-dA forms two conformers in the asymmetric unit which are connected by hydrogen bonds. The sugar moiety of each conformer is arranged in a `clamp'-like fashion with respect to the other conformer, forming hydrogen bonds to its nucleobase and sugar residue. For both conformers, a syn conformation of the nucleobase with respect to the sugar moiety was found. This is contrary to the anti conformation usually preferred by α-nucleosides. The sugar conformation of both conformers is C2'-endo, and the 5'-hydroxyl groups are in a +sc orientation, probably due to the hydrogen bonds formed by the conformers. The formation of the supramolecular assembly of α-dA is controlled by hydrogen bonding and stacking interactions, which was verified by a Hirshfeld and curvedness surface analysis. Chains of hydrogen-bonded nucleobases extend parallel to the b direction and are linked to equivalent chains by hydrogen bonds involving the sugar moieties to form a sheet. A comparison of the solid-state structures of the anomeric 2'-deoxyadenosines revealed significant differences of their conformational parameters. Full Article text
s: Relationship between synthesis method–crystal structure–melting properties in cocrystals: the case of caffeine–citric acid By journals.iucr.org Published On :: 2024-05-07 The influence of the crystal synthesis method on the crystallographic structure of caffeine–citric acid cocrystals was analyzed thanks to the synthesis of a new polymorphic form of the cocrystal. In order to compare the new form to the already known forms, the crystal structure of the new cocrystal (C8H10N4O2·C6H8O7) was solved by powder X-ray diffraction thanks to synchrotron experiments. The structure determination was performed using `GALLOP', a recently developed hybrid approach based on a local optimization with a particle swarm optimizer, particularly powerful when applied to the structure resolution of materials of pharmaceutical interest, compared to classical Monte-Carlo simulated annealing. The final structure was obtained through Rietveld refinement, and first-principles density functional theory (DFT) calculations were used to locate the H atoms. The symmetry is triclinic with the space group Poverline{1} and contains one molecule of caffeine and one molecule of citric acid per asymmetric unit. The crystallographic structure of this cocrystal involves different hydrogen-bond associations compared to the already known structures. The analysis of these hydrogen bonds indicates that the cocrystal obtained here is less stable than the cocrystals already identified in the literature. This analysis is confirmed by the determination of the melting point of this cocrystal, which is lower than that of the previously known cocrystals. Full Article text
s: Using cocrystals as a tool to study non-crystallizing molecules: crystal structure, Hirshfeld surface analysis and computational study of the 1:1 cocrystal of (E)-N-(3,4-difluorophenyl)-1-(pyridin-4-yl)methanimine and acetic By journals.iucr.org Published On :: 2024-07-05 Using a 1:1 cocrystal of (E)-N-(3,4-difluorophenyl)-1-(pyridin-4-yl)methanimine with acetic acid, C12H8F2N2·C2H4O2, we investigate the influence of F atoms introduced to the aromatic ring on promoting π–π interactions. The cocrystal crystallizes in the triclinic space group P1. Through crystallographic analysis and computational studies, we reveal the molecular arrangement within this cocrystal, demonstrating the presence of hydrogen bonding between the acetic acid molecule and the pyridyl group, along with π–π interactions between the aromatic rings. Our findings highlight the importance of F atoms in promoting π–π interactions without necessitating full halogenation of the aromatic ring. Full Article text
s: A brief review on computer simulations of chalcopyrite surfaces: structure and reactivity By journals.iucr.org Published On :: 2024-08-08 Chalcopyrite, the world's primary copper ore mineral, is abundant in Latin America. Copper extraction offers significant economic and social benefits due to its strategic importance across various industries. However, the hydrometallurgical route, considered more environmentally friendly for processing low-grade chalcopyrite ores, remains challenging, as does its concentration by froth flotation. This limited understanding stems from the poorly understood structure and reactivity of chalcopyrite surfaces. This study reviews recent contributions using density functional theory (DFT) calculations with periodic boundary conditions and slab models to elucidate chalcopyrite surface properties. Our analysis reveals that reconstructed surfaces preferentially expose S atoms at the topmost layer. Furthermore, some studies report the formation of disulfide groups (S22−) on pristine sulfur-terminated surfaces, accompanied by the reduction of Fe3+ to Fe2+, likely due to surface oxidation. Additionally, Fe sites are consistently identified as favourable adsorption locations for both oxygen (O2) and water (H2O) molecules. Finally, the potential of computer modelling for investigating collector–chalcopyrite surface interactions in the context of selective froth flotation is discussed, highlighting the need for further research in this area. Full Article text
s: Further evaluation of the shape of atomic Hirshfeld surfaces: M⋯H contacts and homoatomic bonds By journals.iucr.org Published On :: 2024-08-08 It is well known that Hirshfeld surfaces provide an easy and straightforward way of analysing intermolecular interactions in the crystal environment. The use of atomic Hirshfeld surfaces has also demonstrated that such surfaces carry information related to chemical bonds which allow a deeper evaluation of the structures. Here we briefly summarize the approach of atomic Hirshfeld surfaces while further evaluating the kind of information that can be retrieved from them. We show that the analysis of the metal-centre Hirshfeld surfaces from structures refined via Hirshfeld Atom Refinement (HAR) allow accurate evaluation of contacts of type M⋯H, and that such contacts can be related to the overall shape of the surfaces. The compounds analysed were tetraaquabis(3-carboxypropionato)metal(II), [M(C4H3O4)2(H2O)4], for metal(II)/M = manganese/Mn, cobalt/Co, nickel/Ni and zinc/Zn. We also evaluate the sensitivity of the surfaces by an investigation of seemingly flat surfaces through analysis of the curvature functions in the direction of C—C bonds. The obtained values not only demonstrate variations in curvature but also show a correlation with the hybridization of the C atoms involved in the bond. Full Article text
s: 2,4-Diarylpyrroles: synthesis, characterization and crystallographic insights By journals.iucr.org Published On :: 2024-08-08 Three 2,4-diarylpyrroles were synthesized starting from 4-nitrobutanones and the crystal structures of two derivatives were analysed. These are 4-(4-methoxyphenyl)-2-(thiophen-2-yl)-1H-pyrrole, C15H13NOS, and 3-(4-bromophenyl)-2-nitroso-5-phenyl-1H-pyrrole, C16H11BrN2O. Although pyrroles without substituents at the α-position with respect to the N atom are very air sensitive and tend to polymerize, we succeeded in growing an adequate crystal for X-ray diffraction analysis. Further derivatization using sodium nitrite afforded a nitrosyl pyrrole derivative, which crystallized in the triclinic space group Poverline{1} with Z = 6. Thus, herein we report the first crystal structure of a nitrosyl pyrrole. Interestingly, the co-operative hydrogen bonds in this NO-substituted pyrrole lead to a trimeric structure with bifurcated halogen bonds at the ends, forming a two-dimensional (2D) layer with interstitial voids having a radius of 5 Å, similar to some reported macrocyclic porphyrins. Full Article text
s: Salt forms of amides: protonation of acetanilide By journals.iucr.org Published On :: 2024-08-06 Treating the amide acetanilide (N-phenylacetamide, C8H9NO) with aqueous strong acids allowed the structures of five hemi-protonated salt forms of acetanilide to be elucidated. N-(1-Hydroxyethylidene)anilinium chloride–N-phenylacetamide (1/1), [(C8H9NO)2H][Cl], and the bromide, [(C8H9NO)2H][Br], triiodide, [(C8H9NO)2H][I3], tetrafluoroborate, [(C8H9NO)2H][BF4], and diiodobromide hemi(diiodine), [(C8H9NO)2H][I2Br]·0.5I2, analogues all feature centrosymmetric dimeric units linked by O—H⋯O hydrogen bonds that extend into one-dimensional hydrogen-bonded chains through N—H⋯X interactions, where X is the halide atom of the anion. Protonation occurs at the amide O atom and results in systematic lengthening of the C=O bond and a corresponding shortening of the C—N bond. The size of these geometric changes is similar to those found for hemi-protonated paracetamol structures, but less than those in fully protonated paracetamol structures. The bond angles of the amide fragments are also found to change on protonation, but these angular changes are also influenced by conformation, namely, whether the amide group is coplanar with the phenyl ring or twisted out of plane. Full Article text
s: From femtoseconds to minutes: time-resolved macromolecular crystallography at XFELs and synchrotrons By journals.iucr.org Published On :: 2024-01-24 Over the last decade, the development of time-resolved serial crystallography (TR-SX) at X-ray free-electron lasers (XFELs) and synchrotrons has allowed researchers to study phenomena occurring in proteins on the femtosecond-to-minute timescale, taking advantage of many technical and methodological breakthroughs. Protein crystals of various sizes are presented to the X-ray beam in either a static or a moving medium. Photoactive proteins were naturally the initial systems to be studied in TR-SX experiments using pump–probe schemes, where the pump is a pulse of visible light. Other reaction initiations through small-molecule diffusion are gaining momentum. Here, selected examples of XFEL and synchrotron time-resolved crystallography studies will be used to highlight the specificities of the various instruments and methods with respect to time resolution, and are compared with cryo-trapping studies. Full Article text
s: Persistence of atoms in molecules: there is room beyond electron densities By journals.iucr.org Published On :: 2024-02-20 Evidence that the electronic structure of atoms persists in molecules to a much greater extent than has been usually admitted is presented. This is achieved by resorting to N-electron real-space descriptors instead of one- or at most two-particle projections like the electron or exchange-correlation densities. Here, the 3N-dimensional maxima of the square of the wavefunction, the so-called Born maxima, are used. Since this technique is relatively unknown to the crystallographic community, a case-based approach is taken, revisiting first the Born maxima of atoms in their ground state and then some of their excited states. It is shown how they survive in molecules and that, beyond any doubt, the distribution of electrons around an atom in a molecule can be recognized as that of its isolated, in many cases excited, counterpart, relating this fact with the concept of energetic promotion. Several other cases that exemplify the applicability of the technique to solve chemical bonding conflicts and to introduce predictability in real-space analyses are also examined. Full Article text
s: Analysis of COF-300 synthesis: probing degradation processes and 3D electron diffraction structure By journals.iucr.org Published On :: 2024-05-10 Although COF-300 is often used as an example to study the synthesis and structure of (3D) covalent organic frameworks (COFs), knowledge of the underlying synthetic processes is still fragmented. Here, an optimized synthetic procedure based on a combination of linker protection and modulation was applied. Using this approach, the influence of time and temperature on the synthesis of COF-300 was studied. Synthesis times that were too short produced materials with limited crystallinity and porosity, lacking the typical pore flexibility associated with COF-300. On the other hand, synthesis times that were too long could be characterized by loss of crystallinity and pore order by degradation of the tetrakis(4-aminophenyl)methane (TAM) linker used. The presence of the degradation product was confirmed by visual inspection, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). As TAM is by far the most popular linker for the synthesis of 3D COFs, this degradation process might be one of the reasons why the development of 3D COFs is still lagging compared with 2D COFs. However, COF crystals obtained via an optimized procedure could be structurally probed using 3D electron diffraction (3DED). The 3DED analysis resulted in a full structure determination of COF-300 at atomic resolution with satisfying data parameters. Comparison of our 3DED-derived structural model with previously reported single-crystal X-ray diffraction data for this material, as well as parameters derived from the Cambridge Structural Database, demonstrates the high accuracy of the 3DED method for structure determination. This validation might accelerate the exploitation of 3DED as a structure determination technique for COFs and other porous materials. Full Article text
s: Statistical optimization of guest uptake in crystalline sponges: grading structural outcomes By journals.iucr.org Published On :: 2024-06-12 Investigation of the analyte soaking conditions on the crystalline sponge {[(ZnI2)3(tpt)2·x(solvent)]n} method using a statistical design of experiments model has provided fundamental insights into the influence of experimental variables. This approach focuses on a single analyte tested via 60 experiments (20 unique conditions) to identify the main effects for success and overall guest structure quality. This is employed as a basis for the development of a novel molecular structure grading system that enables the quantification of guest exchange quality. Full Article text
s: Crossing length scales: X-ray approaches to studying the structure of biological materials By journals.iucr.org Published On :: 2024-08-28 Biological materials have outstanding properties. With ease, challenging mechanical, optical or electrical properties are realised from comparatively `humble' building blocks. The key strategy to realise these properties is through extensive hierarchical structuring of the material from the millimetre to the nanometre scale in 3D. Though hierarchical structuring in biological materials has long been recognized, the 3D characterization of such structures remains a challenge. To understand the behaviour of materials, multimodal and multi-scale characterization approaches are needed. In this review, we outline current X-ray analysis approaches using the structures of bone and shells as examples. We show how recent advances have aided our understanding of hierarchical structures and their functions, and how these could be exploited for future research directions. We also discuss current roadblocks including radiation damage, data quantity and sample preparation, as well as strategies to address them. Full Article text
s: Roodmus: a toolkit for benchmarking heterogeneous electron cryo-microscopy reconstructions By journals.iucr.org Published On :: 2024-10-15 Conformational heterogeneity of biological macromolecules is a challenge in single-particle averaging (SPA). Current standard practice is to employ classification and filtering methods that may allow a discrete number of conformational states to be reconstructed. However, the conformation space accessible to these molecules is continuous and, therefore, explored incompletely by a small number of discrete classes. Recently developed heterogeneous reconstruction algorithms (HRAs) to analyse continuous heterogeneity rely on machine-learning methods that employ low-dimensional latent space representations. The non-linear nature of many of these methods poses a challenge to their validation and interpretation and to identifying functionally relevant conformational trajectories. These methods would benefit from in-depth benchmarking using high-quality synthetic data and concomitant ground truth information. We present a framework for the simulation and subsequent analysis with respect to the ground truth of cryo-EM micrographs containing particles whose conformational heterogeneity is sourced from molecular dynamics simulations. These synthetic data can be processed as if they were experimental data, allowing aspects of standard SPA workflows as well as heterogeneous reconstruction methods to be compared with known ground truth using available utilities. The simulation and analysis of several such datasets are demonstrated and an initial investigation into HRAs is presented. Full Article text
s: Lattice response to the radiation damage of molecular crystals: radiation-induced versus thermal expansivity By journals.iucr.org Published On :: 2024-01-04 The interaction of intense synchrotron radiation with molecular crystals frequently modifies the crystal structure by breaking bonds, producing fragments and, hence, inducing disorder. Here, a second-rank tensor of radiation-induced lattice strain is proposed to characterize the structural susceptibility to radiation. Quantitative estimates are derived using a linear response approximation from experimental data collected on three materials Hg(NO3)2(PPh3)2, Hg(CN)2(PPh3)2 and BiPh3 [PPh3 = triphenylphosphine, P(C6H5)3; Ph = phenyl, C6H5], and are compared with the corresponding thermal expansivities. The associated eigenvalues and eigenvectors show that the two tensors are not the same and therefore probe truly different structural responses. The tensor of radiative expansion serves as a measure of the susceptibility of crystal structures to radiation damage. Full Article text
s: Three-dimensional electron diffraction on clinkers: the belite α'H incommensurate modulated structure By journals.iucr.org Published On :: 2024-03-06 Traditional X-ray methods are extensively applied to commercial cement samples in order to determine their physical and chemical properties. Powder patterns are routinely used to quantify the composition of these phase mixtures, but structure determination becomes difficult because of reflection overlapping caused by the high number of different crystal structures. The fast-growing 3D electron diffraction technique and its related automated acquisition protocols arise as a potentially very interesting tool for the cement industry, since they enable the fast and systematic acquisition of diffraction data from individual particles. In this context, electron diffraction has been used in the investigation of the different crystalline phases present in various commercial clinkers for cement. Automated data collection procedures and subsequent data processing have enabled the structural characterization of the different crystal structures from which the α'H polymorph of Ca2SiO4 (belite) exhibited satellite reflections. Its average crystal structure has been known since 1971 and satellite reflections have been reported previously, yet the modulation was never fully described by means of the superspace formalism. Here, the incommensurately modulated structure is solved and refined using harmonic and crenel functions in the superspace group Pnma(α00)0ss, showing the potential of 3D electron diffraction for systematic crystallographic characterizations of cement. A full description of the different belite polymorphs is provided considering this modulated structure. Full Article text
s: Following the guidelines for communicating commensurate magnetic structures: real case examples By journals.iucr.org Published On :: 2024-07-17 A few real case examples are presented on how to report magnetic structures, with precise step-by-step explanations, following the guidelines of the IUCr Commission on Magnetic Structures [Perez-Mato et al. (2024). Acta Cryst. B80, 219–234]. Four examples have been chosen, illustrating different types of single-k magnetic orders, from the basic case to more complex ones, including odd-harmonics, and one multi-k order. In addition to acquainting researchers with the process of communicating commensurate magnetic structures, these examples also aim to clarify important concepts, which are used throughout the guidelines, such as the transformation to a standard setting of a magnetic space group. Full Article text