Second-generation ruthenium olefin metathesis catalysts were investigated with systematic variation of the unsymmetrical uNHC ligands. Depending on the uNHC steric bulk, the catalysts exhibited ...different activity and selectivity in metathesis reactions. DFT calculations and X-ray crystallographic data were used to understand the influence of uNHC ligand structure on the catalyst properties. Furthermore, the catalysts were examined in the context of reactions that are problematic for general-purpose Ru catalysts, including industrially important self-cross metathesis of α-olefins and ethenolysis of ethyl oleate.
The regulatory function of Article 199a Tax Ordinance Act, hereinafter: T.O. is to supplement tax authoritiescompetences deriving from other regulations of evidence proceeding to establish the facts. ...Determination of a transaction hidden under apparently correct fiscal and legal state of affairs results in consequences that can be seen in private law, tax law and, ultimately, penal fiscal law. The purpose of the paper is to point out to inter-dependencies that relate to final decisions and to the whole process of decision taking in the above-mentioned aspects of application of law.
As an emerging class of flexible materials, mechanically bendable molecular crystals are broadly classified as elastic or plastic. Nevertheless, flexible organic crystals with mutually exclusive ...elastic and plastic traits, with contrasting structural requirements, co-existing under different stress settings are exceptional; hence, it is imperative to establish the concurring factors that beget this rare occurrence. We report a series of halogen-substituted benzil crystals showing elastic bending (within ∼2.45% strain), followed by elastoplastic deformation under ambient conditions. Under higher stress settings, they display exceptional plastic flexibility that one could bend, twist, or even coil around a capillary tube. X-ray diffraction, microscopy, and computational data reveal the microscopic and macroscopic basis for the exciting co-existence of elastic, elastoplastic, and plastic properties in the crystals. The layered molecular arrangement and the weak dispersive interactions sustaining the interlayer region provide considerable tolerance towards breaking and making upon engaging or releasing the external stress; it enables restoring the original state within the elastic strain. Comparative studies with oxalate compounds, wherein the twisted diketo moiety in benzil was replaced with a rigid and coplanar central oxalate moiety, enabled us to understand the effect of the anisotropy factor on the crystal packing induced by the C&z.dbd;O C tetral interactions. The enhanced anisotropy depreciated the elastic domain, making the oxalate crystals more prone to plastic deformation. Three-point bending experiments and the determined Young's moduli further corroborate the co-existence of the elastic and plastic realm and highlight the critical role of the underlying structural elements that determine the elastic to plastic transformation. The work highlights the possible co-existence of orthogonal mechanical characteristics in molecular crystals and further construed the concurrent role of microscopic and macroscopic elements in attaining this exceptional mechanical trait.
Structural and mechanical studies of benzil and oxalate crystals highlight the microscopic and macroscopic basis for the co-existence of orthogonal mechanical traits and the elastic to plastic transformation under different stress settings.
This article is a retrospective analysis of postmortem computed tomography scans of ossification stages of the anterior and posterior intra-occipital sutures, the anterior arch of the atlas, and the ...neurocentral junction of the axis. We also analyzed the development of secondary ossification centers in the proximal humeral, femoral, and tibial epiphyses, and the distal femoral and tibial epiphyses. Additionally, the development of primary ossification centers in the wrist and metacarpals, and maxillary and mandibular deciduous tooth maturation. A total of 58 cadavers (35 males, 23 females), whose age ranged from 3rd month of pregnancy to 14 years, were analyzed. The results of this study show that analysis of synchondrosis closure, primary, and secondary ossification center development and deciduous tooth changes are a good tool for age estimation in subadults group (fetuses, newborns, infants, and children). The results of the study in a Polish population are consistent with those reported by other authors.
The aim of this study was to determine the influence of age and gender on the incidence of calcification in laryngeal cartilage diagnosed on lateral cephalometric radiographs routinely taken for ...orthodontic diagnosis. The lateral cephalometric radiographs of 957 patients who met the study criteria were analyzed from among the 1000 lateral radiographs originally collected. The images were evaluated independently by two investigators. Given the dichotomous dependent variable (calcification or no calcification), a mixed logistic regression model was used to test how age and gender affected calcification. The effect of age and gender reliably determined the likelihood of laryngeal cartilage calcification. The greatest differences in the degree of calcification by gender were found at ages 20-25 years. The degree of calcification increased with age, reaching 100% in women at age 30 and in men at age 50. In women, the degree of calcification was higher than in men from the age of 13 years and levelled off at the age of 50 years. The interrater agreement was strong k = 0.97, z = 30.0, p < .001. Calcification can be detected by orthodontists trained in lateral cephalogram analysis and can be used as a screening or diagnostic tool to detect calcified areas in the larynx.
Cyclic dipeptides with two intramolecular peptide bonds forming a six-membered 2,5-diketopiperazine ring are gaining significant attention due to their biological and chemical properties. Small ...changes in the local geometry of such molecules (from
to
) can lead to significant structural differences. This work presents the results of a study of cyclo(l-Cys-d-Cys), a dipeptide comprising two cysteine molecules in opposite chiral configurations, with the functional groups situated at both sides of the diketopiperazine ring. X-ray diffraction (XRD) experiment revealed that the molecule crystallises in the
-1 space group, which includes the centre of inversion. The IR and Raman vibrational spectra of the molecule were acquired and interpreted in terms of the potential energy distribution (PED) according to the results of density functional theory (DFT) calculations. The DFT-assisted analysis of energy frameworks for the hydrogen bond network within molecular crystals was performed to support the interpretation of X-ray structural data. The optimisation of the computational model based on three-molecule geometry sections from the crystallographic structure, selected to appropriately reflect the intermolecular interactions responsible for the formation of 1D molecular tapes in cyclo(l-Cys-d-Cys) crystal, allowed for better correspondence between theoretical and experimental vibrational spectra. This work can be considered the first complete structural characterisation of cyclo(l-Cys-d-Cys), complemented via vibrational spectroscopy results with full band assignment aided with the use of the DFT method.
A comprehensive analysis of crystal packing and energetic features of the selected uracil derivatives (i.e., 1-methyluracil, 1,5-dimethyluracil, 5-fluorouracil, 2-thiouracil, 4-thiouracil, ...2,4-dithiouracil, and 6-methyl-2-thiouracil) is reported. High-quality X-ray diffraction data sets of the studied compounds were subjected to the TAAM procedure (Transferable Aspherical Atom Model based on the Hansen–Coppens formalism), which gave results comparable both with the optimized and neutron-diffraction-derived geometries. Crystal packing motifs were investigated with the aid of Hirshfeld surface fingerprint plots. Most of the structures form hydrogen-bonded layers kept together by π-stacking interactions. The only exception is 2,4-dithiouracil, which exhibits a rather complex 3D network based on N–H···S and C–H···S contacts. The TAAM procedure allows also for a quite reliable reconstruction of the electron density distribution in a crystal structure. It was therefore possible to rationalize the existence of some F···F interactions in 5-fluorouracil on the basis of the derived deformation density map. Additional insight into the nature of crystal architectures was obtained through theoretical computations, concerning cohesive energy, dimer interaction energy, and molecule deformation energy evaluation. The balance between molecular layer stabilization and their mutual interactions is essential for crystal growth, and thus it is reflected in crystal morphology and quality. Cohesive energy ranges from −100 kJ·mol–1 for 2,4-thiouracil to about −140 kJ·mol–1 for uracil and 5-fluorouracil, and there is no significant correlation with the melting point temperature observed. Hydrogen-bonded layers are more strongly stabilized one with another, when methyl substituents or sulfur atoms are present. Remarkable differences between 2-thio and 4-thio derivatives were found and supported by the corresponding values of aromaticitity indices. Furthermore, the energy calculations revealed the particular importance of properly determined positions of hydrogen atoms.
Gamification is known to enhance users’ participation in education and research projects that follow the citizen science paradigm. The Cosmic Ray Extremely Distributed Observatory (CREDO) experiment ...is designed for the large-scale study of various radiation forms that continuously reach the Earth from space, collectively known as cosmic rays. The CREDO Detector app relies on a network of involved users and is now working worldwide across phones and other CMOS sensor-equipped devices. To broaden the user base and activate current users, CREDO extensively uses the gamification solutions like the periodical Particle Hunters Competition. However, the adverse effect of gamification is that the number of artefacts, i.e., signals unrelated to cosmic ray detection or openly related to cheating, substantially increases. To tag the artefacts appearing in the CREDO database we propose the method based on machine learning. The approach involves training the Convolutional Neural Network (CNN) to recognise the morphological difference between signals and artefacts. As a result we obtain the CNN-based trigger which is able to mimic the signal vs. artefact assignments of human annotators as closely as possible. To enhance the method, the input image signal is adaptively thresholded and then transformed using Daubechies wavelets. In this exploratory study, we use wavelet transforms to amplify distinctive image features. As a result, we obtain a very good recognition ratio of almost 99% for both signal and artefacts. The proposed solution allows eliminating the manual supervision of the competition process.
As a result of external compression applied to crystals, ions relax, in addition to shortening the bond lengths, by changing their shape and volume. Modern mineralogy is founded on spherical atoms, ...i.e., the close packing of spheres, ionic or atomic radii, and Pauling and Goldschmidt rules. More advanced, quantum crystallography has led to detailed quantitative studies of electron density in minerals. Here we innovatively apply it to high-pressure studies up to 4.2 GPa of the mineral hsianghualite. With external pressure, electron density redistributes inside ions and among them. For most ions, their volume decreases; however, for silicon volume increases. With growing pressure, we observed the higher contraction of cations in bonding directions, but a slighter expansion towards nonbonding directions. It is possible to trace the spatial redistribution of the electron density in ions even at the level of hundredths parts of an electron per cubic angstrom. This opens a new perspective to experimentally characterise mineral processes in the Earth's mantle. The use of diamond anvil cells with quantum crystallography offers more than interatomic distances and elastic properties of minerals. Interactions, energetic features, a branch so far reserved only to the first principle DFT calculations at ultra-high-pressures, become available experimentally.
In this work, the quality of the electron density in crystals reconstructed by the multipolar model (MM) and by X‐ray wavefunction refinement (XWR) is tested on a set of high‐resolution X‐ray ...diffraction data sets of four amino acids and six tripeptides. It results in the first thorough validation of XWR. Agreement statistics, figures of merit, residual‐ and deformation‐density maps, as well as atomic displacement parameters are used to measure the quality of the reconstruction relative to the measured structure factors. Topological analysis of the reconstructed density is carried out to obtain atomic and bond‐topological properties, which are subsequently compared to the values derived from benchmarking periodic DFT geometry optimizations. XWR is simultaneously in better agreement than the MM with both benchmarking theory and the measured diffraction pattern. In particular, the obvious problems with the description of polar bonds in the MM are significantly reduced by using XWR. Similarly, modeling of electron density in the vicinity of hydrogen atoms with XWR is visibly improved.
Quantum crystallography: In X‐ray wavefunction refinement (XWR), crystallographic data are enhanced with quantum mechanical data, and subsequently the quantum mechanical data are enhanced with the measured structure factors. XWR is validated against benchmark experimental and theoretical methods, and provides both accurate structural and electronic properties of molecules.
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