Isotropic Shifts Research Articles

Investigation of the Binary Nitrides YN, LaN and LuN by Solid-State NMR Spectroscopy

Based on their various and outstanding properties, binary nitrides are used as (synthesis) materials in industry and research. Hence, their comprehensive characterization by analytical methods is of particular interest. Since Nuclear Magnetic Resonance (NMR) spectroscopy is very sensitive to the symmetry of the electronic density distribution, it is a suitable tool for the investigation of rock-salt structure types and, especially, for those with known stoichiometry issues. Here, we report on magic-angle spinning NMR spectra of the nuclides 89Y (I=12), 139La (I=72) and 14N (I=1) in polycrystalline samples of YN, LaN and LuN. Due to the high symmetry of their crystal structures, the spectra of all nuclides do not exhibit anisotropic effects of significant magnitude. The resulting isotropic chemical shift values are δiso(89Y) = 516 ppm for YN, δiso(139La) =1294 ppm for LaN, and δiso(14N) = 457 ppm (YN), 788 ppm (LaN) and 384 ppm (LuN). The newly determined δiso(14N) values for these three binary nitrides fit well into the previously reported linear correlation between nitrogen distance to the nearest cation and isotropic chemical shift, leading to a better correlation coefficient and reduced error margins for the fit parameters.

Comparative Analysis of Tetravalent Actinide Schiff Base Complexes: Influence of Donor and Ligand Backbone on Molecular Geometry and Metal Binding.

A series of isostructural early actinide AnIV complexes was synthesized in order to investigate the influence of a conjugated framework in the ligand backbone on An bonding. Therefore, the AnIV complexes [An(pyrophen)2] (An = Th, U, Np, and Pu) with the pure N-donor ligand bis(2-pyrrolecarbonylaldehyde)-o-phenylenediamine referred to as pyrophen, were synthesized and characterized. Solid state analysis via single-crystal X-ray diffraction (SC-XRD) reveals two sets of ligands binding in an almost orthogonal arrangement to the actinide center. For the larger actinides Th and U, the coordination sphere allows for additional coordination by a solvent molecule. Nuclear magnetic resonance spectroscopy (NMR) studies show the presence of highly symmetrical complexes in solution in good agreement with the solvent-free solid structures. While SC-XRD suggests mainly ionic binding, an analysis of paramagnetic NMR contributions and quantum chemical bond analysis hint towards significant covalency in the U, Np, and Pu compounds. This series of An complexes allowed for a thorough structural and theoretical comparison of a conjugated system to a closely related N-donor ligand (pyren)[1] as well as to the mixed N,O Schiff base ligands salophen (conjugated) and salen (non-conjugated).

Aktivierung von Kohlenstoff‐Kohlenstoff Bindungen durch Chrom(I): Spaltung von Dialkinen durch einen 11‐Elektronenkomplex

AbstractEin T‐förmiger Chrom(I)‐11‐Elektronenkomplex wurde durch Reduktion eines [PNP]‐stabilisierten Chrom(II)iodid‐Komplexes erhalten. Seine high‐spin d5‐Elektronenkonfiguration wurde mittels paramagnetischer NMR‐, EPR‐, UV/Vis‐ und magnetischer Messungen (SQUID) charakterisiert. Der Komplex reagiert leicht mit konjugierten Dialkinen unter Spaltung der internen C−C‐Bindung und Ausbildung des jeweiligen Acetylidkomplexes. Variation der Alkinsubstituenten ermöglichte die Isolierung und Charakterisierung von zweikernigen Dialkindichrom‐Intermediaten, die sich thermisch in die Produkte umwandeln.

Carbon-Carbon Bond Activation at Chromium(I): An 11-Electron Complex Cleaving Dialkynes.

An 11-electron T-shaped chromium(I) complex was obtained by reduction of a PNP-supported chromium(II) iodide complex. Its d5 high-spin electronic structure was characterized employing paramagnetic NMR, EPR, UV/Vis and magnetic measurements (SQUID). The complex readily reacts with conjugated dialkynes to cleave the internal C-C bond, forming the respective acetylide complexes. Varying the alkyne substituents enabled the isolation and characterization of dinuclear dialkynedichromium intermediates which thermally convert to the products.

Oxoammonium-Catalyzed Ether Oxidation via Hydride Abstraction: Methodology Development and Mechanistic Investigation Using Paramagnetic Relaxation Enhancement NMR.

Hydride abstraction represents a promising yet underexplored approach in the functionalization of C-H bonds. In this work, we report the oxidation of α-C-H bonds of ethers via oxoammonium catalysis using 3-chloroperbenzoic acid (mCPBA) as the terminal chemical oxidant or by means of electrochemistry. Mechanistic studies revealed intricate equilibria and interconversion events between various catalytic intermediates in the presence of mCPBA, which alone however was incompetent to drive catalytic turnover. The addition of a small amount of strong acid HNTf2 or weakly coordinating salt NaSbF6 turned on catalytic turnover and promoted ether oxidation with excellent efficiency. NMR experiments leveraging paramagnetic relaxation enhancement effect allowed for quantification of open-shell catalytic intermediates in real time during the reaction course, which aided the identification of catalyst resting states and elucidation of reaction mechanisms.

Distinct association of HRAS and KRAS with Mn(II) ion illustrated by paramagnetic NMR

Rat sarcoma virus oncogene (RAS) proteins are among crucial oncogenic proteins and are involved in several essential intracellular processes. The RAS protein has an intrinsic metal binding site for Mg2+, which is important for the conformational stability of the active site. Recently, it was reported that a second metal ion binding site, located further from the active site in HRAS (Harvey RAS homolog), binds Ca2+ with millimolar affinity. As one of the most abundant metal ions in cells, Mn2+ is a potential candidate for the second metal ion binding site in RAS proteins. Here, we examined the interaction of Mn2+ with HRAS and KRAS (Kirsten RAS homolog) using high resolution NMR spectroscopy. The NMR data showed that both the second metal ion binding site and the switch I and II regions bind Mn2+ in the RAS proteins. Furthermore, our paramagnetic NMR results disclosed the conformational differences in helix α3 and the following loop between HRAS and KRAS, accompanied by the association with metal ion binding. These results provide new insights into the interaction of RAS proteins and Mn2+ in the respective biological processes in cells.

Exploring Charge Redistribution at the Cu/Co6Se8 Interface.

This study investigates the electronic interactions and charge redistribution at the dopant-support interface using a Cu/Co6Se8 cluster construct. Specifically, the redox cluster series [Cu3Co6Se8L6]n ([1-Cu3]n; n = 0, -1, -2, -3; L = Ph2PNTol-, Ph = phenyl, Tol = p-tolyl) spanning four distinct oxidation states is synthesized and characterized using a multitude of techniques, including multinuclear NMR, UV-vis, XANES, and X-ray crystallography. Structural investigations indicate that the clusters are isostructural and chiral, adopting a pseudo-D3 symmetry. Paramagnetic 31P NMR spectroscopy and solution-phase magnetic measurements together with DFT calculations are employed to interrogate the electronic structure and spin-state changes across the [1-Cu3]3- to 1-Cu3 redox series, revealing that the copper edge sites retain a +1 oxidation state while the Co/Se core becomes increasingly oxidized, yielding a highly zwitterionic cluster.

A tale of two old drugs tetracycline and salicylic acid with new perspectives—Coordination chemistry of their Co(II) and Ni(II) complexes, redox activity of Cu(II) complex, and molecular interactions

Extensive use of the broad-spectrum tetracycline antibiotics (TCs) has resulted their wide spread in the environment and drive new microecological balances, including the infamous antibiotic resistance. TCs require metal ions for their antibiotic activity and resistance via interactions with ribosome and tetracycline repressor TetR, respectively, at specific metal-binding sites. Moreover, the Lewis-acidic metal center(s) in metallo-TCs can interact with Lewis-basic moieties of many bioactive secondary metabolites, which in turn may alter their associated chemical equilibria and biological activities. Thus, it is ultimately important to reveal detailed coordination chemistry of metallo-TC complexes. Herein, we report (a) conclusive specific Co2+, Ni2+, and Cu2+-binding of TC revealed by paramagnetic 1H NMR, showing different conformations of the coordination and different metal-binding sites in solution and solid state, (b) significant metal-mediated activity of Cu-TC toward catechol oxidation with different mechanisms by air and H2O2 (i.e., mono- and di-nuclear pathways, respectively), (c) interactions of metallo-TCs with bioactive salicylic acid and its precursor benzoic acid, and (d) noticeable change of TC antibiotic activity by metal and salicylic acid. The results imply that TCs may play broad and versatile roles in maintaining certain equilibria in microecological environments in addition to their well-established antibiotic activity. We hope the results may foster further exploration of previously unknown metal-mediated activities of metallo-TC complexes and other metalloantibiotics.

An analysis of three dimensional changes to comprehensively evaluate the occlusion time, disclusion time, point of first contact and force distribution at various head positions using Tekscan III: An in vivo study

Aim: This study aims to evaluate the changes in occlusal contacts resulting from variations in head postures (supine[S], semi-supine [SS], upright with head rest support [HR], and without head rest support [WHR]) after occlusal adjustment of conventional fixed dental prostheses using Tekscan III. Settings and Design: A cross-sectional study on 15 patients with missing single molars and undergone replacement with a fixed dental prosthesis. Materials and Methods: Fifteen patients with a three-unit tooth-supported fixed dental prosthesis replacing a missing single posterior tooth were included. Tekscan III was used to analyze occlusion time (OT), disclusion time (DT), initial tooth contact, and relative bite force in different head postures by adjusting the backrest position before and after equilibration. Occlusal adjustments were performed to achieve the balance between the right and left halves. Statistical Analysis Used: The data were statistically analyzed using ANOVA and paired t-test. Results: Posterior shift of initial tooth contact was observed from SS to supine and upright positions, whereas an anterior shift occurred from SS to WHR support posture. High-intensity forces were observed before the occlusal adjustment in various head positions, and these forces changed after adjustments in SS position. However, medium-intensity force occlusal prematurities persisted in other head postures even after corrections in SS position. There was a significant difference in OT but not in DT in all head postures after equilibration. When OT was compared from SS to remaining posture after equilibration, the major difference was found from SS to head rest (HR) and supine to HR posture which infers the need for selective grinding in these postures. Conclusion: Considering the various changes while changing the head position from the SS position to the other functional position, it can be inferred that there is a need to consider recalibration of occlusal contacts in all the functional postures.

Nondissociative Activated Dihydrogen Binding on CeO2 Revealed by High-Pressure Operando Solid-State NMR Spectroscopy.

Dihydrogen complexes, which retain the H-H bond, have been extensively studied in molecular science and found to be prevalent in homogeneous and enzymatic catalysis. However, their counterparts in heterogeneous catalysis, specifically nondissociative chemisorbed dihydrogen binding on the catalyst surface, are rarely reported experimentally. This scarcity is due to the complexity of typical material surfaces and the lack of effective characterization techniques to prove and distinguish various dihydrogen binding modes. Herein, using high-pressure operando solid-state NMR technology, we report the first unambiguous experimental observation of activated dihydrogen binding on a reduced ceria catalyst through interactions with surface oxygen vacancies. By employing versatile NMR structural and dynamical analysis methods, we establish a proportional relationship between the degree of ceria surface reduction and dihydrogen binding, as evidenced by NMR observations of H-D through-bond coupling (JHD), T1 relaxation, and proton isotropic chemical shifts. In situ NMR analysis further reveals the participation of bound dihydrogen species in a room-temperature ethylene hydrogenation reaction. The remarkable similarities between surface-activated dihydrogen in heterogeneous catalysis and dihydrogen model molecular complexes can provide valuable insights into the hydrogenation mechanism for many other solid catalysts, potentially enhancing hydrogen utilization.

Structure, Covalency, and Paramagnetism of Homoleptic Actinide and Lanthanide Amidinate Complexes.

Isostructural trivalent lanthanide and actinide amidinates bearing the N,N'-bis(isopropyl)benzamidinate (iPr2BA) ligand [LnIII/AnIII(iPr2BA)3] (Ln = La, Nd, Sm, Eu, Yb, Lu; An = U, Np) have been synthesized and characterized in both solid and solution states. All compounds were examined in the solid state utilizing single crystal X-ray diffraction (SC-XRD), revealing a notable deviation in the actinide series with shortened bond lengths compared to the trend in the lanthanide series, suggesting a nonionic contribution to the actinide-ligand bonding. Quantum-chemical bonding analysis further elucidated the nature of these interactions, highlighting increased covalency within the actinide series, as evidenced by higher delocalization indices and greater 5f orbital occupation, except for Th(III) and Pa(III), which demonstrated substantial 6d orbital occupancies. An in-depth paramagnetic NMR study in solution also sheds light on the covalent character of actinide-ligand bonding, with the separation of pseudocontact (PCS) and contact shift (FCS) contributions employing the Bleaney and Reilley method. This analysis unveiled significant contact contributions in the actinide complexes, indicating enhanced covalency in actinide-ligand bonding. To corroborate these observations, an accurate PCS calculation method based on the Kuprov equation, incorporating both the distribution of electronic spin density and magnetic susceptibility obtained from CASSCF calculations, was applied and compared with experimental values.

Ethnic integration and evolution of the phonological features of Northern Standard Chinese Language

ABSTRACT: Ethnic integration is often accompanied by language contact and language shift. The process of "ethnic integration" is the process of "remolding" northern standard Chinese language into an inter-ethnic language and ultimately into a common national language. Only by reevaluating the phonological rules and structure of the languages (mainly Altaic) of northern non-Han ethnic groups and investigating the interference with and influence on Chinese during the language shift by the non-Han ethnic groups, can we comprehend that the common national language is a language community jointly shaped by the Han people and other ethnic groups during ethnic integration. The speakers of ethnic languages are, therefore, not only the transmitters but also the co-modelers in forming the common national language. 摘要: 民族融合往往伴随着语言接触和语言转换。"民族融合"的过程就是 将北方标准汉语"重塑"为族际共同语进而成为民族共同语的过程。 只有基于以阿尔泰语为主的北方诸民族语音系规则和音韵结构特征重 新思考并深入研究以阿尔泰为主的北方诸民族在转用汉语过程中对汉 语形成的干扰和影响，才能理解民族共同语是在民族融合过程中汉族 与其他民族共同塑造的语言共同体。在民族共同语形成的过程中，民 族语者不仅是民族共同语的传播者，也是民族共同语的共同塑造者。

Entropy-stabilized materials as a platform to explore terbium-based pyrochlore frustrated magnets

Two decades of work have shown that the physics of Tb-based pyrochlores is controlled by a subtle equilibrium between quadrupole-quadrupole and dipolar-dipolar magnetic interactions, as exemplified by the ordered spin ice Tb2Sn2O7 and the quantum spin liquid candidate Tb2Ti2O7. The high-entropy approach is thus quite promising, as it offers the possibility of a delicate tuning of chemical disorder. In this work, we investigate the entropy-stabilized pyrochlore compound Tb2(TiZrHfGeSn)2O7. We report the lack of long range magnetic order, yet the observed magnetic diffuse scattering is characteristic of antiferromagnetic first-neighbor correlations. The crystal field excitation spectrum, with broaden levels, visibly reflects the smooth environmental disorder of the Tb environment. The low energy dynamics are characterized by a narrow mode at about 0.4 meV, consistent with specific heat. Remarkably, as illustrated by a model of random isotropic shifts of oxygen atoms around Tb ions, the spectral weight of this mode is a direct consequence of deviations from the D3d symmetry at Tb sites. In the light of these results, quadrupolar interactions are also discussed.

Paramagnetic Solid-State NMR Study of Solid Solutions of Cobaltocene with Ferrocene and Nickelocene

Paramagnetic Solid-State NMR Study of Solid Solutions of Cobaltocene with Ferrocene and Nickelocene

Effect of the Solvent Nature on a Spin Equilibrium in the Solutions of the Phenylboron-Capped Hexa-n-Butylsulfide Cobalt(II) Clathrochelate Stadied by the Paramagnetic NMR Spectroscopy

A spin state of the phenylbon-capped hexa-n-butylsulfide cobalt(II) clathrochelate in solutions was studied by paramagnetic NMR spectroscopy. This cage complex is found to undergo the temperature – induced spin crossover in solvents of different nature (acetonitrile, chloroform, dichloromethane, and benzene). The previously developed method for an analysis of paramagnetic shifts in NMR spectra allows to calculate of the thermodynamic parameters (enthalpy and entropy) of a given spin equilibrium in the solutions. In spite of the conformational rigidity of the macrobicyclic tris-α-dioximate molecules, the substantial changes in their electronic structures and spin crossover parameters were observed, being affected by a polarity of the solvent used. This provides an opportunity for the fine tuning of spin switch characteristics by changing this medium parameter.

Synthesis, structural analysis, and molecular docking of a novel 1,3,4-thiadiazole derivative: An experimental and molecular modeling studies

This study reports on the synthesis and characterization of a new thiadiazole derivative, (E)-N-(5-(2-nitrostyryl) -4-acetyl -4,5-dihydro -1,3,4-thiadiazol -2-yl) -N-phenylacetamide (ETDZ). The crystal structure was determined by single-crystal X-ray diffraction. ETDZ belongs to the monoclinic I2/a space group. The contribution of intermolecular interactions was assessed by Hirshfeld surface analysis and fingerprint plots. FT-IR, UV–Vis, and NMR (1H and 13C) techniques were used for spectroscopic characterization. The 1H and 13C NMR spectra were recorded in CDCl3 solvent. Density functional theory, employing the B3LYP functional and 6–311G(d,p) basis set in chloroform solvent, was used to calculate the structural and spectroscopic parameters of the molecule in the ground state. The vibrational wavenumbers were calculated and compared with the experimental FT-IR spectrum using the scaled quantum mechanics method. Isotropic chemical shifts were calculated using the Gauge invariant atomic orbital method. The calculated NMR chemical shifts and absorption wavelengths were compared with the experimental values, indicating good results from the DFT and TD-DFT methods. To get more information about charge transfer within the molecule, electronic properties such as HOMO and LUMO energies were studied using the DFT approach. The molecular electrostatic potential, frontier molecular orbital analysis, energy band gap, density of state, global chemical reactivity descriptors, and some thermodynamic functions were also calculated. Reduced density gradient and atom-in-molecule analysis were performed to investigate inter- and intra-non-covalent interactions. Molecular docking was carried out with the Eg5 kinesin protein, confirming the biological assets of the ETDZ ligand as a mitochondria disease and cancer agent.

Supramolecular Binding of Phosphonate Dianions by Nanojars and Nanojar Clamshells.

Despite the widespread use of phosphonates (RPO32-) in various agricultural, industrial, and household applications and the ensuing eutrophication of polluted water bodies, the capture of phosphonate ions by molecular receptors has been scarcely studied. Herein, we describe a novel approach to phosphonate binding using chemically and thermally robust supramolecular coordination assemblies of the formula [RPO3⊂{cis-CuII(μ-OH)(μ-pz)}n]2- (Cun; n = 27-31; pz = pyrazolate ion, C3H3N2-; R = aliphatic or aromatic group). The neutral receptors, termed nanojars, strongly bind phosphonate anions by a multitude of hydrogen bonds within their highly hydrophilic cavities. These nanojars can be synthesized either directly from their constituents or by depolymerization of [trans-CuII(μ-OH)(μ-pz)]∞ induced by phosphonate anions. Electrospray-ionization mass spectrometry, UV-vis and variable-temperature, paramagnetic 1H and 31P NMR spectroscopy, single-crystal X-ray diffraction, along with chemical stability studies toward NH3 and Ba2+ ions, and thermal stability studies in solution are employed to explore the binding of various phosphonate ions by nanojars. Crystallographic studies of 12 different nanojars offer unprecedented structural characterization of host-guest complexes with doubly charged RPO32- ions and reveal a new motif in nanojar chemistry, nanojar clamshells, which consist of phosphonate anion-bridged pairs of nanojars and double the phosphonate-binding capacity of nanojars.

A bright red low symmetry nine-coordinate Eu3+ complex: Synthesis, crystal structure and photophysical studies

This paper reports a novel crystallographically characterized Eu3+ complex, [Eu(fod)3(terpy)] (fod = anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione and terpy = terpyridine). The single crystal XRD result shows that the Eu ion have a nine-coordinated structure where Eu is attached to six oxygen atoms of three fod ligand and three nitrogen atoms of one terpyridine ligand with a coordination polyhedron as EuO6N3. The paramagnetic NMR result is in line with SC-XRD and confirms the same coordination structure of the complex in solution as well. The photophysical properties were studied in solid state, solution and as a thin film. The band gap value of the complex is determined which is found to be in the range of semiconductors, suggesting application of complex in optoelectronics. Upon excitation with UV-radiation, the complex displays characteristic emission transitions of europium ion. The complex shows high experimental emission lifetime in solid state which suggests that the antenna affect is effective in the present complex. Finally, various color parameters of the complex were calculated and the CCT value reveals the complex as a warm light source.

Effect of the Sauvé–Kapandji method on the wrist contact surface for distal radial ulnar joint disorders

BackgroundThe Sauvé–Kapandji (S-K) method is a surgical procedure performed for chronic deformities of the distal radial ulnar joint (DRUJ). Changes to the joint contact surface from pre- to postoperatively under physiological in vivo conditions have not yet been determined for this useful treatment. The aim of the present study was therefore to compare the articular contact area of the wrist joint between before and after the S-K method for DRUJ disorders.MethodsThe SK method was performed for 15 patients with DRUJ osteoarthritis and ulnar impaction syndrome. We calculated the Mayo Wrist Score as the patient’s clinical findings and created 3-dimensional bone models of cases in which the S-K method was performed and calculated the contact area and shift in the center of the contact area using customized software.ResultsThe Mean modified Mayo Wrist Score improved significantly from 60.3 preoperatively to 80.3 postoperatively (P < 0.01). Scaphoid contact area to the radius increased significantly from 112.6 ± 37.0 mm2 preoperatively to 127.5 ± 27.8 mm2 postoperatively (P = 0.03). Lunate contact area to radius-ulna was 121.3 ± 43.3 mm2 preoperatively and 112.5 ± 37.6 mm2 postoperatively, but this decrease was not significant (P = 0.38). Contact area ratio of scaphoid to lunate increased significantly from 1.01 ± 0.4 preoperatively to 1.20 ± 0.3 postoperatively (P = 0.02). Postoperative translations of the center of the scaphoid and lunate contact areas were decomposed into ulnar and proximal directions. Ulnar and proximal translation distances of the scaphoid contact area were 0.8 ± 1.7 mm and 0.4 ± 0.6 mm, respectively, and those of the lunate contact area were 1.1 ± 1.7 mm and 0.4 ± 1.1 mm, respectively. This study revealed changes in wrist contact area and center of the contact area before and after the S-K method.ConclusionThese results may accurately indicate changes in wrist joint contact area from pre- to postoperatively using the S-K method for patients with DRUJ disorder. Evaluation of changes in contact area due to bone surface modeling of the wrist joint using 3DCT images may be useful in considering surgical methods.

Low-Temperature Thermal Treatment and Boron Speciation Analysis from Coals

Despite urgent calls for decarbonization, the continued increasing demand for electricity, primarily from coals, has presented challenges in managing coal-derived wastes such as coal fly ash (CFA), which are enriched with environmentally hazardous substances like boron. This study explores a low-temperature heating process to remove boron from coal, aimed at preventing its condensation and enrichment into CFA during combustion. Initial boron concentrations in coals varied widely from 50 to 500 ppm by weight and were found to correlate with fixed carbon content (FC) through the following polynomial equation: [B]o = 0.0929(FC)2 − 14.388(FC) + 601.85; R2 = 0.9173. This relationship suggests that as coal undergoes coalification, boron-containing compounds are decomposed and released, resulting in a decline in boron levels as the coal matures. Boron-removal efficiency was investigated by drying coal samples at 110 °C, 160 °C, and 210 °C under natural air convection, and nuclear magnetic resonance (NMR) spectroscopy was used to assess changes in boron speciation during heating. Our results demonstrate that boron removal ranged from 5% to 82%, with minimal improvements observed beyond 110 °C. In addition, the 11B MAS-NMR spectra of the coal samples showed four peaks at isotropic chemical shift values of −1.0, 2.0, 8.0, and 14.0 ppm and suggested that the species of boron volatilized at low temperatures is the inorganic BO4 assigned to peak no. 0 at −1.0 ppm. The association of boron with inorganic components in coal suggests potential for efficient removal, particularly in coals with higher fixed carbon content. These findings highlight the viability of low-temperature thermal treatment as a cost-effective method for boron removal, which is crucial in mitigating the risks associated with coal combustion by-products.