Cationic Center Research Articles

Tuning Electron Transfer Coupling and Exchange Interaction in Bis-triarylamine Radical Cations and Dications by Bridge Electron Density.

The influence of the electron density of a bridge connecting two redox centers on both the intervalence hole transfer and the magnetic superexchange was investigated in a series of bridged bis-triarylamine mono- and dications. In this series, the bridge was 2,7-fluorenyl, where the bridge electron density was modified by substituents at the 9-position. For the mixed-valence monocations, the observation of both an intervalence charge transfer (IVCT) band and an absorption band associated with an electron transfer from the bridging fluorene to the triarylamine radical cation centers allowed determination of the electron transfer couplings in the framework of the three-state generalized Mulliken-Hush theory. Comparison of the derived couplings with those obtained from a classical two-state approach demonstrates an enhancement of the electronic coupling which increases with decreasing bridge state energy. For the dicationic diradical counterparts, the singlet-triplet gap (exchange interaction) was determined both experimentally and by quantum chemical methods. Hereby, an increase of antiferromagnetic coupling with a lowering of the bridge state energy by electron donating substituents was observed. Analysis of the involved molecular orbitals suggests that the ferromagnetic coupling is inversely proportional to the square of the bridge energy, which is also supported by the experimental findings. This influence of the bridge state energy on both types of interactions, electron transfer and magnetic exchange, provides a design guideline for fine-tuning the properties of electronically coupled organic redox dyads by variation of the bridge electron density.

Effects of Secondary Amine and Molecular Weight on the Biological Activities of Cationic Amphipathic Antimicrobial Macromolecules.

Cationic amphipathic antimicrobial agents inspired by antimicrobial peptides (AMPs) have shown potential in combating multidrug-resistant bacteria because of minimal resistance development. Here, this study focuses on the development of novel cationic amphipathic macromolecules in the form of dendrons and polymers with different molecular weights that employ secondary amine piperidine derivative as the cationic moiety. Generally, secondary amine compounds, especially at low molecular weights, have stronger bacteriostatic, bactericidal, and inner membrane disruption abilities than those of their primary amine counterparts. Low molecular weight D2 dendrons with two cationic centers and one hydrophobic dodecyl chain produce outstanding synergistic activity with the antibiotic rifampicin against Escherichia coli, where one-eighth of the standalone dose of D2 dendrons could reduce the concentration of rifampicin required by up to 4000-fold. The low molecular weight compounds are also less toxic and therefore have higher therapeutic index values compared to compounds with larger molecular weights. This study thus reveals key information that may inform the design of future synthetic AMPs and mimics, specifically, the design of low-molecular-weight compounds with secondary amine as the cationic center to achieve high antimicrobial potency and biocompatibility.

Tailoring the oxidizing intermediate in the Fenton reaction, OH• or FeIV=Oaq, by modifying the pKa of the (H2O)5FeII(H2O2) complex, and the case of PDS - a DFT study.

A DFT analysis of the Fenton and Fenton-like reactions points out that the pH effect on the nature of the oxidizing intermediate formed is due to a pKa of the peroxide when hydroperoxides are used. When S2O82- is used, the pH effect is due to the pKa of one of the water ligands of the central iron cation. The results suggest that the choice of the hydroperoxide and the ligands present affects the pH at which the transition from the formation of hydroxyl radicals to the formation of FeIV=Oaq occurs.

From +I to +IV, Alkalis to Actinides: Capturing Cations across the Periodic Table with Keggin Polyoxometalate Ligands.

Coordination chemistry trends across the periodic table are often difficult to probe experimentally due to limitations in finding a versatile but consistent chelating platform that can accommodate various elements without changing its coordination mode. Herein, we present new metal/ligand systems covering a wide range of ionic radii, charges, and elements. Five different ligands derived from the Keggin structure (HBW11O398-, PW11O397-, SiW11O398-, GeW11O398-, and GaW11O399-) were successfully crystallized with six different cations (Na+, Sr2+, Ba2+, La3+, Ce4+, and Th4+) and characterized by single-crystal X-ray diffraction. Twenty-five new compounds were obtained by using Cs+ as the counterion, yielding a consistent base formula of Csx[M(XW11O39)2]·nH2O. Despite having a similar first-coordination sphere geometry (i.e., 8-coordinated), the nature of the central cation was found to impact the long-range geometry of the complexes. This unique crystallographic data set shows that, despite the traditional consensus, the local geometry of the cation (i.e., metal-oxygen bond distance) is not enough to depict the full impact of the complexed metal ion. The bending and twisting of the complexes, as well as ligand-ligand distances, were all impacted by the nature of the central cation. We also observed that counterions play a critical role by stabilizing the geometry of the M(XW11)2 complex and directing complex-complex interactions in the lattice. We also define certain structural limits for this type of complex, with the large Ba2+ ion seemingly approaching those limits. This study thus lays the foundation for capturing the coordination chemistry of other rarer elements across the periodic table such as Ra2+, Ac3+, Bk4+, Cf3+, etc.

Challenges and Opportunities in Preparing Fe-N-C Layers Supported on Non-Carbon Supports

Global energy demand will be continuously rising in the foreseeable future. To mitigate the results of climate change it is necessary to reduce the emittance of greenhouse gases. One promising approach is to switch to hydrogen as energy carrier and use proton exchange membrane fuel cells (PEMFCs) to efficiently convert H2 into electric power. Here, hydrogen and oxygen/air are used to directly generate electrical energy with only water as byproduct. Both reactions need to happen efficiently at the same time. The oxygen reduction reaction (ORR), however, is a very sluggish four-electron-reaction and needs efficient catalysts.The state-of-the-art ORR catalyst in PEMFC is platinum but that is a very scarce and expensive metal. Hence, it is important to switch to precious-metal-group (PGM) free catalysts. In recent years, bio inspired iron-based FeNC catalysts have been shown to approach ORR activities that are competitive with those of platinum, even though they need a higher catalyst loading than Pt to reach the desired high current densities.1–3 Those catalysts feature single Fe atoms surrounded by four N atoms in graphitic carbon. The drawback of those materials is their lower stability compared to PGM materials. In a nutshell, the carbon matrix oxidizes during operation in PEMFCs, changing the morphology of the catalytic center and rendering it less active, or inactive, depending on the carbon oxidation extent. Direct demetallation phenomena are also possible, leaving a N4 cavity without metal cation center. It was shown recently by Wu et al.4 that it is possible to raise durability by adding an additional carbon layer on the catalyst. One alternative approach to reduce those degradations is to interface Fe-N4 sites with a carbon-free support. The targeted support material must be immune to corrosion in acid and withstand the typical ORR electrochemical potentials. It also has to be electrically conductive to facilitate electron transfers, both locally and on long scale.In this work, conductive ceramic metal oxide materials (Ta doped SnO2, TTO) was investigated as a possible alternative catalyst supports. This material is resistant to acid and can withstand prolonged potentials at operating conditions in PEMFCs.5 During the synthesis of the FeNC catalysts, high temperatures are generally applied. Such treatments can be detrimental to the conductivity of ceramics due to metal aggregation (in case of doped materials) and may also lead to morphological changes as well as the reduction of the ceramics to metallic materials. A robust method to synthesize FeNC catalysts is by mixing the separate Fe, N and C precursors and using optimized thermal treatment. In this study, the effect of the pyrolysis conditions as well as the ratio of FeNC precursors to TTO was investigated with various characterization methods, e.g. X-ray absorption spectroscopy, Mossbauer spectroscopy, and high resolution TEM. The characterization techniques confirm the presence of single atom Fe as well as different Sn species that might contribute to the activity. The resulting materials were electrochemically characterized with rotating disc electrode techniques and in PEM fuel cells for their ORR-activity and durability. It was shown that the activity of materials with a high FeNC precursor content relative to TTO can outperform a reference FeNC synthesized similarly but without TTO, in both RDE (Figure) and PEMFC.The presentation will report in detail the effects of pyrolysis conditions and FeNC precursor/TTO content on the structure, activity and stability of materials.(1) Mehmood, A. et al. High Loading of Single Atomic Iron Sites in Fe–NC Oxygen Reduction Catalysts for Proton Exchange Membrane Fuel Cells. Nat. Catal. 2022, 5 (4), 311–323. https://doi.org/10.1038/s41929-022-00772-9.(2) Gasteiger, H. A.; Marković, N. M. Just a Dream—or Future Reality? Science 2009, 324 (5923), 48–49. https://doi.org/10.1126/science.1172083.(3) Zion, N. et al.. Electrocatalysis of Oxygen Reduction Reaction in a Polymer Electrolyte Fuel Cell with a Covalent Framework of Iron Phthalocyanine Aerogel. ACS Appl. Energy Mater. 2022, 5 (7), 7997–8003. https://doi.org/10.1021/acsaem.2c00375.(4) Liu, S.et al. Atomically Dispersed Iron Sites with a Nitrogen–Carbon Coating as Highly Active and Durable Oxygen Reduction Catalysts for Fuel Cells. Nat. Energy 2022, 7 (7), 652–663. https://doi.org/10.1038/s41560-022-01062-1.(5) Jiménez-Morales, et al. Strong Interaction between Platinum Nanoparticles and Tantalum-Doped Tin Oxide Nanofibers and Its Activation and Stabilization Effects for Oxygen Reduction Reaction. ACS Catal. 2020, 10 (18), 10399–10411. https://doi.org/10.1021/acscatal.0c02220. Figure 1

Formation of Delocalized Linear M-B-M Covalent Bonds: A Combined Experimental and Theoretical Study of BM2(CO)8+ (M = Co, Rh, Ir) Complexes.

Investigations of transition-metal boride clusters not only lead to novel structures but also provide important information about the metal-boron bonds that are critical to understanding the properties of boride materials. The geometric structures and bonding features of heteronuclear boron-containing transition metal carbonyl cluster cations BM(CO)6+ and BM2(CO)8+ (M = Co, Rh, and Ir) are studied by a combination of the infrared photodissociation spectroscopy and density functional calculations at B3LYP/def2-TZVP level. The completely coordinated BM2(CO)8+ complexes are characterized as a sandwich structure composed of two staggered M(CO)4 fragments and a boron cation, featuring a D3d symmetry and 1Eg electronic ground state as well as metal-anchored carbonyls in an end-on manner. In conjunction with theoretical calculations, multifold metal-boron-metal bonding interactions in BM2(CO)8+ complexes involving the filled d orbitals of the metals and the empty p orbitals of the boron cation were unveiled, namely, one σ-type M-B-M bond and two π-type M-B-M bonds. Accordingly, the BM2(CO)8+ complexes can be described as a linear conjugated (OC)4M═B═M(CO)4 skeleton with a formal B-M bond index of 1.5. The three delocalized d-p-d covalent bonds render compensation for the electron deficiency of the cationic boron center and endow both metal centers with the favorable 18-electron structure, thus contributing much to the overall structural stability of the BM2(CO)8+ cations. As a comparison, the saturated BRh(CO)6+ and BIr(CO)6+ complexes are determined to be a doublet Cs-symmetry structure with an unbridged (OC)2B-M(CO)4 pattern, involving a two-center σ-type (OC)2B → M(CO)4+ dative single bond along with a weak covalent B-M half bond. This work offers important insight into the structure and bonding of late transition metal boride carbonyl cluster cations.

Ab initio investigation of the geometrical behavior in solution and electronic structure of the anion complexes [bis(1,3-dithiole-2-thione-4,5-dithiolate)M], for M = Bi(III), Sb(III), and Zn(II).

1,3-Dithiole-2-thione-4,5-dithiolate (dmit) ligands are known for their conductive and optical properties. Dmit compounds have been assessed for use in sensor devices, information storage, spintronics, and optical material applications. Associations with various metallic centers endow dmit complexes with magnetic, optical, conductive, and antioxidant properties. Optical doping can facilitate the fabrication of magnetic conductor materials from ground-state nonmagnetic cations. While most studied complexes involve transition-metal centers due to their diverse chemistry, compounds with representative elements are less explored in the literature. This study investigated the structural and electronic properties of bisdmit complexes with representative Bi(III), Sb(III), and Zn(II) cations. AIMD calculations revealed two new geometries for Bi(III) and Zn(II) complexes, diverging from the isolated geometry typically used in quantum chemical calculations. The coordination of acetonitrile molecules to the cationic centers of the complexes resulted in unstable structures, while the dimerization of the complexes was stable. SA-CASSCF/NEVPT2 calculations were applied to the structures of the isolated complexes and stable dimers, confirming the multireference character of the electronic structure of the three systems and the multiconfigurational character of the Bi(III) complex. The electronic spectra simulated by the STEOM-DLPNO-CCSD calculations accurately reproduced the experimental UV‒Vis spectra indicating the participation of the isolated Bi(III) dmit complex and its dimeric form in solution. AIMD calculations of the dmit salts were conducted using the GFN2-xTB method with 60 explicit acetonitrile molecules as the solvent at 300K for a total simulation time of 50.0ps, with printing intervals of 0.5fs. The final geometries were optimized employing the PBEh-3c compound method, incorporating implicit conductor-like polarizable continuum model (CPCM) solvation for acetonitrile. Local energy decomposition (LED) analysis at the DLPNO-CCSD(T)/Def2-TZVP level of theory was utilized to investigate the stability of the complex geometries identified by AIMD. The electronic structures of the complexes were assessed using the SA-CASSCF/NEVPT2/Def2-TZVP method to confirm the multiconfigurational and multireference nature of their electronic structures. Electronic spectra were analyzed using the STEOM-DLPNO-CCSD/Def2-TZVP method, with CPCM used to simulate an acetonitrile medium.

Hydrogen splitting at a single phosphorus centre and its use for hydrogenation.

Catalytic processes are largely dominated by transition-metal complexes. Main-group compounds that can mimic the behaviour of the transition-metal complexes are of great interest due to their potential to substitute or complement transition metals in catalysis. While a few main-group molecular centres were shown to activate dihydrogen via the oxidative addition process, catalytic hydrogenation using these species has remained challenging. Here we report the synthesis, isolation and full characterization of the geometrically constrained phosphenium cation with the 2,6-bis(o-carborano)pyridine pincer-type ligand. Notably, this cation can activate the H-H bond by oxidative addition to a single PIII cationic centre, producing a dihydrophosphonium cation. This phosphenium cation is also capable of catalysing hydrogenation reactions of C=C double bonds and fused aromatic systems, making it a main-group compound that can both activate H2 at a single molecular main-group centre and be used for catalytic hydrogenation. This finding shows the potential of main-group compounds, in particular phosphorus-based compounds, to serve as metallomimetic hydrogenation catalysts.

Cationic Bis(hydrosilane)-Coinage-Metal Complexes: Synthesis, Characterization, and Use as Catalysts for Outer-Sphere C=O Hydrosilylation Not Involving Metal Hydrides.

The preparation of cationic bis(hydrosilane)-coinage-metal complexes by chloride abstraction from the neutral metal chloride precursors with Na[BArF 4] is described. Unlike previously reported hydrosilane-stabilized copper and silver complexes, the presented complexes are cationic and feature two bidentate (ortho-silylphenyl)phosphine ligands. These complexes were fully characterized by NMR spectroscopy and X-ray diffraction analysis, revealing that both Si-H bonds are activated by the Lewis acidic cationic metal center. The new complexes were found to be effective in catalytic carbonyl hydrosilylation, leading to the corresponding silyl ethers under mild conditions without the addition of an external base. Combined mechanistic control experiments and quantum chemical calculations support an ionic outer-sphere mechanism, in which a neutral metal alkoxide species instead of a metal hydride is the key intermediate that interacts with the silylcarboxonium ion to generate the silyl ether.

Cationic Bis(hydrosilane)−Coinage Metal Complexes: Synthesis, Characterization, and Use as Catalysts for Outer‐Sphere C=O Hydrosilylation Not Involving Metal Hydrides

The preparation of cationic bis(hydrosilane)–coinage‐metal complexes by chloride abstraction from the neutral metal chloride precursors with Na[BArF4] is described. Unlike previously reported hydrosilane‐stabilized copper and silver complexes, the presented complexes are cationic and feature two bidentate ortho‐(silylphenyl)phosphine ligands. These complexes were fully characterized by NMR spectroscopy and X‐ray diffraction analysis, revealing that both Si–H bonds are activated by the Lewis acidic cationic metal center. The new complexes were found to be effective in catalytic carbonyl hydrosilylation, leading to the corresponding silyl ethers under mild conditions without the addition of an external base. Combined mechanistic control experiments and quantum chemical calculations support an ionic outer‐sphere mechanism, in which a neutral metal alkoxide species instead of a metal hydride is the key intermediate that interacts with the silylcarboxonium ion to generate the silyl ether.

Typical MOFs-derived nanoporous carbon: Insight into structures, properties and Pb(II) adsorption mechanism

A series of nanoporous carbon (NC) materials were synthesized by direct carbonization of traditional metal organic frameworks (MOFs) including copper-based (HKUST-1), nickel-based (Ni-MOF), zinc-based (ZIF-8), zirconium-based (UiO-66) and iron-based (Fe-BTC) for the removal of Pb(II) from simulated waste water. The physical and chemical characteristics before and after adsorption were thoroughly investigated by Fourier transforms infrared spectroscopy (FTIR), X-Ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption/desorption analyses. The adsorption kinetics and isothermal thermodynamic properties and the effects of five central different cations on the removal of Pb(II) were compared. The adsorption kinetics were well described by the quasi-second-order model and the adsorption isotherm consistent with the Langmuir equation. The adsorption process of Pb (II) is feasible, spontaneous, endothermic and reusable on the five nanoporous carbons. Among them, Fe-BTC-NC showed the best adsorption performance for Pb (II), and the maximum adsorption capacity was 479.93 mg/g. This work highlights the applications of MOFs derived nanocarbon in heavy metal contaminated water treatment and offers a facile method for the design of novel nanocarbon materials.

Thermodynamic H-Abstraction Abilities of Nitrogen Centered Radical Cations as Potential Hydrogen Atom Transfer Catalysts in Y-H Bond Functionalization.

Y-H bond functionalization has always been the focus of research interest in the area of organic synthesis. Direct hydrogen atom transfer (HAT) from the Y-H bond is one of the most efficient and practical methods to activate the Y-H bond. Recently, nitrogen centered radical cations were broadly utilized as H-abstraction catalysts to activate Y-H bonds via the HAT process. As a type of HAT catalyst, the H-affinity of nitrogen centered radical cations is a significant thermodynamic parameter to quantitatively evaluate the thermodynamic H-abstraction potentials of nitrogen centered radical cations. In this work, the pK a values of 120 protonated N-containing compounds in acetonitrile (AN) are predicted, and the H-affinities of 120 nitrogen centered radical cations in AN are derived from the reduction potentials of nitrogen centered radical cations and pK a of protonated N-containing compounds using Hess' law. This work focuses on the H-abstraction abilities of 120 nitrogen centered radical cations in AN to enrich the molecule library of novel HAT catalysts or H-abstractors and provides valuable thermodynamic guidelines for the application of nitrogen centered radical cations in Y-H bond functionalization.

Chlorido-[5,10,15,20-tetra-kis-(quinoline-7-carboxamido)-porphinato]iron(III).

The title compound, [Fe(C84H52N12O4)Cl], crystallizes in space group C2/c. The central FeIII cation (site symmetry 2) is coordinated in a fivefold manner, with four pyrrole N atoms of the porphyrin core in the basal sites and one Cl atom (site symmetry 2) in the apical position, which completes a slightly distorted square-pyramidal environment. The porphyrin macrocycle shows a characteristic ruffled-shape distortion and the iron atom is displaced out of the porphyrin plane by 0.42 Å with the average Fe-N distance being 2.054 (4) Å; the Fe-Cl bond length is 2.2042 (7) Å. Inter-molecular C-H⋯N and C-H⋯O hydrogen bonds occur in the crystal structure.

Mechanistic insights into C(sp2)-H activation in 1-Phenyl-4-vinyl-1H-1,2,3-triazole derivatives: a theoretical study with palladium acetate catalyst.

The activation of C-H bonds is a fundamental process in synthetic organic chemistry, which enables their replacement by highly reactive functional groups. Coordination compounds serve as effective catalysts for this purpose, as they facilitate chemical transformations by interacting with C-H bonds. A comprehensive understanding of the mechanism of activation of this type of bond lays the foundation for the development of efficient protocols for cross-coupling reactions. We explored the activation of C(sp2)-H bonds in 1-Phenyl-4-vinyl-1H-1,2,3-triazole derivatives with CH3, OCH3, and NO2 substituents in the para position of the phenyl ring, using palladium acetate as catalyst. The studied reaction is the first step for subsequent conjugation of the triazoles with naphthoquinones in a Heck-type reaction to create a C-C bond. The basic nitrogen atoms of the 1,2,3-triazole coordinate preferentially with the cationic palladium center to form an activated species. A concerted proton transfer from the terminal vinyl carbon to one of the acetate ligands with low activation energy is the main step for the C(sp2)-H activation. This study offers significant mechanistic insights for enhancing the effectiveness of C(sp2)-H activation protocols in organic synthesis. All calculations were performed using the Gaussian 09 software package and density functional theory (DFT). The structures of all reaction path components were fully optimized using the CAM-B3LYP functional with the Def2-SVP basis set. The optimized geometries were analyzed by computing the second-order Hessian matrix to confirm that the corresponding minimum or transition state was located. To account for solvent effects, the Polarizable Continuum Model of the Integral Equation Formalism (IEFPCM) with water as the solvent was used.

Silyliumylidene Ion Stabilized by Two σ-Donating Ni(0)- and Pd(0)-Fragments.

A silyliumylidene ion 2 stabilized by two σ-donating Ni(0)- and Pd(0)-fragments was successfully synthesized. Due to the σ-donation of M→Si interactions, 2 presents a pyramidalized cationic silicon center with a localized lone pair. The additional coordination of basic Pd(0) fragment to the mono-Ni(0)-stabilized silyliumylidene 1 results in a higher HOMO level and an unchanged HOMO-LUMO gap and thus, 2 remains highly reactive. Interestingly, the coordination mode at the Si center is closely related to the nature of M-ligands. Indeed, the donor/donor-stabilized silyliumylidene ion 2 has been transformed into a donor/acceptor-stabilized ion 13, featuring a trigonal planar Si center with a vacant orbital, just via a ligand exchange reaction from PCy3/NHC toward PMe3.

Revisiting the mechanism of β-O-4 bond cleavage during acidolysis of lignin part 10: reactions of C6–C2-type non-phenolic syringyl model compounds and comparison of the reactions with those of the guaiacyl analogues

A C6–C2-type non-phenolic syringyl lignin model compound (I, 2-(2-methoxyphenoxy)-1-(3,4,5-trimethoxyphenyl)ethanol) as well as its derivatives was acidolyzed in aqueous 82vol% 1,4-dioxane containing 0.2 mol/L HBr, HCl, or H2SO4 at 85ºC. The results were compared with those on the guaiacyl analogues (V as well as its derivatives) obtained in our previous reports. The acidolysis of compound I was slower than that of compound V, which is in accordance with our previous result on the formation rates of the benzyl cation intermediates (BC) from a syringyl compound and its guaiacyl analogue. The enol ether-type compound was primarily produced in the acidolysis of compound I, similar to that of compound V. The acidolysis using HBr or HCl was faster than that using H2SO4, indicating the participation of Br¯ or Cl¯, respectively, in the acidolysis. It was suggested that Br¯ (as well as Cl¯) adds to the cation center of the BC to afford the adduct in the acidolysis of compound I, similar to that of compound V, and hence, this adduct formation is a major bypass of the common route. The bypass activity in the acidolysis of compound I was about half in that of compound V.

Enhanced photocatalytic H2 production activity by loading Ni complex on flower-like MoS2 nanomaterials

BackgroundExploring efficient H2-production photocatalysts is very important for converting solar energy to chemical energy. Some approaches were developed to prevent the recombination of photogenerated electron-hole pairs, ultimately enhancing the photocatalytic H2 production activity. Methods3D flower-like MoS2 nanomaterials were surface-modified by the Ni complex as the redox mediator to make the composite photocatalysts. This work investigated the effect of zeta potential on the Ni-complex loading, charge separation, and photocatalytic H2 production activity of MoS2. Significant findingsThe Ni-complex with central cation can be loaded on MoS2 with negative zeta potential due to the columb attraction force. The photogenerated carriers can transfer from MoS2 to the central Ni ion of the complex due to the ligands-stabilized multiple oxidation states of Ni, leading to suppressed charge recombination. The FE-TEM mapping and XPS confirm the loading of Ni complex. The photoluminescence, photocurrent response, and EIS tests confirm the improved photoinduced charge separation of the Ni complex-modified photocatalyst. The flower-like microstructure of MoS2 provides a large specific surface area and high light absorption. The H2 production activity of MoS2-Ni complex photocatalyst (3320 μmol g−1 h−1) is higher than that of the pristine MoS2 photocatalyst (2576 μmol g−1 h−1).

A Digermanium(III) 1,2-Dication Stabilized by Amidinate and cAAC-Phosphinidenide Ligands.

A digermanium(III) 1,2-dication comprises two cationic centers located at two interconnected Ge atoms. The strong Coulombic repulsion between two positively charged germanium cations hinders their bond formation. Balancing these two oppositions was achieved by using amidinate and cyclic (alkyl)amino carbene (cAAC)-phosphinidenide ligands, where an amidinato cAAC-phosphinidenidogermylene complex, [LGeP(cAACMe)] (2, where L = PhC(NtBu)2, cAACMe = :C{C(Me)2CH2C(Me)2NAr}, and Ar = 2,6-iPr2C6H3), underwent one-electron oxidation with a bis(phosphinidene) radical cation, [(cAACMe)P]2•+, to form a digermanium(III) 1,2-dication, [LGeP(cAACMe)]22+, in compound 4.

ONTOGENETIC TRANSFORMATIONS OF BONES OF THE HUMAN ORBIT

Introduction. Elucidation of the sources of human orbital bones, clarifi cation of the sequence of their ossifi cation will allow to create a morphological basis for eff ective interpretation of the data of fetal condition monitoring, will contribute to early diagnosis of variants of the structure and possible malformations of the head, organ of vision and related structures.The aim of the study. The aim of this work was to fi nd out the sources of origin, the chronology of ossifi cation, the characteristics of age-related topographic and anatomical changes in the bones of the orbit.Material and methods. 18 series of histological sections of samples of human embryos and pre-fetuses at the age of 4-12 weeks of intrauterine development (4,0-80,0 mm parietal- coccygeal length) and samples of 12 fetuses at the age of 4-9 months of intrauterine development (130,0-450. 0 mm parietal- calcaneal length) using a complex of morphological research methods (anthropometry, morphometry, preparation of histological sections, dissection, three- dimensional reconstruction of series of histological sections and computer tomography, statistical analysis).The study was conducted in accordance with the main provisions of the European Union Convention on Human Rights andBiomedicine (1997), as well as the Helsinki Declaration on Ethical Principles of Medical Research Involving Human Subjects(1964-2008), EU Directive No. 609 (1986), Order of the Ministry of Health of Ukraine dated 23.09.2009 No. 690.The work was carried out within the framework of the initiative research work of the Department of Histology, Cytology andEmbryology of the Bukovinian State Medical University «Structural and functional peculiarities of tissues and organs in ontogenesis, regularities of variant, constitutional, sex and age-related and comparative human morphology». State registration number: 0121U110121. Deadlines: 01.2021-12.2025.The results. The fi rst signs of the appearance of ossifi cation centers around the main nervous and visceral contents of the rudiment of the orbit are determined in 6-week-old embryos in the form of seven cartilaginous bone models, and the fi rst centers of ossifi cation among the rudiments of bones participating in the formation of the orbit are found in the rudiment of the maxilla. In the 6th month of intrauterine development, the processes of ossifi cation of the frontal, sphenoid, ethmoid and maxillary bones begin. At the end of the 8th month of intrauterine development, due to the ossifi cation processes of the lesser wing of the sphenoid and frontal bones, the orbit acquires features of a defi nitive structure.From the beginning of the fetal period of human ontogenesis, ossifi cation of the structures of the sphenoid bone continues, which leads to morphological transformations of the orbit in 5-month fetuses – it is separated from the sphenopalatine and infratemporal fossa by a bone layer, the optic canal is formed, and in 6-month fetuses processes of ossifi cation of the frontal, sphenoid, ethmoid and maxillary bones, and Müller’s orbital muscle changes its structure into a fi brous one.The analysis of the age-related dynamics of the morphometric parameters of the orbit during the fetal period of intrauterine development made it possible to establish the peculiarities of changes in its diameter, circumference and area, which are expressed by mathematical functions: diameter of the orbit, mm = –0. 2285+0.4704*x; circumference of the orbit, mm = –0.2924+1.4595*x; area of the orbit, mm2 = –87.8597+8.0387*x, where x is the age of the human fetus in weeks.Conclusion. The critical periods of the development of the orbit are the 6th month of prenatal ontogenesis, during which there is an uneven growth rate of the horizontal size of the orbit in relation to the vertical one, and its shape returns to the mesoconchal, which was previously observed in fetuses, as well as the 8th month, during which the growth of all parameters of the orbit slows down due to intensive processes of organogenesis of its visceral structures.

Unraveling Spatially Dependent Hydrophilicity and Reactivity of Confined Carbocation Intermediates during Methanol Conversion over ZSM-5 Zeolite.

Carbocations play a pivotal role as reactive intermediates in zeolite-catalyzed methanol-to-hydrocarbon (MTH) transformations. However, the interaction between carbocations and water vapor and its subsequent effects on catalytic performance remain poorly understood. Using micro-magnetic resonance imaging (μMRI) and solid-state NMR techniques, this work investigates the hydrophilic behavior of cyclopentenyl cations within ZSM-5 pores under vapor conditions. We show that the polar cationic center of cyclopentenyl cations readily initiates water nucleus formation through water molecule capture. This leads to an inhomogeneous water adsorption gradient along the axial positions of zeolite, correlating with the spatial distribution of carbocation concentrations. The adsorbed water promotes deprotonation and aromatization of cyclopentenyl cations, significantly enhancing the aromatic product selectivity in MTH catalysis. These results reveal the important influence of adsorbed water in modulating the carbocation reactivity within confined zeolite pores.