STUDY OF POTASSIUM INTERCALATION IN TO THE GRAPHENE/MoS STRUCTURE

Используя современные расчеты из первых принципов, в данной работе мы систематически изучали интеркаляцию атомов калия в гибридную двухслойную структуру графене/ MoS. В ходе исследования были определенны концентрации атомов калия при которых энергия формирования является отрицательной. Так в частности при концентрации атомов калия, по отношению к атомам молибдена, не более x = 0,43 формирование слоя атомов калия между слоями графен/ MoS является энергетически выгодным. Начиная с концентрации атомов калия x > 0,75 наблюдается увеличение расстояние между слоями графен и MoS, что в дальнейшем приводит к разрушению структуры. Расчет зарядов показал, что атом калия при небольших концентрациях отдает примерно 0,8 - 0,85 электрона, 0,35 из которых перетекает на атомы углерода, а 0,4 - 0,5 перетекает на дисульфид молибдена. Расчёт разность электронных плотностей показал, что связь между слоями графена, дисульфид молибдена и калия имеет ковалентный характер. Using modern ab-initio calculations, in this work, we systematically studied the intercalation of potassium atoms into a hybrid two-layer graphene/MoS structure. In the course of the study, concentrations of potassium atoms were determined at which the formation energy is negative. So, in particular, when the concentration of potassium atoms (in relation to molybdenum atoms) is not more than x = 0,43, formation of a layer of potassium atoms between the graphene/ MoS layers is energetically favorable. Beginning with the concentration of potassium atoms x > 0,75 , an increase in the distance between the graphene and MoS layers is observed, which further leads to destruction of the structure. Calculation of charges showed that a potassium atom at low concentrations gives up about 0,8 - 0,85 electrons, 0,35 of which flow on carbon atoms, and 0,4 - 0,5 to molybdenum disulfide. Calculation of the difference in electron densities showed that the bond between the layers of graphene, molybdenum and potassium disulfide has a covalent nature.

Computational Study of Halogen-Halogen Interactions in Polyhalide Ionic Liquids

Recent years have seen many specific applications of polyhalide ionic liquids (ILs) such as oxidizing solvents for metals and alloys, immersion fluids for optical mineralogy, and electrolyte components for dye-sensitized solar cells. In this work, interhalogen interactions in a set of polyhalide ILs composed of polyhalide anions, [X3]−, [X5]− and [X7]− (X = I or Br), with two typical cations, tetramethylammonium [NMe4]+ and 1,3-dimethylimidazolium [DMIM]+, were thoroughly studied from a computational point of view. In addition, a halogen-bonded supramolecular anion, [C6F13-I∙∙∙I∙∙∙I-C6F13]−, was also taken into account for comparison. Unlike those in bare polyhalide ions, halogen-halogen interactions in ionic pairs for the investigated ILs are somewhat asymmetric caused by the interactions between the cations and the anions. Most interhalogen contacts in ionic pairs have some covalent content, while I∙∙∙I interactions in the complexes of the supramolecular anion are purely noncovalent. In general, there are two classes of interhalogen bonds in ionic pairs: one class with longer X∙∙∙X distances shows primarily ionic character, while the other with shorter distances has a larger degree of covalency, i.e. intermediate ionic/covalent nature.

Electride Characteristics of M2(h5-E5)2 (M= Be, Mg; E= Sb5-)

Ab initio computation is performed on the binuclear sandwich complexes, M 2 ( h 5 -Sb 5 ) 2 . Eclipsed and staggered conformations are generated due to the h 5 mode of binding by Sb 5 - ligand with the alkaline earth metals (Be and Mg metals). The complexes are thermodynamically stable at room temperature. The electron density descriptors and the natural bond orbital (NBO) analysis confirmed the covalent nature of the M-M bond. Both Be 2 ( h 5 -Sb 5 ) 2 and Mg 2 ( h 5 -Sb 5 ) 2 complexes have one non-nuclear attractor (NNA) at the center of the M-M bond which is predicted and confirmed by the electron density analysis. At the NNA the values of the Laplacian of electron density are negative and an electron localization function basin (ELF) is present at the center of the M-M bond for localized electrons. Both the complexes show large values of nonlinear optical properties (NLO). Both the designed binuclear sandwich complexes Be 2 ( h 5 -Sb 5 ) 2 and Mg 2 ( h 5 -Sb 5 ) 2 behave as electride.

A proteome-wide map of 20(S)-hydroxycholesterol interactors in cell membranes

Oxysterols (OHCs) are hydroxylated cholesterol metabolites that play ubiquitous roles in health and disease. Due to the non-covalent nature of their interactions and unique partitioning in membranes, the analysis of live-cell, proteome-wide interactions of OHCs remains an unmet challenge. In this Resource, we present a structurally precise chemoproteomics probe for the osteogenic molecule 20(S)-hydroxycholesterol (20(S)-OHC) and provide a map of its proteome-wide targets in the membranes of living cells. Our target catalogue consolidates diverse OHC ontologies and demonstrates that OHC-interacting proteins cluster with specific processes in immune response and cancer. Competition experiments reveal that 20(S)-OHC is a chemo-, regio-, and stereoselective ligand for the protein Tmem97 (σ2 receptor), enabling molecular reconstruction of the Tmem97:20(S)-OHC binding site. Our results demonstrate that multiplexed, quantitative analysis of cellular target engagement can expose new dimensions of OHC activity and identify actionable targets for molecular therapy.

Revisiting the covalent nature of halogen bonding: a polarized three-center four-electron bond

The halogen bond could be described with a polarized 3c-4e bond.

New Family of Ionic Supersalts with Covalent-like Directionality and Unconventional Multiferroicity

Ionic crystals composed of elemental ions such as NaCl are centro-symmetric and, thus, non-polar due to directionless ionic bonding interactions. To develop polar materials, the directionality feature of covalent bonding is necessary. Here, we propose a novel way where ionically bonded crystals can develop polarity by changing their building blocks from elemental ions to cluster-ions. Superalkalis and superhalogens are clusters which mimic the chemistry of alkali and halogen atoms. Equally important, unlike the elemental ions, the geometries of these superions are not spherical. Endowed with these unique features, ionic supersalts form anisotropic polar structures with ionic bonding, yet covalent-like directionality, akin to sp3 hybridized systems. Using density functional theory and extensive structure searches, we predict a series of stable supersalts, PnH4MX4 (Pn = N, P; M = B, Al, Fe; X = Cl, Br) composed of superalkali PnH4 and superhalogen MX4 ions with unprecedented properties: (1) ferroelectricity with ultra-long ion displacements (~ 3 Å); (2) ferroelasticity with ultra-large reversible strain (> 40%); and (3) both with ultra-low switching barriers (about 6 to 13 meV/atom). These values are inconceivable in traditional ferroelectric/ferroelastic materials owing to their brittle covalent nature. Coupling of ferroelectricity with ferroelasticity can further enable strain-controlled polarization as well as electrically-controlled strain. In particular, PnH4FeX4 exhibits triferroic coupling of ferroelectricity, ferroelasticity, and antiferromagnetism where the spin directions can be altered via either ferroelastic or 90-degree ferroelectric switching. These ionic supersalts can be synthesized using facile solution-processed fabrication by exothermic reactions, MPn + 4HX→PnH4MX4 or PnH4X + MX3→PnH4MX4, which may open a new chapter in multiferroics.

Energy Gap-Refractive Index Relations in Perovskites

In this study, the energy gap-refractive index relations of perovskites are examined in detail. In general, the properties of perovskites are dependent on the structural reorganization and covalent nature of their octahedral cages. Based on this notion, a simple relation governing the energy gap and the refractive index is proposed for perovskites. The results obtained with this relation are in good accord with the literature values and are consistent with some well-established relations.

Structural, Photoluminescence and Electron Density Distribution Analysis of Rutile Phase TiO2

In this work, the mixed anatase and rutile phases of commercial TiO2 sample was purchased and converted to single rutile phase by sintering at 1000°C. Structural and spectroscopic analysis of the single phased rutile TiO2 were analyzed by PXRD, SEM, EDS, PL analysis, respectively. Rietveld profile refinement technique was performed to fit the observed and calculated PXRD profiles. Charge density distribution studies were used to determine the chemical bonding nature of Ti-O bond by maximum entropy method (MEM). From the MEM calculations, Ti-O bond exhibited covalent nature. PL measurements showed that the emission wavelength of rutile TiO2 at around 470 nm which may be due to band to band transitions of Ti and O atoms.

New Zampanolide Mimics: Design, Synthesis, and Antiproliferative Evaluation

Zampanolide is a promising microtubule-stabilizing agent (MSA) with a unique chemical structure. It is superior to the current clinically used MSAs due to the covalent nature of its binding to β-tubulin and high cytotoxic potency toward multidrug-resistant cancer cells. However, its further development as a viable drug candidate is hindered by its limited availability. More importantly, conversion of its chemically fragile side chain into a stabilized bioisostere is envisioned to enable zampanolide to possess more drug-like properties. As part of our ongoing project aiming to develop its mimics with a stable side chain using straightforward synthetic approaches, 2-fluorobenzyl alcohol was designed as a bioisosteric surrogate for the side chain based on its binding conformation as confirmed by the X-ray structure of tubulin complexed with zampanolide. Two new zampanolide mimics with the newly designed side chain have been successfully synthesized through a 25-step chemical transformation for each. Yamaguchi esterification and intramolecular Horner–Wadsworth–Emmons condensation were used as key reactions to construct the lactone core. The chiral centers at C17 and C18 were introduced by the Sharpless asymmetric dihydroxylation. Our WST-1 cell proliferation assay data in both docetaxel-resistant and docetaxel-naive prostate cancer cell lines revealed that compound 6 is the optimal mimic and the newly designed side chain can serve as a bioisostere for the chemically fragile N-acetyl hemiaminal side chain in zampanolide.

Ullmann Reactions of Carbon Nanotubes—Advantageous and Unexplored Functionalization toward Tunable Surface Chemistry

We demonstrate Ullmann-type reactions as novel and advantageous functionalization of carbon nanotubes (CNTs) toward tunable surface chemistry. The functionalization routes comprise O-, N-, and C-arylation of chlorinated CNTs. We confirm the versatility and efficiency of the reaction allowing functionalization degrees up to 3.5 mmol g−1 by applying both various nanotube substrates, i.e., single-wall (SWCNTs) and multi-wall CNTs (MWCNTs) of various chirality, geometry, and morphology as well as diverse Ullmann-type reagents: phenol, aniline, and iodobenzene. The reactivity of nanotubes was correlatable with the nanotube diameter and morphology revealing SWCNTs as the most reactive representatives. We have determined the optimized conditions of this two-step synthetic protocol as: (1) chlorination using iodine trichloride (ICl3), and (2) Ullmann-type reaction in the presence of: copper(I) iodide (CuI), 1,10-phenanthroline as chelating agent and caesium carbonate (Cs2CO3) as base. We have analyzed functionalized CNTs using a variety of techniques, i.e., scanning and transmission electron microscopy, energy dispersive spectroscopy, thermogravimetry, comprehensive Raman spectroscopy, and X-ray photoelectron spectroscopy. The analyses confirmed the purely covalent nature of those modifications at all stages. Eventually, we have proved the elaborated protocol as exceptionally tunable since it enabled us: (a) to synthesize superhydrophilic films from—the intrinsically hydrophobic—vertically aligned MWCNT arrays and (b) to produce printable highly electroconductive pastes of enhanced characteristics—as compared for non-modified and otherwise modified MWCNTs—for textronics.