Photocatalytic oxygen-atom transmutation of oxetanes.

Intramolecular reorganization energy (RE) of molecules derived from the diketopyrrolopyrrole (DPP) unit has been studied using B3LYP/6-31G(d,p) theory. It was found that the replacement of the oxygen atoms with sulfur in the DPP unit led to a smaller RE for both the hole and electron transfer processes. One disadvantage of the sulfur replacement is the twist of the conjugated backbone, which might impair the $\pi - \pi $ interactions in the solid state. The RE calculated from the adiabatic potential energy surfaces and that derived from the normal mode analysis agreed well for both systems. Electronic structure data showed that the replacement of oxygen atoms with sulfur in the DPP unit might lead to the development of ambipolar compounds with low RE.

Selenium, a group 16 (chalcogen) element, can endow metal oxides with unique properties when replacing oxygen atoms from specific sites. Polyoxometalates (POMs), a class of anionic metal oxide clusters, exhibit structure-dependent properties and applications. Despite the potential of chalcogen substitution, the replacement of oxygen atoms in POMs with chalcogens has been rarely explored. In a recent study, we demonstrated site-selective oxygen-to-sulfur substitution in the Keggin-type POM [SiW12O40]4-. Building on this, we now report the first synthesis of a polyoxoselenidotungstate, featuring terminal selenido ligands (W[double bond, length as m-dash]Se bonds), using a site-selective oxygen-to-selenium substitution reaction. By reacting [SiW12O40]4- with Woollins' reagent (2,4-diphenyl-1,3,2,4-diselenadiphosphetane 2,4-diselenide) in organic solvents, all twelve terminal oxido ligands (W[double bond, length as m-dash]O) were selectively converted to selenido ligands (W[double bond, length as m-dash]Se). The resulting compound [SiW12O28Se12]4- retains the Keggin-type framework and exhibits distinct optical and electronic properties owing to the incorporated selenium atoms. These findings pave the way for the systematic modification of oxygen sites in POMs with the heavier chalcogens sulfur and selenium, opening new avenues for tailoring their properties and expanding their utility across diverse fields of materials science.

The new macrocyclic and acyclic complexes of the uranyl ion—uranyl–oxygen cluster formation in fast atom bombardment mass spectra

Magnetism without magnetic ions in non-magnetic perovskites SrTiO 3, SrZrO 3 and SrSnO 3

The interaction of nitric (NO) and nitrous (N2O) oxide with ultrathin (∼1.5–3.5 nm) oxide and oxynitride films on silicon has been studied by performing high resolution depth profiling using medium energy ion scattering and isotopic labeling methods. We observe that, after NO annealing at 850 °C, both O and N incorporate near the SiO2/Si interface. There is no nitrogen and little newly incorporated oxygen observed at the surface, implying that NO diffuses through the oxide film and dissociates and reacts at the interface. For N2O annealing, atomic oxygen resulting from decomposition of the gas can replace oxygen atoms in both oxide and oxynitride films. This replacement is most important at the surface, but also, to a smaller extent, occurs in the middle of the film. For ultrathin oxynitride films, oxide growth during reoxidation is faster in N2O than in pure O2. Atomic oxygen also influences the nitrogen distribution, which moves further into the film and accumulate at the new interface. We discuss the roles of atomic oxygen and peroxyl bridging oxygen species in explaining the observed phenomena.

We studied the structural change of perhydropolysilazane to silicon nitride during the process of heat treatment by means of in situ X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS), together with Fourier transformed infra-red (FT-IR) and temperature programmed desorption (TPD) spectroscopies. It was revealed that nucleophilic attack on silicon atoms in the polymer began to proceed above 200° C, by nitrogen atoms in the polymer itself and also in atmospheric ammonia. From 400° C to 600° C, dehydrogenation also occurred and produced dangling bonds which were attacked by ammonia molecules to form the network of SiN4 tetrahedra. Although oxidation by residual moisture was observed to some extent at 600° C, further heat treatment in ammonia formed Si–N bonds via replacement of oxygen atoms by nitrogen atoms to complete the formation of Si3N4-like structure.

This paper presents the results on the synthesis and study of the properties of NiCo2O4 and NiCo2S4 nanostructures obtained by hydrothermal synthesis for their use as supercapacitor electrodes. A method is developed for growing a nanostructure from a ternary metal oxide NiCo2O4 on a nickel substrate. The structural features of the synthesized NiCo2O4and NiCo2S4 nanostructures are studied using X-ray phase analysis. The obtained samples have a cubic modification NiCo2O4 and NiCo2S4. The data on the morphology of the synthesized samples obtained by scanning electron microscopy are presented. The samples are in the form of nanoneedles and nanowires grown on a nickel substrate. Methods for the synthesis of NiCo2O4 nanostructures have been studied, optimal conditions for the growth of nanostructures from NiCo2O4 have been determined, and a NiCo2O4 sulfurization method has been developed to obtain a NiCo2O4 nanostructure. Comparative studies have been carried out on the effects of sulfurization on the electrochemical characteristics of the obtained electrodes. It is found that, despite the fact that NiCo2O4 oxide nanostructures have a high theoretical capacitance, the replacement of oxygen atoms by sulfur atoms increases the conductivity of the materials and leads to a further increase in the specific capacitance of the end electrodes. The maximum Cs obtained specific capacitance for NiCo2S4 is 1976 F g-1 and while for NiCo2O4 it is 413 F g-1 at a scan rate of 5 mV/s. The results of the dependence of the specific capacitance on the scanning speed during measurements are also presented.

The development of polymer‐based conductive inks has gained increasing interest in the areas of printed and molded electronics. Graphene‐based materials are explored in this scope, reduced graphene oxide (rGO) being among the most used conductive filler components of the inks. Herein, rGO is doped with nitrogen to obtain N‐rGO; the replacement of oxygen atoms by nitrogen ones increases the electrical conductivity of graphene. Polymer‐based conductive inks reinforced with graphene are developed based on polyvinylpyrrolidone (PVP) as polymer binder and dihydrolevoglucosenone (Cyrene) as solvent, leading thus to environmentally friendly conductive inks. Screen‐printable inks are optimized in terms of viscosity and adhesion properties, leading to printed films with sheet resistance close to Rs = 1 kΩ sq−1, the graphene:PVP inks being also biocompatible and nontoxic.

Glasses: Oxynitride Glass Formation and Structure

The PCM/COSMO approach was employed to calculate the relative stability of radicals derived from the antimalarial artemisinin. The calculations were performed in polar (water) and apolar (THF) solvent at the density functional level [B3LYP/6‐31g(d)]. Relative stabilities were calculated by means of isodesmic equations using artemisinin as reference. Replacement of oxygen atoms by CH2 unities was found to decrease the relative stability of the anionic radical intermediates. The degree of destabilization is reduced in the presence of solvent, being less in water than in THF. The dipole moment and the corresponding solvation free energies of these species modulate this effect. Derivatives with inverted stereochemistry are more stable than those with the artemisinin‐like stereochemistry, although the solvent attenuates this stabilization effect. As was found in the in vacuo calculations, the radicals centered on carbon are always more stable than the corresponding radicals centered on oxygen. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006

Sugars with heteroatoms other than oxygen have attained considerable importance in glycobiology and in drug design since they are often more stable in blood plasma due to their resistance to enzymes, such as glycosidases, phosphorylases and glycosyltransferases. The replacement of oxygen atoms in sugars with sulfur forms thio-sugars, which are potentially useful for the treatment of diabetes and some bacterial and viral infections. Here, we evaluated the antibacterial activity of thio-functionalized carbohydrate derivatives. A set of 21 compounds was screened against acid-fast Mycobacterium tuberculosis (Mtb), gram-negative Escherichia coli and gram-positive Staphylococcus aureus. The tested carbohydrate derivatives were most effective against tubercle bacilli, with as many as five compounds (thioglycoside 6, thiosemicarbazone 16A, thiosemicarbazone 20, aminothiadiazole 23, and thiazoline 26) inhibiting its growth with MIC50 ≤ 50 µM/CFU. Only two compounds (aminothiadiazole 23 and thiazoline 26) were able to inhibit the growth of E. coli at concentrations below 1 mM, and one of them, aminothiadiazole 23, inhibited the growth of S. aureus at a concentration ≤1 mM. The five compounds affecting the growth of mycobacteria were either thiodisaccharides (6, 16A, and 20) or thioglycosides (23 and 26). All of these compounds (6, 16A, 20, 23, and 26) were able to inhibit the growth of Mtb deposited within human macrophages. However, three of the five selected compounds (6, 23, and 26) exhibited relatively high cytotoxicity in mouse fibroblasts at micromolar concentrations. The selected thio-sugars are very promising compounds, thus making them candidates for further modifications that would decrease their cytotoxicity against eukaryotic cells without affecting their antimycobacterial potential.

Photoinduced electron transfer in azatriangulenium salts

Synthetic anion carriers are essential for studying natural ion transporters and channels and for useful applications, such as treatment of channelopathies, supramolecular architecture, anion sensing and catalysis. Driven by the hypothesis that replacement of oxygen atoms in bambusurils (BUs) by other heteroatoms could significantly modify their anion binding properties, we calculated their molecular electrostatic potential and found a general trend of anion‐affinity: S>O>NH. We confirmed these predictions experimentally by synthesizing semithio‐ and semiaza‐BUs and studying their binding and transport properties. Although all analogs are excellent anion binders, only semithio‐bambus[6]uril is an effective transmembrane transporter capable of polarizing lipid membranes through selective anion uniport. Semiaza‐BUs exhibit simultaneous accommodation of three anions, linearly positioned along the main symmetry axis, which is reminiscent of natural chloride channels in E. coli.

Anions [formula omitted] and [formula omitted] and the superacidic properties of their conjugate acids

We present theoretical results for the dipole moment, linear polarizability, and first hyperpolarizability of the urea and thiourea molecules in solid phase. The in-crystal electric properties were determined by applying a supermolecule approach in combination with an iterative electrostatic scheme, in which the surrounding molecules are represented by point charges. It is found for both urea and thiourea molecules that the influence of the polarization effects is mild for the linear polarizability, but it is marked for the dipole moment and first hyperpolarizability. The replacement of oxygen atoms by sulfur atoms increases, in general, the electric responses. Our second-order Møller-Plesset perturbation theory based iterative scheme predicts for the in-crystal dipole moment of urea and thiourea the values of 7.54 and 9.19 D which are, respectively, increased by 61% and 58%, in comparison with the corresponding isolated values. The result for urea is in agreement with the available experimental result of 6.56 D. In addition, we present an estimate of macroscopic quantities considering explicit unit cells of urea and thiourea crystals including environment polarization effects. These supermolecule calculations take into account partially the exchange and dispersion effects. The results illustrate the role played by the electrostatic interactions on the static second-order nonlinear susceptibility of the urea crystal.