Synthesis and characteristics of nanocrystalline materials in Ti,B, C and N containing system

In this work, the results of investigations of manufacturing ceramic materials on the basis of Ti, B, C and N containing systems are presented. The nanocrystalline ceramics were synthesized using a non-hydrolytic sol-gel method. The process was carried out in two stages. In the first low-temperature stage the precursor was obtained. The synthesis of ceramic phases, however, was conducted in the second high-temperature stage, in an argon atmosphere. Depending on the initial composition of the mixtures, the temperature and the time, the following products were obtained: TiC_x, TiC_xN_1−x, TiB₂ and B₄C.     

One single-step synthesis of multifunctional methylene blue-coated magnetite nanoparticles

This work reports the preparation of hybrid nanoparticles with magnetic and fluorescent properties. The material is based on magnetite nanoparticles (NPs) coated with fluorophore methylene blue (MB). The synthesis of a multifunctional material with magnetic and fluorescent features is carried out in a single step by electrooxidation. The effect of the presence of methylene blue in the synthetic medium is discussed. The presence of MB polymer at the NP surface is demonstrated with visible UV, infrared and Raman spectroscopy. The NPs morphology, structure and size are determined by transmission electron microscopy (TEM) and X-ray diffraction. The magnetic properties are measured with a vibrating sample magnetometer (VMS). In overall, the results show that magnetite NPs generated electrochemically in the presence of MB present a core/shell structure, being the NP at the core surrounded by methylene blue polymer, leading to a nanocomposite or hybrid material.     

Gas-phase reactions of the bare Th2+ and U2+ ions with small alkanes, CH4, C2H6, and C3H8: experimental and theoretical study of elementary organoactinide chemistry

The gas-phase reactions of two dipositive actinide ions, Th(2+) and U(2+), with CH(4), C(2)H(6), and C(3)H(8) were studied by both experiment and theory. Fourier transform ion cyclotron resonance mass spectrometry was employed to study the bimolecular ion-molecule reactions; the potential energy profiles (PEPs) for the reactions, both observed and nonobserved, were computed by density functional theory (DFT). The experiments revealed that Th(2+) reacts with all three alkanes, including CH(4) to produce ThCH(2)(2+), whereas U(2+) reacts with C(2)H(6) and C(3)H(8), with different product distributions than for Th(2+). The comparative reactivities of Th(2+) and U(2+) toward CH(4) are well explained by the computed PEPs. The PEPs for the reactions with C(2)H(6) effectively rationalize the observed reaction products, ThC(2)H(2)(2+) and UC(2)H(4)(2+). For C(3)H(8) several reaction products were experimentally observed; these and additional potential reaction pathways were computed. The DFT results for the reactions with C(3)H(8) are consistent with the observed reactions and the different products observed for Th(2+) and U(2+); however, several exothermic products which emerge from energetically favorable PEPs were not experimentally observed. The comparison between experiment and theory reveals that DFT can effectively exclude unfavorable reaction pathways, due to energetic barriers and/or endothermic products, and can predict energetic differences in similar reaction pathways for different ions. However, and not surprisingly, a simple evaluation of the PEP features is insufficient to reliably exclude energetically favorable pathways. The computed PEPs, which all proceed by insertion, were used to evaluate the relationship between the energetics of the bare Th(2+) and U(2+) ions and the energies for C-H and C-C activation. It was found that the computed energetics for insertion are entirely consistent with the empirical model which relates insertion efficiency to the energy needed to promote the An(2+) ion from its ground state to a prepared divalent state with two non-5f valence electrons (6d(2)) suitable for bond formation in C-An(2+)-H and C-An(2+)-C activated intermediates.     

Iridium complexes of the doubly cyclometalated NHC ligand IMes'

Two consecutive C-H bond activations at the coordination sphere of Ir transform the commonly employed NHC ligand IMes into the new κ(3)-C fac-coordinating ligand IMes'. The preparation and structure of Ir(III) complexes featuring this ligand together with selected reactions toward small molecules that illustrate their reactivity keys are described.     

Selective catalytic reduction at quasi-perfect Pt(100) domains: a universal low-temperature pathway from nitrite to N2

The highly selective conversion of nitrite to N(2) at a quasi-perfect Pt(100) electrode in alkaline media was investigated with a particular emphasis on its structure sensitivity and its mechanism. High-quality (100) terraces are required to optimize the catalytic activity and steer the selectivity to N(2): defects of any symmetry dramatically reduce the N(2) evolution at [(100) × (110)] and [(100) × (111)] surfaces. On the other hand, nitrite reduction proves to be an additional example of the unique intrinsic ability of (100) surfaces to catalyze reactions involving bond breaking and successive bond formation. In the present case, (100) is able to reduce nitrite to NH(2,ads), which in a certain potential window combines with NO(ads) to give N(2) in a Langmuir-Hinshelwood reaction. Our findings are similar to those for other processes generating N(2), from bacterial anoxic ammonia oxidation ("anammox") to the high-temperature NO + NH(3) reaction at Pt(100) crystals under ultra-high-vacuum conditions, thus suggesting that the combination of these two nitrogen-containing species is a universal (low-temperature) pathway to N(2). The advantages of this pathway over other N(2)-generating pathways are pointed out.     

Flammability Tests and Investigations of Properties of Lignin-Containing Polymer Composites Based on Acrylates

In this paper flammability tests and detailed investigations of lignin-containing polymer composites’ properties are presented. Composites were obtained using bisphenol A glycerolate (1 glycerol/phenol) diacrylate (BPA.GDA), ethylene glycol dimethacrylate (EGDMA), and kraft lignin (lignin alkali, L) during UV curing. In order to evaluate the influence of lignin modification and the addition of flame retardant compounds on the thermal resistance of the obtained biocomposites, flammability tests have been conducted. After the modification with phosphoric acid (V) lignin, as well as diethyl vinylphosphonate, were used as flame retardant additives. The changes in the chemical structures (ATR-FTIR), as well as the influence of the different additives on the hardness, thermal (TG) and mechanical properties were discussed in detail. The samples after the flammability test were also studied to assess their thermal destruction.     

Embedding a Planar Hypercoordinate Carbon Atom into a [4n+2] π-System

Through delicate tuning of the electronic structure, we report herein a rational design of seventeen new putative global minimum energy structures containing a planar tetra- or pentacoordinate carbon atom embedded in an aromatic hydrocarbon. These structures are the result of replacing three consecutive hydrogen atoms of an aromatic hydrocarbon by less electronegative groups, forming a multicenter σ-bond with the planar hypercoordinate carbon atom and participating in the π-electron delocalization. This strategy that maximizes both mechanical and electronic effects through aromatic architectures can be extended to several molecular combinations to achieve new and diverse compounds containing planar hypercoordinate carbon centers.     

Breaking the barrier: an osmium photosensitizer with unprecedented hypoxic phototoxicity for real world photodynamic therapy

Hypoxia presents a two-fold challenge in the treatment of cancer, as low oxygen conditions induce biological changes that make malignant tissues simultaneously more aggressive and less susceptible to standard chemotherapy. This paper reports the first metal-based photosensitizer that approaches the ideal properties for a phototherapy agent. The Os(phen)₂-based scaffold was combined with a series of IP-nT ligands, where phen = 1,10-phenanthroline and IP-nT = imidazo[4,5-f][1,10]phenanthroline tethered to n = 0–4 thiophene rings. Os-4T (n = 4) emerged as the most promising complex in the series, with picomolar activity and a phototherapeutic index (PI) exceeding 10⁶ in normoxia. The photosensitizer exhibited an unprecedented PI > 90 (EC₅₀ = 0.651 μM) in hypoxia (1% O₂) with visible and green light, and a PI > 70 with red light. Os-4T was also active with 733 nm near-infrared light (EC₅₀ = 0.803 μM, PI = 77) under normoxia. Both computation and spectroscopic studies confirmed a switch in the nature of the lowest-lying triplet excited state from triplet metal-to-ligand charge transfer (³MLCT) to intraligand charge transfer (³ILCT) at n = 3, with a lower energy and longer lifetime for n = 4. All compounds in the series were relatively nontoxic in the dark but became increasingly phototoxic with additional thiophenes. These normoxic and hypoxic activities are the largest reported to date, demonstrating the utility of osmium for phototherapy applications. Moreover, Os-4T had a maximum tolerated dose (MTD) in mice that was >200 mg kg^–1, which positions this photosensitizer as an excellent candidate for in vivo applications.     

Investigation of the thermal behavior of 4-vinylpyridine–trimethylolpropane trimethacrylate copolymeric microspheres

The study describes the thermal properties of porous microspheres synthesized with functional monomer 4-vinylpyridine (4VP) and crosslinking agent trimethylolpropane trimethacrylate (TRIM). Polymeric 4VP–TRIM microspheres were prepared via seed polymerization, using polystyrene microbeads as a shape template. The resulting 4VP–TRIM microspheres were in the range of 9–12 μm, with specific surface area of about 200 m² g^?1. The thermal properties of 4VP–TRIM materials were evaluated by thermogravimetry and differential scanning calorimetry. By TG/FTIR/MS, it was observed that new porous materials exhibited multi-staged decomposition patterns, different from poly(TRIM) microspheres. DSC and TG experiments showed that water molecules were absorbed on the materials’ surface. The synthesized 4VP–TRIM microspheres exhibited rather high thermal stability. Their initial decomposition temperature was about 300 °C. During the microspheres’ decomposition, an evolution of carbon dioxide, water, and carbon monoxide as main gases, as well as of pyridine and aliphatic compounds, was observed. It was confirmed that the evolved pyridine accelerated the degradation of copolymeric network.     

Dimerization of Pyramidalized 3,4,8,9‐Tetramethyltetracyclo [4.4.0.03,9.04,8]dec‐1(6)‐ene to a Hydrocarbon Featuring Four Cyclohexane Rings in Boat Conformations

The synthesis, chemical trapping, and dimerization of a highly pyramidalized alkene is reported. Its dimer is a unique nonacycle featuring three planar cyclobutane rings, four cyclopentane rings, and four cyclohexane rings in boat conformations. The X‐ray diffraction analysis showed a H–H distance between the flagpole hydrogen atoms of 1.999 Å and a separation of 2.619 Å between the two flagpole carbon atoms. The three cyclobutane rings of the dimer were thermally stable.