Synthesis of Honeycomb-Structured Beryllium Oxide via Graphene Liquid Cells

Using high-resolution transmission electron microscopy and electron energy-loss spectroscopy, we show that beryllium oxide crystallizes in the planar hexagonal structure in a graphene liquid cell by a wet-chemistry approach. These liquid cells can feature van-der-Waals pressures up to 1 GPa, producing a miniaturized high-pressure container for the crystallization in solution. The thickness of as-received crystals is beyond the thermodynamic ultra-thin limit above which the wurtzite phase is energetically more favorable according to the theoretical prediction. The crystallization of the planar phase is ascribed to the near-free-standing condition afforded by the graphene surface. Our calculations show that the energy barrier of the phase transition is responsible for the observed thickness beyond the previously predicted limit. These findings open a new door for exploring aqueous-solution approaches of more metal-oxide semiconductors with exotic phase structures and properties in graphene-encapsulated confined cells.     

Magnetization and EPR of a series of Cr squarate dimers

A series of Cr(III) dimers were synthesized from a parent compound [Cr₂(μ-oxo)₂(μ_1,2-C₄O₄)₂(H₂O)₄]·2H₂O (I) by ligand substitution. The compounds have been analyzed using variable frequency EPR (9–110 GHz) and magnetic susceptibility as a function of field (0–9 T) and temperature (1.9–300 K) to obtain their electronic g-values, exchange energies, and zero-field parameters. The parent compound exhibits a broad maximum around 34 K characteristic of a dimer with antiferromagnetic coupling that fit the Van Vleck susceptibility model well. It was found that the maxima could be tuned from 34 to 80 K by ligand substitution of the waters. Each compound possesses a characteristic color spanning the range of teal to pink. The g-value of each compound was found to be ∼1.98 using spectral simulation. The DMSO derivative is water soluble and has a high LC₅₀ for PC3 cancer cells, suggesting its use as a magnetic resonance imaging agent. X-ray crystal structure of the DMSO derivative [Cr₂(μ-oxo)₂(μ_1,2-C₄O₄)₂(C₂H₆SO)₄]·2H₂O (II) revealed that the DMSO ligands are equatorial, and the squarate groups bridge the two chromiums. This is in contrast to the previously proposed structure of the parent compound where the water ligands were axial and the equatorial squarate groups did not bridge the chromiums. These compounds are interesting because of their ease of synthesis, and their wide range of magnetic behavior. The compounds are good probes into antiferromagnetic dimer exchange by controlling the ligand field surrounding the superexchange pathway present in the molecule.     

Investigating the formation and the properties of monoalkyl carbonates in aqueous medium using capillary electrophoresis with capacitively coupled contactless conductivity detection

Although alkyl carbonic acids (ACAs) and their salts are referred to as instable species in aqueous medium, we demonstrate that a monoalkyl carbonate (MAC) can in fact be easily formed from bicarbonate and an alcohol even in the presence of a high amount of water. A CE system with two capacitively coupled contactless conductivity detectors (C?Ds) was used to obtain different parameters about these species and their reactions. Based on the mobilities obtained for a series of alcohols ranging from 1 to 5 carbons, the coefficients of diffusion and the hydrodynamic radii were calculated. When compared with the equivalent carboxylates, MACs have radii systematically smaller. Although the precise pK(a) values of the ACAs could not be obtained, because of the fast decomposition in acid medium, it was possible, for the first time, to show that they are below 4.0. This result suggests that the acidity of an ACA is quite similar to the first hydrogen of H?CO?. Using a new approach to indirectly calibrate the C?D, the kinetic constants and the equilibrium constants of formation were also obtained. The results suggest that the increase in the chain length makes the MACs less stable and more inert.     

Observation of ligand binding to cytochrome P450 BM-3 by means of solid-state NMR spectroscopy

A broad understanding of the binding modes of ligands and inhibitors to cytochrome P450 is vital for the development of new drugs. We investigated ligand binding in a site-specific fashion on cytochrome P450 BM-3 from Bacillus megaterium, a 119 kDa paramagnetic enzyme, using solid-state magic angle spinning nuclear magnetic resonance methods. Selective labeling and longitudinal relaxation effects were utilized to identify the peaks in a site-specific fashion and to provide evidence for binding. Well-resolved one-dimensional and two-dimensional NMR spectra of cytochrome P450 BM-3 reveal shifts upon binding of its substrate, N-palmitoylglycine. These data are consistent with the crystallographic result that a biochemically important amino acid residue, Phe87, moves upon ligation. This experimental scheme provides a tool for probing ligand binding for complex systems.     

Surface states of titanium dioxide nanoparticles modified with enediol ligands

Control of surface states of titanium dioxide nanoparticles using 2-(3,4-dihydroxyphenyl)ethylamine (dopamine) and 3,4-dihydrophenylacetic acid, which act as ligands to the undercoordinated surface sites (carrier traps), is demonstrated by electrochemical techniques. The deepest traps were found to be most reactive and are selectively removed by the addition of the ligands which enhances the kinetics of electron accumulation in the film. Furthermore, a shift in the Fermi level to more positive potentials was detected for electrodes modified with the negatively charged ligand (3,4-dihydrophenylacetic acid) compared to that of electrodes modified with the positively charged ligand (dopamine). The presence of the negative charge on the ligand also contributed to the underpotential of hydrogen evolution on 3,4-dihydrophenylacetic acid-modified electrodes.     

Antibacterial and antifungal screening of Centaurium pulchellum crude extracts and main secoiridoid compounds

The main principles of C. pulchellum (Sw.) Druce, secoiridoid glycosides, have been studied as potent bioactive compounds. Here we scored their content in extracts of ten populations of this species. Antibacterial and antifungal assays of the extracts and pure secoiridoid glycosides were performed against eight bacterial strains and five fungal species. Methanol extracts from both aerial parts and roots exhibited excellent antibacterial (0.05-0.2 mg mL(-1)) and very good antifungal (0.1-2 mg mL(-1)) activity. Pure secoiridoid glycosides isolated from these extracts demonstrated very strong antibacterial (0.01-0.04 mg mL(-1)) and especially antifungal (0.001-0.1 mg mL(-1)) activity.     

Thermal behavior of gamma-irradiated urea–formaldehyde composites based on the differently activated montmorillonite K10

Journal of Thermal Analysis and Calorimetry - This work investigated the thermal characteristics of irradiated composite materials formulated on the urea–formaldehyde resin (UF) and...