Crystal structure and magnetic properties of two new cobalt selenite halides: Co5(SeO3)4X2 (X=Cl, Br)

Two new isostructural cobalt selenite halides Co₅(SeO₃)₄Cl₂ and Co₅(SeO₃)₄Br₂ have been synthesized. They crystallize in the triclinic system space group P−1 with the following lattice parameters for Co₅(SeO₃)₄Cl₂: a=6.4935(8) Å, b=7.7288(8) Å, c=7.7443(10) Å, α=66.051(11)°, β=73.610(11)°, γ=81.268(9)°, and Z=1. The crystal structures were solved from single-crystal X-ray data, R1=3.73 and 4.03 for Co₅(SeO₃)₄Cl₂ and Co₅(SeO₃)₄Br₂, respectively. The new compounds are isostructural to Ni₅(SeO₃)₄Br₂.Magnetic susceptibility measurements on oriented single-crystalline samples show anisotropic response in a broad temperature range. The anisotropic susceptibility is quantitatively interpreted within the zero-field splitting schemes for Co²⁺ and Ni²⁺ ions. Sharp low-temperature susceptibility features, at T_N=18 and 20 K for Co₅(SeO₃)₄Cl₂ and Co₅(SeO₃)₄Br₂, respectively, are ascribed to antiferromagnetic ordering in a minority magnetic subsystem. In isostructural Ni₅(SeO₃)₄Br₂ magnetically ordered subsystem represents a majority fraction (T_N=46 K). Nevertheless, anisotropic susceptibility of Ni₅(SeO₃)₄Br₂ is dominated at low temperatures by a minority fraction, subject to single-ion anisotropy effects and increasing population of S_z=0 (singlet) ground state of octahedrally coordinated Ni²⁺.     

Thermal decomposition of hexamminecobalt(III) chloride

The results of comparative thermal analysis (TG-DTG-DTA-DSC) of the thermal decomposition of hexamminecobalt(III) chloride in air atmosphere are reported. The kinetics and mechanism of the thermal decomposition, the process enthalpy and the variation in specific thermal capacity of the solid product reaction with temperature were determined.     

The non-oxidative thermal degradation of poly (Di-2-chloroethyl itaconate)

The non-oxidative thermal degradation of poly (di-2-chloroethyl itaconate) (PD2CEI) was studied by TG and by analysing the thermal products. The major processes occurring during thermal analysis are crosslinking, depolymerisation and carbonisation. The thermal degradation activation energy increased with increasing sample mass loss. The thermal degradation of PD2CEI was compared to that of the structurally similar poly(2-chloroethyl methacrylate) (P2CMA).     

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.     

Speaker Recognition Using Constrained Convolutional Neural Networks in Emotional Speech

Speaker recognition is an important classification task, which can be solved using several approaches. Although building a speaker recognition model on a closed set of speakers under neutral speaking conditions is a well-researched task and there are solutions that provide excellent performance, the classification accuracy of developed models significantly decreases when applying them to emotional speech or in the presence of interference. Furthermore, deep models may require a large number of parameters, so constrained solutions are desirable in order to implement them on edge devices in the Internet of Things systems for real-time detection. The aim of this paper is to propose a simple and constrained convolutional neural network for speaker recognition tasks and to examine its robustness for recognition in emotional speech conditions. We examine three quantization methods for developing a constrained network: floating-point eight format, ternary scalar quantization, and binary scalar quantization. The results are demonstrated on the recently recorded SEAC dataset.     

The number of primes is finite

For a positive integer let and let . The number of primes of the form is finite, because if , then is divisible by . The heuristic argument is given by which there exists a prime such that for all large ; a computer check however shows that this prime has to be greater than . The conjecture that the numbers are squarefree is not true because .

     

Efficient chromatography-free synthesis of the oxy-analogue of fingolimod

Fingolimod (FTY720) and its analogue derivatives are not only promising therapeutics in sphingolipid signaling but also valuable tools for understanding the roles of sphingolipids in (patho)physiological conditions. A practical method for the synthesis of the ether analogue of FTY720 is described. Our final synthetic approach allows high yield and efficient synthesis of O-FTY in only four steps without chromatographic purifications.     

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.     

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.     

Physico-chemical investigation of slag occurrences

Results of physico-chemical investigations of slag occurrences from site Rgotski Kamen (Timok region, Serbia), obtained by using chemical analysis, XRD analysis, EDXRF spectroscopy, thermal analysis, mass spectrometry and optical microscopy, are presented in this paper. This revised version was published online in August 2006 with corrections to the Cover Date.