Novel Highly Energetic Pyrazoles: N‐Trinitromethyl‐Substituted Nitropyrazoles

A new family of energetic compounds, nitropyrazoles bearing a trinitromethyl moiety at the nitrogen atom of the heterocycle, was designed. The desirable high‐energy dense oxidizers 3,4‐dinitro‐ and 3,5‐dinitro‐1‐(trinitromethyl)pyrazoles were synthesized in good yields by destructive nitration of the corresponding 1‐acetonylpyrazoles. All of the prepared compounds were fully characterized by multinuclear NMR and IR spectroscopy, as well as by elemental analysis. Single‐crystal X‐ray diffraction studies show remarkably high density. Impact sensitivity tests and thermal stability measurements were also performed. All of the pyrazoles possess positive calculated heats of formation and exhibit promising energetic performance that is the range of 1,3,5‐trinitroperhydro‐1,3,5‐triazine and pentaerythritol tetranitrate. The new pyrazoles exhibit positive oxygen balance and are promising candidates for new environmentally benign energetic materials.     

Elemental Chemometrics as Tools to Depict Stalked Barnacle (Pollicipes pollicipes) Harvest Locations and Food Safety

The stalked barnacle Pollicipes pollicipes is an abundant species on the very exposed rocky shore habitats of the Spanish and Portuguese coasts, constituting also an important economical resource, as a seafood item with high commercial value. Twenty-four elements were measured by untargeted total reflection X-ray fluorescence spectroscopy (TXRF) in the edible peduncle of stalked barnacles sampled in six sites along the Portuguese western coast, comprising a total of 90 individuals. The elemental profile of 90 individuals originated from several geographical sites (N = 15 per site), were analysed using several chemometric multivariate approaches (variable in importance partial least square discriminant analysis (VIP-PLS-DA), stepwise linear discriminant analysis (S-LDA), linear discriminant analysis (LDA), random forests (RF) and canonical analysis of principal components (CAP)), to evaluate the ability of each approach to trace the geographical origin of the animals collected. As a suspension feeder, this species introduces a high degree of background noise, leading to a comparatively lower classification of the chemometric approaches based on the complete elemental profile of the peduncle (canonical analysis of principal components and linear discriminant analysis). The application of variable selection approaches such as the VIP-PLS-DA and S-LDA significantly increased the classification accuracy (77.8% and 84.4%, respectively) of the samples according to their harvesting area, while reducing the number of elements needed for this classification, and thus the background noise. Moreover, the selected elements are similar to those selected by other random and non-random approaches, reinforcing the reliability of this selection. This untargeted analytical procedure also allowed to depict the degree of risk, in terms of human consumption of these animals, highlighting the geographical areas where these delicacies presented lower values for critical elements compared to the standard thresholds for human consumption.     

Multicanonical Monte Carlo modelling of BER penalty in transmission systems with optical regeneration

A quantitative analysis of the BER penalty due to deviations from the optimal decision level in systems employing optical regeneration is presented. Applying extensive Multicanonical Monte Carlo modelling we study the accumulation of BER with propagation and compare different analytical approximations of the regenerator nonlinear transfer function.     

Classification of Curves in 2D and 3D via Affine Integral Signatures

We propose new robust classification algorithms for planar and spatial curves subjected to affine transformations. Our motivation comes from the problems in computer image recognition. To each planar or spatial curve, we assign a planar signature curve. Curves, equivalent under an affine transformation, have the same signature. The signatures are based on integral invariants, which are significantly less sensitive to small perturbations of curves and noise than classically known differential invariants. Affine invariants are derived in terms of Euclidean invariants. We present two types of signatures: the global and the local signature. Both signatures are independent of curve parameterization. The global signature depends on a choice of the initial point and, therefore, cannot be used for local comparison. The local signature, albeit being slightly more sensitive to noise, is independent of the choice of the initial point and can be used to solve local equivalence problem. An experiment that illustrates robustness of the proposed signatures is presented.     

Ionic liquid matrices for MALDI mass spectrometry of lignin

Analytical and Bioanalytical Chemistry - The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the study of lignin is still extremely limited due to its low...     

Highly Proton-Conductive Zinc Metal-Organic Framework Based On Nickel(II) Porphyrinylphosphonate

The design of new solid-state proton-conducting materials is a great challenge for chemistry and materials science. Herein, a new anionic porphyrinylphosphonate-based MOF ( IPCE-1Ni ), which involves dimethylammonium (DMA) cations for charge compensation, is reported. As a result of its unique structure, IPCE-1Ni exhibits one of the highest value of the proton conductivity among reported proton-conducting MOF materials based on porphyrins (1.55×10⁻³ S cm⁻¹ at 75 °C and 80 % relative humidity).     

Radical Anions,Radical-Anion Salts,and Anionic Complexes of 2,1,3-Benzochalcogenadiazoles

By means of cyclic voltammetry (CV) and DFT calculations, it was found that the electron-acceptor ability of 2,1,3-benzochalcogenadiazoles 1 – 3 (chalcogen: S, Se, and Te, respectively) increases with increasing atomic number of the chalcogen. This trend is nontrivial, since it contradicts the electronegativity and atomic electron affinity of the chalcogens. In contrast to radical anions (RAs) [ 1 ]^.− and [ 2 ]^.−, RA [ 3 ]^.− was not detected by EPR spectroscopy under CV conditions. Chemical reduction of 1 – 3 was performed and new thermally stable RA salts [K(THF)]⁺[ 2 ]^.− ( 8 ) and [K(18-crown-6)]⁺[ 2 ]^.− ( 9 ) were isolated in addition to known salt [K(THF)]⁺[ 1 ]^.− ( 7 ). On contact with air, RAs [ 1 ]^.− and [ 2 ]^.− underwent fast decomposition in solution with the formation of anions [ECN]⁻, which were isolated in the form of salts [K(18-crown-6)]⁺[ECN]⁻ ( 10 , E=S; 11 , E=Se). In the case of 3 , RA [ 3 ]^.− was detected by EPR spectroscopy as the first representative of tellurium–nitrogen π-heterocyclic RAs but not isolated. Instead, salt [K(18-crown-6)]⁺₂[ 3 -Te₂]²⁻ ( 12 ) featuring a new anionic complex with coordinate Te−Te bond was obtained. On contact with air, salt 12 transformed into salt [K(18-crown-6)]⁺₂[ 3 -Te₄- 3 ]²⁻ ( 13 ) containing an anionic complex with two coordinate Te−Te bonds. The structures of 8 – 13 were confirmed by XRD, and the nature of the Te−Te coordinate bond in [ 3 -Te₂]²⁻ and [ 3 -Te₄- 3 ]²⁻ was studied by DFT calculations and QTAIM analysis.     

Stability and instability properties of rotating Bose–Einstein condensates

We consider the mean-field dynamics of Bose–Einstein condensates in rotating harmonic traps and establish several stability and instability properties for the corresponding solution. We particularly emphasize the difference between the situation in which the trap is symmetric with respect to the rotation axis and the one where this is not the case.

     

1H-1,2,4-Triazolo-5-diazonium salts in the synthesis of novel [1,2,4]triazolo[1,5-c][1,2,4]benzotriazin-6-ols

Chemistry of Heterocyclic Compounds - Condensation of 1H-1,2,4-triazolo-5-diazonium salts with 1,3-cyclohexanedione, accompanied by cascade processes of cyclization and oxidative aromatization,...