Charge Fluctuations and Ethylene‐Group‐Ordering Transition in β′′‐(BEDT‐TTF)4[(H3O)Fe(C2O4)3]⋅Y Molecular Charge‐Transfer Salts

The polarized infrared reflectance and Raman spectra of the three quasi‐two‐dimensional β′′‐(BEDT‐TTF)₄[(H₃O)Fe(C₂O₄)₃]?Y bifunctional charge‐transfer salts, where BEDT‐TTF=bis(ethylenedithio)tetrathiafulvalene and Y=C₆H₅Br, (C₆H₅CN)_0.17(C₆H₅Br)_0.83, (C₆H₅CN)_0.4(C₆H₅F)_0.6, have been measured as a function of the temperature. Signatures of charge inhomogenity have been found in both Raman and infrared spectra of the β′′‐(BEDT‐TTF)₄[(H₃O)Fe(C₂O₄)₃]?Y superconductors. A 100 K transition to a mixed insulating/metallic state is clearly seen for the first time in the temperature dependence of the electronic spectra of superconducting β′′‐(BEDT‐TTF)₄[(H₃O)Fe(C₂O₄)₃]?C₆H₅Br. We suggest that this phase transition is due to subtle changes in the ethylene groups ordering, which are related to a structural phase transition in the anionic layer. The infrared and Raman spectra of quasi‐two‐dimensional metal α‐′pseudo‐κ′‐(BEDT‐TTF)₄[(H₃O)Fe(C₂O₄)₃]C₆H₄Br₂ are also investigated.     

N-Nitrosodimethylamine Contamination in the Metformin Finished Products

A GC–MS/MS method with EI ionization was developed and validated to detect and quantify N-nitrosodimethylamine (NDMA) and seven other nitrosamines in 105 samples of metformin tablets from 13 different manufactures. Good linearity for each compound was demonstrated over the calibration range of 0.5–9.5 ng/mL. The assay for all substances was accurate and precise. NDMA was not detected in the acquired active pharmaceutical ingredient (API); however, NDMA was detected in 64 (85.3%) and 22 (91.7%) of the finished product and prolonged finished product samples, respectively. European Medicines Agency recommends the maximum allowed limit of 0.032 ppm in the metformin products. Hence, 28 finished products and 7 pronged dosage products were found to exceed the acceptable limit of daily intake of NDMA contamination. The implications of our findings for the testing of pharmaceutical products are discussed.     

TLC Analysis of Inhibitors of Cyclooxygenase and Videodensitometric Determination of Meloxicam and Tiaprofenic Acid

JPC – Journal of Planar Chromatography – Modern TLC - The cyclooxygenase inhibitors lornoxicam, meloxicam, piroxicam, and tiaprofenic acid have been separated by normal- and...     

Defining rules of aromaticity: a unified approach to the Hückel, Clar and Randić concepts

The molecular structure of any system may be unambiguously described by its adjacency matrix, A, in which bonds are assigned entry a(ij) = 1 and non-bonded pairs of atoms entry a(ij) = 0. For π-electron-containing conjugated hydrocarbons, this matrix may be modified in order to represent one of the possible Kekulé structures by assigning entry 1 to double bonds and entry 0 to single bonds, leading to the Kekulé matrix K which can be obtained from the A matrix by subtracting 1 from elements a(pq) that represent single bonds in the Kekulé structure. The A and K matrices are the boundary cases of a general matrix A(ε), named perturbation matrix, in which from elements a(pq) that represent single bonds is subtracted a value ε∈<0,1> representing the magnitude of the perturbation. The determinant of the A(ε) matrix is unambiguously represented by an appropriate polynomial that, in turn, can be written in a form containing terms ±(1-ε)(N/2) that identify types of π-electron conjugated cycles (N is the corresponding number of π-electrons). If the sign before the term is (+), then the contribution is stabilizing, but if it is (-) the contribution is destabilizing. The approach shows why and how the Hückel rule works, how the Randi? conjugated circuits result from the analysis of canonical structures, and also how the Clar rule may be extended to include aromatic cycles larger than six-membered (aromatic sextet).     

Peroxidic perfluoropolyether for the covalent binding of perfluoropolyether chains on carbon black surface

Peroxidic perfluoropolyethers (PFPEs) are suitable tools for the covalent linkage of fluorinated groups on substrates containing aromatic moieties. Thus the thermal decomposition process of such fluorinated peroxides allowed the covalent linkage of PFPE radicals to the polycyclic aromatic structure of a graphitic carbon black. Contact angle measurements on molded pellets made with modified carbon black powders revealed a gradual enhancement of the hydrophobicity, which follows the increase of the fluorine content on the surface according to XPS experiments. BET analyses also revealed variations of the surface area of carbonaceous samples. Products and by-products were also evaluated by mass balances of decomposed portions of PFPE residues, respectively, PFPE chains bonded on carbon black and PFPE fluids obtained by homocoupling side-reactions. Modified carbonaceous materials were analyzed by solid state ¹⁹F-MAS NMR and the results are in agreement with the proposed radical mechanism.     

Effect of the peptide secondary structure on the peptide amphiphile supramolecular structure and interactions

Bottom-up fabrication of self-assembled nanomaterials requires control over forces and interactions between building blocks. We report here on the formation and architecture of supramolecular structures constructed from two different peptide amphiphiles. Inclusion of four alanines between a 16-mer peptide and a 16 carbon long aliphatic tail resulted in a secondary structure shift of the peptide headgroups from α helices to β sheets. A concomitant shift in self-assembled morphology from nanoribbons to core-shell worm-like micelles was observed by cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM). In the presence of divalent magnesium ions, these a priori formed supramolecular structures interacted in distinct manners, highlighting the importance of peptide amphiphile design in self-assembly.     

Example of a Model for AdS/QFT Duality

Models of hadrons that are rooted in light-front (LF) formulation of QCD have been linked to the classical field equations in a 5-dimensional anti-de Sitter (AdS) gravitational background in terms of the Brodsky-de Téramond LF holography. We discuss the classical equations of motion for the expectation values of operators in quantum field theory whose nature resembles the Ehrenfest equations of quantum mechanics and which thus appear to provide a general justification for the holographic picture. The required expectation values are obtained by distinguishing one effective constituent of a hadron, the one that is struck by an external electro-weak or gravitational probe, and integrating over relative motion variables of all other constituents in all Fock components. The scale-dependent Fock decomposition of hadronic states is defined using the renormalization group procedure for effective particles. The AdS modes dual to the incoming and outgoing hadrons in the corresponding transition matrix elements are thus found equivalent to the Gaussian form distribution functions for the effective partons struck by external probes.     

Algebras with finitely many conjugacy classes of left ideals versus algebras of finite representation type

Let A be a finite dimensional algebra over an algebraically closed field with the radical nilpotent of index 2. It is shown that A has finitely many conjugacy classes of left ideals if and only if A is of finite representation type provided that all simple A-modules have dimension at least 6.     

Numerical assessment of friction damping at turbine blade root joints by simultaneous calculation of the static and dynamic contact loads

In turbomachinery, the perfect detuning of turbine blades in order to avoid high cycle fatigue damage due to resonant vibration is often unfeasible due to the high modal density of bladed disks.     

Identification of chaos in a cutting process by the 0–1 test

We have examined the cutting process by using a two degrees of freedom non-smooth model with a friction component. Instead of the standard Lyapunov exponent treatment a statistical ‘0–1’ test based on the asymptotic properties of a non-harmonic Brownian motion chain has been successively applied to reveal the nature of the cutting process. In this test we calculated the control parameter K which is approaching asymptotically to 0 or 1 for regular and chaotic motions, respectively. The presented approach is independent on the integration procedure as we defined a characteristic distance between the points forming the time series used in the test separately.