Thermal degradation of copolymers based on selected alkyl methacrylates

The thermal stability and thermal degradation of copolymers based on selected alkyl methacrylates at temperatures between 250 and 400?°C have been studied using pyrolysis?Cgas chromatography. The type and composition of thermal degradation products gave useful information about the mechanism of pyrolysis of copolymers synthesized by using typical commercially available alkyl methacrylates. It was observed that the main thermal degradation products from alkyl methacrylate copolymers are monomers of alkyl methacrylates using by synthesis. Other pyrolysis by-products formed during thermal degradation were carbon dioxide, carbon monoxide, methane, ethane, methanol, ethanol, and propanol-1.     

Spectrochemical Properties of Noncubical Transition Metal Complexes in Solution. XII. Angular Overlap Studies of Salicylideneethylenediamine Cu(II) Complex in Various Solvents

As a part of our general interest in the UV-Vis spectroscopy of multidentate mixed-donor ligands, the (salicylideneethylenediamine)Cu(II) complex has been prepared and characterized by elemental analyses, solubility in common solvents, molar conductivities, and ultraviolet (UV), and visible (Vis) spectroscopy. The combined results of spectrophotometric measurements and EPR spectra, as well as known the X-ray structure for solids, were used to determine the structure of the investigated complex in solutions. The spectra of [Cu(salen)] (H₂salen = salicylideneethylenediamine), were measured in various solvents at room temperature, resolved by Gaussian analysis, and angular overlap model (AOM) treated in C _2v symmetry. Because of overparametrization problems, the bis(salicylaldehyde)Cu(II) complex has been characterized and AOM treated. The results of this have been used for AOM studies of [Cu(salen)]. The effect of the solvents upon the - and -bonding ligand abilities is discussed.     

Isolation of a Neutral Boron‐Containing Radical Stabilized by a Cyclic (Alkyl)(Amino)Carbene

Utilizing a cyclic (alkyl)(amino)carbene (CAAC) as a ligand, neutral CAAC‐stabilized radicals containing a boryl functionality could be prepared by reduction of the corresponding haloborane adducts. The radical species with a duryl substituent was fully characterized by single‐crystal X‐ray structural analysis, EPR spectroscopy, and DFT calculations. Compared to known neutral boryl radicals, the isolated radical species showed larger spin density on the boron atom. Furthermore, the compound that was isolated is extraordinarily stable to high temperatures under inert conditions, both in solution and in the solid state. Electrochemical investigations of the radical suggest the possibility to generate a stable formal boryl anion species.     

5‐(3,4‐Dimethoxybenzyl)‐7‐isopropyl‐1,3,5‐triazepane‐2,6‐dione acetonitrile solvate refined using a multipolar atom model

The crystal structure of the title compound, C₁₆H₂₃N₃O₄·CH₃CN, was refined using a multipolar atom model transferred from an experimental electron‐density database. The refinement showed some improvement in crystallographic statistical indices compared with the independent atom model. The triazepane ring adopts a twist‐boat conformation. In the crystal structure, the molecule forms intermolecular contacts with 14 different neighbours. There are two N—H...O and one C—H...O intermolecular hydrogen bond.     

Chromatographic and Computational Studies of the Physicochemical Properties of Cholinesterase Inhibitors — Alkyl- and Arylcarbamate Derivatives of N-Benzylpiperidine and N-Benzylpiperazine

JPC – Journal of Planar Chromatography – Modern TLC - This paper reports an investigation of physicochemical properties of four series of carbamates of 3-hydroxy and...     

Substituent effects in trans‐p,p′‐disubstituted azobenzenes: X‐ray structures at 100 K and DFT‐calculated structures

The crystal and molecular structures of two para‐substituted azobenzenes with π‐electron‐donating –NEt₂ and π‐electron‐withdrawing –COOEt groups are reported, along with the effects of the substituents on the aromaticity of the benzene ring. The deformation of the aromatic ring around the –NEt₂ group in N,N,N′,N′‐tetraethyl‐4,4′‐(diazenediyl)dianiline, C₂₀H₂₈N₄, (I), may be caused by steric hindrance and the π‐electron‐donating effects of the amine group. In this structure, one of the amine N atoms demonstrates clear sp²‐hybridization and the other is slightly shifted from the plane of the surrounding atoms. The molecule of the second azobenzene, diethyl 4,4′‐(diazenediyl)dibenzoate, C₁₈H₁₈N₂O₄, (II), lies on a crystallographic inversion centre. Its geometry is normal and comparable with homologous compounds. Density functional theory (DFT) calculations were performed to analyse the changes in the geometry of the studied compounds in the crystalline state and for the isolated molecules. The most significant changes are observed in the values of the N=N—C—C torsion angles, which for the isolated molecules are close to 0.0°. The HOMA (harmonic oscillator model of aromaticity) index, calculated for the benzene ring, demonstrates a slight decrease of the aromaticity in (I) and no substantial changes in (II).     

Original paper application of cyclodextrins as modifiers in electrophoretic separation of metalloporphyrins

Several metallocomplexes of tetrakis-carboxyphenylporphyrin (TCPP) were separated on fused-silica capillary using CZE with UV-VIS detection. Metalloporphyrins of Co(II), Cu(II), Mn(II), Ni(II), and Zn(II) were formed directly in TCPP solution with addition of Cd(II) to increase the formation reaction rate. The composition of BGE, its concentration, and pH were optimized to ensure the stability of complexes and proper resolution. In particular, the problem of signals' shape was investigated and discussed. The presence of beta-CD in borate buffer significantly improved separation efficiency and signal shapes due to formation of inclusion complexes. Under the best separation conditions (50 mM borate running buffer at pH 9 with addition of 2 mM beta-CD, 30 kV applied voltage) a separation of metal complexes with TCPP was accomplished in 16 min.     

Stability studies of an electrochemically formed [C60]fullerene-palladium two-component film

The stability of C₆₀ and palladium two-component films, C₆₀/Pd, has been investigated. The effect of different polymerization conditions on the electrochemical stability of the film upon prolonged potential cycling has been studied. Stable voltammetric behavior was observed for polymers formed at potentials less negative than the potential of third C₆₀ reduction step. The incorporation of palladium particles into the structure of C₆₀/Pd polymers increases the polymer stability. The C₆₀/Pd films are doped with supporting electrolyte cations during reduction. The size of these cations is a crucial factor in determining the stability of the film. A strong solvent effect on the potential stability of the film was also observed. The wildest range of stable voltammetric properties was found for acetonitrile and N,N-dimethylformamide. No effect of the temperature on the film stability was observed. The results reported in this work allow for the determination of the optimal conditions for the formation of stable C₆₀/Pd films.     

Collective rotations of ferroelectric liquid crystals at the air/water interface

We study the Langmuir monolayers of four different ferroelectric liquid crystals on water surface. Two of them are attached to water surface by their polar groups, and the chiral groups, at the opposite ends of the elongated molecules, remain well above the interface. The other two ferroelectrics have both groups (polar and chiral) at close proximity, and therefore the chiral group is also attached to the surface or even submerged in water. We demonstrate that only when the chiral group of the ferroelectric liquid crystal in Langmuir monolayer is not attached to the interface and stays in the air does the system exhibit the collective rotations induced by evaporation of water (described for the first time by: Tabe, Y.; Yokoyama, H. Nat. Mater. 2003, 2, 806). The isotherms of surface pressure and surface potential versus molecular area of four compounds were measured with simultaneous observations using Brewster angle microscopy. Experimental data of the compression isotherms are described with a van der Waals model with very good accuracy, and the fitted parameters were used for calculations of compressibility coefficients for different phases found in the compounds under investigations. The ability of the two compounds for rotation and the disability of the two others is discussed in a context of thermodynamic properties of the monolayers.