Highly syndiospecific polymerization of styrene catalyzed by allyl lanthanide complexes

Allylic complexes of lanthanides bearing a fluorenyl-based ligand are active single-component catalysts for the polymerization of styrene, giving highly syndiotactic polymers (rrrr > 99%) with low to high molecular weight (Mn = 8000-135 000) and narrow polydispersities (Mw/Mn = 1.25-2.1).     

On benzo[b][1,4]diazepinium-olates, -thiolates and -carboxylates as anti-Hückel mesomeric betaines

2,3-Diaminophenol 4, 3,4-diaminophenol 5, 4-methoxy-1,2-diaminobenzene 6, 3,4-diaminobenzenethiol 7, 2,3-diaminobenzoic acid 8, and 3,4-diaminobenzoic acid 9 were reacted with 2,4-pentanedione to yield the corresponding benzo[b][1,4]diazepinium salts, respectively. The hydroxy-benzo[b][1,4]diazepinium salts 17 and 18 do not form mesomeric betaines (MB) on deprotonation. Instead, they are converted into the diimines 24 and 25. By contrast, the 7-mercaptobenzo[b][1,4]diazepinium salt 20 yields the corresponding thiolate on increasing the pH of the solution. This MB, which possesses 4n pi-electrons, does not fit into the classification system of heterocyclic mesomeric betaines accepted today. Deprotonation of the betaine results in the formation of an instable anionic thiolate 31 which oxidizes immediately to the disulfide 32. The carboxy derivatives 21 and 22 readily form cross-conjugated mesomeric betaines. Whereas the diimine 34 proved to be instable, the sodium salt of the diimine 36 was unambiguously characterized. An X-ray single crystal analysis of 22 as its picrate is presented in order to gain additional insights into these 4n pi-electron systems.     

Geometrical freedom for constructing variable size photonic bandgap structures

In order to study the design flexibility of photonic bandgap structures, we investigate different examples of 1D traditional Bragg layers and 2D photonic crystals. We have also considered a simple case of 3D woodpile structures. It turns out that in systems with large gaps, the evanescent waves penetrate into the bulk only distances comparable to one lattice constant. Therefore confinement of light can also be achieved without long range order, which leads to the introduction of novel photonic bandgap designs. Adhering to some constraints, the changes in the photonic bandgap in disordered structures are negligible. The important quantity to characterize the presence or absence of modes is the local photonic density of states, however bandgap phenomena in size and position disordered arrangements can also be verified with plane wave supercell calculations as well as finite difference time domain techniques.     

Instability of a planar liquid layer in an alternating longitudinal magnetic field with non-zero mean

The conducting liquid interface is found to undulate in an alternating magnetic field. It was shown earlier that ifM =B ₀ ²/μηω, B₀, ω, μ andη being the amplitude (complex) of the alternating longitudinal magnetic field imposed at the interface, the angular frequency of the field, the magnetic permeability and the viscosity respectively, and ifM _c was the critical value ofM then the planar layer was stable or unstable according asM < M _c orM > M _c. In this paper we have determined the stability criterion when in addition to the alternating longitudinal field there acts a uniform field in the same direction. After comparing our results with those obtained earlier, in the absence of the uniform field, we find that the additional uniform field has a significant destabilizing effect.     

Chemiluminescence characteristics of cumarin derivatives as blue fluorescers in peroxyoxalate-hydrogen peroxide system

The chemiluminescence characteristics of seven different cumarin derivatives were studied in detail. The fluorescence and chemiluminescence spectra were compared; all cumarins used were found to act as blue fluorescers. The intensity and kinetic parameters for the chemiluminescent systems were evaluated from computer fitting of the resulting intensity-time plots. Among different cumarin derivatives used, 7-amino-4-trifluoromethylcumarin revealed the most promising characteristics as an efficient blue fluorescent emitter.     

Investigation of the effect of cobalt on the Ni–Al2O3 catalyst prepared by the mechanochemical method for CO2 methanation

Research on Chemical Intermediates - Various Ni–Co catalysts supported on alumina were produced by the mechanochemical technique and applied to CO2 Methanation. X-ray diffraction,...     

An inimitable and ecological pleasant technique for the assessment of trace amount of copper (II) in tangible samples with new complexing reagent

A simple and rapid spectrophotometric technique has been designed for the trace copper analysis employing 1-(2-Thiazolylazo)-2-naphthol (TAN) reagent in aqueous micellar solution of cetyl trimethylammonium bromide (CTAB) as a surfactant. Copper complexed with 1-(2-Thiazolylazo)-2-naphthol to form bis[1-(2-Thiazolylazo)-2-naphthol]copper. The present spectrophotometric technique was very important since the micellar system was used in place of the toxic, high cost and time-consuming solvent extraction steps. The technique showed an enhanced detection efficiency, specificity, and molar absorptivity. It was found that the molar absorption coefficient and sensitivity of Sandel were ε 2.45 × 10⁴ L mol^?1cm^?1 and 2.6 ngcm^?2 at λ_max 578.4 nm. A linear calibration plot in the range 0.12–5.0 μg mL^?1 was obtained; a stoichiometric metal ligand ratio [M:L] of 1:2 was found for the formation of Cu-[TAN]₂. The complex was formed at pH 9.5 and was stable up to 24 h. The proposed technique has been employed to study copper from different alloys, biological, environmental and pharmaceutical samples.     

A New Algorithm for Digital Image Encryption Based on Chaos Theory

In recent decades, image encryption, as one of the significant information security fields, has attracted many researchers and scientists. However, several studies have been performed with different methods, and novel and useful algorithms have been suggested to improve secure image encryption schemes. Nowadays, chaotic methods have been found in diverse fields, such as the design of cryptosystems and image encryption. Chaotic methods-based digital image encryptions are a novel image encryption method. This technique uses random chaos sequences for encrypting images, and it is a highly-secured and fast method for image encryption. Limited accuracy is one of the disadvantages of this technique. This paper researches the chaos sequence and wavelet transform value to find gaps. Thus, a novel technique was proposed for digital image encryption and improved previous algorithms. The technique is run in MATLAB, and a comparison is made in terms of various performance metrics such as the Number of Pixels Change Rate (NPCR), Peak Signal to Noise Ratio (PSNR), Correlation coefficient, and Unified Average Changing Intensity (UACI). The simulation and theoretical analysis indicate the proposed scheme’s effectiveness and show that this technique is a suitable choice for actual image encryption.