(La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O3: A new titano-manganate with a high dielectric constant and antiferromagnetic interactions

A new perovskite-based titano-manganate, (La_0.4Ba_0.4Ca_0.2)(Mn_0.4Ti_0.6)O₃, has been prepared by the ceramic route at 1100°C. This oxide was found to possess the cubic perovskite structure with  Å (space group ). The refined composition as obtained by Rietveld analysis of powder X-ray data was found to be (La_0.44Ba_0.38Ca_0.18)(Mn_0.43Ti_0.57)O_2.91(3) (R_p=0.0704, wR_p=0.0828). The composition was also ascertained by Energy dispersive X-ray analysis. Iodometric studies led to a slightly higher oxygen content (compared to Rietveld refinement) corresponding to an average manganese oxidation state of 3.05. The above oxide was found to exhibit high dielectric constant (ε) of 6980 at 1 kHz decreasing to 590 at 100 kHz. At high temperatures (200°C) it shows an unusually high dielectric constant of 20,000 at 1 kHz. In addition to the dielectric properties, detailed magnetic studies show evidence of long-range antiferromagnetic interactions near 5 K. The presence of unusually high dielectric constant coupled with the long-range magnetic interactions may open up interesting applications.     

A note on the torsional potential functionV(φ) in the dipeptide model

The studies made on N-methyl acetamide (NMA), N-ethyl acetamide (NEA), N-isopropyl acetamide (NIA), using semi-empirical quantum chemical methods have indicated that NMA is not the proper model compound for arriving at the form ofV(φ), whereas NEA and NIA molecules are suggested as model systems for arriving at the form of the potential functionV(φ). The present calculations have indicated thatV(φ) is of the form 1/2 and not (1 — cos3φ); however the value of barrier heightV(φ) was found to be very small. So it is suggested that there is no need of separately adding theV(φ) term in empirical potential energy calculations.     

Constrained anisotropic dipole oscillator strength distribution techniques,and reliable results for anisotropic and isotropic dipole molecular properties,with applications to H2 and N2

Summary Constrained anisotropic dipole oscillator strength distribution techniques are discussed and applied to obtain reliable results for a wide variety of the anisotropic and isotropic dipole properties of H₂ and N₂. These include the dipole oscillator strength sumsS _k, k=2, 1, –1/2(–1/2) –2, –3, –4, ..., the logarithmic dipole sumsL _k and mean excitation energiesI _k, k=2(–1) – 2, and, as a function of wavelength, the dynamic polarizability and the associated anisotropy, the total depolarization ratio, the Rayleigh scattering cross section, and the Verdet constant. The anisotropic components of the DOSD for a molecule are obtained from a given recommended isotropic DOSD by using a constrained least squares procedure and a series of known anisotropic constraints. Assuming that sufficient input is available, the constrained DOSD approach used in this paper is the only available method for the reliable evaluation ofall the relevant anisotropic and isotropic dipole properties for a wide variety of atoms and molecules.This research was supported by a grant from the Natural Sciences and Engineering Research Council of CanadaOn leave from Department of Physics, Meerut University, Meerut, India     

Metal complexes of 1-hydroxy-2,3-dimethyl-4-(3′-methyl-4′-amino-5′-mercapto-1′, 2′, 4′-triazole)-1,4-diaza-1, 3-butadiene with manganese(II), cobalt(II), nickel(II) and copper(II)

Summary Binuclear metal complexes of the type [M(HDDB)-(H₂O)₂]₂: where HDDB=1-hydroxy-2,3-dimethyl-4-(3-methyl-4-amino-5-mercapto-1, 2, 4-triazole)-1,4-diaza-1, 3-butadiene and M=manganese(II), cobalt(II), nickel(II) and copper(II), have been prepared and characterised by elemental and thermal analyses, magnetic measurements, electronic and i.r. spectra. Octahedral geometry around the metal(II) ions is proposed and the crystal field parameters of the cobalt(II) and nickel(II) complexes are also calculated. Fungicidal screening of the complexes has been made aginstHelminthosporium oryzae andFusarium oxysporium.     

The Equivalence Principle and an Electric Charge in a Gravitational Field II. A Uniformly Accelerated Charge Does Not Radiate

The electromagnetic field of a charge supported in a uniform gravitational field is examined from the viewpoint of an observer falling freely in the gravitational field. It is argued that such a charge, which from the principle of equivalence is moving with a uniform acceleration with respect to the (inertial) observer, could not be undergoing radiation losses at a rate implied by Larmor's formula. It is explicitly shown that the total energy in electromagnetic fields, including both velocity and acceleration fields, of a uniformly accelerated charge, at any given instant of the inertial observer's time, is just equal to the self-energy of a non-accelerated charge moving with a velocity equal to the instantaneous present velocity of the accelerated charge. At any given instant of time, and as seen with respect to the present position of the uniformly accelerated charge, although during the acceleration phase there is a radially outward component of the Poynting vector, there is throughout a radially inward Poynting flux component during the deceleration phase, and a null Poynting vector at the instant of the turn around. From Poynting's theorem, defined for any region of space strictly in terms of fixed instants of time, it is shown that a uniformly accelerated charge does not emit electromagnetic radiation, in contrast to what is generally believed. Contrary to some earlier suggestions in the literature, there is no continuous passing of electromagnetic radiation from a uniformly accelerated charge into the region inaccessible to a co-accelerating observer.     

Calcinized eggshell: an environmentally benign green catalyst for synthesis of 2-arylbenzothiazole derivatives

The calcinized eggshell as an efficient and green catalyst has been prepared from chicken eggshell waste and is characterized by different analytical techniques such as FT-IR, XRD, TGA, SEM, and EDAX. A series of substituted 2-arylbenzothiazoles have been synthesized by reaction of o-aminothiophenol and aromatic aldehydes under solvent free conditions using a grinding method at room temperature. The reaction proceeds smoothly in excellent yields (86–97 %), short reaction time (15–48 min), and with an easy work-up procedure. The reuse of catalyst and purification of products by non-chromatographic methods are some additional features of the present protocol. The calcinized eggshell is a safe, inexpensive, and a green catalyst with high catalytic efficiency obtained from renewable resources.     

Green synthesis and antibacterial evaluation of some new 1-aryl-3-(1-aryl-1<Emphasis Type="Italic">H</Emphasis>-[1,2,3]triazol-4-yl)-propenones

A new series of 1-aryl-3-(1-aryl-1H-[1,2,3]triazol-4-yl)propenones (6a–6j) was synthesized by condensation of substituted acetophenones (5a–5c) with substituted 1-aryl-1H-[1,2,3]triazole-4-carbaldehydes (4a–4d) in the presence of potassium hydroxide under conditions of grinding and microwave irradiation. All the newly synthesized compounds were characterized by the IR, NMR, and mass spectroscopic analyses and their antibacterial activity against gram-positive and gram-negative bacterial strains was evaluated. Among the compounds synthesized, better activity was exhibited by 6a, 6c, 6f, 6g, and 6i.     

Two‐Dimensional Crowding Uncovers a Hidden Conformation of α‐Synuclein

The intrinsically disordered protein (IDP), α‐synuclein (αS), is well‐known for phospholipid membrane binding‐coupled folding into tunable helical conformers. Here, using single‐molecule experiments in conjunction with ensemble assays and a theoretical model, we present a unique case demonstrating that the interaction–folding landscape of αS can be tuned by two‐dimensional (2D) crowding through simultaneous binding of a second protein on the bilayer surface. Unexpectedly, the experimental data show a clear deviation from a simple competitive inhibition model, but are consistent with a bimodal inhibition mechanism wherein membrane binding of a second protein (a membrane interacting chaperone, Hsp27, in this case) differentially inhibits two distinct modules of αS–membrane interaction. As a consequence, αS molecules are forced to access a hidden conformational state on the phospholipid bilayer in which only the higher‐affinity module remains membrane‐bound. Our results demonstrate that macromolecular crowding in two dimensions can play a significant role in shaping the conformational landscape of membrane‐binding IDPs with multiple binding modes.     

Cu‐Based Nanocomposites as Multifunctional Catalysts

Herein, we report the synthesis of Cu/Cu₂O nanocomposites by a one‐step hydrothermal process at 180 °C, for which the resulting morphology is dependent on the hydrothermal reaction time (24, 72, and 120 h). With a longer reaction time of 120 h, a rod‐shape morphology is obtained, whereas at 72 and 24 h assemblies of nanoparticles are obtained. The rod‐shaped (120 h) particles of the Cu/Cu₂O nanocomposites show a much higher efficiency (6.3 times) than the agglomerates and 2.5 times more than the assemblies of nanoparticles for the hydrogen‐evolution reaction. During the oxygen‐evolution reaction, the nanorods produce a current that is 5.2 and 3.7 times higher than that produced by the agglomerated and assembled nanoparticles, respectively. The electrocatalysts are shown to be highly stable for over 50 cycles. As catalysts for organic synthesis, a 100 % yield is achieved in the Sonogashira cross‐coupling reaction with the nanorods, which is higher than with the other nanocomposite particles. This result demonstrates the significant enhancement of yield obtained with the nanorods for cross‐coupling reactions.     

Characterization and optimization of poly(glycidyl methacrylate-co-styrene) synthesized by atom transfer radical polymerization

Styrene (S) and glycidyl methacrylate (GMA) copolymers were synthesized by atom transfer radical polymerization (ATRP) under different conditions. The effect of initiators, ligands, solvents, and temperature to the linear first-order kinetics and polydispersity index (PDI) was investigated for bulk polymerization. First-order kinetics was observed between linearly increasing molecular weight versus conversion and low polydispersities (PDI) were achieved for ethyl 2-bromo isobutyrate (EBiB) as an initiator and N,N′,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA)/CuBr as a catalyst. The copolymers with different compositions were synthesized using different in-feed ratios of monomers. Copolymers composition was calculated from ¹H NMR spectra which were further confirmed by quantitative ¹³C{¹H} NMR spectra. The monomer reactivity ratios were obtained with the help of Mayo-Lewis equation using genetic algorithm method. The values of reactivity ratios for glycidyl methacrylate and styrene monomers are r_G = 0.73 and r_S = 0.42, respectively.