A family of ferro- and antiferromagnetically coupled decametallic chromium(III) wheels

The synthesis and crystal structures of a family of decametallic Cr(III) "molecular wheels" are reported, namely [Cr10(OR)20(O2CR')10] [R' = Me, R = Me (1), Et (2); R' = Et, R = Me (3), Et (4); R' = CMe3, R = Me (5), Et (6)]. Magnetic studies on 1-6 reveal a remarkable dependence of the magnetic behaviour on the nature of R. In each pair of complexes with a common carboxylate (R') the nearest neighbour CrCr magnetic exchange coupling is more antiferromagnetic for the ethoxide-bridged (R = Et) cluster than for the methoxide analogue. In complexes 2, 4 and 6 the overall coupling is weakly antiferromagnetic resulting in diamagnetic (S = 0) ground states for the cluster, whilst in 1 and 5 it is weakly ferromagnetic thus resulting in very high-spin ground states. This ground state has been probed directly in the perdeuterated version of 1 ([D]1) by inelastic neutron scattering experiments, and these support the S = 15 ground state expected for ferromagnetic coupling of ten Cr(III) ions, and they also indicate that a single J-value model is inadequate. The ground state of 5 is large but not well defined. The trends in J on changing R are further supported by density functional calculations on 1-6, which are in excellent agreement with experiment. The very large changes in the nature of the ground state between 1 and 2, and 5 and 6 are the result of relatively small changes in J that happen to cross J = 0, hence changing the sign of J.     

Palladium-catalyzed intramolecular N-arylation of heteroarenes: a novel and efficient route to benzimidazo[1,2-a]quinolines

An efficient new route for the synthesis of benzimidazo[1,2-a]quinolines has been developed via the palladium-catalyzed intramolecular Buchwald-Harwtig aryl amination of newly synthesized 2-(2'-bromoanilino)quinolines.     

Photophysical and Electrochemical Studies of 4-Dicyanomethylene 2,6-Dimethyl-4H-Pyran (DDP) Dye with Amides in Water

Photophysical and electrochemical studies of DDP dye with Formamide and alkyl substituted amides were carried out in water. Addition of Formamide (F), Acetamide (ACM), N,N-Dimethylformamide (DMF), Dimethylacetamide (DMAC) to DDP dye result in an isosbestic point. A fluorescence enhancement of DDP dye is observed on the addition of amides. Apart from the fluorescence enhancement, the addition of formamide result in no significant shift in the position of emission maxima of DDP dye whereas addition of ACM and DMF result in a shift towards the blue and red region respectively. DDP dye exhibits three lifetime components which are unique in lifetime and amplitude. The fluorescence lifetime and relative amplitude of DDP dye varies significantly by addition of amides in aqueous solution which are influenced by amidewater hydrogen-bonding network and hydrophobic influences of the alkyl substituted amides. The nature of interaction between dye and amide be predominantly through hydrogen-bonding wherein the carbonyl oxygen (C=O) of amides are bonded to N-H hydrogen of DDP dye through water molecule. The existence of more than one microenvironment of DDP dye in aqueous phase is elucidated by Electrochemical Impedence Spectroscopy (EIS) through Nyquist plots wherein it signifies that there exist at least three different micro environments which support the existence of different fluorescence lifetimes. Fluorescence spectral technique is used as an efficient tool to elucidate the nature of interaction of water soluble probe with hydrogen-bonding solutes is established in our studies.     

Electromechanical response of (3–0, 3–1) particulate,fibrous, and porous piezoelectric composites with anisotropic constituents: A model based on the homogenization method

An analytical framework based on the homogenization method has been developed to predict the effective electromechanical properties of periodic, particulate and porous, piezoelectric composites with anisotropic constituents. Expressions are provided for the effective moduli tensors of n-phase composites based on the respective strain and electric field concentration tensors. By taking into account the shape and distribution of the inclusion and by invoking a simple numerical procedure, solutions for the electromechanical properties of a general anisotropic inclusion in an anisotropic matrix are obtained. While analytical forms are provided for predicting the electroelastic moduli of composites with spherical and cylindrical inclusions, numerical evaluation of integrals over the composite microstructure is required in order to obtain the corresponding expressions for a general ellipsoidal particle in a piezoelectric matrix. The electroelastic moduli of piezoelectric composites predicted by the analytical model developed in the present study demonstrate excellent agreement with results obtained from three-dimensional finite-element models for several piezoelectric systems that exhibit varying degrees of elastic anisotropy.     

Estimation of capsaicin through scanning densitometry and evaluation of different varieties of capsicum in India

Capsicum annuum L. (family: Solanaceae) possesses therapeutic benefits for the treatment of rheumatism, neuropathy, psoriasis, flatulence and so on. In this study fruits of four different varieties of C. annuum from four different geographical regions in India were evaluated based on their total content of capsaicin. Ethanol extracts of the fruits were used. HPTLC plates were developed in a mobile phase containing benzene, ethyl acetate and methanol (75:20:5). Densitometric scanning was performed at a wavelength of 283 nm in the absorbance mode. The calibration curve was described by the equation Y=393.587+3.836*X with a correlation coefficient (r) of 0.99890. The content of capsaicin in Nagaland, Manipur, West Bengal and Shimla varieties was found to be 3.71%, 1.78%, 0.54% and 0.06%, respectively. The developed densitometric method was found to be specific, accurate and precise. A recovery study and precision showed low levels of %RSD values. The linearity range of the curve for capsaicin was found to be 300-900 ng per spot. The limit of detection and the limit of quantification values were determined to be 31 and 94 ng, respectively, proving the sensitivity of the method. Thus the method can be used to control the total content of capsaicin on an industrial scale.     

A computational examination on the structure, spin-state energetics and spectroscopic parameters of high-valent Fe(IV)[double bond, length as m-dash]NTs species

The imidoiron(iv) species are relatively less explored compared to the oxoiron(iv) intermediates. Recently, generation and characterization of a novel imido/oxoiron(iv) species ([(N(4)Py)Fe(IV)[double bond, length as m-dash]X](2+) X = NTs; 1, O; 2) has been reported with an S = 1 ground state. Although the ground state for 1 and 2 are the same, they are reported to be distinctly different in other aspects. Unlike the oxoiron(iv) species, the Fe(iv) and nitrene combination in 1 lead to eight different spin states. Bearing in mind the complexity arising here, we have undertaken a detailed DFT study on this transient intermediate and probed its electronic structure and bonding in comparison to the oxoiron(iv) unit. Our Molecular Orbital, Energy Decomposition Analysis, and Natural Bond Orbital analysis indicates a weaker σ and non-degenerate π* orbitals for 1 in comparison to a stronger σ and degenerate π* orbitals for 2. The implication of these intricate bonding differences in reactivity is discussed along with the computation of absorption and other spectral parameters. Our results broadly support the proposed S = 1 ground state for 1 and provides some useful insight into its electronic structure.     

Kamlet-Taft and Catalan Studies of Some Novel Y-Shaped Imidazole Derivatives

Some novel Y-shaped imidazole derivatives were developed and characterized by NMR and mass spectral techniques. The photophysical properties of these imidazole derivatives were studied in several solvents. The Kamlet-Taft and Catalan’s solvent scales were found to be the most suitable for describing the solvatochromic shifts of the absorption and fluorescence emission. The adjusted coefficient representing the electron releasing ability or basicity of the solvent, C _β or C _SB has a negative value, suggesting that the absorption and fluorescence bands shift to lower energies with the increasing electron-donating ability of the solvent. This effect can be interpreted in terms of the stabilization of the resonance structures of the chromophore. The observed lower fluorescence quantum yield may be due to an increase in the non-radiative deactivation rate constant. This is attributed to the loss of planarity in the excited state provided by the non co-planarity of the cinnamaldehyde ring attached to C(2) atom of the imidazole ring. Such a geometrical change in the excited state leads to an important Stokes shift, reducing the reabsorption and reemission effects in the detected emission in highly concentrated solutions.     

Thermal decomposition paths in A<Subscript>2</Subscript>CuCl<Subscript>4</Subscript> complexes: anilinium and its derivatives

The thermal decomposition paths of anilinium, 4-chloro anilinium tetrachlorocopper(II) complexes are compared to their benzilinium derivative. All these complexes crystallize in the layered structure, typical for a A₂MX₄ family, are studied in literature for their magnetic, semiconducting properties. TG analyses of (anilinium)₂CuCl₄ (A) and (4-chloro anilinium)₂CuCl₄ (B) loses one molecule of organic ammonium hydrochloride along with one molecule of amine, to form (H)CuCl₃, which subsequently completely decomposes to Cu above 500 °C. On the other hand, (benzilinium)₂CuCl₄ (C) loses two molecules of hydrochloride along with chlorine molecule first then two molecules of benzyl amine with formation of Cu above 300 °C. DSC studies on C have shown reversible endothermic phase transition at 130.95 °C (−1.98 J g⁻¹) while heating and exothermic phase transition at 117.07 °C (0.93 J g⁻¹) while cooling. Thus, the observed changes in the decomposition pathway can be correlated to the order–disorder phase transition occurred in the compound C.     

A study on the binding interaction between the imidazole derivative and bovine serum albumin by fluorescence spectroscopy

The interaction between the imidazole derivative 2-(2,4-difluorophenyl)-1-phenyl-1H-imidazo[4,5-f][1,10]phenanthroline (dfppip) and bovine serum albumin (BSA) was investigated by fluorescence and UV–vis absorbance spectroscopy. From the experimental results, it was found that the imidazole derivative has strong ability to quench the intrinsic fluorescence of BSA by forming complexes. Electrostatic interactions play an important role to stabilize the complex. The binding constants and the number of binding sites have been determined in detail. The distance (r) between the donor and the acceptor was obtained according to fluorescence resonance energy transfer (FRET). Conformational changes of BSA were observed from synchronous fluorescence spectroscopy. The effect of metal ions such as Cu²⁺, Zn²⁺, Ca²⁺, Mg²⁺, Ni²⁺, Co²⁺ and Fe²⁺ on the binding constants between the imidazole derivative and BSA were also studied.     

Constrained melting of graphene-based phase change nanocomposites inside a sphere

Journal of Thermal Analysis and Calorimetry - In the present work, the melting behavior of a fatty acid-based phase change material (PCM) with the addition of functionalized graphene nanoplatelets...