New barium,strontium and strontium‐doped barium squarates: synthesis,crystal structures and DNA/BSA binding,antioxidant and in vitro cytotoxicity studies

A new set of differently hydrated barium and strontium squarates, namely poly[[triaqua(μ‐1,2‐dioxocyclobut‐3‐ene‐1,2‐diolato)barium] monohydrate], {[Ba(C₄O₄)(H₂O)₃]·H₂O}_n ( 1 ), poly[[diaqua(μ‐1,2‐dioxocyclobut‐3‐ene‐1,2‐diolato)strontium] monohydrate], {[Sr(C₄O₄)(H₂O)₂]·H₂O}_n ( 2 ), and poly[[triaqua(μ‐1,2‐dioxocyclobut‐3‐ene‐1,2‐diolato)barium/strontium(0.85/0.15)] monohydrate], {[Ba_0.85Sr_0.15(C₄O₄)(H₂O)₃]·H₂O}_n ( 3 ), is reported. The study of their crystal structures indicates that all the complexes crystallize in the triclinic space group P. Complexes 1 and 3 have a rare combination of squarate units coordinated through monodentate O atoms to two different metal atoms and through two bidentate O atoms to three different metal atoms. Furthermore, they have three coordinated water molecules to give a coordination number of nine. The squarate ligands in complex 2 exhibit two different coordination modes: (i) monodentate O atoms coordinated to four different Sr atoms and (ii) two monodentate O atoms coordinated to two different metal atoms with the other two O atoms bidentate to four different Sr atoms. All the compounds decompose to give the respective carbonates when heated to 800 °C, as evidenced by thermogravimetry/differential thermal analysis (TG‐DTA), which are clusters of nanoparticles. Complexes 1 and 3 show additional endothermic peaks at 811 and 820 °C, respectively, indicating the phase transition of BaCO₃ from an orthorhombic (α‐Pmcn) to a trigonal phase (β‐R3m). All three complexes have significant DNA‐binding constants, ranging from 2.45 × 10⁴ to 9.41 × 10⁴ M^?1 against EB‐CT (ethidium bromide–calf thymus) DNA and protein binding constants ranging from 1.1 × 10⁵ to 8.6 × 10⁵ with bovine serum albumin. The in vitro cytotoxicity of the complexes is indicated by the IC₅₀ values, which range from 128.8 to 261.3 µg ml^?1. Complex 3 shows better BSA binding, antioxidant activity against the DPPH radical and cytotoxicity than complexes 1 and 2 .     

Synthesis and molecular structure of biologically significant bis(1,3‐dimesityl‐4,5‐naphthoquinoimidazol‐2‐ylidene)gold(I) complexes with chloride and dichloridoaurate counter‐ions

Diffraction‐quality single crystals of two gold(I) complexes, namely bis(1,3‐dimesityl‐4,5‐naphthoquinoimidazol‐2‐ylidene)gold(I) chloride benzene monosolvate, [Au(C₂₉H₂₆N₂O₂)₂]Cl·C₆H₆ or [(NQMes)₂Au]Cl·C₆H₆, 2 , and bis(1,3‐dimesityl‐4,5‐naphthoquinoimidazol‐2‐ylidene)gold(I) dichloridoaurate(I) dichloromethane disolvate, [Au(C₂₉H₂₆N₂O₂)₂][AuCl₂]·2CH₂Cl₂ or [(NQMes)₂Au][AuCl₂]·2CH₂Cl₂, 4 , were isolated and studied with the aid of single‐crystal X‐ray diffraction analysis. Compound 2 crystallizes in a monoclinic space group C2/c with eight molecules in the unit cell, while compound 4 crystallizes in the triclinic space group P with two molecules in the unit cell. The crystal lattice of compound 2 reveals C—H…Cl^? interactions that are present throughout the entire structure representing head‐to‐tail contacts between the aromatic (C—H) hydrogens of naphthoquinone and Cl^? counter‐ions. Compound 4 stacks with the aid of short interactions between a naphthoquinone O atom of one molecule and the mesityl methyl group of another molecule along the a axis, leading to a one‐dimensional strand that is held together by strong π–η² interactions between the imidazolium backbone and the [AuCl₂]^? counter‐ion. The bond angles defined by the Au^I atom and two carbene C atoms [C(carbene)—Au—C(carbene)] in compounds 2 and 4 are nearly rectilinear, with an average value of ～174.1 [2]°. Though 2 and 4 share the same cation, they differ in their counter‐anion, which alters the crystal lattice of the two compounds. The knowledge gleaned from these studies is expected to be useful in understanding the molecular interactions of 2 and 4 under physiological conditions.     

Efficient total syntheses of phytoalexin and (+/-)-paniculidine B and C based on the novel methodology for the preparation of 1-methoxyindoles

A general route to 2-unsubstituted-1-methoxyindoles, based on our methodology for the synthesis of 1-methoxyindoles, is reported. This synthesis renders accessibility to a variety of natural products possessing the said skeleton. A direct synthesis of phytoalexin (1), (+/-)-paniculidine B (2), and (+/-)-paniculidine C (3) is disclosed based on the methodology. The synthesis of paniculidine B (2) has been achieved from aldehyde 10 in only two steps in 88% yield and in five steps from a methoxyindole compound 8 obtained using our earlier methodology.     

Study of in-situ surface cleaning for Si and SiGe epitaxy on Si with a novel ion beam vapor/assisted deposition technique

Ion beam vapor deposition is a new technique to grow Si and SiGe layers on Si substrates at low temperatures. The in situ surface cleaning prior to the deposition is a crucial step in the epitaxial growth of Si and SiGe films and is achieved by Ar ion bombardment with substrates kept at ambient temperature. A high temperature annealing (800 °C) is needed to repair the damage caused by this bombardment. We studied the effects of ion beam energy and the substrate temperature during the in situ cleaning on the quality of the grown films. An ion beam energy of 150–200eV is found to be sufficient to clean the surface for epitaxial growth. While the films deposited on properly cleaned surfaces are epitaxially grown, the inadequately cleaned surface leads to the formation of polycrystalline layers especially at low substrate temperatures.     

Classification of rings with toroidal Jacobson graph

Let R be a commutative ring with nonzero identity and J(R) the Jacobson radical of R. The Jacobson graph of R, denoted by J_R, is defined as the graph with vertex set RJ(R) such that two distinct vertices x and y are adjacent if and only if 1 ? xy is not a unit of R. The genus of a simple graph G is the smallest nonnegative integer n such that G can be embedded into an orientable surface S_n. In this paper, we investigate the genus number of the compact Riemann surface in which J_R can be embedded and explicitly determine all finite commutative rings R (up to isomorphism) such that J_R is toroidal.     

Alumina Polished Glassy Carbon Electrode as a Simple Electrode for Lower Potential Electrochemical Detection of Dopamine in its Sub‐micromolar Level

The electrochemical behaviour of dopamine (DA) at a cleaned and alumina polished glassy carbon electrode (GCE) was studied using cyclic voltammetry (CV). The CV studies revealed that alumina polished GCE (AGCE) shows an enhanced oxidation peak current response with 217 mV negative potential shift towards DA than that of cleaned GCE. The differential pulse voltammetry result shows that the AGCE detects the DA in the linear concentration ranges from 0.15 to 25.25 µmol L^?1. The limit of detection was calculated as 0.046 µmol L^?1 with a sensitivity of 3.74 µA µmol L^?1 cm^?2 for the determination of DA. The fabricated AGCE shows a satisfactory selectivity, practicality along with appreciable repeatability and reproducibility.     

Temperature dependence vapour pressure measurements of Mg(tmhd)2(tmeda) [(tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione, tmeda = N,N,N′,N′-tetramethylethylenediamine]

The reaction between the magnesium β-diketonate complex Mg(tmhd)₂(H₂O)₂ and 1 equiv. of N,N,N′,N′-tetramethylethylenediamine (tmeda = Me₂NCH₂CH₂NMe₂) in hexane at room temperature yielded Mg(tmhd)₂(tmeda). The standard enthalpy of sublimation (83.2 ± 2.3 kJ mol⁻¹) and entropy of sublimation (263 ± 6.3 J mol⁻¹ K⁻¹) of Mg(tmhd)₂(tmeda) were obtained from the temperature dependence vapour pressure, determined by adopting a horizontal dual arm single furnace thermogravimetric analyser as a transpiration apparatus. From the observed melting point depression DTA, the standard enthalpy of fusion (58.3 ± 5.2 kJ mol⁻¹) was evaluated, using the ideal eutectic behaviour of Mg(tmhd)₂(tmeda) as a solvent with bis(2,4-pentanedionato)magnesium(II), Mg(acac)₂ as a non-volatile solute.     

Fracture studies of polypropylene/nanoclay composite. Part I: Effect of loading rates on essential work of fracture

Polypropylene (PP)/Montmorillonite (MMT) nanoclay based composite was prepared by melt compounding with maleic anhydride grafted polypropylene (MA-g-PP) as a compatibilizer in a twin-screw extruder, and the test specimens were injection molded. Mechanical properties such as tensile modulus, flexural modulus, yield strength and maximum percent strains were measured for pure PP and PP based nanocomposite to establish the effect of clay platelet reinforcement. The fracture properties were measured by using the essential work of fracture (EWF) method. PP/clay nanocomposite shows 25% improvement in specific EWF compared to pure PP. The variation of EWF parameters with loading rate is discussed, whilst the mechanisms of fracture are considered in a subsequent paper.     

EPR studies of Cu(II) doped glycine lithium sulphate single crystals – a case of low hyperfine coupling constant

In order to rationalize the low hyperfine value for the parallel component of copper nucleus, another system with lithium as host has been investigated using Electron Paramagnetic Resonance (EPR) technique. Single crystal EPR studies have been carried out at 300 K on Cu(II) doped glycine lithium sulphate system. Angular variation of hyperfine structure lines in the three orthogonal planes show the presence of two sites which are magnetically inequivalent but chemically equivalent with g and A values as: g_xx = 2.084, g_yy = 2.057, g_zz = 2.311 and A_xx = 8.96 mT, A_yy = 3.26 mT, A_zz = 15.95 mT respectively. The impurity entered the lattice interstitially. The admixture and molecular coefficients are evaluated by collaborating EPR data with optical data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)