Trace characterisation of lithium niobate by neutron activation analysis

Summary Coprecipitation behaviour of As, Au, Co, Cr, Cu, Eu, Fe, Ir, La, Lu, Mn, Mo, Nb, Ni, Pd, Pt, Sb, Sc, Ta, W, Zn and Zr during precipitation of hydrous oxide of niobium from lithium niobate was investigated. The matrix was dissolved in HF-HNO₃, evaporated to dryness and niobium was precipitated from HNO₃-H₂O₂ medium. The recovery studies were made using radiotracers. A radiochemical separation scheme based on group precipitation has been developed for the determination of Au, Co, Cr, Cu, Fe, Mn, Ni, Pd, Pt, Zn, Zr and rare earth elements. The method was applied to the analysis of lithium niobate. This analysis has provided fruitful information for improving the quality of the crystal.     

Hexabromide salt of a tiny octaazacryptand as a receptor for encapsulation of lower homolog halides: structural evidence on halide selectivity inside the tiny cage

Tiny azacryptand 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexacosane (L) upon reaction with 48% hydrobromic acid (containing <0.05% chloride contamination) forms hexabromide salt (1). Single crystal X-ray crystallographic investigation of the hexaprotonated bromide (1) shows no guest encapsulation inside the tiny cage. This bromide salt 1 with an empty proton cage has been utilized as the receptor for encapsulation of chloride (2) and fluoride (3). Crystallographic results of mixed chloride/bromide (2) and fluoride/bromide (3) complexes of L are examined, which show monotopic recognition of chloride in the case of 2 and fluoride in the case of 3 inside the proton cage with five bromide and three water molecules outside the cavity. Single crystals obtained from an experiment on mixed anionic system (chloride and fluoride), 1 shows selective encapsulation of fluoride, which supports the formation of complex 3 and crystals obtained upon treatment of 2 with tetrabutyl ammonium fluoride also yields complex 3. In a separate reaction between L and 49% hydrobromic acid containing higher chloride contamination (<0.2%) forms chloride/bromide salt (2). ¹H NMR studies of 1 with sodium chloride and fluoride support the encapsulation of the respective anions inside the proton cage.     

Coordinatively Unsaturated Lanthanide(III) Helicates: Luminescence Sensors for Adenosine Monophosphate in Aqueous Media

Coordinatively unsaturated double‐stranded helicates [(H₂L)₂Eu₂(NO₃)₂(H₂O)₄](NO₃)₄, [(H₂L)₂Tb₂(H₂O)₆](NO₃)₆, and [(H₂L)₂Tb₂(H₂O)₆]Cl₆ (H₂L=butanedioicacid‐1,4‐bis[2‐(2‐pyridinylmethylene)hydrazide]) are easily obtained by self‐assembly from the ligand and the corresponding lanthanide(III) salts. The complexes are characterized by X‐ray crystallography showing the helical arrangement of the ligands. Co‐ligands at the metal ions can be easily substituted by appropriate anions. A specific luminescence response of AMP in presence of ADP, ATP, and other anions is observed. Specificity is assigned to the perfect size match of AMP to bridge the two metal centers and to replace quenching co‐ligands in the coordination sphere.     

Auto-redox reaction: tin(II) chloride-mediated one-step reductive cyclization leading to the synthesis of novel biheterocyclic 5,6-dihydro-quinazolino[4,3-b]quinazolin-8-ones with three-point diversity

[reaction: see text] A tin(II) chloride-mediated short, efficient, and practical regioselective synthesis of biheterocyclic 5,6-dihydro-quinazolino[4,3-b]quinazolin-8-ones with three-point diversity is reported. A one-step reductive transformation of 2-(2-nitrophenyl)-3H-quinazolin-4-one in various alcohols furnished the desired tetracyclic product in good yields with high purity.     

Selective hydrogenation of substituted styrene to alkylbenzene catalyzed by Al2O3 nanoparticles

Research on Chemical Intermediates - A straightforward and suitable protocol is described for the conversion of substituted styrene to alkylbenzenes in the presence of Al2O3 nanoparticles...     

Metallosurfactants of Chromium(III) Coordination Complexes. Synthesis, Characterization and Determination of CMC Values

A number of mixed ligand chromium(III)–surfactant coordination complexes, of the type cis-[Cr(en)₂(A)X]²⁺ and cis-α-[Cr(trien)(A)X]²⁺ (A = Dodecyl or Cetylamine; X = F⁻, Cl⁻, Br⁻) were synthesized from the corresponding dihalogeno complexes by ligand substitution. These compounds form foam in aqueous solution when shaken. The critical micelle concentration (CMC) values of these surfactant metal complexes in aqueous solution were obtained from conductance measurements. Specific conductivity data (at 303, 308 and 313 K) served for evaluation of the temperature-dependent critical micelle concentration (cmc) and the thermodynamics of micellization (Δ G_m⁰, Δ H_m⁰ and Δ S_m⁰).     

Iron(III) bis-complexes of Schiff bases of S-methyldithiocarbazates: Synthesis,structure, spectral and redox properties and cytotoxicity

A series of iron(III) bis-complexes of the type [FeL₂]X 1-4 , X = OH⁻ ( 1 ), Cl^¯ ( 3 ), and FeCl₄^¯ ( 2 , 4 ), where LH is a tridentate (N,N,S) ligands such as N′-(1-pyridin-2-ylethylidene)-hydrazinecarbodithioic acid methyl ester ( HL1 ), N′-(phenylpyridin-2-ylmethylene)-hydrazinecarbodithioic acid methyl ester ( HL2 ), N′-quinolin-2-ylmethylene-hydrazinecarbodithioic acid methyl ester ( HL3 ), or N′-(1-methyl-1H-imidazol-2-yl-methylene)hydrazinecarbodithioic acid methyl ester ( HL4 ) has been isolated in moderate to good yields and completely characterized by elemental analyses, conductivity studies, and infrared and UV-visible spectral measurements. The single crystal X-ray structures of 1 , 2 and 4 revealed that two deprotonated tridentate (NNS) ligands are meridionally coordinated to constitute a distorted octahedral coordination geometry around iron(III). In acetonitrile solution, all the complexes show quasi-reversible Fe(III)/Fe(II) redox behavior. The in vitro cytotoxicity of the ligands HL1–HL4 (IC₅₀: HL1 , 64.5; HL2 , 51.0; HL3 , 124.0; HL4 , 45.0 μM at 24 h) and complexes 1–4 (IC₅₀: 1 , 84.5; 2 , 40.0; 3 , 168.5; 4 , 50.5 μM at 24 h) towards A549 lung cancer cell lines are similar to cisplatin (69.0 μM), revealing that free ligands cause cancer cell death with potency higher than the corresponding iron(III) complexes. Also, both the ligands and the complexes cause cell death mainly through apoptotic mode, as revealed by the observation of a higher percentage of apoptotic cells in acridine orange (AO)/ ethidium bromide (EB), and Annexin V-Cy3 stained cancer cells.     

Kinetics and the Mechanism of Iron(II) Reduction of cis-α-halogeno(cetylamine) (triethylenetetramine)cobalt(III) Complex Ion in Aqueous Acid Medium

The kinetics and mechanism of iron(II) reduction of cis- α-chloro/bromo(cetylamine)(triethylenetetramine) cobalt(III) surfactant complex ions were studied spectrophotometrically in an aqueous acid medium by following the disappearance of Co^III using an excess of the reductant under pseudo-first-order conditions: [Fe^II = 0.25 mol dm⁻³, [H⁺ = 0.1 mol dm⁻³, [μ = 1.0 mol dm⁻³ ionic strength in a nitrogen atmosphere at 303, 308 and 313 K. The reaction was found to be second order and showed acid independence in the range [H⁺ = 0.05−0.25 mol dm⁻³. The second order rate constant increased with Co^III concentration and the presence of aggregation of the complex itself altered the reaction rate. The effects of [Fe^II], [H⁺] and [ μ] on the rate were determined. Activation and thermodynamic parameters were computed. It is suggested that the reaction of Fe²⁺(aq) with Co^III complex proceeds by an inner-sphere mechanism.     

A new hexaaza bicyclic cyclophane with dual binding sites

A new C3-symmetric drum-shaped homoditopic haxaamino bicyclic cyclophane and its hexachloride and hexaiodide complexes have been synthesized and characterized and dual recognition of guests has been demonstrated. Single-crystal X-ray analysis illustrates that bicyclic cyclophane has a cavity and side pockets for acetone molecules. The hexaprotonated state of this bicycle shows encapsulation of an iodide inside its cavity, and in hexachloride complex, chloride is recognized as Cl(-)...H2O in each of the three side pockets which are in extensive hydrogen bonding interactions with the water and chlorides. (1)H NMR experiments have also been carried out on hexatosylated cyclophane with the halides to study solution state binding.