Thermal behaviour of copper oxalate and its mixed ligand complexes with amines

The thermal decomposition behaviour of copper oxalate hemihydrate and its complexes with different amines has been studied by TG and DTA methods in nitrogen and air atmospheres. The complexes CuC₂O4 · 0.5 H₂O, CuC₂O₄(NH₃)₂ and CuC₂O₄(py) produced Cu₂O as final residue after decomposition, whereas, another group of complexes, CuC₂O₄(EtNH₂)₂, CuC₂O₄(MeNH₂)₂, CuC₂O₄(en)₂ and CuC₂O₄(An)₂, gave a final residue of CuO. All the complexes decomposed without forming any isolable stable intermediate; an exception was CuC₂O₄(en)₂, which formed a binuclear intermediate complex, [CuC₂O₄en]₂.     

Physico-chemical behaviour of the carbonate rocks of Western Son Valley Region,India

The techniques of DTA and TG were employed to study the thermal characteristics of unfossiliferous carbonate litho-units, viz. Fawn dolomitic limestone (microdolsparite) and Rohtas limestone (micrite) belonging to the Vindhyan Supergroup (PreCambrian) of India. The DTA of Fawn dolomitic limestone displayed two successive endothermic peaks at 725° and 860° whereas only one endothermic change at 910° was recorded in the DTA curve of Rohtas limestone. It was confirmed by chemical analyses, TG, IR and X-ray diffraction studies that the two peaks in the first case are due to dissociation of CO₂ from magnesium and calcium lattice positions, while the sole peak in the second case is due to complete decarbonation. A tentative correlation between the thermal characteristics and structural changes of these carbonate rocks at various transition temperatures is presented.     

Tetrakisisopropoxy tantalum(V)O,O′-alkylene dithiophosphate complexes

Summary Tetrakisisopropoxytantalum(V) alkylene dithiophosphato complexes, (G=–CMe₂CMe₂–, –CHMeCHMe–, –CH₂CMe₂CH₂– and –CH₂CEt₂CH₂–) have been prepared from equimolar ratios of tantalum(V) isopropoxide and alkylene dithiophosphoric acids in benzene. These moisture-sensitive compounds, which are soluble in common organic solvents and are monomeric, have been characterized by elemental analysis, molecular weight determinations and by their i.r. and n.m.r. spectra. An octahedral geometry is suggested in which the ligand is bidentate.     

Telluranes: potential synthons for charge-transfer complexes (involving hypervalent Te-I bonds) and serendipitous synthesis of the first triphenyl methyl phosphonium salts containing [C4H8TeI4] and [TeI6]anions

Hypervalent Te-I bonds of telluranes (C₄H₈TeI₂, C₅H₁₀TeI₂ and α-Me₂TeI₂) have been utilised to form the charge transfer (CT) complexes (1-3). The reaction of cyclic tellurane (1,1-diiodotetrahydro tellurophene, C₄H₈TeI₂) with I₂/ICl yields C₈H₁₆Te₂I₆ [IC₄H₈TeI-I-I-ITeC₄H₈I] (1); an unusual dinuclear species while the reaction of another cyclic tellurane (1,1-diiodo telluracyclohexane, C₅H₁₀TeI₂) with I₂ yields C₅H₁₀TeI₄ (2) possessing different structural motif than 1. In 2 the iodine molecules are on both sides bonded to iodine atom of hypervalent Te-I bond of C₅H₁₀TeI₂ which is analogous to the structural type present in Me₂TeI₄ (3) obtained by the reaction of α-Me₂TeI₂ with ICl. The reaction of C₄H₈TeI₂ with PPh₃, serendipitously, yields the first triphenyl methyl phosphonium salts [PPh₃Me]₂ ²⁺[C₄H₈TeI₄]²⁻ (4) and [PPh₃Me]₂ ²⁺[TeI₆]²⁻ (5), indicating the oxidation of PPh₃ whereas C₄H₈TeI₂ itself, is converted into [C₄H₈TeI₄]²⁻ and [TeI₆]²⁻ anions. All the complexes 1-5 have been characterised through single crystal X-ray diffraction studies.     

Effect of temperature and pressure on growth and methane utilization by several methanotrophic cultures

Several methanotrophic microorganisms, i.e.,Methylococcus capsulatus (Bath),Methylomonas albus (BG-8),Methylosinus trichosporium OB3b, andMethylocystis parvus (OBBP), were evaluated for growth and methane utilization. The effect of temperature was examined in the range of 25 to 45°C for growth and methane utilization. The temperature variations (25–35°C) had minimal effect on growth ofM. albus and M. parvus. Methane consumption varied at different temperatures with a maximum of 0.67 mol%/h and 0.53 mol%/h. at 30 and 35°C, respectively, forM. albus and M. parvus. The growth and methane consumption was slower forM. trichosporium OB3b as a maximum methane consumption of 0.07 mol%/h was obtained at 25°C and growth was inhibited at 35°C.M. capsulatus grew the best at 37°C and growth was affected at higher temperature of 45°C. Of the different cultures examined,M. albus andM. capsulatus grew the best and were further evaluated for the effect of pressure in the range of 10–50 psi. The results obtained usingM. albus demonstrated an enhancement in methane consumption rate by fourfold and final cell concentration by 40% at a pressure of 20 psi by injecting a methane/oxygen mixture, however further increase in the pressure up to 50 psi inhibited the growth. The inhibition was not seen with nitrogen incorporated mixture of oxygen and methane, which suggest that the high partial pressure of methane and/or oxygen are inhibitory for the growth ofM. albus. M. capsulatus was more sensitive to pressure as evidenced by inhibition at the relatively low pressure of 10 psi     

Theoretical and Experimental Determination of Thermomechanical Properties of Epoxy-SiO2 Nanocomposites

Improvements in the thermomechanical properties of epoxy upon inclusion of well-dispersed SiO₂ nanoparticles have been demonstrated both experimentally and through molecular dynamics simulations. The SiO₂ was represented by two different dispersion models: dispersed individual molecules and as spherical nanoparticles. The calculated thermodynamic and thermomechanical properties were consistent with experimental results. Radial distribution functions highlight the interactions of different parts of the polymer chains with the SiO₂ between 3 and 5 nm into the epoxy, depending on the particle size. The findings from both models were verified against experimental results, such as the glass transition temperature and tensile elastic mechanical properties, and proved suitable for predicting thermomechanical and physicochemical properties of epoxy-SiO₂ nanocomposites.     

Application of ruthenium catalyzed oxidation of [tris(2-aminoethyl)amine] in trace determination of ruthenium in environmental water samples

The ruthenium catalyzed oxidation of tris(2-aminoethyl)amine (TREN) by hexacyanoferrate(III) has been utilized for the development of a new and sensitive catalytic kinetic method (CKM) for the determination of ruthenium(III). The reaction was followed spectrophotometrically by the decrease in absorbance at 420nm (lambda(max) of [Fe(CN)(6)](3-)). The CKM developed utilizes fixed time procedure under optimum reaction conditions where the change in absorbance (DeltaA(t)) versus ruthenium(III) concentrations is plotted. The calibration curve recommended for the method is linear in the concentration range 10.11-252.67ngml(-1) with very good accuracy and reproducibility and a maximum error 2.20%. The detection limits of the method for ruthenium(III) corresponding to 10, 15 and 20min are 8.02, 5.03 and 3.15ngml(-1), respectively. The ruthenium(III) has also been determined in the presence of several other interfering and non-interfering cations and anions and no foreign ions interfered in the determination of ruthenium(III) up to five-fold higher concentration of the foreign ions tested. The method is highly sensitive, selective and stable. It has successfully been applied for the determination of trace ruthenium(III) in some synthetic and environmental water samples. A review of most of the published catalytic kinetic and some other important methods for the determination of ruthenium has also been presented.     

Electrochemical behavior of nicotinamide using carbon paste electrode modified with macrocyclic compounds

The electrochemical behavior of nicotinamide was studied at a carbon paste electrode and the electrodes modified with macrocyclic compounds using voltammetric and impedance measurements. The electrodes so formed were able to bind nicotinamide ions chemically and gave better voltammetric responses than the unmodified ones. The macrocycles used as modifiers for the electrode preparation were 18-crown-6, dicyclohexano-18-crown-6, dibenzo-18-crown-6, 7,16-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, 1,4,7,10,13,16-hexathiacyclooctadecane (Hexathia), 1,4,7,10-tetratosyl-1,4,7,10-tetraazacyclododecane, 1,4,8,11-tetraazacyclooctadecane, c-Methylcalix[4]resorcenarene and calix[8]arene. Among these macrocyclic modified electrodes, hexathia showed more affinity towards nicotinamide and a 2.3-fold increase in voltammetric signal was obtained. Impedance measurement was used to confirm this enhancement observed on modified electrode. This increase in anodic peak current was then used for finding linear working range, which was 0.1–500 μg mL⁻¹ with a detection limit of 0.03 μg mL⁻¹ by DPV. Interference from other vitamins like thiamine HCl (Vit. B₁), riboflavin (Vit. B₂), pyridoxine HCl (Vit. B₆) cynocobamine (Vit. B₁₂), para-aminobenzoic acid (PABA) and ascorbic acid (Vit. C) was also studied. The modified electrode could be used for the simultaneous determination of riboflavin, nicotinamide and pyridoxine HCl. It has also been utilized for the analysis of nicotinamide in pharmaceutical preparations.