An acid method for the volumetric estimation of water-soluble dithiocarbamates

Dithiocarbamates have been estimated previously by reaction with a strong acid, the carbon disulfide evolved being converted into a xanthate and the latter estimated iodimetrically. In the present method, a water-soluble dithiocarbamate is reacted with a decinormal mineral acid and the excess acid is determined to compute the amount of dithiocarbamate present. This method is applicable for the determination of a dithiocarbamate in a mixture containing thiuram disulfide.

Nature of the colour-forming species in peroxy titanium sulphate

ALTHOUGH titanium is determined colorimetrically in aqueous sulphuric acid medium in presence of excess of hydrogen peroxide, the nature of the colour-forming species is not known definitely. Schwarz1 suggested that the colour was due to the peroxo-disulphato titanate anion [O 2Ti(SO4)2]2-. On the other hand, Jahr2 and later Gastinger3 considered that the colour of the compound was due to the peroxy titanyl cation [TiO2 aq.] 2+, and suggested the following equilibrium in solution: Schaeppi and Treadwell4 attributed the colour bo O2TiSO4 or [O2Ti(SO4)2]2-, whereas Babko and Volkova5 represented the coloured complex ion as [Ti(H 2O2)]4+. Mori, Shibata, Kyuno and Ito 6 regarded the coloured species as [TiO2 aq.]2+ or [Ti(OH)2 (H2O)(H2O2)] 2+, assuming the co-ordination number of titanium to be four. Thus, a variety of constitutions has been proposed to explain the colour-forming species of the titanium complex, based on the investigations carried out in dilute sulphuric acid medium, but the complex has not been isolated so far.

Determination of carbon disulphide by chloramine-T

Carbon disulphide, on treatment with alcoholic potash, can readily be oxidised quantitatively by chloramine-T, converting all the sulphur to sulphuric acid. Fourteen equivalents of the oxidant are consumed for every mole of carbon disulphide. Since excess of chloramine-T may be determined iodimetrically, this reaction may be used for the determination of carbon disulphide. It may also be applied to the determination of xanthates.

Reaction of dialkyl 2-butynoate with aniline and formaldehyde: revision of the structure of the product

Dimethyl 3-(aryl)-3,6-dihydro-2H-1,3-oxazine4,5-dicarboxylate structure assigned for the products obtained in the Bronsted acid catalyzed reaction of dimethyl but-2-ynoates with anilines and an excess of formaldehyde in methanol has been revised to methyl 1-(aryl)-3-(methoxymethyl)-4,5-dioxopyrrolidine-3-carboxylate. (C) 2010 Elsevier Ltd. All rights reserved.

A study of the slow reaction in Al-5 wt.% Ag alloy by resistivity measurements

The slow reaction in an Al-5 wt.% Ag alloy has been investigated by resistivity measurements. The "slope change" method gave an activation energy of 1.25 eV for silver diffusion during the slow reaction. The existence of an excess concentration of vacancies in equilibrium with the dislocation loops seems to be responsible for the slow reaction. The presence of silver inhibits the nucleation of dislocation loops by holding up the quenched-in vacancies in solution. There is no indication of the presence of a third stage in the low-temperature ageing process of this alloy.

Geochemistry of fluoride rich groundwater in Kolar and Tumkur Districts of Karnataka

Groundwater is a significant water resource in India for domestic, irrigation, and industrial needs. By far the most serious natural groundwater-quality problem in India, in terms of public health, derives from high fluoride, arsenic, and iron concentrations. Hydrogeochemical investigation of fluoride contaminated groundwater samples from Kolar and Tumkur Districts in Karnataka are undertaken to understand the quality and potability of groundwater from the study area, the level of fluoride contamination, the origin and geochemical mechanisms driving the fluoride enrichment. Majority of the groundwater samples did not meet the potable water criteria as they contained excess (>1.5 mg/L) fluoride, dissolved salts (>500 mg/L) and total hardness (75-924 mg/L). Hydrogeochemical facies of the groundwater samples suggest that rock weathering and evaporation-crystallization control the groundwater composition in the study area with 50-67% of samples belonging to the Ca-HCO3 type and the remaining falling into the mixed Ca-Na-HCO3 or Ca-Mg-Cl type. The saturation index values indicated that the groundwater in the study area is oversaturated with respect to calcite and under-saturated with respect to fluorite. The deficiency of calcium ion concentration in the groundwater from calcite precipitation favors fluorite dissolution leading to excess fluoride concentration.

Oxygen chemistry in copper oxides: evidence for O− species

Core-level spectroscopic studies suggest that cuprates nominally supposed to contain Cu3+ions are likely to have the excess positive charge on oxygen instead, giving rise to O-type species (oxygen holes)

Starburst in the ultraluminous galaxy Arp 220: Constraints from observations of radio recombination lines and continuum

We present observations of radio recombination lines (RRL) from the starburst galaxy Arp 220 at 8.1 GHz (H92 alpha) and 1.4 GHz (H167 alpha and H165 alpha) and at 84 GHz (H42 alpha), 96 GHz (H40 alpha) and 207 GHz (H31 alpha) using the Very Large Array and the IRAM 30 m telescope, respectively. RRLs were detected at all the frequencies except 1.4 GHz, where a sensitive upper limit was obtained. We also present continuum flux measurements at these frequencies as well as at 327 MHz made with the VLA. The continuum spectrum, which has a spectral index alpha similar to -0.6 (S-nu proportional to nu(alpha)) between 5 and 10 GHz, shows a break near 1.5 GHz, a prominent turnover below 500 MHz, and a flatter spectral index above 50 GHz. We show that a model with three components of ionized gas with different densities and area covering factors can consistently explain both RRL and continuum data. The total mass of ionized gas in the three components is 3.2 x 10(7) M., requiring 3 x 10(5) O5 stars with a total Lyman continuum production rate N-Lyc similar to 1.3 x 10(55) photons s(-1). The ratio of the expected to observed Br alpha and Br gamma fluxes implies a dust extinction A(V) similar to 45 mag. The derived Lyman continuum photon production rate implies a continuous star formation rate (SFR) averaged over the lifetime of OB stars of similar to 240 M yr(-1). The Lyman continuum photon Production rate of similar to 3% associated with the high-density H II regions implies a similar SFR at recent epochs (t < 10(5) yr). An alternative model of high-density gas, which cannot be excluded on the basis of the available data, predicts 10 times higher SFR at recent epochs. If confirmed, this model implies that star formation in Arp 220 consists of multiple starbursts of very high SFR (few times 10(3) M. yr(-1)) and short duration (similar to 10(5) yr). The similarity of IR excess, L-IR/L-Ly alpha similar to 24, in Arp 220 to values observed in starburst galaxies shows that most of the high luminosity of Arp 220 is due to the ongoing starburst rather than to a hidden active galactic nucleus (AGN). A comparison of the IR excesses in Arp 220, the Galaxy, and M33 indicates that the starburst in Arp 220 has an initial mass function that is similar to that in normal galaxies and has a duration longer than 107 yr. If there was no infall of gas during this period, then the star formation efficiency (SFE) in Arp 220 is similar to 50%. The high SFR and SFE in Arp 220 is consistent with their known dependences on mass and density of gas in star-forming regions of normal galaxies.

Thermodynamic and structural studies of cavity formation in proteins suggest that loss of packing interactions rather than the hydrophobic effect dominates the observed energetics

The hydrophobic effect is widely believed to be an important determinant of protein stability. However, it is difficult to obtain unambiguous experimental estimates of the contribution of the hydrophobic driving force to the overall free energy of folding. Thermodynamic and structural studies of large to small substitutions in proteins are the most direct method of measuring this contribution. We have substituted the buried residue Phe8 in RNase S with alanine, methionine, and norleucine, Binding thermodynamics and structures were characterized by titration calorimetry and crystallography, respectively. The crystal structures of the RNase S F8A, F8M, and F8Nle mutants indicate that the protein tolerates the changes without any main chain adjustments, The correlation of structural and thermodynamic parameters associated with large to small substitutions was analyzed for nine mutants of RNase S as well as 32 additional cavity-containing mutants of T4 lysozyme, human lysozyme, and barnase. Such substitutions were typically found to result in negligible changes in Delta C-p and positive values of both Delta Delta H degrees and aas of folding. Enthalpic effects were dominant, and the sign of Delta Delta S is the opposite of that expected from the hydrophobic effect. Values of Delta Delta G degrees and Delta Delta H degrees correlated better with changes in packing parameters such as residue depth or occluded surface than with the change in accessible surface area upon folding. These results suggest that the loss of packing interactions rather than the hydrophobic effect is a dominant contributor to the observed energetics for large to small substitutions. Hence, estimates of the magnitude of the hydrophobic driving force derived from earlier mutational studies are likely to be significantly in excess of the actual value.

Phase diagram and dielectric studies of binary organic materials

The phase equilibrium studies of organic system, involving resorcinol (R) and p-dimethylaminobenzaldehyde (DMAB), reveal the formation of a 1:1 molecular complex with two eutectics. The heat of mixing, entropy of fusion, roughness parameter, interfacial energy, and the excess thermodynamic functions were calculated based on enthalpy of fusion data determined via differential scanning calorimetric (DSC) method. X-ray powder diffraction studies confirm that the eutectics are not simple mechanical mixture of the components under investigation. The spectroscopic investigations (IR and NMR) suggest the occurrence of hydrogen bonding between the components forming the molecular complex. The dielectric measurements, carried out on hot-pressed addition compound (molecular complex), show higher dielectric constant at 320 K than that of individual components. The microstructural investigations of eutectic and addition compound indicate dendritic and faceted morphological features. (C) 2000 Elsevier Science B.V. All rights reserved.

A modified least squares algorithm to treat associations in liquid alloys

The associated model for binary systems has been modified to include volume effects and excess entropy arising from preferential interactions between the associate and the free atoms or between the free atoms. Equations for thermodynamic mixing functions have been derived. An optimization procedure using a modified conjugate gradient method has been used to evaluate the enthalpy and entropy interaction energies, the free energy of dissociation of the complex, its temperature dependance and the size of the associate. An expression for the concentration—concentration structure factor [Scc (0)] has been deduced from the modified associated solution model. The analysis has been applied to the thermodynamic mixing functions of liquid Ga-Te alloys at 1120 K, believed to contain Ga2Te3 associates. It is observed that the modified associated solution model incorporating volume effects and terms for the temperature dependance of interaction energies, describes the thermodynamic properties of Ga-Te system satisfactorily.

Neutron diffraction evidence for oxygen dimers in Bi-Ca-Sr-Cu-O superconductors

A comparative neutron diffraction study of Bi2CaSr2Cu2O8+δ, Bi2Ca2SrCu2O8+δ and Bi2Ca1.5Y0.5SrCu2O8+δ has not only shown the presence of considerable oxygen excess in the Bi layers, but also evidence for oxygen pairing giving rise to O1−2 or O2−2 type species, probably the latter. The proportion of the paired species increases when Y partly replaces Ca. Furthermore, the Tc decreases with an increase in paired species.

Extension of Darken's Quadratic Formalism to Dilute Multicomponent Solutions

Darken's quadratic formalism is extended to multicomponent solutions. Equations are developed for the representation of the integral and partial excess free energies, entropies and enthalpies in dilute multicomponent solutions. Quadratic formalism applied to multicomponent solutions is thermodynamically consistent. The formalism is compared with the conventional second order Maclaurin series or interaction parameter representation and the relations between them are derived. Advantages of the quadratic formalism are discussed.

Effect of phenoxy acids and their derivatives on lipid metabolism in groundnut (Arachis hypogaea) leaves

The effect of four phenoxy compounds [2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid, 4-chlorophenoxyacetic acid 2-(dimethylamino)ethyl ester (centrophenoxine), and 4-chlorophenoxy ethyl 2-(dimethylamino) ethyl ether (neophenoxine)] on lipid metabolism in groundnut (Arachis hypogaea) leaves was investigated under nonphotosynthetic conditions. In experiments with leaf disks, the uptake of [1-14C]acetate, [32P]orthophosphate, [35S]sulfate and [methyl-14C]choline was substantially inhibited by all the phenoxy compounds except neophenoxine. When the incorporation of these precursors into lipids was measured and expressed as percentage of total uptake, there was significant inhibition of incorporation of [1-14C]acetate and [32P]orthophosphate into lipids by all the compounds except neophenoxine. The incorporation of [methyl-14C]choline was unaffected by all except centrophenoxine which showed stastically significant stimulation. [35S]Sulfate incorporation into lipids was markedly inhibited only by centrophenoxine. The fatty acid synthetase of isolated chloroplasts assayed in the absence of light was inhibited 20–50% by the phenoxy compounds at 0.5 mM concentration. This inhibition showed a dependence on time of preincubation with the herbicide suggesting an interaction with the enzyme. It was, however, reversible and excess substrate did not prevent the inhibition, suggesting that the herbicide interaction may not be at the active site. sn-Glycerol-3-phosphate acyltransferase in the chloroplast and microsomal fractions was inhibited by 2,4-D while the phosphatidic acid phosphatase was insensitive to all the phenoxy compounds. It is concluded that phenoxy compounds affect precursor uptake, their incorporation into lipids, and the chloroplast fatty acid synthetase. The free acids were the most potent compounds while the ester (centrophenoxine) was less effective and the ether (neophenoxine) was completely ineffective in their influence on lipid metabolism.

An investigation of the PrBa2Cu3O7-δ system

Members of the PrBa2Cu3O7–delta system possessing the orthorhombic structure over a wide range of oxygen stoichiometry (delta=–0.5 to +0.5) have been prepared and characterized. Similar compositions with a tetragonal structure have also been prepared. None of the oxides is superconducting, independent of the structure or stoichiometry. Praseodymium seems to be present to a small extent in the 4+ state in oxygen-excess (negative delta) samples. Orthorhombic PrBa2Cu3O7–delta samples show the presence of twins suggesting that twins arise from orthorhombicity and have no relation to the superconductivity. A neutron diffraction study of a near-stoichiometric sample has shown a disordered orthorhombic structure with 72% occupancy of the 01 (chain) sites and with no interchange between Pr and Ba sites.