Exploring the Colour of 3d Transition-Metal Ions in Trigonal Bipyramidal Coordination: Identification of Purple-Blue (CoO5) and Beige-Red (NiO5) Chromophores in LiMgBO3 Host

In an attempt to develop new coloured inorganic oxides, we have investigated the substitution of 3d transition-metal ions in LiMgBO3 host where Mg-II has a trigonal bipyramidal (TBP) oxygen coordination]. We find that single-phase materials are formed for (LiMg1-xCoxBO3)-B-II (0 < x 1.0), (LiMg1-xNixBO3)-B-II (0 < x 0.1), (LiMg1-xCuxBO3)-B-II (0 < x 0.1) and also (Li1-xMg1-xFexBO3)-B-III (0 < x 0.1) of which the Co-II and Ni-II derivatives are strongly coloured, purple-blue and beige-red, respectively, thus identifying TBP CoO5 and NiO5 as new chromophores for these colours.

Structure of nonactin-calcium perchlorate, C40H64O12.Ca(ClO4)2, and a comparative study of metal-nonactin complexes

M r= 975.9, orthorhombic, Pnna, a = 20.262 (3), b= 15.717 (2), c= 15.038 (1)A, V= 4788.97 A 3, z = 4, D x = 1.35 Mg m -3, Cu Kct radiation, 2 = 1.5418 A, /t = 2.79 mm -1, F(000) -= 2072, T = 293 K, R = 0.08, 3335 observed reflections. The molecular structure and the crystal packing are similar to those observed in the nonactin complexes of sodium thiocyanate and potassium thiocyanate. The eight metal-O distances are nearly the same in the potassium complex whereas the four distances involving carbonyl O atoms are shorter than the remaining four involving the tetrahydrofuran-ring O atoms in the Na and the Ca complexes. This observation can be explained in terms of the small ionic radii of Na + and Ca 2+, and leads to a plausible structural rationale for the stronger affinity of nonactin for K + than for the other two metal ions.

Effect of pressure on the resistivity of lead oxide-lead halide glasses

Resistivity behaviour of PbO---PbX2 (X=F,Cl) glasses has been investigated as a function of pressure at laboratory temperature. All PbO---PbX2 glasses undergo crystallization under pressure and the resistivities of crystallized samples are lower than the corresponding glasses. Transitions in PbO---PbF2 glasses exhibit a first order behaviour while transitions in PbO---PbCl2 glasses possess features of a continuous transition. The differences in the pressure behaviour of the two glass systems have been attributed to the differences in the ionic sizes of F− and Cl− ions and also to pressure induced modifications of Pb---O bonding.

Effect of radiation on the Peierls transition

The effect of radiation on the Peierls transition in a one-dimensional metal is investigated. It is pointed out that an external radiation field satisfying appropriate frequency conditions reduces the width of the Peierls gap.

Flow of metal in constrained plane-strain extrusion forging- Part II

With many innovations in process technology, forging is establishing itself as a precision manufacturing process: as forging is used to produce complex shapes in difficult materials, it requires dies of complex configuration of high strength and of wear-resistant materials. Extensive research and development work is being undertaken, internationally, to analyse the stresses in forging dies and the flow of material in forged components. Identification of the location, size and shape of dead-metal zones is required for component design. Further, knowledge of the strain distribution in the flowing metal indicates the degree to which the component is being work hardened. Such information is helpful in the selection of process parameters such as dimensional allowances and interface lubrication, as well as in the determination of post-forging operations such as heat treatment and machining. In the presently reported work the effect of aperture width and initial specimen height on the strain distribution in the plane-strain extrusion forging of machined lead billets is observed: the distortion of grids inscribed on the face of the specimen gives the strain distribution. The stress-equilibrium approach is used to optimise a model of flow in extrusion forging, which model is found to be effective in estimating the size of the dead-metal zone. The work carried out so far indicates that the methodology of using the stress-equilibrium approach to develop models of flow in closed-die forging can be a useful tool in component, process and die design.

Effect of lutein on the transport of Ca2+ across phospholipid bilayer and mitochondrial membrane

Lutein (3,3'-dihydroxy alpha-carotene), a xanthophyll present in plant chloroplasts, increases the permeability of phospholipid vesicles to Ca2+, even though the pigment does not bind the metal ion. Energy-dependent uptake of Ca2+ by mitochondria is inhibited by lutein, which permits a rapid efflux of the ion from Ca2+-loaded mitochondria. These results are consistent with the view that the deleterious action of lutein on mitochondrial oxidative phosphorylation results from its destabilizing action on membrane structure.

Effect of pressure on the electrical resistivity of bulk Ge20Te80 glass

An irreversible pressure induced semiconductor-to-metal transition in bulk Ge20Te80 glass is observed at about 5 GPa pressure. The high pressure phase has a face centered cubic structure with a lattice constant 6.42 A° as deduced by X-ray diffraction studies on the pressure quenched samples. The temperature and pressure dependence of the electrical resistivity confirms the observed transition to be a semiconductor-to-metal transition. The temperature dependence of thermo electric power is also reported.

ESR study of metal ion-guanosine monophosphate interaction

The addition of guanosine 5-monophosphate (5′-GMP) to an aqueous solution of Mn2+ ions results in a decrease in ESR signal intensity and an increase in line-width of Mn2+ ions. This can be interpreted in terms of stepwise formation of outersphere and inner-sphere complexes as When Mg2+ is added to a mixture of Mn2+ and 5′-GMP, ESR signal intensity increases, presumably due to the replacement of Mn2+ by Mg2+ in the complex. From the variation of ESR signal intensity as a function of concentration of Mg2+, the product K1K2 for the magnesium complex i s calculated as 125 M−1. This difference in stability constants may indicate that both phosphate group and guanine base are involved in the formation of Mn2+-5′-GMP complex.

Effect of manganese dioxide on the thermal decomposition of ammonium perchlorate

Thermal decomposition of powdered ammonium perchlorate, catalysed by manganese dioxide (MnO2), has been studied in the low concentration ranges of the catalyst. MnO2 sensitises the thermal decomposition of ammonium perchlorate. The activation energy estimations of catalysed ammonium perchlorate show that the value is about 30 kcal/mol throughout the low and the high temperature regions whereas uncatalysed ammonium perchlorate gives two activation energies, 20 kcal/mol in the low temperature region (280-320°C) and 60 kcal/mol in the higher temperature region (350-390°C). This behaviour has been explained on the basis of an electron transfer process. The effectiveness of MnO2 in the thermal decomposition further increases on pre-heating the sample at 50°C for two weeks; manganese ions enter the ammonium perchlorate lattice during the process of pre-heating.

Thermodynamics of metal ion binding and denaturation of a calcium binding protein from Entamoeba histolytica

The thermodynamics of tie binding of calcium and magnesium ions to a calcium binding protein from Entamoeba histolytica was investigated by isothermal titration calorimetry (ITC) in 20 mM MOPS buffer (pH 7.0) at 20 degrees C. Enthalpy titration curves of calcium show the presence of four Ca2+ binding sites, There exist two low-affinity sites for Ca2+, both of which are exothermic in nature and with positive cooperative interaction between them. Two other high affinity sites for Ca2+ exist of which one is endothermic and the other exothermic, again with positive cooperative interaction. The binding constants for Ca2+ at the four sites have been verified by a competitive binding assay, where CaBP competes with a chromophoric chelator 5, 5'-Br-2 BAPTA to bind Ca2+ and a Ca2+ titration employing intrinsic tyrosine fluorescence of the protein, The enthalpy of titration of magnesium in the absence of calcium is single site and endothermic in nature. In the case of the titrations performed using protein presaturated with magnesium, the amount of heat produced is altered. Further, the interaction between the high-affinity sites changes to negative cooperativity. No exchange of heat was observed throughout the addition of magnesium in the presence of 1 mM calcium, Titrations performed on a cleaved peptide comprising the N-terminus and the central linker show the existence of two Ca2+ specific sites, These results indicate that this CaBP has one high-affinity Ca-Mg site, one high-affinity Ca-specific site, and two low-affinity Ca-specific sites. The thermodynamic parameters of the binding of these metal ions were used to elucidate the energetics at the individual site(s) and the interactions involved therein at various concentrations of the denaturant, guanidine hydrochloride, ranging from 0.05 to 6.5 M. Unfolding of the protein was also monitored by titration calorimetry as a function of the concentration of the denaturant. These data show that at a GdnHCl concentration of 0.25 M the binding affinity for the Mg2+ ion is lost and there are only two sites which can bind to Ca2+, with substantial loss cooperativity. At concentrations beyond 2.5 M GdnHCl, at which the unfolding of the tertiary structure of this protein is observed by near UV CD spectroscopy, the binding of Ca2+ ions is lost. We thus show that the domain containing the two low-affinity sites is the first to unfold in the presence of GdnHCl. Control experiments with change in ionic strength by addition of KCI in the range 0.25-1 M show the existence of four sites with altered ion binding parameters.

Chelating and bridging diphosphinoamine (PPh2)(2)N(Pr-i) complexes of copper(I)

The ligand bis(diphenylphosphino) isopropylamine (dppipa) has been shown to be a versatile ligand sporting different coordination modes and geometries dictated by copper(I). Most of the molecular structures were confirmed by X-ray crystallography. It is found in a chelating mode, in a monomeric complex when the ligand to copper ratio is 2:1. A tetrameric complex is formed when low ratios of ligand to metal (1: 2) were used. But with increasing ratios of ligand to metal (1: 1 and 2: 1), a trimer or a dimer was obtained depending on the crystallization conditions. Variable temperature P-31{H-1} NMR spectra of these complexes in solution showed that the Cu-P bond was labile and the highly strained 4-membered structure chelate found in the solid state readily converted to a bridged structures. On the other hand, complexes with the ligand in a bridging mode in the solid state did not form chelated structures in solution. The effect of adding tetra-alkylammonium salts to solutions of various complexes of dppipa were probed by P-31{H-1} NMR and revealed the effect of counter ions on the stability of complexes in solution. (C) 2008 Elsevier B.V. All rights reserved.

Effect of Crystallographic Structure of MnO2 on Its Electrochemical Capacitance Properties

MnO2 is currently under extensive investigations for its capacitance properties. MnO2 crystallizes into several crystallographic structures, namely, α, β, γ, δ, and λ structures. Because these structures differ in the way MnO6 octahedra are interlinked, they possess tunnels or interlayers with gaps of different magnitudes. Because capacitance properties are due to tercalation/deintercalation of protons or cations in MnO2, only some crystallographic structures, which possess sufficient gaps to accommodate these ions, are expected to be useful for capacitance studies. In order to examine the dependence of capacitance on crystal structure, the present study involves preparation of these various crystal phases of MnO2 in nanodimensions and to evaluate their capacitance properties. Results of α-MnO2 prepared by a microemulsion route (α-MnO2(m)) are also used for comparison. Spherical particles of about 50 nm, nanorods of 30−50 nm in diameter, or interlocked fibers of 10−20 nm in diameters are formed, which depend on the crystal structure and the method of preparation. The specific capacitance (SC) measured for MnO2 is found to depend strongly on the crystallographic structure, and it decreases in the following order: α(m) > α δ > γ > λ > β. A SC value of 297 F g-1 is obtained for α-MnO2(m), whereas it is 9 F g-1 for β-MnO2. A wide (4.6 Å) tunnel size and large surface area of α-MnO2(m) are ascribed as favorable factors for its high SC. A large interlayer separation (7 Å) also facilitates insertion of cations in δ-MnO2 resulting in a SC close to 236 F g-1. A narrow tunnel size (1.89 Å) does not allow intercalation of cations into β-MnO2. As a result, it provides a very small SC.

Effect of increased manganese addition and mould type on the slurry erosion characteristics of Cr-Mn iron systems

The wear resistance of high chromium iron is well recorded. However, the same is not the case as regards the use of manganese at higher percentages in high chromium irons and its influence on wear behaviour. Hence, this work highlights the slurry wear characteristics of chromium 16–19%) iron following the introduction of manganese at two levels i.e. 5 and 10%. It is known that the wear properties are dictated by the microstructural features. To alter the structure, the cooling rate of casting has been varied by adopting two different types of moulds (i.e. sand and metal) and subsequently subjecting to thermal treatment. The as-cast and heat treated samples are examined for microstructure and then evaluated for hardness and slurry erosion properties. As the manganese content is increased from 5 to 10%, the hardness showed a decrease in value both in the as-cast and heat treated conditions. The slurry erosion loss, expectedly, showed an increase irrespective of the sample condition (i.e. mould type/heat treatment adopted). The findings are corroborated with the microstructural features obtained through optical and scanning electron microscopy.

Phase-Field Simulation of Fusion Interface Events during Solidification of Dissimilar Welds: Effect of Composition Inhomogeneity

We investigate the events near the fusion interfaces of dissimilar welds using a phase-field model developed for single-phase solidification of binary alloys. The parameters used here correspond to the dissimilar welding of a Ni/Cu couple. The events at the Ni and the Cu interface are very different, which illustrate the importance of the phase diagram through the slope of the liquidus curves. In the Ni side, where the liquidus temperature decreases with increasing alloying, solutal melting of the base metal takes place; the resolidification, with continuously increasing solid composition, is very sluggish until the interface encounters a homogeneous melt composition. The growth difficulty of the base metal increases with increasing initial melt composition, which is equivalent to a steeper slope of the liquidus curve. In the Cu side, the initial conditions result in a deeply undercooled melt and contributions from both constrained and unconstrained modes of growth are observed. The simulations bring out the possibility of nucleation of a concentrated solid phase from the melt, and a secondary melting of the substrate due to the associated recalescence event. The results for the Ni and Cu interfaces can be used to understand more complex dissimilar weld interfaces involving multiphase solidification.

Effect of substituent on the thermodynamics of D-glucopyranoside binding to concanavalin A, pea (Pisum sativum) lectin and lentil (Lens culinaris) lectin

Titration calorimetry measurements of the binding of phenyl-alpha (alpha PhOGlu), 3-methoxy (3MeOGlu), fluorodeoxy and deoxy derivatives of alpha-D-glucopyranose (Glu) to concanavalin A (conA), pea lectin and lentil lectin were performed at approx. 10 and 25 degrees C in 0.01 M dimethylglutaric acid/NaOH buffer, pH 6.9, containing 0.15 M NaCl and Mn2+ and Ca2+ ions. Apparently the 3-deoxy, 4-deoxy and 6-deoxy as well as the 4-fluorodeoxy and 6-fluorodeoxy derivatives of Glu do not bind to the lectins because no heat release was observed on the addition of aliquots of solutions of these derivatives to the lectin solutions. The binding enthalpies, delta H0b, and entropies, delta S0b, determined from the measurements were compared with the same thermodynamic binding parameters for Glu, D-mannopyranoside and methyl-alpha- D-glucopyranoside (alpha MeOGlu). The binding reactions are enthalpically driven with little change in the heat capacity on binding, and exhibit enthalpy-entropy compensation. Differences between the thermodynamic binding parameters can be rationalized in terms of the interactions apparent in the known crystal structures of the methyl-alpha-D-mannopyranoside-conA [Derewenda, Yariv, Helliwell, Kalb (Gilboa), Dodson, Papiz, Wan and Campbell (1989) EMBO J. 8, 2189-2193] and pea lectin-trimanno-pyranoside [Rini, Hardman, Einspahr, Suddath and Carber (1993) J. Biol. Chem. 268, 10126-10132] complexes. Increases in the entropy change on binding are observed for alpha MeOGlu binding to pea and lentil lectin, for alpha PhOGlu binding to conA and pea lectin, and for 3MeOGlu binding to pea lectin relative to the entropy change for Glu binding, and imply that the phenoxy and methoxy substituents provide additional hydrophobic interactions in the complex. Increases in the binding enthalpy relative to that of Glu are observed for deoxy and fluoro derivatives in the C-1 and C-2 positions and imply that these substituents weaken the interaction with the surrounding water, thereby strengthening the interaction with the binding site.