In vitro and in vivo regulation of assimilatory nitrite reductase from Candida utilis

The nitrate assimilation pathway in Candida utilis, as in other assimilatory organisms, is mediated by two enzymes: nitrate reductase and nitrite reductase. Purified nitrite reductase has been shown to be a heterodimer consisting of 58- and 66-kDa subunits. In the present study, nitrite reductase was found to be capable of utilising both NADH and NADPH as electron donors. FAD, which is an essential coenzyme, stabilised the enzyme during the purification process. The enzyme was modified by cysteine modifiers, and the inactivation could be reversed by thiol reagents. One cysteine was demonstrated to be essential for the enzymatic activity. In vitro, the enzyme was inactivated by ammonium salts, the end product of the path way, proving that the enzyme is assimilatory in function. In vivo, the enzyme was induced by nitrate and repressed by ammonium ions. During induction and repression, the levels of nitrite reductase mRNA, protein, and enzyme activity were modulated together, which indicated that the primary level of regulation of this enzyme was at the transcriptional level. When the enzyme was incubated with ammonium salts in vitro or when the enzyme was assayed in cells grown with the same salts as the source of nitrogen, the residual enzymatic activities were similar. Thus, a study of the in vitro inactivation can give a clue to understanding the mechanism of in vivo regulation of nitrite reductase in Candida utilis.

In vitro regeneration from immature cotyledon explant and protein profile changes during organogenesis in groundnut (Arachis hypogaea L.)

Complete plants were regenerated from in vitro cultured immature cotyledon segments of groundnut (Arachis hypogaea L. cv. TMV-7) by organogenesis. Callus cultures were best Initiated from immature cotyledon segments on MS (Murashige and Skoog) salts containing B5 vitamins supplemented with indole-3-acetic acid (IAA) and alpha -naphthalene acetic acid (NAA; 4.0 mg L-1) and kinetin (KIN; 0.5 L-1). Calluses were transferred to a medium containing KIN (2.0 mg L-1) and IAA and NAA (0.5 mg L-1) for shoot Initiation. The regenerated shoots were transferred to a medium containing Indole-3-butyric acid (IBA; 2.0 mg L-1) and KIN (0.2 mg L-1) for developing roots. In vitro produced plantlets developed sucessfully, matured, and set seed. The protein profiles [sodium dodecyl sulphate - polyacrylamide gel electrophoresis (SDS-PAGE)] of callus, callus with shoot, and callus with shoot and root showed differences.

Role of hydrophobic effect and surface charge in surfactant-DNA association

Ethidium bromide is one of the best known DNA intercalator. Upon intercalation inside DNA, the fluorescence due to ethidium bromide gets enhanced by many orders of magnitude. In this paper, we employed ethidium bromide as a probe for studying surfactant-DNA complexation using fluorescence spectroscopy and agarose gel electrophoresis. Surfactants of different charge types and chain lengths were used and the results were compared with that of the related small organic cations or salts under comparable conditions. The cationic surfactants induced destabilization of the ethidium bromide-DNA complex at concentrations in orders of magnitude lower than that of the small organic cations or salts. In contrast however, the anionic surfactants failed to promote any such destabilization of probe-DNA complex. DNA loses its ethidium bromide stainability in the presence of high concentration of cationic surfactant aggregates as revealed from agarose gel electrophoresis experiments. Inclusion of surfactants and other additives into the DNA generally enhanced the DNA double-strand to single strand transition melting temperatures by a few degrees, in a concentration-dependent manner and at high surfactant concentration melting profiles got broadened.

Local environmental structures of Mo in the superionic conducting glass (AgI)(0.6)(Ag2MoO4)(0.4) by anomalous X-ray scattering

The anomalous X-ray scattering (AXS) method using Mo K absorption edges has been employed for obtaining the local structural information of superionic conducting glass having the composition (AgI)(0.6)(Ag2MoO4)(0.4). The possible atomic arrangements in the near-neighbor region of this glass were estimated by coupling the results with the least-squares variational analysis so as to reproduce the differential intensity profile for Mo as well as the ordinary scattering profile. The coordination number of oxygen around Mo is found to be about 4 at the distance of 0.180 mn. This implies that the most probable structural entity in the glass is the MoO4 tetrahedral unit which has been proposed based on infrared spectroscopy. The value of the coordination number of I- around Ag+ is estimated as 4.4 at 0.287 nm, suggesting an arrangement similar to that of crystalline or molten AgI.

Microstructure and properties of squeeze cast Cu-carbon fibre metal matrix composite

There have been reported attempts of producing Cu based MMCs employing solid phase routes. In this work, copper was reinforced with short carbon fibres by pressure infiltration (squeeze casting) of molten metal through dry-separated carbon fibres. The resulting MMC's microstructure revealed uniform distribution of fibres with minimum amount of clustering. Hardness values are considerably higher than that for the unreinforced matrix. Addition of carbon fibres has brought in strain in the crystal lattice of the matrix, resulting in higher microhardness of MMCs and improved wear resistance. Tensile strength values of MMCs at elevated temperatures are considerably higher than that of the unreinforced matrix processed under identical conditions. (C) 1999 Kluwer Academic Publishers.

Spectral, thermal and electrical properties of poly(o- and m-toluidine) PVC blends prepared by solution blending

Poly(o-toluidine) (POT) and poly(m-toluidine) (PMT) blends with polyvinylchloride (PVC) of five different compositions have been prepared by solution blending. The POT-PVC and PMT-PVC blends were prepared using THF as a solvent in which POT-HNO3, PMT-HNO3 bases and PVC are soluble. The blends have been characterized by spectral, thermal and electrical measurements. The results indicate the formation of blends at all the compositions presently studied. The thermal stability of the POT-PVC and PMT-PVC blends is higher than that of POT-HNO3 and PMT-HNO3 salts, respectively. Using the present method, POT/PMT can conveniently be blended with 30% wt/wt of PVC without significant loss in its conductivity. (C) 1998 Elsevier Science Ltd. All rights reserved.

Structure and stability of Li2F

The equilibrium geometries and fundamental vibration frequencies of the Li2F system were calculated by ab initio methods at the MP2 = full/6-311(+ +)G** and CCSD(T) levels. Two isomers were observed and are best described as salts of the Li-2(+) cation with F-. A linear isomer with an arrangement of atoms such as Li-Li-F and a bent C-2v structure are predicted. The stability of these structures are discussed in terms of charge resonance between Li and Li+. (C) 1999 Elsevier Science B.V. All rights reserved.

Synthesis and structures of oxyanion encapsulated copper(I)-dppm complexes (dppm = bis(diphenylphosphino) methane)

Copper(I)-dppm complexes encapsulating the oxyanions ClO4-, NO3-, CH3C6H4CO2-, SO42-, and WO42- have been synthesized either by reduction of the corresponding Cu(II) salts and treatment with dppm, or by treating the complex [Cu-2(dppm)(2)(dmcn)(3)](BF4)(2) (1) (dmcn = dimethyl cyanamide) with the respective anion. The isolated complexes [Cu-2(dppm)(2)(dmcn)(2)(ClO4)] (ClO4) (2), [Cu-2(dppm)(2)(dmcn)(2)(NO3)] (NO3) (3), Cu-2(dppm)(2)(NO3)(2) (4), [Cu-2(dppm)(2)(CH3C6H4CO2)(2)]dmcn.2THF (5), Cu-2(dppm)(2)(SO4) (6), and [Cu-3(dppm)(3)(Cl)(WO4)] 0.5H(2)O (7) have been characterized by IR, H-1 and P-31{H-1} NMR, UV-vis, and emission spectroscopy. The solid-state molecular structure of complexes 1, 2, 4, and 7 were determined by single-crystal X-ray diffraction. Pertinent crystal data are as follows: for 1, monoclinic P2(1)/c, a = 11.376(10) Angstrom, b = 42.503(7) Angstrom, c = 13.530(6) Angstrom, beta = 108.08(2)degrees, V = 6219(3) Angstrom(3), Z = 4; for 2, monoclinic P2(1)/c, a = 21.600(3) Angstrom, b = 12.968(3) Angstrom, c = 23.050(3) Angstrom, beta = 115.97(2)degrees, V = 5804(17) Angstrom(3), Z = 4; for 4, triclinic , a = 10.560(4) Angstrom, b = 10.553(3) Angstrom, c = 22.698(3) Angstrom, alpha = 96.08(2)degrees, beta = 96.03(2)degrees, gamma = 108.31(2)degrees, V = 2362(12) Angstrom(3), Z = 2; and for 7, orthorhombic P2(1)2(1)2(1), a = 14.407(4) Angstrom, b = 20.573(7) Angstrom, c = 24.176(6) Angstrom, V = 7166(4) Angstrom(3), Z = 4. Analyses of the crystallographic and spectroscopic data of these complexes reveal the nature of interactions between the Cu-I-dppm core and oxyanion. The anchoring of the oxyanion to the Cu-n(dppm)(n) unit is primarily through coordination to the metal, but the noncovalent C-H ... O interactions between the methylene and phenyl protons of the dppm and oxygen atoms of the oxyanion play a significant role. The solid-state emission spectra for complexes 1-6 are very similar but different from 7. In CDCl3 solution, addition of ClO4- or NO3- (as their tetrabutylammonium salts) to 1 establishes a rapid equilibrium between the anion-complexed and uncomplexed forms. The association constant values for ClO4- and NO3- have been estimated from the P-31{H-1} NMR spectra.

Organically templated linear and layered cadmium sulfates

By reacting cadmium salts with H2SO4 in the presence of organic amines or directly with amine sulfates under hydrothermal conditions, it has been possible to prepare three linear cadmium sulfates of linarite topology, with the compositions [H3N(CH2)(2)NH3](2)[CdCl2(SO4)][SO4].H2O, I, [HN(CH2)(6)NH][CdBr2(SO4)], II, [HN(CH2)(6)NH][CdCl2-(SO4)], III. A layered cadmium sulfate of composition [H3N(CH2)(3)NH3][Cd-2(H2O)(2)(SO4)(3)], IV, has also been obtained. These sulfates are the first examples of a family of organically templated metal sulfates with interesting structural features. In the linarite chains, the CdX4O2 (X = Cl, Br) octahedron shares two trans-edges to form an [Mphi(4)] (phi = anionic ligand) chain decorated by the SO4 tetrahedron that adopts a staggered arrangement on either side of the chain. IV is constructed by the fusion of four-membered ring ladders involving edge sharing between the sulfate tetrahedron and metal octahedron. IV appears to be the first member of a family of organically templated metal sulfates containing an octahedral-tetrahedral 2D net wherein the sulfate tetrahedron is connected at all four corners.

Sol-gel derived, magnesium based ionically conducting composites

Composite ionic conductors based on magnesium salts and sol-gel derived silicate-tetraethylene glycol hybrids have been synthesized. The structure of these materials has been studied by FT-IR, FT-Raman, Si-29 and C-13 NMR and XRD techniques. The composite systems can be best described as diphasic with silicate as filters in the organic phase that provides solubility of the ionic dispersants. The ionic interactions in the matrix are clearly observed in the FT-Raman spectra. The ionic conductivity is determined to be of the order of 10(-7) to 10(-5) S cm(-1) at room temperature for MgCl2 and Mg(ClO4)(2) salts respectively. The conductivity reaches 10(-4) and 10(-3) S cm(-1) at 80degreesC respectively.

Three-dimensional computational modeling of momentum, heat, and mass transfer in a laser surface alloying process

A three- dimensional, transient model is developed for studying heat transfer, fluid flow, and mass transfer for the case of a single- pass laser surface alloying process. The coupled momentum, energy, and species conservation equations are solved using a finite volume procedure. Phase change processes are modeled using a fixed-grid enthalpy-porosity technique, which is capable of predicting the continuously evolving solid- liquid interface. The three- dimensional model is able to predict the species concentration distribution inside the molten pool during alloying, as well as in the entire cross section of the solidified alloy. The model is simulated for different values of various significant processing parameters such as laser power, scanning speed, and powder feedrate in order to assess their influences on geometry and dynamics of the pool, cooling rates, as well as species concentration distribution inside the substrate. Effects of incorporating property variations in the numerical model are also discussed.

278. Studies on ass's milk: Composition

The total solids of samples of ass's milk ranged from 7·80 to 9·10, the solids-not-fat from 7·14 to 8·50, and the fat from 0·54 to 0·71%. The nitrogen distribution in ass's milk is: casein 39·5, albumin 35·0, globulin 2·7 and non-protein nitrogen 22·8% of the total nitrogen. Ass's milk contains: casein 0·70, albumin 0·62 and globulin 0·07%. The total protein content is 1·39%. Ass's milk is therefore characterized by a low casein, a low globulin and a high albumin content. The non-protein nitrogen consists of amino nitrogen 8·1, urea nitrogen 24·3 and uric acid 0·7 mg./100 ml. of milk. The urea content is twice that present in cow's milk. The mean chloride and lactose contents of the milk samples are 0·037 and 6·1% respectively. The average calcium and phosphorus content of ass's milk are 0·081 and 0·059% respectively. Half the calcium is ionic, and half is in colloidal form. The phosphorus distribution is: total acid soluble 84·0, acid soluble organic 38·5, easily hydrolysable ester 27·4, inorganic 46·0, and colloidal inorganic 23·0 % of the total phosphorus. The ratio of CaO: P2O5 is 1:1. 46 % of the total phosphorus is in ester form; this is high when compared with only 12 % in cow's milk; most of the phosphoric ester forms soluble barium salts, which is a distinguishing feature of ass's milk. The total sulphur content is 15·8 mg./100 ml. The fat has a penetrating odour and is coloured orange-yellow. It has an iodine value of about 86, which is much higher than that for human milk fat. The Reichert (9·5) and Kirschner values (5·7) are low. In general, the composition of ass's milk resembles that of human rather than of cow's milk.

Crucible Steel in South India-Preliminary Investigations on Crucibles from Some Newly Identified Sites

European accounts from the 17th century onwards have referred to the repute and manufacture of “wootz’, a traditional crucible steel made especially in parts of southern India in the former provinces of Golconda, Mysore and Salem. Pliny's Natural History mentions the import of iron and steel from the Seres which have been thought to refer to the ancient southern Indian kingdom of the Cheras. As yet the scale of excavations and surface surveys is too limited to link the literary accounts to archaeometallurgical evidence, although pioneering exploratory investigations have been made by scholars, especially on the pre-industrial production sites of Konasamudram and Gatihosahalli discussed in 18th-19th century European accounts. In 1991–2 during preliminary surveys of ancient base metal mining sites, Srinivasan came across unreported dumps with crucible fragments at Mel-Siruvalur in Tamil Nadu, and Tintini and Machnur in Karnataka and she collected surface specimens from these sites as well as from the known site of Gatihosahalli. She was also given crucible fragments by the Tamil University, Tanjavur, from an excavated megalithic site at Kodumanal, dated to ca 2nd c. Bc, mentioned in Tamil Sangam literature (ca 3rd c. BC-3rd c. AD), and very near Karur, the ancient capital of the Sangam Cheras. Analyses of crucible fragments from the surface collection at Mel-Siruvalur showed several iron prills with a uniform pearlitic structure of high-carbon hypereutectoid steel (∼1–1.5% C) suggesting that the end product was uniformly a high-carbon steel of a structure consistent with those of high-carbon steels used successfully to experimentally replicate the watered steel patterns on ‘Damascus’ swords. Investigations indicate that the process was of carburisation of molten low carbon iron (m.p. 1400° C) in crucibles packed with carbonaceous matter. The fabric of crucibles from all the above mentioned sites appears similar. Preliminary investigations on these crucibles are thus reported to establish their relationship to crucible production of carbon steel and to thereby extend the known horizons of this technology further.

Segregation in the MgO–MgAl2O4 system processed from nitrate precursors

The occurrence of segregation and its influence on microstructural and phase evolution have been studied in MgO–MgAl2O4 powders synthesized by thermal decomposition of aqueous nitrate precursors. When the nitrate solutions of Mg and Al were spray-pyrolyzed on a substrate held at 673 or 573 K, homogeneous mixed oxides were produced. Spraying and drying the nitrate solutions at 473 K resulted in the formation of compositionally inhomogeneous, segregated oxide mixtures. It is suggested that segregation in the dried powders was caused by the difference in solubility of the individual nitrate salts in water which caused Mg-rich and Al-rich salts to precipitate during dehydration of the solutions. The occurrence of segregation in the powders sprayed at 473 K and not 573 or 673 K is ascribed to the sluggish rate at which the early stages of decomposition occurred during which the cations segregated. The phase evolution in segregated and segregation-free MgO–MgAl2O4 powders has been compared. The distinguishing feature of the segregated powders was the appearance of stoichiometric periclase grain dimensions in excess of 0.3 μm at temperatures as low as 973 K. By comparison, the segregation-free powders displayed broad diffraction peaks corresponding to fine-grained and nonstoichiometric periclase. The grain size was in the range 5–30 nm at temperatures up to 1173 K. The key to obtaining fine-grained periclase was the ability to synthesize (Mg Al)O solid solutions with the rock salt structure. In the temperature range 973–1173 K, spinel grain size varied from 5 to 40 nm irrespective of its composition and did not appear to be influenced by segregation.

Fracture and R-curves in high volume fraction Al2O3/Al composites

Fracture toughness and fracture mechanisms in Al2O3/Al composites are described. The unique flexibility offered by pressureless infiltration of molten Al alloys into porous alumina preforms was utilized to investigate the effect of microstructural scale and matrix properties on the fracture toughness and the shape of the crack resistance curves (R-curves). The results indicate that the observed increment in toughness is due to crack bridging by intact matrix ligaments behind the crack tip. The deformation behavior of the matrix, which is shown to be dependent on the microstructural constraints, is the key parameter that influences both the steady-state toughness and the shape of the R-curves. Previously proposed models based on crack bridging by intact ductile particles in a ceramic matrix have been modified by the inclusion of an experimentally determined plastic constraint factor (P) that determines the deformation of the ductile phase and are shown to be adequate in predicting the toughness increment in the composites. Micromechanical models to predict the crack tip profile and the bridge lengths (L) correlate well with the observed behavior and indicate that the composites can be classified as (i) short-range toughened and (ii) long-range toughened on the basis of their microstructural characteristics.