Studies on the reduction of hematite by carbon

Single pellet experiments have been carried out in a nitrogen atmosphere to study the reduction of hematite by graphite in the temperature range 925 to 1060°C. The effect of variables such as c/Fe2O3 molar ratio, pellet size, and so forth, has been investigated. Gas analysis data show a continuous decrease in CO2/CO ratio during reduction, the values being far away from Fe/FeO equilibrium for wustite reduction by CO. The activation energies associated with different degrees of reduction appear to be widely different suggesting a possible changeover in reaction mechanism during the progress of reduction. X-ray diffraction studies confirm the stepwise nature of hematite reduction.

Studies on the variants of the protein toxins ricin and abrin

his study elucidates some structural and biological features of galactose-binding variants of the cytotoxic proteins ricin and abrin. An isolation procedure is reported for ricin variants from Ricinus communis seeds by using lactamyl-Sepharose affinity matrix, similar to that reported previously for variants of abrin from Abrus precatorius seeds [Hegde, R., Maiti, T. K. & Podder, S. K. (1991) Anal. Biochem. 194, 101–109]. Ricin variants, subfractionated on carboxymethyl-Sepharose CL-6B ion-exchange chromatography, were characterized further by SDS/PAGE, IEF and a binding assay. Based on the immunological cross-reactivity of antibody raised against a single variant of each of ricin and abrin, it was established that all the variants of the corresponding type are immunologically indistinguishable. Analysis of protein titration curves on an immobilized pH gradient indicated that variants of abrin I differ from other abrin variants, mainly in their acidic groups and that variance in ricin is a cause of charge substitution. Detection of subunit variants of proteins by two-dimensional gel electrophoresis showed that there are twice as many subunit variants as there are variants of holoproteins, suggesting that each variant has a set of subunit variants, which, although homologous, are not identical to the subunits of any other variant with respect to pI. Seeds obtained from polymorphic species of R. communis showed no difference in the profile of toxin variants, as analyzed by isoelectric focussing. Toxin variants obtained from red and white varieties of A. precatorius, however, showed some difference in the number of variants as well as in their relative intensities. Furthermore, variants analyzed from several single seeds of A. precatorius red type revealed a controlled distribution of lectin variants in three specific groups, indicating an involvement of at least three genes in the production of Abrus lectins. The complete absence or presence of variants in each group suggested a post-translational differential proteolytic processing, a secondary event in the production of abrin variants.

X-ray studies on crystalline complexes involving amino acids and peptides. XXIII. Variability in ionization state, conformation and molecular aggregation in the complexes of succinic acid with DL- and L-lysine

Crystalline complexes of succinic acid with DL- and L-lysine have been prepared and analysed by X-ray diffraction. DL-Lysine complex: C6HIsN202 + 1 2- 1 ~C4H404 .~C4H604, Mr -- 264"2, PI, a = 5"506 (4), =8.070(2), c=14.089(2) A,, a=92.02(1), /3= 100"69 (3), y = 95"85 (3) ~>, Z = 2, Dx = 1"44 g cm -3, R = 0.059 for 2546 observed reflections. Form I of the e-lysine complex: C6HIsN20-, ~ .C4H504, Mr = 264.2, P1, a = 5" 125 (2), b = 8"087 (1), c = 8"689 (1) A,, a = 112.06 (1), /3 = 99.08 (2), y = 93"77(2) °, Z--l, D,,,=1"34(3), Dx=l"34gcm 3 R = 0.033 for 1475 observed reflections. Form II of + I 2- the e-lysine complex: C6H15N202 .,iC4H404 .- 1 I ") 4C4H604.4(C4HsO4""H'"CaH404)" , Mr = 264"2, P1, a = 10.143 (4), b = 10.256 (2), c = 12"916 (3) A,, a = 105.00 (2),/3 = 99-09 (3), y = 92"78 (3)::, Z = 4, Dm= 1"37(4), D,.= 1.38gcm 3, R=0.067 for 2809 observed reflections. The succinic acid molecules in the structures exhibit a variety of ionization states. Two of the lysine conformations found in the complexes have been observed for the first time in crystals containing lysine. Form II of the L-lysine complex is highly pseudosymmetric. In all the complexes, unlike molecules aggregate into separate alternating layers. The basic element of aggregation in the lysine layer in the complexes is an S2-type head-to-tail sequence. This element combines in different ways in the three structures. The basic element of aggre gation in the succinic acid layer in the complexes is a hydrogen-bonded ribbon. The ribbons are interconnected indirectly through amino groups in the lysine layer.

NMR and X-ray crystallographic studies on cyclic tetrapeptide, cyclo (D-Phe-Pro-Sar-Gly)

The conformation of the synthetic cyclic tetrapeptide cyclo(D-Phe-Pro-Sar-Gly) has been determined in solution using the nuclear magnetic resonance technique and in the crystal state by X-ray crystallography. Results showed that the peptide exhibited two different conformations in solution, conformer 1 having cis-trans-cis-trans peptide bonds and conformer 2 having trans-cis-trans-cis peptide bonds. No intramolecular hydrogen bonds were observed in the structures. The X-ray diffraction studies showed the crystals to be orthorhombic with space group P2(1)2(1)2(1) with unit-cell dimensions, a = 5.790, b = 10.344, c = 31.446 A, Z = 4, R = 0.104 for 2301 observed reflections. The crystal structure showed only one type of conformer having cis-trans-cis-trans peptide bonds similar to the conformer 1 in solution.

Stereochemical studies on cyclic peptides: Detailed energy minimization studies on hydrogen bonded all-trans cyclic pentapeptide backbones

Conformational studies have been carried out on hydrogenbonded all-trans cyclic pentapeptide backbone. Application of a combination of grid search and energy minimization on this system has resulted in obtaining 23 minimum energy conformations, which are characterized by unique patterns of hydrogen bonding comprising of β- and γ-turns. A study of the minimum energy conformationsvis-a-vis non-planar deviation of the peptide units reveals that non-planarity is an inherent feature in many cases. A study on conformational clustering of minimum energy conformations shows that the minimum energy conformations fall into 6 distinct conformational families. Preliminary comparison with available X-ray structures of cyclic pentapeptide indicates that only some of the minimum energy conformations have formed crystal structures. The set of minimum energy conformations worked out in the present study can form a consolidated database of prototypes for hydrogen bonded backbone and be useful for modelling cyclic pentapeptides both synthetic and bioactive in nature.

Theoretical Studies on Coupled Electron and Proton Transfer in Cytochrome c Oxidase

The complexity of life is based on an effective energy transduction machinery, which has evolved during the last 3.5 billion years. In aerobic life, the utilization of the high oxidizing potential of molecular oxygen powers this machinery. Oxygen is safely reduced by a membrane bound enzyme, cytochrome c oxidase (CcO), to produce an electrochemical proton gradient over the mitochondrial or bacterial membrane. This gradient is used for energy-requiring reactions such as synthesis of ATP by F0F1-ATPase and active transport. In this thesis, the molecular mechanism by which CcO couples the oxygen reduction chemistry to proton-pumping has been studied by theoretical computer simulations. By building both classical and quantum mechanical model systems based on the X-ray structure of CcO from Bos taurus, the dynamics and energetics of the system were studied in different intermediate states of the enzyme. As a result of this work, a mechanism was suggested by which CcO can prevent protons from leaking backwards in proton-pumping. The use and activation of two proton conducting channels were also enlightened together with a mechanism by which CcO sorts the chemical protons from pumped protons. The latter problem is referred to as the gating mechanism of CcO, and has remained a challenge in the bioenergetics field for more than three decades. Furthermore, a new method for deriving charge parameters for classical simulations of complex metalloenzymes was developed.

Experimental studies on web crippling strength of hollow flange channels under EOF and IOF load cases

LiteSteel beam (LSB) is a hollow flange channel made from cold-formed steel using a patented manufacturing process involving simultaneous cold-forming and dual electric resistance welding. LSBs are currently used as floor joists and bearers in buildings. However, there are no appropriate design standards available due to its unique hollow flange geometry, residual stress characteristics and initial geometric imperfections arising from manufacturing processes. Recent research studies have focused on investigating the structural behaviour of LSBs under pure bending, predominant shear and combined actions. However, web crippling behaviour and strengths of LSBs still need to be examined. Therefore, an experimental study was undertaken to investigate the web crippling behaviour and strengths of LSBs under EOF (End One Flange) and IOF (Interior One Flange) load cases. A total of 23 web crippling tests were performed and the results were compared with the current AS/NZS 4600 and AISI S100 design standards, which showed that the cold-formed steel design rules predicted the web crippling capacity of LSB sections very conservatively under EOF and IOF load cases. Therefore, suitably improved design equations were proposed to determine the web crippling capacity of LSBs based on experimental results. In addition, new design equations were also developed under the Direct Strength Method format. This paper presents the details of this experimental study on the web crippling behaviour and strengths of LiteSteel beams under EOF and IOF load cases and the results.

X-ray photoelectron spectroscopic studies on Se/As2S3 and Sb/As2S3 nanomultilayered film

Photoinduced diffusion in Se/As2S3 and Sb/As2S3 nanomultilayered thin films are studied by X-ray photoelectron spectroscopy (XPS). The XPS measurements show the atomic movements during photoinduced diffusion in Se/As2S3 and Sb/As2S3 nanomultilayered film. The analysis of experimental data describes the nature of light induced changes indifferent structural units. (C) 2009 Elsevier B.V. All rights reserved.

In situ pump probe optical absorption studies on Sb/As2S3 nanomultilayered film

We report the in situ optical transmission change in the complete visible region of the electromagnetic spectrum to asses the kinetics of photo induced interdiffusion in Sb/As2S3 nanomultilayered film. The interdiffusion of Sb into As2S3 matrix results in the formation of Sb-As2S3 ternary solid solutions which is explained by the change in optical band gap, absorption coefficients and Tauc parameter (B-1/2) with evolution of time. The wavelength dependence of the time constants provides a better description of photo induced effects. The time evolution of the absorption coefficients and optical band gap are significantly faster in this process. (C) 2009 Elsevier B.V. All rights reserved.

Thermal Decomposition and Combustion Studies on Potassium Perchlorat e/Polystyrene Propellant Systems

STUDIES on potassium perchlorate/polystyrene (KP/PS) propellant systems have been carried out by using such techniques as thermogravimetry (TG), differential thermal analysis (DTA), and mass spectrometry (MS). It has been found that the thermal decomposition (TD) behavior of the KP/PS propellant is similar to that of the AP/PS propellant studied earlier.! It has also been observed that the TD of KP in the melt has a correlation with the burning rate (r) of KP/PS propellant at atmospheric pressure.

Substance flow analysis in Finland : Four case studies on N and P flows

Nitrogen (N) and phosphorus (P) are essential elements for all living organisms. However, in excess, they contribute to several environmental problems such as aquatic and terrestrial eutrophication. Globally, human action has multiplied the volume of N and P cycling since the onset of industrialization. The multiplication is a result of intensified agriculture, increased energy consumption and population growth. Industrial ecology (IE) is a discipline, in which human interaction with the ecosystems is investigated using a systems analytical approach. The main idea behind IE is that industrial systems resemble ecosystems, and, like them, industrial systems can then be described using material, energy and information flows and stocks. Industrial systems are dependent on the resources provided by the biosphere, and these two cannot be separated from each other. When studying substance flows, the aims of the research from the viewpoint of IE can be, for instance, to elucidate the ways how the cycles of a certain substance could be more closed and how the flows of a certain substance could be decreased per unit of production (= dematerialization). In Finland, N and P are studied widely in different ecosystems and environmental emissions. A holistic picture comparing different societal systems is, however, lacking. In this thesis, flows of N and P were examined in Finland using substance flow analysis (SFA) in the following four subsystems: I) forest industry and use of wood fuels, II) food production and consumption, III) energy, and IV) municipal waste. A detailed analysis at the end of the 1990s was performed. Furthermore, historical development of the N and P flows was investigated in the energy system (III) and the municipal waste system (IV). The main research sources were official statistics, literature, monitoring data, and expert knowledge. The aim was to identify and quantify the main flows of N and P in Finland in the four subsystems studied. Furthermore, the aim was to elucidate whether the nutrient systems are cyclic or linear, and to identify how these systems could be more efficient in the use and cycling of N and P. A final aim was to discuss how this type of an analysis can be used to support decision-making on environmental problems and solutions. Of the four subsystems, the food production and consumption system and the energy system created the largest N flows in Finland. For the creation of P flows, the food production and consumption system (Paper II) was clearly the largest, followed by the forest industry and use of wood fuels and the energy system. The contribution of Finland to N and P flows on a global scale is low, but when compared on a per capita basis, we are one of the largest producers of these flows, with relatively high energy and meat consumption being the main reasons. Analysis revealed the openness of all four systems. The openness is due to the high degree of internationality of the Finnish markets, the large-scale use of synthetic fertilizers and energy resources and the low recycling rate of many waste fractions. Reduction in the use of fuels and synthetic fertilizers, reorganization of the structure of energy production, reduced human intake of nutrients and technological development are crucial in diminishing the N and P flows. To enhance nutrient recycling and replace inorganic fertilizers, recycling of such wastes as wood ash and sludge could be promoted. SFA is not usually sufficiently detailed to allow specific recommendations for decision-making to be made, but it does yield useful information about the relative magnitude of the flows and may reveal unexpected losses. Sustainable development is a widely accepted target for all human action. SFA is one method that can help to analyse how effective different efforts are in leading to a more sustainable society. SFA's strength is that it allows a holistic picture of different natural and societal systems to be drawn. Furthermore, when the environmental impact of a certain flow is known, the method can be used to prioritize environmental policy efforts.