Vortrag UNIX-Stammtisch 05/98

The infrared absorption spectra of single crystals of strontium formate and strontium formate dihydrate have been recorded between 4000 and 500 cm⁻¹. Crystal slices cut perpendicular to the crystal axes were employed; the spectra were recorded using polarized radiation, the electric vector being parallel to the direction defined by the crystal axis in question. For Sr(CHO₂)₂it was possible to assign 20 of the 36 infrared active internal fundamentals. In addition lattice modes at: 10, 12, 15, 20, 23, 70, 155, 180 and 200 cm⁻¹ were infered from combinations with internal fundamentals. For Sr(CHO₂)₂.2H₂O it was possible to observe only 10 of the 36 internal fundamentals associated with the formate ions as the absorbing species. Of the 18 internal fundamentals associated with the water molecules as the absorbing species only one mode could be unambiguously assigned. Lattice modes at: 642, 710, 750, 797, 840, 856 and 872 cm⁻¹ were observed and two additional lattice modes at 18 and 110 cm⁻¹ were infered from combinations with internal fundamentals. From the intensity ratios of the internal fundamentals of Sr(CHO₂)₂ it was possible to calculate the direction cosines associated with each of the two crystallographically non-equivalent formate ions contained in the unit cell. / Science, Faculty of / Chemistry, Department of / Graduate

A multitude of microorganisms possess the ability to metabolise molecular hydrogen (H2). The major enzyme family involved in hydrogen metabolism are Hydrogenases. These enzymes catalyse the reversible conversion of molecular hydrogen to protons and electrons (H2 ↔ 2H+ + 2e-). These enzymes have the potential to be utilised for biotechnological applications such as hydrogen fuel cells, but they also represent promising drug targets for inhibition of bacterial energy metabolism both within the gastrointestinal tract and after infection. Therefore, further understanding and discoveries made in the hydrogenase field warrants progression into applied medical and biotechnological research areas. Hydrogenases are also interesting due to their phylogeny and physiology in a large number of microbial species. These enzymes are categorised by their active site architecture. One well studied, ancient group is termed the [NiFe]-hydrogenases, which all harbour a complex NiFe(CN-)2CO active site in the 'large' catalytic subunit and usually have three iron-sulfur clusters within a 'small' electron transferring partner subunit. [NiFe]-hydrogenases have undergone massive diversification, with four major phylogenetic subgroups arising. The major part of this Thesis concerns work on a Group 4 [NiFe]-hydrogenase that functions in partnership with a formate dehydrogenase as a formate hydrogenlyase (FHL). This FHL complex generates H2 and CO2 from the disproportionation of formate (CHOO- + H+ ↔ H2 + CO2). In this Thesis, genetic and biochemical characterisation of Pectobacterium atrosepticum SCRI1043, a potato pathogen, led to the identification of a novel FHL complex. The [NiFe]-hydrogenase in this organism is similar to that of Escherichia coli Hydrogenase-4, with an extended membrane domain similar to that of respiratory Complex I. Importantly, the P. atrosepticum formate dehydrogenase is selenium-free, while previously characterised FHL complexes have selenocysteine-containing formate dehydrogenases. Using genetic and biochemical approaches it was shown that the [NiFe]-hydrogenase and a formate dehydrogenase were vital for H2 production by P. atrosepticum. Using plant infection assays it was also shown that the gene encoding the formate dehydrogenase was important for full infective ability of P. atrosepticum in potato plants and tubers. The latter part of this Thesis focuses on developing genetic tools to study this novel FHL from P. atrosepticum as well as Hydrogenase-1 and -2 from E. coli.

No description available.

The reaction of methanol with the nearly-stoichiometric and oxygen-terminated surfaces of Cr₂O₃ (101̅2) was studied using thermal desorption spectroscopy and x-ray photoelectron spectroscopy. Dissociative adsorption of methanol occurs on the nearly-stoichiometric surface and is attributed to the presence of cation/anion site-pairs. An array of products including CH₄, CH₂O, CO, CO₂, and H₂ are produced above 550 K on the nearly-stoichiometric surface. Monolayer coverage of methanol yields a 58% conversion to products. Of these products, selectivity to CO is the highest (41%), followed by CH₂O (28%), CH₄ (24%), and CO₂ (7%). At higher temperatures methoxides reversibly undergo dehydrogenation and nucleophilic from lattice oxygen to form dioxymethylene. Hydrogenation of methoxides leads to the formation of CH₄ and CH₃OH above 550 K. Formate is formed as a surface intermediate by reversible dehydrogenation of dioxymethylene. Formaldehyde is produced via C-O bond cleavage of dioxymethylene, and the decomposition of formate yields CO, CO₂, and H₂. The oxygen-terminated surface is unreactive for methanol dissociation due cation site blocking by terminal chromyl oxygen. / Master of Science

Formate-based mud has been used to drill deep gas wells in Saudi Arabia since 2004. This mud typically contains XC-polymer, starch, polyanionic cellulose, and a relatively small amount of calcium carbonate particles, and is used to drill a deep sandstone reservoir (310°F). Calcium carbonate particles are frequently used as weighting material to maintain the pressure that is required for well control and minimize the leak-off. Such solids become consolidated and trapped in the polymeric material and this makes the filter cake a strong permeability barrier. Various cleaning fluids were proposed to remove drilling mud filter cake; including: solid-free formate brine and formate brine doped with organic acids (acetic, formic, and citric acids), esters, and enzymes. The main objective of this research is to assess the effectiveness of these cleaning fluids in removing drilling mud filter cake. A dynamic high-pressure/high-temperature (HPHT) cell was used to determine characteristics of the drilling mud filter cake. Drilling mud and completion fluids were obtained from the field. Compatibility tests between potassium formate brine, cleaning fluids, and formation brine were performed at 300ºF and 200 psi using HPHT visual cells. Surface tensions of various cleaning fluids were also measured at high temperatures. The conventional method for cleaning the filter cake is by circulating solid-free formate brines at a high flow rate. This mechanical technique removes only the external drilling fluid damage. Citric acid at 10 wt%, formic acid, and lactic acid were found to be incompatible with formate brine at room temperature. However, these acids were compatible with formate brine at temperatures greater than 122°F. Only acetic acid was compatible with formate brine. A formula was developed that is compatible at room and reservoir temperature. This formula was effective in removing filter cake. A corrosion inhibitor was added to protect downhole tubulars. In general detail, this research will discuss the development of this formula and all tests that led to its development.

This thesis consists of the structures of two compounds as determined by single crystal x-ray diffraction. The first structure is that of a phosphazene - iodine complex: hexamethylcyclotriphosphazene - iodine (1:1 adduct) and the second structure is the redetermination of sodium formate. Crystals of hexamethylcyclotriphosphazene - iodine (1:1 adduct) are triclinic, a = 10.707(13), b = 8.873 (5), c = 8.871(6)Å, α = 96. 65 (6), β = 103.91 (12), ɤ = 97.81(12)°, Z = 2, space-group PI. The structure was determined with Mo-K« diffractometer data by Patterson and Fourier synthesis, and was refined by full-matrix least-squares calculations to R = 0.053 for 1934 observed reflexions. The iodine molecule is weakly bonded to a nitrogen atom on the phosphazene ring, N - I = 2.417(7), I - I = 2. 823 (1) Å, N - I - I = 177.8(2)°. The six-membered phosphazene ring is slightly, but significantly, ncn-planar, the conformation being that of a chair. The molecule has pseudo-m symmetry. Two distinct P-N bonds are present; the longer ones, mean P - N = 1.64 Å, involve the nitrogen that is weakly bonded to the iodine molecule, while the other four P-N bonds are equivalent, mean P - N = 1.598 Å. All the P - C bonds are equivalent, mean P - C = 1.789 Å. The mean endocyclic N - P - N and P - N - P angles are 114.7 and 124.0° respectively, while the mean exocyclic C - P - C angle is 104°. Crystals of sodium formate are mcnoclinic, a = 6.2590 (6), b = 6.7573 (16) , c = 6.716 (5) Å, β = 116.140(6)°, Z = 4, space-grcup C2/c. The structure was determined by direct methods, and was refined by electron density and full-matrix least-squares procedures to E = 0.022 for 250 reflexions. Sodium formate is planar and has C2V symmetry. Partial charges were refined on the formate ion. The partial charges found on each atom are as follows: 0 -0.23(1)e, C +0.16(3)e, H -0.49(10)e, and Sa +0.79(14)e. The sodium ion has six oxygen neighbours at an average distance of 2.45 Å and there are weak Na. ..0 interactions. There is a C - H...Na hydrogen bond which forms continuous rows of sodium formate ions. The C - 0 bond distance is 1.246(1)Å and the 0 - C - 0 angle is 126.3(2)°. / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

Call number: LD2668 .T4 1966 P298 / Master of Science

There is a need to develop techniques for conversion of carbon dioxide to other useful products such as methanol, formaldehyde, formic acid, formate, methane, and hydrocarbons. Carbon dioxide can be converted into these products using different methods such as photochemical, electrochemical, thermochemical and hydrogenation by bacteria. Formate is of interest due to its wide industrial applications which include it’s use in direct liquid fuel cells, as an additive in pyrolysis vapors, a precursor for biological fuels, and it is a key intermediate in methanogenesis breaking down complex organic compounds. In this work, conversion of carbon dioxide to formate was accomplished photochemically. The concentration of formate obtained was quantified using ion chromatography. The yield of formate, based on the amount of carbon dioxide in solution, was 1.54%, while the quantum yield was near 2.0%. Detailed studies of the photoreduction process showed that the amount of sensitizer, light intensity and pH affect the amount of formate generated.