Raymond L. Ward

Isotropic NMR Shifts in Pyridine‐Type Bases Complexed with Paramagnetic NiII and CoII Acetylacetonates

Isotropic contact interaction shifts in the proton NMR spectra of pyridine‐type molecules coordinated with paramagnetic nickel (II) and cobalt (II) acetylacetonates have been observed. The role of π‐ and σ‐ bonding frameworks in the transfer of unpaired electron spin density from the metal ion to ligand protons is considered. Pseudocontact interactions appear to be significant in the cobalt systems but not in the nickel systems. When the pseudocontact contribution to isotropic shifts in cobalt systems is factored out there remain contact shifts which are in good agreement with the observed nickel shifts. It is concluded that the unpaired electrons in metal eg orbitals of both cobalt and nickel systems cause contact shifts in the pyridine‐type ligands whereas the t2g electron in the cobalt system does not. The t2g electron gives isotropic shifts by contributing to anisotropy in the electronic g factor.

Decomposition kinetics and mechanism of n-hexadecane-1,2-13C2 and dodec-1-ene-1,2-13C2 doped in petroleum and n-hexadecane

Abstract Isotopically labeled n-hexadecane doped at the percent level in three crude oils is used to determine the intrinsic decomposition kinetics and mechanism of n-alkanes in petroleum. Adjacent 13C labels at the end of the hexadecane and dodecene give a mass fragment sufficiently unique that its disappearance and many of its products can be followed by ordinary gas chromatography-mass spectrometry. Additional structural details of the labeled reaction products are measurable by the NMR INADEQUATE technique, which detects only adjacent 13C atoms. Samples were heated at temperatures ranging from 310 to 360°C in capillary glass tubes and Dickson autoclaves. At temperatures around 350°C, n-alkane decomposition in dissimilar oil matrices forms primarily normal alkanes smaller than the starting alkane at a rate about 60% as fast as the decomposition of the neat alkane. Unlike in neat hexadecane, no significant branched alkanes are formed from the labeled hexadecane in crude oil by alkylation of alkene intermediates. Doping the oils and n-hexadecane with labeled dodecene confirms that alkenes in two of the three oils are rapidly converted primarily to the corresponding alkanes, while reaction of alkenes in hexadecane forms primarily branched alkanes. Reaction of alkenes in the high paraffin oil was intermediate in characteristics. One autoclave experiment included water to assess the importance of water during pyrolysis, with the result that the alkane decomposition rate is affected very little. However, coking of aromatics is inhibited, and there is a significant increase in the production of both H2 and CO2 gas with water present, indicating that water is chemically reactive under these conditions. At temperatures around 310°C, the decomposition rate of neat hexadecane is roughly equal to that in a high paraffin oil and substantially slower than in North Sea and high sulfur oil, suggesting that the effect of the oil matrix has switched from suppression of propagation reactions to enhancement of initiation reactions. The activation energy for doped hexadecane cracking in sealed glass capillaries ranges from about 53 kcal/mol in a North Sea oil to about 62 kcal/mol in high paraffin and high sulfur oils. These values are both lower than for neat hexadecane over the same temperature range but still imply substantial subsurface stability for crude oil.

Photoinduced Paramagnetism in Solutions of Nitrobenzene in Tetrahydrofuran

ESR studies are reported of photoinduced paramagnetism in solutions of nitrobenzene in undeuterated and deuterated tetrahydrofuran (THF). The ESR spectrum exhibits a widely spaced set of identical triplets, and the extra proton hyperfine interaction (0.38 plus or minus 0.04 Oe) is due to a single alpha proton of the THF molecule. The experiments of Lagercrantz and Yhland with trinitrobenzene were also repeated, and the following mechanism for the production of the paramagnetic species is proposed: Light irradiation causes the nitro group to abstract an alpha hydrogen atom from the THF molecule, and the resulting THF free radicais rapidly dimerize or disproportionate, leaving a neutral nitrobenzene free radical in solution. The radical has a totai decay time of approximates 2 sec and is suspected to reside on an oxygen atom. (D.L.C.)

Electron Spin Resonance Studies of the Potassium Salt of m-Dinitrobenzene Negative Ion

A detailed analysis of the electron spin resonance spectrum for the potassium salt of m‐dinitrobenzene negative ion in DME is presented. Isotopic substitution has been performed in various positions in the molecule. m‐Dinitrobenzene negative ion exhibits only one nitrogen hyperfine interaction of 9.0 gauss, and possesses proton hyperfine interactions of 4.6 gauss for the number 2, 4, and 6 protons and 1.2 gauss for the number 5 proton. The hyperfine spectrum is different for each of the alkali metals, Li, Na, K, Rb, and Cs, but still retains only one nitrogen hyperfine interaction. An enriched Li6 metal salt of m‐dinitrobenzene indicates no alkali metal hyperfine interaction.

Temperature and competitive anion-binding studies of carbonic anhydrase☆

Abstract The 35Cl-nmr line width for solutions of human carbonic anhydrase B in 0.5 m NaCl at pH 6.46 and 8.59 has been examined as a function of temperature. An Arrhenius plot of the line width decreases linearly with decreasing temperature over the temperature range 0–38.5 °C. This behavior indicates that the lifetime of the enzyme-zinc-chloride complex is the dominating relaxation time of the system. The value of koff at pH 6.46 and 8.59 at 25 °C is 1 × 106 sec−1 and 7.3 × 105 sec−1, respectively. Using a value of Ki of 0.2 m values for kon are 5 × 106 m −1 sec−1 and 3.7 × 106 m −1 sec−1. These values are somewhat lower than that for aqueous zinc ion and may be related to the hindered nature of the zinc site in the enzyme. The energy of activation obtained for the chloride exchange process is 3.6 kcal/mole. Anion competitive binding studies for bovine carbonic anhydrase have also been made for a number of monovalent anions. KI values obtained by analysis of chloride line broadening are in agreement with those determined kinetically. Although chloride and iodide competitive binding studies can be interpreted in terms of zinc-iodide binding, the results do not distinguish between the possible E-Zn-OH2-I and E-Zn-I forms of the complex.

Identification by 13C n.m.r. of carbon types in shale oil and their relation to pyrolysis conditions

Abstract A number of samples of shale oil prepared under various conditions have been examined by 13C n.m.r. using multiple-pulse techniques that allow carbon-type assignments. Previous assignments by Netzel et al. (Fuel 1981, 60, 307) are confirmed and several new ones made. Product chemistry is then examined as a function of heating conditions. New or verified observations are: 1. (1) isoprenoids are evolved in the early stages of oil generation, and the average length of normal hydrocarbons in the evolved oil is approximately independent of the extent of kerogen conversion; 2. (2) alkene content depends strongly on the heating rate during pyrolysis but average normal chain length does not; and 3. (3) the ratio of isoprenoid to normal carbons and the average normal chain length in bitumen are greater than in shale oil, but there are greater questions about the correct equation for calculating the average normal chain length of bitumen.

A new spectrophotometric arginase assay

Abstract We wish to report a new method for the assay of arginase ( l -arginine amidinohydrolase, EC 3.5.3.1). Arginase, the terminal enzyme of the urea-ornithine cycle (1), catalyzes the cleavage of arginine to ornithine and urea. Present assays for arginase determine the released urea either by a colorimetric procedure (2) or by a manometric procedure with urease (3). Our new assay is a spectrophotometric method based on the fact that the absorbancy of arginase below 2100 A is larger than the combined absorbancies of ornithine and urea. A cleavage of arginine catalyzed by the enzyme thus results in a net decrease in absorbancy at these wavelengths, allowing a rapid and accurate assay for arginase activity.

35Cl NMR studies of the active site zinc of horse liver alcohol dehydrongenase

Abstract 35 Cl-NMR has been used to study the active site Zn ions of horse liver alcohol dehydrogenase. The Cl − probe interaction with the Zn ions is completely removed by the binding of two molecules of reduced coenzyme per molecule of enzyme. Adenosine diphosphate ribose (ADPR) also effectively removed the Cl − Zn interaction. Orthophenanthroline (OP) has no effect on the Cl − line width, but is an effective competitor with coenzyme and ADPR for the Zn ions. The OP results suggest that the Zn is octahedrally coordinated in the enzyme. The pH profile of the Cl − broadening is relatively flat from pH 5.5 to pH 9.0. It decreases above pH 9.0 with an apparent pK of 9.8 ± 0.2 in 0.5M NaCl.

A magnetic resonance study on the citrate lyase of Streptococcus diacetilactis

Summary By the use of pulsed nuclear magnetic resonance techniques, the dissociation constant of Mn2+-citrate lyase (citrate oxaloacetate-lyase, EC 4.1.3.6) has been determined to be 0.4 · 10−4 M. This value is in agreement with the kinetically determined value. No evidence for ternary complex formation was found. The reaction would seem to be one that involves a metal-enzyme acting upon citrate (or acetate and oxaloacetate) rather than an enzyme acting upon a metal-citrate complex.

Optical multilayer films based on an amorphous fluoropolymer

Multilayered coatings were made by physical vapor deposition (PVD) of a perfluorinated amorphous polymer, Teflon AF2400, and with other optical materials. A high reflector for 1064 nm light was made with ZnS and AF2400. An all‐organic 1064 nm reflector was made from AF2400 and polyethylene. Oxide (HfO2 and SiO2) compatibility with AF2400 was also tested. The multilayer morphologies were influenced by coating stress and unintentional temperature rises from the PVD process. Analysis by liquid nuclear magnetic resonance of the thin films showed slight compositional variations between the coating and starting materials of perfluorinated amorphous polymers.