Results Of Dissociation Experiments Research Articles

Equilibrium Data of (tert-Butylamine + CO2) and (tert-Butylamine + N2) Clathrate Hydrates

In this work, experimental hydrate dissociation pressures of the (tert-butylamine + CO2) and (tert-butylamine + N2) systems were reported at (0.005, 0.015, 0.03, 0.056 and 0.093) mole fraction of tert-butylamine with measurements made in the temperature range of (273.5 to 283.3) K and in the pressure range of (2.27 to 13.79) MPa. The equilibrium data were generated using an isochoric pressure-search method. The hydrate dissociation data for the (CO2 + water) system were obtained in advance and compared with experimental data reported in the literature, and the acceptable agreements demonstrate the reliability of the experimental method and apparatus employed in this work. Dissociation experimental results indicated that tert-butylamine had an inhibition effect on the dissociation conditions of carbon dioxide, shifting the dissociation conditions of CO2 hydrate to lower temperatures/higher pressures, while for the (tert-butylamine + N2 + water) system, tert-butylamine showed a hydrate promotion effect, whi...

Synthesis of Methane Hydrate in an Unconsolidated Medium

Abstract Under certain conditions of low temperature and high pressure, mixtures of small gas molecules and water form crystalline, ice-like compounds called clathrate hydrates. It is believed that large quantities of natural deposits of methane hydrate are formed in unconsolidated media from natural gas and water. Development of recovery techniques for this potential natural gas resource requires comprehensive laboratory investigations of engineering properties, which in turn require a capability for reproducibly synthesizing methane hydrate in unconsolidated matrix materials. This paper presents a procedure for synthesizing methane hydrate in an unconsolidated sand matrix. Results of dissociation experiments indicate that the samples prepared according to this procedure are relatively homogeneous and suitable for use in investigations of mechanical and other properties. The methane hydrate content and porosity of the samples can be controlled in the procedure developed.

Structure of Cationized Arginine (Arg·M+, M = H, Li, Na, K, Rb, and Cs) in the Gas Phase: Further Evidence for Zwitterionic Arginine

The gas-phase structures of cationized arginine, Arg.M(+), M = Li, Na, K, Rb, and Cs, were studied both by hybrid method density functional theory calculations and experimentally using low-energy collisionally activated and thermal radiative dissociation. Calculations at the B3LYP/LACVP++** level of theory show that the salt-bridge structures in which the arginine is a zwitterion (protonated side chain, deprotonated C-terminus) become more stable than the charge-solvated structures with increasing metal ion size. The difference in energy between the most stable charge-solvated structure and salt-bridge structure of Arg.M(+) increases from -0.7 kcal/mol for Arg.Li(+) to +3.3 kcal/mol for Arg.Cs(+). The stabilities of the salt-bridge and charge-solvated structures reverse between M = Li and Na. These calculations are in good agreement with the results of dissociation experiments. The low-energy dissociation pathways depend on the cation size. Arginine complexed with small cations (Li and Na) loses H(2)O, while arginine complexed with larger cations (K, Rb, and Cs) loses NH(3). Loss of H(2)O must come from a charge-solvated ion, whereas the loss of NH(3) can come from the protonated side chain of a salt-bridge structure. The results of dissociation experiments using several cationized arginine derivatives are consistent with the existence of these two distinct structures. In particular, arginine methyl esters, which cannot form salt bridges, dissociate by loss of methanol, analogous to loss of H(2)O from Arg.M(+); no loss of NH(3) is observed. Although dissociation experiments probe gas-phase structure indirectly, the observed fragmentation pathways are in good agreement with the calculated lowest energy isomers. The combination of the results from experiment and theory provides strong evidence that the structure of arginine-alkali metal ion complexes in the gas phase changes from a charge-solvated structure to a salt-bridge structure as the size of the metal ion increases.

Structure and function of hemocyanins VII. The smallest subunit of α- and β-hemocyanin of Helix pomatia: Size, composition, N- and C-terminal amino acids

1. 1. The amino acid and carbohydrate composition of α- and β-hemocyanin of Helix pomatia were determined. The amino acid composition is strikingly similar in both hemocyanins; the carbohydrate composition shows small quantitative differences. The presence of an unidentified sugar in both α- and β-hemocyanin is observed. 2. 2. Both α- and β-hemocyanin have N-terminal arginine; the C-terminal amino acid could not be identified by several methods. By application of a quantitative dinitrophenylation micromethod it was shown that 1 mole of arginine is present per 25 000 g of hemocyanin. 3. 3. Dissociation of hemocyanin molecules beyond the state of twentieth molecules is extremely difficult. Application of 70% formic acid leads to dissociation into subunits with a molecular weight of 25 000, readily dimerizing to 50 000. 4. 4. The obtained subunits are highly heterogeneous, in accordance with the results of dissociation experiments. The cause of this phenomenon is still unknown.