Influence of the Cation on the Solubility of CO<Subscript>2</Subscript> and H<Subscript>2</Subscript> in Ionic Liquids Based on the Bis(trifluoromethylsulfonyl)imide Anion

Experimental values for the solubility of carbon dioxide and hydrogen in three room temperature ionic liquids based on the same anion—(bistrifluoromethylsulfonyl)imide [Ntf₂]—and three different cations—1-butyl-3-methylimidazolium, [C₄mim], 1-ethyl-3-methylimidazolium, [C₂mim] and trimethyl-butylammonium, [N₄₁₁₁]—are reported between 283 and 343 K and close to atmospheric pressure. Carbon dioxide, with a mole-fraction solubility of the order of 10⁻², is two orders of magnitude more soluble than hydrogen. The solubility of CO₂ is very similar in the three ionic liquids although slightly lower in the presence of the [C₂mim] cation. In the case of H₂, noticeable differences were observed with larger mole fraction solubilities in the presence of [N₄₁₁₁] followed by [C₄mim]. All of the mole-fraction solubilities decrease with increasing temperature. From the variation of Henry’s law constants with temperature, the thermodynamic functions of solvation were calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry’s law constants from appropriate smoothing equations, is always better than ±1%.     

The submicro determination of carbon,hydrogen and nitrogen by a gas-chromatographic method

A method for the determination of carbon, hydrogen and nitrogen in organic samples weighing 40–80 μg is described. The sample is decomposed conventionally in a helium stream and the water formed is converted to acetylene. Nitrogen, carbon dioxide and acetylene are then separated on a silica-gel column, and the acetylene is burned to carbon dioxide by passage through copper oxide at 900° because the acetylene peak itself is not easily measured. Water from the second combustion is removed on silica gel and the three peaks emerging are measured by means of a micro thermistor cell. The standard deviations obtained for acetanilide are 0.31% for carbon, 0.28% for hydrogen and 0.11% for nitrogen. Results for other compounds are given and the parameters relevant to precision are discussed.     

ABSORPTION AND EMISSION STUDIES OF ELECTRONIC STATES OF N-ARYLBENZAMIDES

Abstract— Absorption and emission spectra of several N-arylbenzamides have been measured. The quantum yields for their fluorescence were found to be dependent on matrix viscosity and temperature. Singlet-triplet splittings for these compounds were determined from their emission spectra and found to be abnormally small for π. π* states (˜ 1500 cm^-1). Indeed, the phosphorescence maxima of N-arylbenzamides occur slightly to the blue relative to their fluorescence maxima. Intersystem crossing efficiencies were determined for several of these compounds and are consistent with S₁→ S ₀ radiationless decay.     

NMR structure determination of a synthetic analogue of bacillomycin Lc reveals the strategic role of L-Asn1 in the natural iturinic antibiotics

Iturins are a group of antifungal produced by Bacillus subtilis. All are cyclic lipopeptides with seven alpha-amino acids of configuration LDDLLDL and one beta-amino fatty acid. The bacillomycin L is a member of this family and its NMR structure was previously resolved using the sequence Asp-Tyr-Asn-Ser-Gln-Ser-Thr. In this work, we carefully examined the NMR spectra of this compound and detected an error in the sequence. In fact, Asp1 and Gln5 need to be changed into Asn1 and Glu5, which therefore makes it identical to bacillomycin Lc. As a consequence, it now appears that all iturinic peptides with antibiotic activity share the common beta-amino fatty acid 8-L-Asn1-D-Tyr2-D-Asn3 sequence. To better understand the conformational influence of the acidic residue L-Asp1, present, for example in the inactive iturin C, the NMR structure of the synthetic analogue SCP [cyclo (L-Asp1-D-Tyr2-D-Asn3-L-Ser4-L-Gln5-D-Ser6-L-Thr7-beta-Ala8)] was determined and compared with bacillomycin Lc recalculated with the corrected sequence. In both cases, the conformers obtained were separated into two families of similar energy which essentially differ in the number and type of turns. A detailed analysis of both cyclopeptide structures is presented here. In addition, CD and FTIR spectra were performed and confirmed the conformational differences observed by NMR between both cyclopeptides.     

Generation and Application of Ultra-High-Intensity Magnetic Field Gradient Pulses for NMR Spectroscopy

Two different concepts of gradient current power supplies are introduced, which are suitable for the generation of ultra-high intensity pulsed magnetic field gradients of alternating polarity. The first system consists of a directly binary coded current source (DBCCS). It yields current pulses of up to ±120 A and a maximum voltage across the gradient coil of ±400 V. The second system consists of two TECHRON 8606 power supplies in push–pull configuration (PSPPC). It yields current pulses of up to ±100 A and a maximum voltage across the gradient coil of ±300 V. In combination with actively shielded anti-Helmholtz gradient coils, both systems are used routinely in NMR diffusion studies with unipolar pulsed field gradients of up to 35 T/m. Until now, alternating pulsed field gradient experiments were successfully performed with gradient intensities of up to ±25 T/m (DBCCS) and ±35 T/m (PSPPC), respectively. Based on the observation of the NMR spin echo in the presence of a small read gradient, procedures to test the stability and the matching of such ultra-high pulsed field gradient intensities as well as an automated routine for the compensation of possible mismatches are introduced. The results of these procedures are reported for the PSPPC system.     

Amine Functionalisations of Glycidyl methacrylate Based PolyHIPE Monoliths

High internal phase emulsions were employed to prepare highly porous (up to 80% pore volume) monoliths of poly(glycidyl methacrylate-co-ethylenegycol dimethacrylate) by free radical polymerisations of continuous phases of emulsions. Monoliths with cavities approximately 4 µm in diameter and with interconnecting pores approximately 0.7 µm in diameter were obtained. In order to obtain monoliths with ion exchange groups on the surface of pores for chromatography applications, functionalisations with different amines were performed and various reaction conditions tested. FTIR spectroscopy and nitrogen content analysis were used to monitor the functionalisation processes. Monoliths were succesfully functionalised with 1,2-diaminoethane, 1,4-diaminobuthane, 1,8-diaminooctane and tris(diethylamino)amine.     

Electron spin resonance studies of 199HgH, 201HgH, 199HgD and 201HgD isolated in neon and argon matrices at 4K: an electronic structure investigation

Various isotopomers of the mercury hydride radical (HgH) have been generated in a microwave discharge and trapped in neon and argon matrices at 4 K for electron spin resonance (ESR) investigations. Both the dipolar (A_dip) and isotropic (A_iso) components of the nuclear hyperfine interactions have been directly measured for ¹⁹⁹Hg, ²⁰¹Hg, H and D. Electronic structure information for HgH in its X²Σ ground state obtained from the hyperfine data is compared with theoretical results from several different computational methods. The hyperfine interactions in HgH are unusually large with A_iso(¹⁹⁹Hg) = 6859(3), A_dip(¹⁹⁹Hg) = 446(3), A_iso(H) = 730(2) and A_dip(H) = 0(2) MHz. A standard analysis of the hyperfine interactions demonstrates the need for a more in-depth theoretical treatment of HgH that should include relativistic effects. An interesting shift in spin density is observed when deuterium replaces hydrogen in HgH. The decreased spin density on deuterium, which was demonstrated in earlier studies, can now be more fully investigated since these new measurements confirm an associated increase in spin density on mercury     

Improved models for the phase behaviour of hydrogen fluoride: chain and ring aggregates in the SAFT approach and the AEOS model

Hydrogen fluoride presents one of the strongest hydrogen bonds known. Ring aggregates exist both in the vapour and liquid phases at low temperatures resulting in an anomalously high low-temperature vapour pressure. The effect of ring-like aggregates on the vapour—liquid phase equilibria of associating fluids is studied within the framework of the statistical associating fluid theory (SAFT) and in the chemical model of Lencka and Anderko (AEOS). The SAFT approach incorporates separate contributions to describe chain formation, association (hydrogen bonding), and long range dispersion forces. The treatment of the association interactions stems from the thermodynamic perturbation theory of Wertheim. At the first level of approximation the contribution of ring-like aggregates is neglected and only chain- and treelike structures are treated. In this work an earlier extension of the approach to incorporate ring aggregates is used to model the phase behaviour of hydrogen fluoride. The chemical model of Lencka and Anderko for associating fluids is also considered together with a modification that takes into account the formation of ring aggregates. Vapour pressures and coexistence densities are examined together with heats of vapourization, and the calculations are compared with experimental data.