Enantioselective comprehensive two‐dimensional gas chromatography of lavender essential oil

The enantiomeric composition of several chiral markers in lavender essential oil was studied by flow modulated comprehensive two‐dimensional gas chromatography operated in the reverse flow mode and hyphenated to flame ionization and quadrupole mass spectrometric detection. Two capillary column series were used in this study, 2,3‐di‐O‐ethyl‐6‐O‐tert‐butyldimethylsilyl‐β‐cyclodextrin or 2,3,6‐tri‐O‐methyl‐β‐cyclodextrin, as the chiral column in the first dimension and α polyethylene glycol column in the second dimension. Combining the chromatographic data obtained on these column series, the enantiomeric and excess ratios for α‐pinene, β‐pinene, camphor, lavandulol, borneol, and terpinen‐4‐ol were determined. This maybe a possible route to assess the authenticity of lavender essential oil.     

On improper interval edge colourings

We study improper interval edge colourings, defined by the requirement that the edge colours around each vertex form an integer interval. For the corresponding chromatic invariant (being the maximum number of colours in such a colouring), we present upper and lower bounds and discuss their qualities; also, we determine its values and estimates for graphs of various families, like wheels, prisms or complete graphs. The study of this parameter was inspired by the interval colouring, introduced by Asratian, Kamalian (1987). The difference is that we relax the requirement on the original colouring to be proper.     

Letter: Silver mediated ester bond formation in the gas phase: substrate structure is important

The silver acetate cation CH(3)CO(2)Ag(2)(+) reacted with allyl iodide via C-O bond coupling to produce Ag(2)I(+) and allyl acetate, but only underwent adduct formation with methyl iodide, highlighting the importance of substrate on reactivity. DFT calculations predicted the reaction with allyl iodide to be exothermic by 0.48 eV, and suggested that intermediates in the reaction benefit from multiple interactions between the allyl and iodide moieties of allyl iodide and the two silver atoms in CH(3)CO(2)Ag(2)(+).     

Quantifying the diffusion of a fluid through membranes by double phase encoded remote detection magnetic resonance imaging

We demonstrate that a position correlation magnetic resonance imaging (MRI) experiment based on two phase encoding steps separated by a delay can be used for quantifying diffusion across a membrane. This method is noninvasive, and no tracer substance or concentration gradient across the membrane is required. Because, in typical membranes, the T1 relaxation time of the fluid spins is usually much longer than the T2 time, we developed and implemented a new position correlation experiment based on a stimulated spin-echo, in which the relaxation attenuation of the signal is dominated by T1 instead of T2. This enables using relatively long delays needed in the diffusion measurements. The sensitivity of the double encoded experiment detected in a conventional way is still low because of the low filling factor of the fluid inside the NMR coil around the sample. We circumvent this problem by using the remote detection technique, which significantly increases the sensitivity, making it possible to do the measurements with gaseous fluids that have a low spin-density compared to liquids. We derive a model that enables us to extract a diffusion constant characterizing the diffusion rate through the membrane from the obtained correlation images. The double phase encoded MRI method is advantageous in any kind of diffusion studies, because the propagator of fluid molecules can directly be seen from the correlation image.     

Spectroscopic studies of dehydrogenation of ammonia borane in carbon cryogel

Ammonia borane (AB) is of great interest for storing hydrogen, an important issue in the growing field of hydrogen technology. The reaction pathways leading to the thermal decomposition of solid-state AB incorporated in carbon cryogels (CC) have been studied by spectroscopic methods. The time-dependent thermal decomposition was followed by in situ 11B nuclear magnetic resonance (NMR) and showed a significant increase in hydrogen release kinetics for AB in CC compared to neat AB. Both 11B NMR and Fourier transform infrared spectroscopy show a new reaction product, formed in the thermal decomposition of AB in CC scaffold (CC-AB) that is assigned to reactions with surface oxygen groups. The results indicate that incorporation of AB in CC enhances kinetics because of the reactions with residual surface-bound oxygen functional groups. The formation of new products with surface -O-B bonds is consistent with the greater reaction exothermicity observed when hydrogen is released from CC-AB materials. Scanning electron microscopy shows different morphology of AB in CC-AB nanocomposite as compared to neat AB.     

Coherent carbon cryogel-ammonia borane nanocomposites for H2 storage

Coherent carbon cryogel-ammonia borane (C-AB) nanocomposites were synthesized, and improved H2 storage properties are reported. Porous carbon cryogels were impregnated with AB in tetrahydrofuran solution at 25 degrees C under argon; 30% of the carbon cryogel pore volume was filled to produce a 24 wt % C-AB nanocomposite. Nitrogen sorption isotherms, X-ray diffraction, differential scanning calorimetry, differential thermal/thermal gravimetric analyses, mass spectrometry, and 11B NMR were used to characterize the coherent C-AB nanocomposites. Findings include a merged two-step hydrogen release reaction with an appreciable reduction in the dehydrogenation temperature to <90 degrees C as well as the suppression of borazine release. The possible nanosize effects on the H2 storage properties are discussed.     

Cyclopentanone ring expansion leading to functionalized delta-lactams: short synthesis of simple sedum alkaloids

Monosubstituted epoxides react with (cyclopentenyloxy)trimethylsilane to afford, after subsequent oxidative fragmentation, a pair of diastereomeric 8-membered iodolactones. When these lactones are separately treated with sodium azide, followed by reduction over Lindlar's catalyst, lactone ring contraction yields 6-membered monosubstituted lactams. When (R)-1,2-epoxypentane is used in this 5 + 3 - 2 overall ring expansion sequence, one final step involving delta-lactam to piperidine reduction yields natural (-)-halosaline and (-)-epihalosaline in five steps and 12% and 23% overall yields, respectively.