Conformations, vibrational frequencies and Raman intensities of short-chain fatty acid methyl esters using DFT with 6-31G(d) and Sadlej pVTZ basis sets

Density functional calculations, using B3LPY/6-31G(d) methods, have been used to investigate the conformations and vibrational (Raman) spectra of three short-chain fatty acid methyl esters (FAMEs) with the formula CnH2nO2 (n = 3-5). In all three FAMEs, the lowest energy conformer has a simple 'all-trans' structure but there are other conformers, with different torsions about the backbone, which lie reasonably close in energy to the global minimum. One result of this is that the solid samples we studied do not appear to consist entirely of the lowest energy conformer. Indeed, to account for the 'extra' bands that were observed in the Raman data but were not predicted for the all-trans conformer, it was necessary to add-in contributions from other conformers before a complete set of vibrational assignments could be made. Provided this was done, the agreement between experimental Raman frequencies and 6-31G(d) values (after scaling) was excellent, RSD = 12.6 cm(-1). However, the agreement between predicted and observed intensities was much less satisfactory. To confirm the validity of the approach followed by the 6-3 1 G(d) basis set, we used a larger basis set, Sadlej pVTZ, and found that these calculations gave accurate Raman intensities and simulated spectra (summed from two different conformers) that were in quantitative agreement with experiment. In addition, the unscaled Sadlej pVTZ, and the scaled 6-3 1 G(d) calculations gave the same vibrational mode assignments for all bands in the experimental data. This work provides the foundation for calculations on longer-chain FAMEs (which are closer to those found as triglycerides in edible fats and oils) because it shows that scaled 6-3 1 G(d) calculations give equally accurate frequency predictions, and the same vibrational mode assignments, as the much more CPU-expensive Sadlej pVTZ basis set calculations.

Substance Use among Young People Living in Residential State Care

Existing empirical evidence on substance use among young people living in residential state care during adolescence is comparatively limited. This paper reports on substance use trends of young people living in residential state care during three annual data-sweeps when aged 14, 15 and 16 years. A repeated cross-sectional research design was utilised in the research. The findings suggest some similarities for lifetime prevalence rates for tobacco and alcohol use for those living in residential state care with a group of same-age young people not living in residential state care who participated in the research. However, solvent abuse and cannabis use was higher among those living in care. More frequent substance use was reported by the residential care sample for all substances at each stage of the study. These findings suggest that young people living in state care continue to merit higher levels of vigilance from researchers and policy-makers in order to fully understand this behaviour and develop appropriate prevention initiatives to meet their needs regarding potential drug problems.

Effect of pH, temperature, and moisture on the formation of volatile compounds in glycine/glucose model systems

Mixtures of glycine, glucose, and starch were extrusion cooked using sodium hydroxide at 0, 3, and 6 g/L of extruder water feed, 18% moisture, and 120, 150, and 180 degreesC target die temperatures, giving extrudates with pH values of 5.6, 6.8, and 7.4. Freeze-dried equimolar solutions of glucose and glycine were heated either dry or after equilibration to similar to 13% moisture at 180 degreesC in a reaction-tube system designed to mimic the heating profile in an extruder. Volatile compounds were isolated onto Tenax and analyzed by gas chromatography-mass spectrometry. For the extrudates, total yields of volatiles increased with decreasing pH at 180 degreesC, reached a maximum at pH 6.S at 150 degreesC, and increased with increasing pH at 120 degreesC. Amounts increased with temperature at all pH values. Pyrazines were the most abundant class for all sets of conditions (54-79% of total volatiles). Pyrroles, ketones, furans, oxazoles, and pyridines were also identified. Yields of volatiles from the reaction-tube samples increased by > 60% in the moist system. Levels of individual classes also increased in the presence of moisture, except pyrazines, which decreased similar to3.5-fold. Twenty-one of the compounds were common to the reaction-tube samples and the extrudates.

Regioselectivity and stereoselectivity of dioxygenase catalysed cis-dihydroxylation of mono- and tri-cyclic azaarene substrates

cis-Dihydrodiol metabolites were obtained from dioxygenase-catalysed asymmetric dihydroxylations of. five monocyclic (azabiphenyl) and four tricyclic (azaphenanthrene) azaarene substrates. Enantiopurity values and absolute configuration assignments were determined using a combination of stereochemical correlation, X-ray crystallography and spectroscopy methods. The degree of regioselectivity found during cis-dihydroxylation of monocyclic azaarenes (2,3 bond >> 3,4 bond) and of tricyclic azaarenes (bay region > non-bay region bonds) was dependent on the type of dioxygenase used. The cis-dihydrodiol metabolite from an azaarene (3-phenylpyridine) was utilised in the chemoenzymatic synthesis of the corresponding trans-dihydrodiol.

NUMERICAL SIMULATIONS OF BURST PROCESSES IN FIBER-BUNDLES

We discuss a very effective numerical method for simulating fibre-bundle models with equal load-sharing and with local load-sharing. Particular attention is paid to the case of the local load-sharing model, in which the critical load x(c) is defined as the average load per fibre that causes the final complete failure. It is shown that x(c) --> 0 when the size of the system N --> infinity. We also show analytically that the power law of the burst size distribution, D(Delta) alpha Delta(-xi), is approximately correct. The exponent xi in the local load-sharing case is not universal, since it depends on the strength distribution as well on as the size of the system.

Soft X-ray harmonic comb from relativistic electron spikes

We demonstrate a new high-order harmonic generation mechanism reaching the "water window" spectral region in experiments with multiterawatt femtosecond lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving mu J/sr pulses. Harmonics are collectively emitted by an oscillating electron spike formed at the joint of the boundaries of a cavity and bow wave created by a relativistically self-focusing laser in underdense plasma. The spike sharpness and stability are explained by catastrophe theory. The mechanism is corroborated by particle-in-cell simulations.