Segmental motion in polyoxymethylene

The proton spin-lattice relaxation times (T₁) of melt-crystallized, solution-crystallized, and solid-state-polymerized polyoxymethylene (POM) were measured between ?60 and +150°C. The three types of samples each have a pronounced T₁ minimum near room temperature which is a high-frequency manifestation of the γ process. From the quantitative dependence of the relaxation intensity on crystallinity as well as from the absolute magnitude of the relaxation times, it is concluded that the γ process in POM arises from hindered rotation of noncrystalline chain segments. The relation between the relaxation times and the long period indicates that these noncrystalline segments constitute disordered lamellar surface layers, the thickness of which depends on thermal history of the material. The temperature dependence of the motion of the relatively thin surface layers of solution crystallized POM is quite straightforward. The γ process in the bulk-crystallized material involves cooperative motion, however, leading to temperature-dependent kinetic parameters.     

Reaction of optically active alpha-aminoallenylstannanes with aldehydes formed in situ from the Lewis-acid-catalyzed rearrangement of epoxides

Reaction of optically active alpha-oxazolidinonylallenylstannanes with oxiranes in the presence of BF3.OEt2 produced beta-hydroxypropargylamines with high syn diastereoselectivity and high enantioselectivity through an initial Lewis-acid-catalyzed rearrangement of the oxirane to the corresponding aldehyde via an alkyl, aryl, or hydride shift. This permits the use of readily available oxiranes as alternatives to aldehydes that are difficult to prepare and/or unstable.     

One pot/two donors/one diol give one differentiated trisaccharide: powerful evidence for reciprocal donor-acceptor selectivity (RDAS)

Three component, one-pot reactions involving equimolar amounts of the acceptor diol and both armed and disarmed donors presented simultaneously, produce a single double-differential glycosidation product; this phenomenon provides evidence for Reciprocal Donor Acceptor Selectivity (RDAS).     

1,2-dinitrile polymers. III. Number-average molecular weight by pulsed NMR technique

In studies of various polymers in the solid state by pulsed and wide-line NMR, a relationship between the spin-lattice relaxation time and the fraction of mobile protons in the polymer sample was observed. This effect has been used to determine the degree of polymerization of a series of fumaronitrile homopolymers. The technique should have wide applicability in the direct determination of the number-average molecular weight M?_n, especially for polymers that may be insoluble and/or infusible though not crosslinked.     

Ground state vs. transition state substituent effects on reactions of aziridinium salts

The possibility that the similarity of Hammett ρ values for several very different reactions of 2-arylaziridinium salts is due to ground state effects was investigated by MO methods and ESCA. Minimum energy structures of p-nitrophenyl-, phenyl-, and p-methoxyphenyl-substituted ions, however, have the same C₂? N bond lengths. This result shows that substituent effects are primarily a transition state phenomenon, even in the three-membered ring heterocycles. In agreement, the ground state does not have significant amino carbocation character based on similar charge distributions of 2-phenyl-N,N-dimethylaziridinium ion and N,N,N-trimethylbenzylammonium ion as well as the same nitrogen ls binding energies by ESCA studies on corresponding salts.     

The octant rule. XVI1. COnformation and circular dichroism of syn and anti 2-methylbicyclo[3.1.0]hexan-3-ones,thujone and isothujone

(lS,5S)-exo-2(R)-Methylbicyclo[3.1.0]hexan-3-one ($\text{1}$) and (lS,5S)-endo-2(S)-methylbicyclo[3.1.0]hexan-3-one (2) were synthesized and their circular dichroism (CD) spectra run. Conformational analysis based on molecular mechanics calculations and Karplus equation analyses of vicinal H¦H NMR coupling constants indicate boat-like sofa conformations for both $\text{1}$ and $\text{2}$, with very little ring distortion from the symmetry of the parent bicyclo[3.1.0]hexan-3-one. The lone dissymmetric ψ-axial and ψ-equatorial methyl groups of $\text{1}$ and $\text{2}$, respectively, are both octant consignate. The natural product analogs of $\text{1}$ and $\text{2}$, (?)-3-isothujone ($\text{3}$) and (+)-3-thujone ($\text{4}$) were prepared and examined similarly. Their α-methyl perturbers dominate the CD n-π^★ Cotton effects.     

The Effect of Dispersion on the Structure of Diphenyl Ether Aggregates

Dispersion interactions can play an important role in understanding unusual binding behaviors. This is illustrated by a systematic study of the structural preferences of diphenyl ether (DPE)–alcohol aggregates, for which OH???O‐bound or OH???π‐bound isomers can be formed. The investigation was performed through a multi‐spectroscopic approach including IR/UV and microwave methods, combined with a detailed theoretical analysis. The resulting solvent‐size‐dependent trend for the structural preference turns out to be counter‐intuitive: the hydrogen‐bonded OH???O structures become more stable for larger alcohols, which are expected to be stronger dispersion energy donors and thus should prefer an OH???π arrangement. Dispersion interactions in combination with the twisting of the ether upon solvent aggregation are key for understanding this preference.     

Optimization of the ADER‐DG method in GPU applied to linear hyperbolic PDEs

We optimized the Arbitrary accuracy DErivatives Riemann problem (ADER) ‐ Discontinuous Galerkin (DG) numerical method using the CUDA‐C language to run the code in a graphic processing unit (GPU). We focus on solving linear hyperbolic partial–differential equations where the method can be expressed as a combination of precomputed matrix multiplications becoming a good candidate to be used on the GPU hardware. Moreover, the method is arbitrarily high order involving intensive work on local data, a property that is also beneficial for the target hardware. We compare our GPU implementation against CPU versions of the same method observing similar convergence properties up to a threshold where the error remains fixed. This behavior is in agreement with the CPU version, but the threshold is slightly larger than in the CPU case. We also observe a big difference when considering single and double precisions where in the first case, the threshold error is significantly larger. Finally, we did observe a speed‐up factor in computational time that depends on the order of the method and the size of the problem. In the best case, our novel GPU implementation runs 23 times faster than the CPU version. We used three partial–differential equation to test the code considering the linear advection equation, the seismic wave equation, and the linear shallow water equation, all of them considering variable coefficients. Copyright © 2015 John Wiley & Sons, Ltd.     

Enzyme-assisted extraction of citrus essential oil

Citrus peels are underutilized in the processing industry and are commonly considered as waste as their chemical composition varies. However, it is possible to recover some value-added products, one of them being essential oil, which is widely used in the food industry. Due to the current increase in global demand for citrus essential oils, it is necessary to implement processes directed to the maximum recovery of oil from waste peels. Numerous efforts have been made without achieving significant improvements in yields. In this work, enzymatic pretreatments of orange, lemon, and grapefruit peels were applied to achieve increased yields of essential oil extracted by hydro-distillation. In two of the sources it was possible to increase the essential oil yield from two to six times. Moreover, a significant amount of fermentable sugars which can be used in the production of certain other compounds of interest through fermentation was obtained.