Cyclic carbonates as sustainable solvents for proline-catalysed aldol reactions

Ethylene and propylene carbonates, which can be prepared from epoxides and carbon dioxide, are effective solvents for the proline-catalysed, 100% atom economical, asymmetric aldol reaction between enolisable and non-enolisable carbonyl compounds. The optimal cyclic carbonate to use for a particular aldol reaction along with the need for water as a cosolvent appear to be determined by the polarities of the various components present in the reaction mixture. Both cyclic and acyclic ketones can be used as the enamine precursor and react best with electron-deficient aldehydes, such as 4-nitrobenzaldehyde and pentafluorobenzaldehyde. Chemical yields of up to 99%, diastereoselectivities of up to 100% and enantioselectivities of up to 99% can be obtained. The relative and/or absolute configuration of three of the aldol products are determined unambiguously by X-ray diffraction.     

Determination of acid-soluble and total rhodium on alumina-supported catalysts

Characterization of alumina-supported catalysts required determination of rhodium by atomic-absorption spectroscopy (AAS). Catalysts were loaded with 0.1-2.0% rhodium chloride and calcined at 400 degrees . Rhodium remaining as the chloride was regarded as the soluble form, while that converted into the oxide or bonded to the alumina was regarded as the bonded form. By selective dissolution procedures, soluble rhodium was leached from the substrate and determined by AAS. Total rhodium was determined after the catalyst had been fused with sodium peroxide. Bonded rhodium can be determined by difference or by analysing leached residue. Optimization of AAS conditions, use of spectroscopic buffer solution and elimination of interelement interferences are discussed.     

Steady-state temperature distribution in a finite spherical cone

A Naylor transform is employed to determine the axisymmetric steady-state temperature distributions in finite spherical cones where the boundary conditions include a variety of conditions at the spherical surface (insulation or heat loss in accordance with Newton's law) and an assigned temperature variation on the conical surface (in particular,f(r)=r ^m ,m0). Solutions are obtained in terms of inversion integrals and in Fourier-Legendre expansions. Computations based on the inversion integrals are carried out for cones of half-angles, =/6 and /2, and with several combinations of parameters relating to the boundary conditions.

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Résumé Une transformation de Naylor est employée afin de déterminer les distributions axisymétriques stationnaires de la température dans les cônes sphériques finis où les conditions aux limites comprennent une variété des conditions à la surface sphérique (isolation ou perte de chaleur conformément à la loi de Newton) et une variation de la température assignée à la surface conique (en particulierf(r)=r ^m ,m0). Les solutions sont obtenues sous forme d'intégrales d'inversion et de développements en série de Fourier-Legendre. Les calculs fondés sur les intégrales d'inversion sont accomplis pour les cônes de demi-angles, -/6 et /2, et pour différentes combinaisons de paramètres qui apparaissent dans les conditions aux limites.

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Acknowledgement. This research was supported in part by Grant AFOSR-69-1779 at North Carolina State University at Raleigh, Raleigh, North Carolina. 27607.     

Magnetic flux penetration and destruction of pion condensates

We show that an external magnetic field can destroy a pion condensate or lead to a vortex ground state stimilar to the mixed phase of a type II superconductor. Critical magnetic fields, determined for the ground state phases of the sigma model, are comparable to those which may be present in neutron stars.     

A glimpse at the chemistry of GeH2 in solution. Direct detection of an intramolecular germylene-alkene π-complex

The photochemistry of 3-methyl-4-phenyl-1-germacyclopent-3-ene (4) and a deuterium-labeled derivative (4-d(2)) has been studied in solution by steady state and laser flash photolysis methods, with the goal of detecting the parent germylene (GeH(2)) directly and studying its reactivity in solution. Photolysis of 4 in C(6)D(12) containing acetic acid (AcOH) or methanol (MeOH) affords 2-methyl-3-phenyl-1,3-butadiene (6) and the O-H insertion products ROGeH(3) (R = Me or Ac) in yields of ca. 60% and 15-30%, respectively, along with numerous minor products which the deuterium-labeling studies suggest are mainly derived from hydrogermylation processes involving GeH(2) and diene 6. The reaction with AcOH also affords H(2) in ca. 20% yield, while HD is obtained from 4-d(2) under similar conditions. Photolysis of 4 in THF-d(8) containing AcOH affords AcOGeH(3) and 6 exclusively, indicating that the nucleophilic solvent assists the extrusion of GeH(2) from 4 and alters the mechanism of the trapping reaction with AcOH compared to that in cyclohexane. Laser flash photolysis of 4 in hexanes yields a promptly formed transient exhibiting λ(max) ≈ 460 nm, which decays on the microsecond time scale with the concomitant growth of a second, much longer-lived transient exhibiting λ(max) ≈ 390 nm. The spectrum and reactivity of the 460 nm species toward various germylene trapping agents are inconsistent with those expected for free GeH(2); rather, the transient is assigned to an intramolecular Ge(II)-alkene π-complex of one of the isomeric substituted hydridogermylenes derived from a solvent-cage reaction between GeH(2) and its diene (6) coproduct, formed by addition of HGe-H across one of the C=C bonds. These conclusions are supported by the results of DFT calculations of the thermochemistry associated with π-complexation of GeH(2) with 6 and the formation of the isomeric vinylgermiranes and 1,2-hydrogermylation products. A different species is observed upon laser photolysis of 4 in THF solution and is assigned to the GeH(2)-THF complex on the basis of its UV-vis spectrum and rate constants for its reaction with AcOH and AcOD.     

Locally linear embedding method for dimensionality reduction of tissue sections of endometrial carcinoma by near infrared spectroscopy

Locally linear embedding (LLE) is introduced here as a nonlinear compression method for near infrared reflectance spectra of endometrial tissue sections. The LLE has been evaluated by using support vector machine (SVM) classifiers and the projected difference resolution (PDR) method. Synthetic data sets devised to resemble near-infrared spectra of tissue samples were used to characterize the performance of the LLE. The LLE was compared using principal component compression (PCC) method to evaluate nonlinear and linear compression. For a set of real tissue samples, if the compressed data were not range-scaled prior to SVM classification, the principal component compressed data gave an average prediction rate of 39 ± 2% while the LLE 94 ± 2%; if range-scaled after compression, the LLE and PCC performed evenly, with maximum average prediction values of 94 ± 2% and 93 ± 2%, respectively. The SVM without compression yielded a classification rate of 92 ± 2%. The prediction accuracy was consistent with PDR results. Without the second derivative preprocessing, the classification rates were 90 ± 3%, 89 ± 2%, and 78 ± 2% for the LLE compressed, the PCC, and no compression classifications by the SVM, respectively.     

Comparison of differential mobility spectrometry and mass spectrometry for gas chromatographic detection of ignitable liquids from fire debris using projected difference resolution

The significance of forensic arson analysis accelerates the applications of new technologies in this area. Based on the previously reported application of differential mobility spectrometry (DMS) as a detection method for gas chromatography (GC) in arson analysis, the performances of DMS and mass spectrometry (MS) were compared using a novel chemometric tool, projected difference resolutions (PDRs). The PDR results show that one-way mass spectra data exhibit higher resolution than DMS data, while total ion chromatograms from GC–DMS show higher resolution than that from GC/MS for differentiating seven kinds of ignitable liquids. Combining the information from both chromatography and spectra, two-way data always have higher resolution than one-way data for these two detection methods, and GC/MS would exhibit better performance than GC–DMS according to the minimum resolution value. To verify the PDR results, a fuzzy rule-building expert system was applied for classifying these seven kinds of ignitable liquids from fire debris based on GC–DMS and GC/MS data, respectively. The prediction accuracies were consistent with PDR results, which proved that PDR is a powerful tool in comparing the performances of different analysis methods for pattern recognition. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.