An accurate quantitative analysis of polymorphs based on artificial neural networks

Measurement precision based on homogeneous and accurate standard samples has been reported to result in significant improvement in the sensitivity and accuracy of the quantitative analysis of polymorphic mixtures. The purpose of this study was to further improve the accuracy of the quantitation based on data processing by artificial neural networks (ANNs), using such high quality standard samples. Homogeneous powder mixtures of - and γ-forms of indomethacin (IMC) at various ratios (0–50% -form content) were subjected to X-ray powder diffractometry. The two diffraction peaks selected as the best combination in multiple linear regression (MLR) were used in the ANN with an extended Kalman filter as a training algorithm. The results obtained by ANN had better predictive accuracy at lower contents (0–5%) compared to those of MLR. ANNs for the diffraction data based on high quality standard samples provide an extremely precise and accurate quantification for polymorphic mixtures.     

Synthesis of tetrasubstituted and functionalized enol ethers by E-selective olefination of esters with ynolates

We have developed the E-selective olefination of ester carbonyls to afford tetrasubstituted, functionalized olefins and the C-S insertion of thiol esters to give beta-keto thiol esters via ynolates.     

Detection of nanoparticles and components in smoke by time-of-flight mass spectrometry

A time-of-flight mass spectrometry (TOFMS) with a newly laboratory-made sampling cone interface fitted to an atmospheric pressure chemical ionization (APCI) positive ion source was successfully applied to easy, rapid on-line measurements of nanoparticles and components generated during combustion. The mass spectra for smoke from a mosquito coil ranged up to m/z 1202, corresponding to 1.2 nm with the carboneous material density as graphite 2.2 g cm⁻³. Typical m/z peaks were assigned to such synthetic pyrethroids, as d-allethrin and d-tetramethrin, at m/z 303 and 332, respectively. A specific pattern with a peak-to-peak interval of 74 was recognized in the higher mass range. The interval of 74 was confirmed by measuring with a standard silica solution in a positive ion mode using a conventional APCI interface under the same APCI conditions. The mass spectrum of the silica solution had a pattern with peak interval of 44 which was assigned to SiO. These results indicate that the pattern with an interval of 74 in the mass spectrum of the mosquito coil smoke is sample-derived peak. We assumed that the interval of m/z 74 is assigned to identified as triacetylene (1,3,5-hexatriyne) that is generated during the combustion.     

An efficient total synthesis of (+)-heliannuol D

An efficient total synthesis of (+)-heliannuol D was accomplished in 14 steps and in 12% overall yield by employing a diastereoselective conjugate addition reaction to create a tertiary benzylic stereogenic center and simple assembly of the functionalized oxepane framework by an efficient one-pot transformation procedure as the key steps.     

Enantioselective total synthesis of (-)-heliannuol A

An efficient and enantiocontrolled total synthesis of (-)-heliannuol A has been accomplished by employing ring closing metathesis and sequential diastereoselective epoxidation and regioselective reductive cleavage of the epoxide ring.     

Morphology and mechanical properties of ultrahigh-molecular-weight polyethylene films prepared from solutions in mixtures of diphenyl and diphenylether as co-solvent

In an attempt to check solvent dependence of drawability of ultra high-molecular-weight polyethylene films, gels were prepared from diphenyl/diphenylether solution, which is well known as -solvent. The content of diphenyl in the mixed solvent was chosen to be 25 wt%. Rapid gelation occurred when the solution had been cooled down to temperature lower than 147°C. The gel shrunk drastically with the further decrease of temperature and formed a bulk specimen. The maximum draw ratio was 20 and the corresponding Young's modulus reached 27 GPa. The value of Young's modulus was higher than the maximum value of melt film stretched up to 30 times, but it was much lower than the value of film which was prepared by gelation from decalin solution and was elongated up to 300. Thus, it turned out that the drastic shrinkage in the process of rapid gelation hampers a suitable level of the entanglement mesh that effectively transmits the drawing force.     

Molecular structures of propene and 3,3,3-trifluoropropene determined by gas electron diffraction

The structures of propene and 3,3,3-trifluoropropene have been studied by electron diffraction intensities measured in the present study and rotational constants reported in the literature. The following average structures have been determined: For propene, r_g(CC) = 1.342 ± 0.002 Å, r_g(C-C) = 1.506 ± 0.003 Å, r_g(C-H)_vinyl = 1.104 ± 0.010 Å, r_g(C-H)_methyl = 1.117 ± 0.008 Å, ∠(C-CC) = 124.3 ± 0.4°, ∠(CC-H) = 121.3 ± 1.4°, and ∠(C-C-H) = 110.7 ± 0.9°; for trifluoropropene, r_g(CC) = 1.318 ± 0.008 Å, r_g(C-C) = 1.495 ± 0.006 Å, r_g(C-H)= 1.100 ± 0.018 Å, r_g(C-F) = 1.347 ± 0.003 Å, ∠(C-CC) = 125.8 + 1.1°, ∠(C-C-F) = 112.0 ± 0.2°, where the valence angles refer to the r_av structure, and the uncertainties represent estimated limits of experimental error. A simple set of quadratic force constants for each molecule has been estimated. Regular trends have been observed in the CC and C-C bond distances and the C-CC angles in these and related molecules. Significant differences between the CC, C-C and C-F distances and the C-C-F angle in trifluoropropene and in hexafluoroisobutene reported by Hilderbrandt et al. have been indicated.     

Molecular rotor of Cs2([18]crown-6)3 in the solid state coupled with the magnetism of [Ni(dmit)2

Nanoscale molecular rotors that can be driven in the solid state have been realized in Cs2([18]crown-6)3[Ni(dmit)2]2 crystals. To provide interactions between the molecular motion of the rotor and the electronic system, [Ni(dmit)2]- ions, which bear one S=1/2 spin on each molecule, were introduced into the crystal. Rotation of the [18]crown-6 molecules within a Cs2([18]crown-6)3 supramolecule above 220 K was confirmed using X-ray diffraction, NMR, and specific heat measurements. Strong correlations were observed between the magnetic behavior of the [Ni(dmit)2]- ions and molecular rotation. Furthermore, braking of the molecular rotation within the crystal was achieved by the application of hydrostatic pressure.     

Identification of oxidation states of metal oxides by MALDI-TOF MS

For the detection of inorganic species, we have developed chemical reaction laser desorption ionization mass spectrometry, and applied it to the analysis of metal oxides in different oxidation states. Metal oxide species insoluble in common organic solvents were finely grounded in a mortar and suspended in a solvent. The turbid suspension was placed on a sample holder on which a suitable chelating reagent had been previously spotted in a similar manner for sample preparation employed in the matrix-assisted laser desorption mass spectrometry (MALDI-MS). By using this method, the mass spectra of manganese (II and IV) oxides (MnO and MnO₂), cobalt (II and III) oxides (CoO and Co₂O₃), and chromium (III and VI) oxides (Cr₂O₃ and CrO₃) were successfully obtained. By adjusting the experimental conditions, such as ionization modes and chelating reagents, the non-identical mass spectra were obtained for the elements in the different oxidation state. Thus, the oxidation states could be identified clearly.