The photolysis of bis(acetonitrile)tetrachlorotungsten in acetonitrile

When WCl₆ is dissolved in CH₃CN it is reduced to WCl₄(CH₃CN)₂ in a first-order process with a half-life of 52 s. Irradiation of the WCl₄(CH₃CN)₂ solution at 365 nm yields WO₂Cl₂(CH₃CN)₂. Further irradiation of this solution with access to air yields a blue, partially reduced form of WO₃ · 2H₂O, which eventually precipitates.     

On the propagation of electromagnetic waves through a time-varying dielectric layer

Expressions are obtained for the electromagnetic fields transmitted through a time-varying dielectric layer when a plane wave is incident normally upon one interface. Solutions are obtained for the case when the dielectric constant is changed in a stepwise fashion, and also for the case when the dielectric constant varies slowly and continuously. It is found that the inclusion of the boundary effects gives rise to frequency components in the transmitted signal which were not predicted by previous theories.Nomenclature c speed of light in vacuum - E electric field strength - H magnetic field strength - L thickness of the dielectric slab - n unit normal to the slab surface - r x–L - R reflection coefficient - t time - T transmission coefficient at x=0 - v speed of light in dielectric - x position - relative permittivity - transmission coefficient at x=L - ₀ incident signal frequency (radians/sec) - instantaneous frequency (radians/sec)     

Influence of Harvest Time on the Chemical Profile of Pereskia aculeate Mill. Using Paper Spray Mass Spectrometry

This study evaluated the physicochemical characteristics and the production of bioactive compounds of Pereskia aculeata Mill. at different harvest times. Here, we performed a qualitative evaluation of the chemical profile by paper spray mass spectrometry (PSMS), the phenolic acid and flavonoid profile by high-performance liquid chromatography (HPLC), antioxidant activity, total carotenoids, total phenolic compounds, total flavonoids, total anthocyanins, color characteristics, total soluble solids (TSS), total solids (TS), pH, and total titratable acidity (TTA). The chemical profile was not affected, with the exception of 4,5-dimethyl-2,6-octadiene and azelaic acid, which was only identified in the leaves harvested during the winter. The content of four phenolic acids and three flavonoids were analyzed; out of these, no significant amounts of ellagic acid and quercetin were detected. There was no difference in production of bioactive compounds between seasons, reflecting the antioxidant activity, which also did not differ. Brightness, chroma, and leaf pH were the only physicochemical characteristics that did not vary between seasons.     

Light-induced fluorescence spectroscopy of adenomas, adenocarcinomas and non-neoplastic mucosa in human colon. I. In vitro measurements.

In an attempt to evaluate whether induced fluorescence could be exploited to discriminate neoplastic from non-neoplastic tissue, fluorescence spectroscopy was performed at 450-800 nm on 83 biopsy specimens of colonic mucosa. Measurements showed that fluorescence spectra of adenoma, adenocarcinoma and non-neoplastic mucosa manifest dissimilar patterns. Nine variables, whose photophysical and/or biological bases need further investigation, were derived from the spectra. Discriminant functions between the groups of lesions were determined by using a stepwise discriminant analysis. The diagnostic test had a sensitivity of 80.6% and 88.2%, and a specificity of 90.5% and 95.2% in discriminating neoplastic from non-neoplastic mucosa and adenoma from non-neoplastic mucosa respectively. These results suggest that fluorescence spectroscopy has the potential to improve endoscopic diagnosis of premalignant and malignant lesions of colonic mucosa.