Electronic spectroscopy of highly polar aromatics. XI. Luminescence of the cyanoanilines

The absorption and emission spectra of the three isomeric cyanoanilines have been investigated. Quantum yields and decay lifetimes are reported for both fluorescence and phosphorescence processes. It is shown that the lowest energy absorption band of p-cyanoaniline consists of two distinct electronic transitions of the ¹π^*←¹π type, whereas, in the o- and m-cyanoanilines, the lowest energy absorption band consists of a single electronic transition of the ¹π^*←¹π type. These conditions are consistent with absorption data, emission data and kinetic analyses. The largest ?_P/?_F ratio is exhibited by the p-cyanoaniline and this observation is rationalized.     

Preparation of sterically hindered geometric isomers of 7-cis-β-ionyl and β-ionylidene derivatives in the vitamin A series

The preparation of the relatively unknown 7-cis isomers of β-ionyl and β-ionylidene derivatives via one way sensitized geometric isomerization is described. These highly sterically crowded isomers, once prepared do not readily thermally revert back to the trans. But the trienes, at temperatures ≥ 100° undergo irreversible cyclization to cyclohexadienes. 7-cis Isomers of β-ionylideneacetone and acetaldehyde as well as higher tetraenes and pentaenes in this series could not be prepared by sensitized isomerization. Partial reduction of 7-cis-β-ionylideneacetonitrile isomers led to the preparation of 7-cis- and 7,9-dicis-β-ionylideneacetaldehyde; and methyl Grignard reaction with the same nitrile gave the triene-methyl ketones.     

Determination of acidic herbicides in surface water by solid-phase extraction followed by capillary zone electrophoresis

A rapid solid-phase extraction-capillary zone electrophoresis (CZE) method for determining 2,4-dichlorophenoxyacetic acid, 4-(2,4-dichlorophenoxy) butyric acid, and 2,4,5-trichlorophenoxyacetic acid in real water samples is described. Factors affecting the recoveries and detection of the targets are investigated. With samples being acidified to pH 2 and salted by sodium sulfate to 2% (w/w), an average recovery of greater than 85% is obtained using ethyl acetate as the eluent on an octadecylsilane-bonded silica cartridge. A running buffer of 5 mM sodium tetraborate in a water-acetonitrile mixture (70:30, v/v) adjusted to pH 9 is employed in the CZE analysis, and the targets can be analyzed within 7 min with good reproducibility and acceptable sensitivity. The method is suitable for detecting herbicide residues of sub-parts-per-billion levels in surface water. A local pond water is analyzed, and the concentrations of 2,4-dichlorophenoxyacetic acid and 4-(2,4-dichlorophenoxy) butyric acid are detected to be 0.27 +/- 0.03 ppb and 0.61 +/- 0.08 ppb, respectively.     

Likelihood Inferences for High-Dimensional Factor Analysis of Time Series With Applications in Finance

This article investigates likelihood inferences for high-dimensional factor analysis of time series data. We develop a matrix decomposition technique to obtain expressions of the likelihood functions and its derivatives. With such expressions, the traditional delta method that relies heavily on score function and Hessian matrix can be extended to high-dimensional cases. We establish asymptotic theories, including consistency and asymptotic normality. Moreover, fast computational algorithms are developed for estimation. Applications to high-dimensional stock price data and portfolio analysis are discussed. The technical proofs of the asymptotic results and the computer codes are available online.