Complementary on-line preconcentration strategies for steroids by capillary electrophoresis

Complementary on-line preconcentration strategies are needed when analyzing different classes of solutes in real samples by capillary electrophoresis (CE) with UV detection. The performance of three different on-line preconcentration (focusing) techniques under alkaline conditions was examined in terms of their selectivity and sensitivity enhancement for a group of steroids, including classes of androgens, corticosteroids and estrogens. Electrokinetic focusing of large sample injection plugs (up to 28% of effective capillary length or 22.1 cm) directly on-capillary can be tuned for specific classes of steroids based on changes in their mobility (velocity) using a multi-section electrolyte system in CE. A dynamic pH junction was applied for the selective resolution and focusing of weakly acidic estrogens using borate, pH 11.0 and pH 8.0 in the background electrolyte and the sample, respectively. Sweeping, using an anionic bile acid surfactant and neutral gamma-cyclodextrin (gamma-CD) under alkaline conditions (pH 8), resulted in focusing and separation of the moderately hydrophobic (non-ionic) classes of steroids, such as androgen and corticosteroids. Optimal focusing and resolution of all test steroids under a single buffer condition was realized by a dynamic pH junction-sweeping format using borate, pH 11.0 and bile acid surfactant with gamma-CD in the BGE, whereas the sample is devoid of surfactant at pH 8.0. The design of selective on-line focusing strategies in CE is highlighted by the analysis of microgram amounts of ethynyl estradiol derived from a female contraceptive pill extract using the dynamic pH junction method, which resulted in over a 100-fold enhancement in concentration sensitivity.     

Photoexcited behavior of nitrogen heteroaromatics (I). photoesterification of phenanthridine in carboxylic acid.

Photoirradiation of phenanthridine (I) derivatives in carboxylic acid caused esterification of (I). Different reactivity from those of other heteroaromatics is discussed.     

Synthesis of aromatic polyethers by Scholl reaction. V. Synthesis and polymerization of 1,3-bis[4-(1-naphthoxy) benzoyl]benzene, 1,4-bis[4-(1-naphthoxy)benzoyl]benzene,bis[4-(1-naphthoxy)phenyl]methane, 1,3-bis[4-(1-naphthoxy) phenylmethyl]benzene,and 1,4-bis-[4-(1-naphthoxy)phenylmethyl]benzene

This article describes the synthesis and the cation-radical polymerization (Scholl reaction) of 1,3-bis[4-(1-naphthoxy) benzoyl] benzene ( 6 ) and 1,4-bis[4-(1-naphthoxy) benzoyl]- benzene ( 7 ) initiated by FeCI₃. This polymerization produced poly(ether ether ketone ketone)s (PEEKK) of number average molecular weight (M?_n) up to 5400 g/mol. The synthesis of bis[4-(1-naphthoxy) phenyl] methane ( 8 ), 1,3-bis[4-(1-napthoxy) phenylmethyl] benzene ( 9 ), and 1,4-bis[4-(1-naphthoxy) phenylmethyl] benzene ( 10 ) are also described. Polyethers of M?_n up to 15400 g/mol at a FeCl₃/monomer molar ratio of 2/1 were obtained. An increased polymerizability of the monomers 9 and 10 containing two CH₂ groups versus that of the corresponding monomers containing two carbonyl groups ( 6 and 7 ) was observed. This enhanced polymerizability was explained based on the increased nucleophilicity of monomers 9 and 10 .     

Synthesis and properties of poly(arylene ether imide ketone)s

Poly(arylene ether ketone)s containing imide units were prepared by the aromatic nucleophilic displacement reaction of the potassium salts of bisphenols with bis(4-fluorobenzoyl)phthalimides in N-methyl-2-pyrrolidone at elevated temperature. The polymers having inherent viscosities of 0.34–0.77 dL/g were obtained in 2 h. The polymers exhibited glass transition temperatures ranging from 216 to 268°C and decomposition temperatures (5% weight loss under air atmosphere) ranging from 450–570°C mainly depending on the bisphenols used in the polymer synthesis. The isothermal TGA measurements (400°C under air or nitrogen atmosphere) revealed that the 4,4'-biphenol- and hydroquinone-based poly(arylene ether ketone imide)s belong to a superior class of heat resistant polymers. The mechanical properties of these polymers are also described. © 1994 John Wiley & Sons, Inc.     

Determination of pyridine and adenine nucleotide metabolites in Bacillus subtilis cell extract by sweeping borate complexation capillary electrophoresis

With a growing interest in new areas of bioanalytical research such as metabolome analysis, the development of sensitive capillary electrophoresis (CE) methods to analyze sub-microM concentrations of analytes in biological samples is required. In this report, the application of CE with sweeping by borate complexation is used to analyze a group of seven pyridine and adenine nucleotide metabolites derived from bacteria Bacillus subtilis cell extracts. Nanomolar (nM) detectability of analytes by CE with UV photometric detection is achieved through effective focusing of large sample plug (approximately 10% of capillary length) using sweeping by borate complexation method, reflected by a limit of detections (S/N = 3) of about 2 x 10(-8) M. Changes in metabolites concentrations were observed in cell extracts when using either glucose or malate as the carbon source in the culture medium. Concentration of pyridine and adenine nucleotides in cell extracts varied widely from 78.6 (+/-7.6) microM for nicotinamide-adenine dinucleotide in malate to 0.66 (+/-0.12) microM for nicotinamide-adenine dinucleotide phosphate in glucose culture medium. Concentrations of metabolites in a single cell were also estimated at millimolar (mM) level. The method was validated in terms of linearity, sensitivity and reproducibility. The application of CE by sweeping borate complexation allows for sensitive and reproducible analyses of nucleotide metabolites in complex biological samples such as bacteria cell extracts.     

Chemical reactivity of sc3n @ c80 and la2 @ c80

Sc3N@C80 has a lower thermal reactivity than La2@C80, although Sc3N@C80 has the same carbon cage (Ih) and oxidation state (C806-) as La2@C80. This result is attributed to the difference in the energy level and distribution of LUMO between Sc3N@C80 and La2@C80.     

Fast 5d → 4f luminescence of Pr in Lu2SiO5 single crystal host

Absorption and photoluminescence spectra including the decay kinetics of the Pr³⁺-doped Lu₂SiO₅ were measured. Fast luminescence originating from the radiative 5d → 4f transition of Pr³⁺ center is revealed with the maximum at 273 nm at room temperature. Low temperature photoluminescence decay is governed by the 25 ns decay, while substantial shortening to 6–7 ns occurs at room temperature. With the help of slow decay measurement in the millisecond time scale we evidence the thermal ionization of the relaxed excited 5d₁ state of Pr³⁺. The ionization can explain the observed temperature dependences of the decay times and emission intensity.     

Syntheses,X‐ray crystal structures,and emission properties of diprotonated tetrapyridylpyrazine and triprotonated terpyridine

A series of metal‐free compounds, that is, planar diprotonated tetraH₂(PF₆)₂ ( 1 ), planar monoprotonated bppzHPF₆ ( 2 ), nonplanar diprotonated bppzH₂(PF₆)₂ ( 3 ), and planar triprotonated terpyH₃Cl(PF₆)₂ ( 4 ), were prepared and characterized by electrospray ionization mass spectrometry, Ultraviolet–visible spectroscopy and cyclic voltammetry. Abbreviations used are tetra = tetra‐2‐pyridylpyrazine, bppz = 2,3‐bis(2‐pyridyl)pyrazine, and terpy = 2,2′:6′,2″‐terpyridine. The X‐ray crystal structures of the four compounds 1 , 2 , 3 , and 4 were determined. Both protonated pyridine rings are hydrogen bonded intramolecularly to the adjacent pyridine ring in compounds 1 and 3 . The π–π* absorption bands in the ultraviolet region for 1 , 2 , 3 , and 4 in acetonitrile were red‐shifted relative to those of the corresponding neutral unprotonated compounds. All the cyclic voltammetry for the protonated species, 1 , 2 , 3 , and 4 , showed the first reduction waves from ?0.37 to ?1.18 V, that were more positive than those of the neutral ones. Density functional theory was applied to interpret the planarity in 1 . The attachment of two protons to the two terminal tetra nitrogens in 1 leads to the remarkable emission (Φ = 0.031). The attachment of three protons to the three terpy nitrogens in 4 also gives the large quantum yield (Φ = 0.48). Copyright © 2015 John Wiley & Sons, Ltd.     

Dispersion Forces,Disproportionation, and Stable High‐Valent Late Transition Metal Alkyls

The transition metal tetra‐ and trinorbornyl bromide complexes, M(nor)₄ (M=Fe, Co, Ni) and Ni(nor)₃Br (nor=1‐bicyclo[2.2.1]hept‐1‐yl) and their homolytic fragmentations were studied computationally using hybrid density functional theory (DFT) at the B3PW91 and B3PW91‐D3 dispersion‐corrected levels. Experimental structures were well replicated; the dispersion correction resulted in shortened M?C bond lengths for the stable complexes, and it was found that Fe(nor)₄ receives a remarkable 45.9 kcal mol^?1 stabilization from the dispersion effects whereas the tetragonalized Co(nor)₄ shows stabilization of 38.3 kcal mol^?1. Ni(nor)₄ was calculated to be highly tetragonalized with long Ni?C bonds, providing a rationale for its current synthetic inaccessibility. Isodesmic exchange evaluation for Fe(nor)₄ confirmed that dispersion force attraction between norbornyl substituents is fundamental to the stability of these species.