Protonation susceptibility and fragmentation capability of functional groups in chemical ionization mass spectrometry of simple bifunctional compounds. Semi-quantitative interpretation of spectra

Positive-ion, methane-mediated chemical ionization mass spectra were measured for simple bifunctional aromatic compounds of the type m-XCH₂C₆H₄CH₂Y, where X = NH₂ and N(CH₃)₂, and Y = OH and OCH₃. Essentially only three peaks of ions, [MH]⁺, [MH – XH]⁺ and [MH – YH]⁺, have appeared for each compound. Since the two functional groups XCH₂– and YCH₂– do not interact with each other after protonation or after fragmentation, they are assumed to be protonated and to undergo fragmentations independently. The relative protonation susceptibility and fraction of fragmenting [MH]⁺ can be estimated for each functional group in these compounds. A semi-quantitative interpretation of the observed spectra is presented.     

Determination of linuron in water samples by high performance liquid chromatography after preconcentration with octadecyl silanized magnetite

A sensitive and selective batch adsorption method is proposed for the preconcentration and determination of linuron. Linuron was preconcentrated on octadecyl silanized (ODS) magnetite as an adsorbent and then determined by high performance liquid chromatography (HPLC). Several parameters on the recovery of the analyte were investigated. The experimental results showed that it was possible to obtain sufficient preconcentration efficiency when the solution pH was 6 using 100 mL of sample solution containing 1.0 μg of linuron and 3 mL of ethanol as a desorption solution. Recovery of linuron was 50.7 ± 1.9% with a relative standard deviation for five determinations of 3.0% under optimum conditions. The calibration curve of linuron was linear up to 200 ng mL^− 1 with a correlation coefficient of 0.998 and the detection limit (3S/N) was 1.0 ng mL^− 1. The capacity of the adsorbent was also examined and found to be 0.15 mg g^− 1 for linuron. ODS-magnetite is suitable for repeated use without decreasing recovery at least 4 adsorption–desorption cycles. The proposed method was successfully applied to the determination of linuron in river water with high precision and accuracy.     

Close-packed colloidal crystalline arrays composed of polystyrene latex coated with titania nanosheets

We have demonstrated that polystyrene latex coated with titania nanosheets can be fabricated into a close-packed colloidal crystalline array, and that these coated colloidal spheres can be used to control the peak position of optical stop bands through the coating. The titania-nanosheets-coated polystyrene latex was prepared by the layer-by-layer (LBL) assembly coating process, involving alternating lamination of cationic polyelectrolytes and anionic titania nanosheets on monodisperse polystyrene latex particles. The Bragg diffraction peak of the colloidal crystalline array shifted to longer wavelengths with the coating of titania nanosheets. This red shift was caused by an increase in refractive index upon coating, as revealed by angle-resolved reflection spectra measurements. The current work suggests new possibilities for the creation of advanced colloidal crystals having tunable optical properties from tailored colloidal spheres.     

New megastigmane glucosides from Excoecaria cochinchinensis LOUR. var. cochinchinensis

Two new megastigmane glucosides, called excoecariosides A and B were isolated from the leaves of a medicinal Vietnamese plant, Excoecaria cochinchinensis LOUR. var. cochinchinensis (Euphorbiaceae) together with seven known compounds. Their structures were elucidated by spectroscopic analyses and chemical reactions including the modified Mosher's method.     

ULTRAVIOLET HYPERSENSITIVITY OF COCKAYNE SYNDROME LYMPHOBLASTOID LINES—THE EFFECTS OF EXOGENOUS β-NICOTINAMIDE ADENINE DINUCLEOTIDE

Four Cockayne Syndrome (CS) lymphoblastoid lines were tested for the lethal effects of UV radiation (254 nm) with or without addition of exogenous β-nicotinamide adenine dinucleotide (β-NAD ⁺) to their culture medium. Two of them exhibited a small but significantly increased resistance to UV radiation when β-NAD⁺ was added to the culture. However, their UV sensitivity after β-NAD ⁺ addition was still much greater than that of normal control lines. Normal control lymphoblastoid lines and those from complementation group A and group C of xeroderma pigmentosum (XP) did not reveal any differences in post-UV sensitivity after the addition of exogenous β-NAD⁺. Thus the abnormal response to the lethal effects of UV radiation of CS lymphoblastoid lines could not be rectified by β-NAD⁺ addition. However, β-NAD⁺ does appear to play some partial role in reducing the high UV sensitivity of some CS lymphoblastoid lines.     

Design of catalysts based on electrochemical microcell models

The concept and the strategy for designing catalytic systems on the basis of electrochemical microcell models have been proposed and demonstrated for Wacker-type oxidation of ethylene, selective hydrogenation of nitric oxide into hydroxylamine and partial oxidation of alkenes and alkanes. For designing active and selective catalysts, at least four fundamental catalytic elements are required. These are (1) the oxidation sites (anode), (2) the reduction sites (cathode), (3) proton conducting medium, and (4) electron conducting medium. The catalytic elements (3) and (4) would electrochemically connect the oxidation (anode reaction) on site (1) and the reduction (cathode reaction) on site (2). A mixture of these four catalytic elements generates an unlimited number of microcells which work as catalysts for desired synthetic reactions.     

Direct aldol reaction of trifluoroacetaldehyde ethyl hemiacetal with ketones by use of the combination of amines and acids

Trifluoroacetaldehyde ethyl hemiacetal reacts with unmodified ketones in the presence of 30-50 each mol % of amines and acids at ambient temperature, affording the corresponding β-hydroxy-β-trifluoromethylated ketones in good yields with good to excellent diastereoselectivities.     

Modeling of retention behavior in capillary electrochromatography from chromatographic and electrophoretic data

A phenomenological approach was presented to describe the retention behaviors of solutes in capillary electrochromatography (CEC). Equations for calculation of the retention time and actual chromatographic retention factor for ionic solutes, weak monoprotic acid and weak monoprotic base were derived, which can be described by two general expressions regardless the charge status of the solute. The general expressions enable calculation of the retention time and retention factor in CEC from chromatographic and electrophoretic data, which were experimentally verified with a variety of compounds and a variety of CEC modes. Based on this approach, the chromatographic retention and the electrophoretic migration in the CEC systems studied were found to be two independent processes. The validity of this approach was also discussed.     

Supramolecular ferroelectric liquid crystals. Hydrogen-bonded complexes between benzoic acids and chiral stilbazoles

Supramolecular ferroelectric liquid crystalline complexes have been obtained from 4-alkoxybenzoic acids and optically active trans-4-substituted-4'-stilbazoles. Chiral smectic C phases are induced by the formation of supramolecular mesogenic structure through the selective intermolecular hydrogen bond between the achiral benzoic acids and the chiral non-mesogenic stilbazoles.     

The effect of humidity on dehydration behavior of nitrofurantoin monohydrate studied by humidity controlled simultaneous instrument for X-ray Diffractometry and Differential Scanning Calorimetry (XRD–DSC)

The dependence of thermal dehydration behavior of nitrofurantoin monohydrate on humidity was studied. Difference in observed crystallinity of resulting anhydrates under three humidity conditions is discussed in relation to the effect of water vapor molecules. Thermal dehydration of nitrofurantoin monohydrate was measured using a humidity controlled simultaneous measurement instrument for X-ray Diffractometry (XRD) and Differential Scanning Calorimetry (DSC) in dry, 27 °C 91% RH and 60 °C 90% RH nitrogen. Dehydration of nitrofurantoin in dry nitrogen gave a mixture of crystalline and amorphous anhydrates in the temperature range of 124–180 °C followed by crystallization around 185–190 °C. Whereas, dehydration in high humidity atmosphere (60 °C 90% RH or 17.7% H₂O–82.3% N₂) gave well crystallized anhydrate at 140 °C soon after dehydration. Dehydration in low humidity nitrogen (27 °C 91% RH or 3.2% H₂O–96.8% N₂) gave not totally crystalline anhydrate, which became pure crystalline at around 190 °C. The effect of high humidity on dehydration and crystallinity of the resulting anhydrate can be attributed to the role of water vapor molecules in two ways such as the acceleration of molecular mobility and high molecular diffusion rate of nitrofurantoin anhydrate, and the formation of hydrogen bonding bridges quickly connecting dehydrated molecules to one another.