Importance of single electron-transfer in singlet oxygen reaction in aqueous solution : Oxidation of electron-rich thioanisoles

Oxidation of substituted thioanisoles by chemically generated singlet oxygen was investigated in polar aqueous media. The formation of the superoxide ion was observed during sulphoxidation of 4-hydroxythioanisole (4) in phosphate buffer at pH 7.5. Control experiments indicated that the superoxide ion was formed by a direct reaction between singlet oxygen and 4. The kinetics of the trapping reaction by diphenylsulphoxide indicated the involvement of a single intermediate. The overall rate constants of the reaction of thioanisoles with singlet oxygen in methanol-water (1:1) are one order of magnitude larger than those in benzene. On the basis of these results, a mechanism involving a charge-transfer complex has been proposed for the reaction of electron-rich thioanisoles with singlet oxygen, whereby the charge-transfer complex would produce persulphoxide directly or dissociate to the cation radical and superoxide ion in polar aqueous media.     

Palladium-catalyzed reaction of allyl carbamates; allylation of carbonucleophiles,and protection-deprotection of amines

Allylation of carbonucleophiles with allylic carbamates under neutral conditions has been studied. The C-allylation of carbonucleophile is competitive with the N-allylation of amines, and the structure of amines is crucial for the selectivity. Bulky secondary amines gave the best results. Also a new method of protection-deprotection of amines as carbamates has been developed. Smooth deprotection is possible by the palladium-catalyzed reaction of allyl carbamates with formic acid. This method is particulary useful for primary amines, including optically active amino acids.     

Regio-controlled hydrogen-deuterium exchange of biologically important indoles under uv irradiation

Photochemical hydrogen-deuterium exchange reaction of biologically important indoles is reported. The regioselectivity of the photodeuteration was found to be controlled by the ammonium group of the side chain.     

A facile photochemical route to C-5 and C-6 allyl-substituted uracil nucleosides

Irradiation of 5-iodouridine or 6-iodo-1,3-dimethyluracil in aq. acetonitrile in the presence of allyltrimethylsilane provided the corresponding 5- or 6-allylated product.     

Continuous Photoreduction of Methyl Viologen Using Disubstituted Terthiophenes and EDTA in Aqueous Solution

The continuous photoreduction of methyl viologen by 5,5″-bis(aminomethyl)-2,2′:5′,2″-terthiophene (AT) and 2,2′:5′,2″-terthiophene-5,5″-dicarboxylic acid (CT), using EDTA as a sacrificial electron donor, has been investigated in aqueous solution at various pH. Apparent rates and efficiencies of production of the methyl viologen radical cation (MV⁺) were found to be dependent on the pH, the concentrations of all three components and the intensity of the incident light. The highest conversion efficiency (77%) was shown by the bis(aminoniethyI (-substituted terthiophene AT at pH 7.7. The quantum yield for the formation of MV⁺ under these conditions was 0.24, which is comparable with other common systems     

Development of a chemical vapor sensor using piezoelectric quartz crystals with coated unusual lipids

Piezoelectric quartz crystal sensors were developed using lipids with various properties for highly sensitive detection of chemical vapors. Lipids with varying lengths of alkyl chains were coated onto 10 MHz AT-cut quartz crystal resonators and the response of these modified crystals to chemical vapors were measured. It was shown that hydrophilic compounds, such as ethanol and methanol, could be recognized efficiently by lipids having shorter alkyl chains, whereas lipids with longer alkyl chains showed affinity to more hydrophobic vapors, such as toluene, hexane and cyclohexane. Frequency changes caused by adsorption of alcohols could be enhanced when cholesterol was co-immobilized in the lipid layer. To confirm the assumption that the sensor-response might be affected by the properties of lipids derived from acyl chains, we have examined the effects of two types of newly synthesized unusual lipids on sensor response. When lipids having one triple bond each at different positions on their alkyl chains were coated onto quartz crystals separately, lower responses were observed compared to responses obtained for a sensor with immobilized, saturated phosphatidylcholine. Lipids containing -branched acyl chains, however, showed good affinity for organic vapors, and sensor responses improved 4–5-fold. Moreover, these sensors were shown to have sensitivity of the same order as the humans' sense of smell (10⁻⁵–10⁻⁶ w/w in liquid paraffin) when measured using standard odorants (isovaleric acid, skatole, etc.) for an olfactometry established in Japan.     

Dominant Li+ ion conduction in Li+/Na+ mixed crystal, 15NaI∙LiBH4

Journal of Solid State Electrochemistry - In the present work, the conduction ions in 15NaI∙LiBH4 are investigated by secondary ion mass spectroscopy (SIMS) and galvanostatic measurements. An...     

An efficient method for 3,4-dihydroisoquinolinium ion formation,leading to a facile introduction of nucleophiles

The ketene silyl acetal derived from ethyl 2-benzyltetrahydroisoquinoline-1-carboxylate undergoes a rapid oxidation reaction with N-bromosuccinimide to form 3,4-dihydroisoquinolinium ion, which reacts with Grignard reagents to give 1,1-disubstituted tetrahydroisoquinolines in good yields.     

Determination of nitrogen- and phosphorus-containing pesticide residues in vegetables by gas chromatography with nitrogen-phosphorus and flame photometric detection after gel permeation chromatography and a two-step minicolumn cleanup

An efficient and reliable multiresidue method for determining pesticide residues in a large number of vegetable samples was studied. First, the important target compounds for monitoring, 52 nitrogen- and/or phosphorus-containing pesticides, were selected. The sample was extracted with acetonitrile, and the separated acetonitrile layer was cleaned up by a salting-out step. The acetonitrile extract was purified by gel permeation chromatography that divided the pesticide eluate into 2 fractions; the pesticide fractions were respectively purified by a 2-step minicolumn cleanup in which the second pesticide fraction was loaded on a silica-gel minicolumn. After a Florisil minicolumn was inserted on the silica-gel minicolumn, the first pesticide fraction was loaded on the tandem minicolumn, which was eluted with acetone-petroleum ether (3 + 7). The combined eluate was subjected to dual-column gas chromatography (GC) with nitrogen-phosphorus and flame photometric detection. By application of the optimum cleanup conditions to the 52 pesticides selected, good resolution and low breakdown levels of the pesticides during GC were maintained. Recoveries of the 52 pesticides from fortified cabbage, lettuce, spring onion, and spinach ranged from 72 to 108% with relative standard deviations of 2-17%, except for the recoveries of methamidophos and chlorothalonil. The detection limits of the pesticides were satisfactory (0.001-0.009 mg/kg) for monitoring pesticide residues in vegetables.     

Fluorometric sensing of alkaline Earth metal cations by new lariat ethers having plural pyrenylmethyl groups on the electron-donating sidearms

[structure: see text] New fluorescent compounds (1), lariat ethers having plural pyrenylmethyl groups on the sidearms, were prepared, and their complexation behavior with alkaline earth metal cations was examined by fluorescence spectrometry. The pyrene excimer emission decreased accompanied with an increase in the monomer emission upon complexation with the metal ion. This finding is ascribed to the cooperative participation of one of the two sidearms in the complexation of the crown ring with the metal ion.