MO Study of the photochemical behavior of the imine bond

The photoisomerization of imine compounds is studied in terms of an ab initio MO CI calculation. The potential curves of the syn-anti isomerization via the rotation and the inversion are examined for benzaldimine. It is suggested that the photoisomerization is initiated through the rotation around the C? N bond in both singlet and triplet states. The ease of the photoisomerization is found to be determined by both the conformation of phenyl ring in the ground state and the energy difference of vertically excited states between two isomers.     

A modified method using static head-space gas chromatography for determining the stability constants of 1-alkanol/alpha-cyclodextrin complexation

A modification of the conventional static head-space gas chromatography method (SHSGC method) to determine stability constants for 1-alkanol/alpha-CD inclusion complexes was investigated. The 1 : 1 stability constants determined by this modified SHSGC method are in reasonable agreement with the corresponding values reported previously. The modified SHSGC method precludes the necessity of the calibration curve by the use of Henry's law constant of guest. Consequently, the modified SHSGC method is more advantageous than the conventional SHSGC method because the experimental time required for determination of the stability constant is markedly reduced.     

Potentiometric flow-injection determination of boron by using a flow-through tetrafluoroborate ion-selective poly(vinyl chloride) membrane electrode

A highly sensitive tetrafluoroborate ion-selective poly(vinyl chloride) membrane electrode was constructed and applied to a detector in the flow-injection determination of boron. Boron at the 10 ng ml^?1 level can be determined by converting it to tetrafluoroborate ion in a flow of hydrofluoric acid. A sampling rate of 30 h^?1 was achieved with a relative standard deviation of less than 2%.     

Semiconductor laser fluorimetry for enzyme and enzymatic assays

Near-infrared semiconductor laser fluorimetry is applied to assays of xanthine and xanthine oxidase. The fluorescence of indocyanine green in the near-infrared region is quenched by hydrogen peroxide. Xanthine is converted to uric acid by xanthine oxidase, in a reaction which also produces hydrogen peroxide; xanthine can be determined by measuring the decrease in fluorescence intensity of the dye added to the sample solution. The calibration graph for xanthine is linear from 5 × 10^?5 M to 5 × 10^?7 M. The enzyme activity can also be determined.     

Enantioface-selective palladium-catalyzed silaboration of allenes via double asymmetric induction

Enantioenriched beta-borylallylsilanes were synthesized by palladium-catalyzed enantioface-selective addition of the silicon-boron bond to terminal allenes using a palladium catalyst possessing a chiral monodentate phosphine ligand. Use of a silylborane bearing a chiral auxiliary on the boron atom was beneficial to gain enantioface selectivities as high as 96% de.     

Novel synthesis of 1,3-dienes from 1-alkenes via /ldene/rd reaction with pummerer rearrangement product: a short synthesis of the sex pheromone of the red bollworm moth

A Pummerer rearrangement product, 4-chlorophenylthiomethyl trifluoroacetate (6), obtained from 4-chlorophenyl methyl sulfoxide (5) and trifluoroacetic anhydride, reacted with 1-alkenes in trifluoroacetic acid to give the ene products 8, which were readily converted into the terminal 1,3-dienes 10 by oxidation and subsequent pyrolysis. Using this method, 9,11-dodecadien-1-yl acetate (12), a sex pheromone of the red bollworm moth, was synthesized.     

Dehydrogenation versus oxygenation in two-electron and four-electron reduction of dioxygen by 9-alkyl-10-methyl-9,10-dihydroacridines catalyzed by monomeric cobalt porphyrins and cofacial dicobalt porphyrins in the presence of perchloric acid

Dehydrogenation of 10-methyl-9,10-dihydroacridine (AcrH(2)) by dioxygen (O(2)) proceeds efficiently, accompanied by the two-electron and four-electron reduction of O(2) to produce H(2)O(2) and H(2)O, which are effectively catalyzed by monomeric cobalt porphyrins and cofacial dicobalt porphyrins in the presence of perchloric acid (HClO(4)) in acetonitrile (MeCN) and benzonitrile (PhCN), respectively. The cobalt porphyrin catalyzed two-electron reduction of O(2) also occurs efficiently by 9-alkyl-10-methyl-9,10-dihydroacridines (AcrHR; R = Me, Et, and CH(2)COOEt) to yield 9-alkyl-10-methylacridinium ion (AcrR+) and H(2)O(2). In the case of R = Bu(t) and CMe(2)COOMe, however, the catalytic two-electron and four-electron reduction of O(2) by AcrHR results in oxygenation of the alkyl group of AcrHR rather than dehydrogenation to yield 10-methylacridinium ion (AcrH+) and the oxygenated products of the alkyl groups, i.e., the corresponding hydroperoxides (ROOH) and the alcohol (ROH), respectively. The catalytic mechanisms of the dehydrogenation vs the oxygenation of AcrHR in the two-electron and four-electron reduction of O(2), catalyzed by monomeric cobalt porphyrins and cofacial dicobalt porphyrins, respectively, are discussed in relation to the C(9)-H or C(9)-C bond cleavage of AcrHR radical cations produced in the electron-transfer oxidation of AcrHR.     

Slipping of a histidine improved the peroxidase activity of a de novo designed polypeptide packing an iron porphyrin

Polypeptides with two histidines and an iron porphyrin (1H⁴⁰-7H⁴⁶) were synthesized with a variety of positions of a histidine. In 4H⁴³, histidine (H⁴³) was in the hydrophobic region of an α-helix. The other polypeptides were of slightly or substantially distorted conformation. In the pH 7.2 buffer solution, two histidines of the polypeptide coordinated the iron porphyrin regardless of their positions. Some polypeptides (1H⁴⁰, 3H⁴², and 5H⁴⁴) showed an enhanced catalytic activity in the peroxidase reaction using cumene hydroperoxide compared to that of 4H⁴³, whereas some polypeptides (2H⁴¹ and 6H⁴⁵) were ineffective catalysts. The distortion of the peptide conformation by the addition of MeOH was also effective for the peroxidase reaction.     

Regioselective synthesis and biological activity of oxidized chitosan derivatives

Oxidized chitosan derivatives with various degrees of oxidation (DS, 0.1–1.0) were prepared by the treatment of chitosan with CrO₃/aq HClO₄ or by the oxidation of ­3‐O‐ and N‐protected chitosan with 30% aq H₂O₂/Na₂WO₄ followed by 3‐O‐ and N‐deprotection. The oxidized products were then N‐acetylated with Ac₂O in order to improve their water‐solubility. Although the oxidized chitosan derivative of DS 0.28 and the degree of N‐acetylation of chitosan (DA) 38% was insoluble in the pH 3–8 region, that of DS 0.26 and DA 76% was soluble in the neutral pH range. The newly‐prepared acetylated and oxidized chitosan derivatives were found to suppress the chemiluminescence response of inflammatory cells such as canine polymorphonuclear cells (PMNs). Analysis by the surface plasmon resonance method revealed that the bind and release behavior of PMNs to acetylated oxidized chitosan derivatives was similar to that against carboxymethylated chitosan derivatives. The amount of water‐soluble chitosan derivative bound to cytokine IL‐8 was found to be affected by the structural and electronic features of the chitosan substituents in the chitosan chain. Copyright © 2003 John Wiley & Sons, Ltd.     

Rapid and simultaneous analysis of dichlorvos, malathion, carbaryl, and 2,4-dichlorophenoxy acetic acid in citrus fruit by flow-injection ion spray ionization tandem mass spectrometry

A simple method for the rapid and simultaneous analysis of dichlorvos (DDVP), malathion, carbaryl, and 2,4-dichlorophenoxy acetic acid (2,4-D) in citrus fruit, which uses flow-injection ion spray ionization tandem mass spectrometry, has been developed for the first time. The method involves the combined use of stable isotopically labeled internal standards (DDVP-d₆, malathion-d₁₀, carbaryl-d₇, and 2,4-D-d₅) and a multiple reaction monitoring technique. The average recoveries for the pesticides at the same concentrations as their tolerance levels (DDVP: 0.1-0.2 μg g⁻¹; malathion: 0.5-4.0 μg g⁻¹; carbaryl: 1.0 μg g⁻¹; 2,4-D: 1.0-2.0 μg g⁻¹) ranged from 90 to 119% with the relative standard deviation (R.S.D.) ranging from 1.0 to 13.1% (n = 5). Analysis time, including sample preparation and determination, was only 15 min. The present method is effective for screening DDVP, malathion, carbaryl, and 2,4-D in citrus fruit.