Expulsion of the CHO radical from the molecular ion of homochromones

For some homochromones, it was confirmed by labelling C-9 with deuterium that the CHO radical expelled from the molecular ion contains either the methine hydrogen or one of the methylene hydrogens of the cyclopropane ring. The origin of the CO group in the expelled CHO radical was also inferred, and a plausible mechanistic interpretation is presented.     

Conversion electron measurement in the β<Superscript>-</Superscript>-decay of <Superscript>151</Superscript>Pr

The β^--decay of ¹⁵¹Pr produced by the thermal neutron-induced fission of ²³⁵U has been studied using an on-line isotope separator. From an internal-conversion electron measurement with a Si(Li) detector, K-conversion coefficients were obtained for 20 γ-transitions. Spins and parities of 6 excited levels in ¹⁵¹Nd were newly determined from the deduced multipolarities: even parities for the 543 and 627 keV levels, odd parities for 250 and 599 keV, (3/2, 5/2)⁺ for 685 keV, and (1/2, 3/2)⁺ for 880 keV. The level structure was compared with the rotation-vibration coupling Nilsson model. Received: 28 June 2002 / Accepted: 31 October 2002 / Published online: 25 February 2003 RID="a" ID="a"e-mail: ykojima@hiroshima-u.ac.jp Communicated by J. ?yst?     

Importance of dual resonance susceptibilities for pi-donor and pi-acceptor substituents regarding a quantitative description of substituent effects. The case of basicity of pyridine N-oxides

Basicities of m- and p-substituted pyridine N-oxides in water were successfully described by means of the generallized LArSR equation which potentially allows dual resonance effect.     

Communication: Relaxed 2/1-Helical Conformation of Type II Chitosan has a Tetrasaccharide Motif

Chitosan, the N-deacetylated chitin, has two crystal forms. One is hydrated and the other is anhydrous. The main chain in both is known to adopt an extended ribbon-like 2/1 helix with about 10.4 Å c-repeat per disaccharide.^1,2 This is the well known canonical structure of (1→4) linked cellulose, chitin and mannan. Among them, chitosan has a remarkable ability to form specific complexes with organic and inorganic acids in addition to transition and post-transition metal ions.^3-7 The complexes studied so far are classified into two groups: the above canonical structure (Type I), and an “8-fold” (8/3 or 8/5) helix⁴ with long 40 Å c-repeat (Type II). The structural details of the latter are yet unknown. The complexes containing monocarboxylic acids, such as formic, acetic and propionic acids, belong to Type II; interestingly, they all undergo a spontaneous removal of the acids accompanying water molecules.⁸ As a result, the Type II complex in the solid state changes to the anhydrous form which corresponds to Type I.² Therefore, the Type II helix must be characterized properly in order to understand the mechanism of crystalline transformation of chitosan from the hydrated to the anhydrous form via chitosan/monocarboxylic acid complexes. Based on recent X-ray diffraction analysis, in this communication, we propose that Type II chitosan has a relaxed 2/1-helical conformation that exploits a tetrasaccharide rather than a monosaccharide as its asymmetric motif.     

Pyridinium ion reactivities: substituent effect on the reverse menschutkin reaction of 1-methylpyridinium cations with iodide anion

Substituent effect on the reverse Menschutkin reaction of 1-methylpyridinium cations with iodide anion can be described in terms of the LArSR equation with ?=3.60 which provides evidence against very late transition state of the nitrogen-to-iodine transmethylation.     

Theoretical study on the transition state of oxaphosphetane formation between ethylidenetriphenylphosphorane and acetaldehyde

The MNDO MO calculations were carried out for the formation of oxaphosphetanes from substituted ylides and aldehydes (Equations 2–4). It was found that the reactions proceed through a nearly planar cyclic four-membered ring transition state (TS) in all cases studied and that phenyl substitution on phosphorus has little effect on the TS geometry. This finding is not in line with the TS models that have been proposed to explain the experimentally observed cis-selectivity.     

In vitro analysis of radioprotective effect of monoterpenes

Monoterpenes are naturally occurring hydrocarbons composed of two units of isoprenes. They exhibit antioxidant activity to scavenge reactive oxygen species, such as hydroxyl radicals. We investigated the potential of monoterpenes such as thymol, linalool, and menthol to act as radioprotectants. The proliferation of EL4 cells, a mouse lymphoma cell line, treated with linalool at a concentration of 500 μM or more was not affected by X-ray irradiation. Plasmid-nicking assay performed using formamidopyrimidine-DNA glycosylase showed that linalool prevented single strand breaks and oxidized purines on pUC19 plasmid DNA. These findings indicate that linalool has the ability to scavenge reactive oxygen species and is a potential radioprotector.     

A simple preparation of 1,3,5-triazine derivatives from 4-pyridones

The reaction of 4-pyridone or 4-quinolone with methyl or benzyl isocyanate in the presence of triethylamine or 1,1,3,3-tetramethylguanidine base gave the corresponding 1,3,5-triazine derivative (e. g., II) in a good yield via stepwise additions.     

Asymmetric epoxidation of hydrocarbon olefins by tert-butyl hydroperoxide with molybdenum(VI) catalysts in the presence of optically active diols. Application to the asymmetric synthesis of (3S)-2,3-oxidosqualene

Catalytic enantioselective epoxidation of prochiral olefins without functional groups was achieved by $\text{tert}$-BuOOH using Mo(O)₂(acac)₂-optically active diols as catalysts.