On the efficiency of water soluble antioxidants

The wide use of high intensity ultrasound (HIU) in modern medicine raises the question of bio-safety. It has been shown that the effect of HIU in biological media may have similarity to the effects of ionizing radiation. Exposure of biological media to HIU field may lead to cavitation phenomenon followed by formation of free radicals such as hydroxyl radical (OH) and the super-oxide ion (O₂-). These are highly reactive species that may cause harmful effects and induce oxidative stress. In the present study we employed electron spin resonance (ESR) spectroscopy together with spin traps to quantify the dynamics of hydroxyl radical formation during exposure to HIU field in the presence of different amounts of six antioxidants. Thus, the efficiency of water-soluble antioxidants, namely Allicin, Melatonin, Deoxyribose, Trolox, Nuphlutine and Hermidin, to suppress accumulation of OH radicals was examined. The results show that among the six, Trolox and Allicin reduce hydroxyl concentration with the highest efficiency.     

Euler flow solutions for transonic shock wave–boundary layer interaction

Steady 2D Euler flow computations have been performed for a wind tunnel section, designed for research on transonic shock wave–boundary layer interaction. For the discretization of the steady Euler equations, an upwind finite volume technique has been applied. The solution method used is collective, symmetric point Gauss–Seidel relaxation, accelerated by non-linear multigrid. Initial finest grid solutions have been obtained by nested iteration. Automatic grid adaptation has been applied for obtaining sharp shocks. An indication is given of the mathematical quality of four different boundary conditions for the outlet flow. Two transonic flow solutions with shock are presented: a choked and a non-choked flow. Both flow solutions show good shock capturing. A comparison is made with experimental results.     

On the mechanism of aromatic hydroxylation by O(3P) atoms

It is shown that O(³P) oxidation of aromatic compounds in the liquid phase leading to phenols may involve the intermediacy of triplet diradicals.     

Analysis of preconditioning and multigrid for Euler flows with low-subsonic regions

For subsonic flows and upwind-discretized, linearized 1-D Euler equations, the smoothing behavior of multigrid-accelerated point Gauss-Seidel relaxation is analyzed. Error decay by convection across domain boundaries is also discussed. A fix to poor convergence rates at low Mach numbers is sought in replacing the point relaxation applied to unconditioned Euler equations, by locally implicit time-stepping applied to preconditioned Euler equations. The locally implicit iteration step is optimized for good damping of high-frequency errors. Numerical inaccuracy at low Mach numbers is also addressed.The work reported was performed in the framework of the BRITE-EURAM Aeronautics R&D Programme of the European Communities (Contract No. AER2-CT92-0040). The work was started during the second author's visit to CWI in 1993.     

Violatinctamine, a new heterocyclic compound from the marine tunicate Cystodytes cf. violatinctus

A new alkaloid designated violatinctamine and four known metabolites were isolated from the tunicate Cystodytes cf. violatinctus collected in Kenya. Violatinctamine has a unique heterocyclic skeleton, which combines a benzothiazole unit and a dihydroisoquinoline unit. The structure of violatinctamine was elucidated by interpretation of MS results as well as 1D and 2D NMR spectra of the alkaloid and of its O,O′-dimethyl derivative. Analysis of the spectral information also implies that violatinctamine exists as a mixture of two tautomers—the imino-phenol and the amino quinone-methide.     

Kitungolides A, B, and C, new diterpenes from a soft coral of a new genus

Three novel compounds, designated kitungolides A (1), B (2), and C (3), were isolated from a soft coral of a new genus collected at Kitungamwe, Kenya. The three new compounds are of a unique heterotricyclic skeleton. The structures and relative stereochemistry of the compounds were elucidated by interpretation of MS, COSY, HMQC, HMBC, and NOESY experiments. [structure: see text]     

A valence bond analysis of electronic degeneracies in Jahn-Teller systems: low-lying states of the cyclopentadienyl radical and cation

The lowest doublet electronic state of the cyclopentadienyl radical (CPDR) and the lowest singlet state of the cyclopentadienyl cation (CPDC) are distorted from the highly symmetric D(5h) structure due to the Jahn-Teller effect. A valence bond analysis based on the phase-change rule of Longuet-Higgins reveals that in both cases the distortion is due to the first-order Jahn-Teller effect. It is shown that, while for the radical an isolated Jahn-Teller degeneracy is expected, in the case of the cation the main Jahn-Teller degeneracy is accompanied by five satellite degeneracies. The method offers a chemically oriented way for identifying the distortive coordinates.     

Reactions in dry media: reactions of cholesterol and cholestanes on silica bound ferric chloride : Cholestane—diacholestene rearrangement

Reaction of cholesterol with silica bound FeCl₃ resulted in a mixture of 3β-cholesteryl chloride and dicholesteryl ether.5-Cholestene and hydroxy- and halogeno-substituted cholestane derivatives gave on heating at 100° with this reagent a 1:1 mixture of 20-epimeric diacholestenes. The 20(R)-isomer gave with meta-chloroperbenzoic acid 20(R)-α-epoxide, while the 20(S)-gave a mixture of 20(S)-α- and 20(S)-β-epoxides.5α,6β-Dihydrocholestane reacted with the FeCl₃/SiO₂ under milder conditions (50°) to give 6β-hydroxy-20(R)-diacholestene, which was converted to the 20(R)-diacholestene.     

Callynormine A, a new marine cyclic peptide of a novel class

[structure: see text] A novel cyclic peptide, callynormine A, was isolated from the Kenyan marine sponge Callyspongia abnormis and its structure elucidated by interpretation of its NMR data and X-ray diffraction analysis. Callynormine A represents a new class of heterodetic cyclic peptides (designated endiamino peptides) possessing an alpha-amido-beta-aminoacrylamide cyclization functionality.