Pinnatoxin H: a new pinnatoxin analogue from a South China Sea Vulcanodinium rugosum isolate

Pinnatoxin H was isolated from a culture of the dinoflagellate Vulcanodinium rugosum isolated from the South China Sea. The structure of pinnatoxin H was elucidated by LC–MS/MS and NMR spectroscopy. It was found to have the same macrocyclic structure and substituents as pinnatoxins D, E and F, but the side chain on the cyclohexenyl ring was an ethenyl group, as found in pinnatoxin G and portimine. The observation that this strain of V. rugosum produced only pinnatoxin H and portimine is consistent with previous findings that the profile of pinnatoxins can vary significantly among strains. The acute toxicity of pinnatoxin H to mice was 67 μg/kg (intraperitoneal) and 163 μg/kg (gavage).     

Voltammetric sizing of inert particles.

The average size of inert particles is determined using a simple electrochemical procedure. Alumina particles are deposited on an edge-plane graphite electrode, and a cyclic voltammogram is recorded. The scan rate employed varies between 0.2 and 2 V s(-1). At these scan rates the diffusion layer thickness is greater than the size of the alumina particles, minimizing the influence of the particles' height on the observed voltammetry. The average size of the particles is determined via comparison of the experimental voltammograms with simulations.     

Polarized Raman scattering in single crystals of Nd0.7Sr0.3MnO3

We report polarized Raman scattering in single crystals of Nd_0.7Sr_0.3MnO₃. The temperature dependence of the MnO₆ octahedral bending and stretching modes observed in the XX spectra points to the existence of local lattice distortions, possibly polarons. The XY spectra have been analyzed using a collision-dominated model, which allows the extraction of the carrier scattering rate.     

Substitution in labile octahedral metal complexes – a retrospective view

Transition Metal Chemistry -     

Some reactions of di-π-cyclopentadienyllead(II)

(C₅H₅)₂Pb reacts with HX to give (C₅H₅)PbX or PbX₂, X = Cl,Br,CH₃CO₂, with BF₃·Et₂O to give (C₅H₅)₂PbBF₃ and with TCNE to give (C₅H₅)₂Pb·O·5TCNE or (C₅H₅)₂Pb·TCNE.     

A graph theoretical approach to structure-property and structure-activity correlations

The structure similarity and dissimilarity implied in many structure-property and structure-activity relationships has been examined from the graph theoretical point of view. The approach outlined is fundamentally different from generally used schemes in that, rather than seeking a new parametrization which will quantitatively fit observed data and trends,similarities among the skeletal forms and connectivities of the compounds of interest are studied quantitatively. The basis of the method is the assumption that skeletal forms of apparent similarity will yield similar enumerations for a number of graph theoretical invariants. In particular, allpaths within molecular skeletons are enumerated and sequences of path numbers (i.e., the number of paths of different length) are compared. The degree of similarity between molecules is proportional to the distance between points in the corresponding structure space obtained by interpreting the entries in molecular path sequences as coordinates inn-dimensional space. As anexample of the use of the concept of structural similarity, structure-activity data relating cerebral dopamine agonist properties for a series of N-substituted 2-aminotetralins are considered. The analysis suggests that the method may find wide application in the field of structure-activity correlations and structure-property studies. The data could be mass spectra, the fingerprint regions of infrared spectra, optical rotation and circular dichroism measurements, or any of many not fullyunderstood complex experimental findings suspected of having an inherent structural basis.On leave from Ames Laboratory - DOE, Iowa State University, Ames, Iowa 50011     

Measurements of crack growth in a solid at elevated temperature by holographic interferometry

Real-time holographic interferometry was used to follow the crack-opening displacement (COD) of a compact tension specimen of zirconium 2.5-percent niobium subjected to a constant tensile load at 120°C for a period of 860 h. This was made possible by a dimensionally stable invar plate placed beside the specimen as the reference for the alignment of holograms. A finite-element elasto-plastic stress-analysis code and measurements on a duplicate specimen with a clip gage were used to correlate the measured COD and the corresponding crack growth.     

Determination of the appearance potentials of [C3H7]+ ions by a computerized electron distribution difference procedure

A simple computerized electron distribution difference method has been developed using a conventional mass spectrometer and an on-line computer. Using the system, ionization potentials for various propyl halides were measured and found to agree well with photoionization data. The appearance potentials for [C₃H₇]⁺ agreed well with literature values, except for 1-propyl bromide and 1- propyliodide which gave values approximately 0.7 eV lower than previous reports. The results are interpreted to indicate threshold formation of the sec-propyl ion from all propul halides.