Kekulé structure counts: General formulations for primitive coronoid hydrocarbons

Summary The Kekulé structure counts (K) for primitive coronoids are treated. TheK formula which involves the trace of a matrix product is recalled and supplemented with new findings. In this way a kind of symmetry in the mathematical formulations is restored. Another general formulation for theK number is provided in terms of polynomials which, for a somewhat mysterious reason, are identified as the matching polynomials of cycles.

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Zählung von Kekulé-Strukturen

Zusammenfassung Es werden Kekulé-Strukturzählungen (K) für einfache Coronoide behandelt. Die Formel fürK wird durch neugefundene Eigenschaften ergänzt. So wird eine Art von Symmetrie in den mathematischen Formulierungen erreicht. Eine andere generelle Formulierung derK-Zahlen wird in Form von Polynomen bereitgestellt, welche aus uneinsichtigen Gründen als die passenden Polynome von Cyclen identifiziert wurden.

     

Renierone,an antimicrobial metabolite from a marine sponge

The major antibacterial metabolite in the sponge $\text{Reniera}$ sp. was shown to be an isoquinoline quinone, renierone ($\text{1}$). The structure of renierone ($\text{1}$) was defined by X-ray crystallography.     

USE OF TRIS (2,2'-BIPYRIDINE) RUTHENIUM(II) DICATION IN A NOVEL METHOD FOR THE DETERMINATION OF SINGLET OXYGEN REACTION RATES: APPLICATION TO STUDIES OF GELATIN

Abstract— A novel method for the determination of singlet oxygen reaction rate constants is described and applied to studies of cyclohexadiene in methanol and gelatins in H₂O and D₂O. The technique uses tris (2,2'-bipyridine) ruthenium(II) dication (Ru(bipy)₃₂₊) as both singlet oxygen sensitizer and in situ oxygen concentration monitor during irradiation of sealed samples. Because of the high efficiency with which the luminescence of Ru(bipy)₃2+* can be detected, and the fact that emission lifetimes are used, the method offers some advantages over those previously described. The advantages and disadvantages of the method are discussed. A rate constant of 2.1 (±0.3) x 10⁶ mol^-1 dm³ s^-1 has been determined for the reaction of ¹O₂ with cyclohexadiene in methanol. For two different photographic gelatins the sums of reaction and quenching rate constants are 2.0 (±0.4) x 10⁶ and 3.1 (±2.0) x 10⁵ mol^-1 dm³ s^-1; for swine skin gelatin this value is 3.9 (±2.4) × 10⁵ mol^-1 dm³ s^-1. Chemical reaction, rather than physical quenching, is the dominant reaction route for gelatins and ¹O₂.     

Determination of mercury by atomic absorption spectrometry using a platinum-lined graphite furnace for in situ preconcentration

Mercury in water samples was reduced by tin(II) chloride and the generated vapour swept in a flow of argon through a platinum-lined graphite tube to permit in situ preconcentration. Subsequent atomization of the mercury was then carried out under essentially gas-stop conditions to maximize sensitivy. The system was optimized with respect to argon gas flow and time of mercury generation/deposition using response surface methodology. Synthetic sea-water samples were analysed to test the applicability of the method. For 50-ml sample volumes, detection limits below 2 ng 1^?1 mercury could be obtained, based on twice the standard deviation of the blank. The most favourable aspect of the procedure is its simplicity, since the mercury generator can be easily constructed and connected to commonly available graphite furnace atomic absorption spectrometers.     

Nuclear magnetic relaxation dispersion measurement of water mobility at a silica surface

Nuclear magnetic relaxation rates are measured as a function of magnetic field strength corresponding to proton Larmor frequencies ranging from 0.01 to 42 MHz for silica gel samples with a nitroxide free radical covalently attached at the surface. The field dependence of the relaxation rate is interpreted using a translational model for the relaxation equation to yield a translational diffusion coefficient for the water, in the immediate vicinity of the radical attached to the surface, of 2.1 × 10^?6 cm² s^?1 at 278 K for Si-4000 silica.     

Fluorescence quantum yields and their relation to lifetimes of rhodamine 6G and fluorescein in nine solvents: improved absolute standards for quantum yields

Absolute fluorescence quantum yields are reported for the rhodamine 6G cation and the fluorescein dianion dyes in nine solvents. This information is combined with previously reported fluorescence lifetimes to deduce radiative and nonradiative decay rates. Along the alcohol series from methanol to octanol, rhodamine 6G displays an increasing radiative rate, in parallel with the square of the refractive index increase, and a slightly decreasing nonradiative rate. Fluorescein is different: the apparent radiative rate actually decreases, suggesting that the emissive species is perturbed in some fashion. For both dyes, fluorescence yields are enhanced in D2O, rising to 0.98, in parallel with a corresponding increase in lifetimes. Protonated solvents invariably give shorter lifetimes and lower quantum yields, contrary to some previous speculation. From this work and an analysis of existing literature values, more precise values have been obtained for two previously proposed absolute quantum yield standards. The yield of fluorescein in 0.1 N NaOH(aq) is 0.925+/-0.015, and for rhodamine 6G in ethanol, it is 0.950+/-0.015. In both cases, the solutions are assumed to be in the limit of low concentration, excited close to their long-wave absorption band and at room temperature but may be either air-saturated or free of oxygen.     

Molecular structure and spectral properties of bromo(2-acetylpyridine4 N-methylthiosemicarbazonato)copper(II)

Summary The anion (loss of³ N hydrogen) of 2-acetylpyridine⁴ N-methylthiosemicarbazone coordinates in a planar conformation to copper(II) through the pyridyl nitrogen, azomethine nitrogen and thiolato sulphur atoms. The fourth coordination site is occupied by a bromo ligand and the complex is mononuclear and essentially planar. Bond distances and angles, as well as solid state and solution spectral properties, are compared to other recently reported copper(II) thiosemicarbazone complexes.     

Spectral and biological studies of copper(II) complexes of 2-acetyl-pyridine thiosemicarbazones with bulky 4N-substituents

Summary Copper(II) complexes of a large number of 2-acetylpyridine ⁴N-alkyl thiosemicarbazones were prepared and characterized. I.r., electronic and e.s.r. spectra of the complexes, as well as ¹H and ¹³C n.m.r. spectra of the thiosemicarbazones, were obtained. Both the thiosemicarbazones and their complexes show either modest or no growth inhibitory activity against Aspergillus niger, but many have considerable activity against Paecilomyces variotii. There is a relationship between the antifungal activity and size of the ⁴N-substituent for both the thiosemicarbazones and their copper(II) complexes.     

Fast automatic registration of images using the phase of a complex wavelet transform: application to proteome gels

Image registration describes the process of manipulating a distorted version of an image such that its pixels overlay the equivalent pixels in a clean, master or reference image. The need for it has assumed particular prominence in the analysis of images of electrophoretic gels used in the analysis of protein expression levels in living cells, but also has fundamental applications in most other areas of image analysis. Much of the positional information of a data feature is carried in the phase of a complex transform, so a complex transform allows explicit specification of the phase, and hence of the position of features in the image. Registration of a test gel to a reference gel is achieved by using a multiresolution movement map derived from the phase of a complex wavelet transform (the Q-shift wavelet transform) to dictate the warping directly via movement of the nodes of a Delaunay-triangulated mesh of points. This warping map is then applied to the original untransformed image such that the absolute magnitude of the spots remains unchanged. The technique is general to any type of image. Results are presented for a simple computer simulated gel, a simple real gel registration between similar "clean" gels with local warping vectors distributed about one main direction, a hard problem between a reference gel and a "dirty" test gel with multi-directional warping vectors and many artifacts, and some typical gels of present interest in post-genomic biology. The method compares favourably with others, since it is computationally rapid, effective and entirely automatic.     

A rigid cavity containing tetra-cobalt(III) [2 x 2] grid complex

The synthesis and structure of a rigid, cavity containing tetra-cobalt(III) [2 x 2] grid complex using an unusual bis(bipyridine)dimethoxynaphthyridine ligand is described.