The millimeter wavelength spectrum of diatomic sulfur

The gas phase spectrum of diatomic sulfur has been detected in the millimeter wave-length region. Six lines have been measured. The rotational and fine structure parameters obtained are B₀ = 8831.8676 ± 0.006 MHz, D₀ = 5.9 ± 0.7 kHz, λ₀ = 353040 ± 27 MHz, and γ₀ = ? 200.9 ± 0.7 MHz. In addition, reanalysis of EPR data has yielded g_z + 1.18g_n = 2.0021 + 0.0014 and g_z - g_⊥ = ?0.0089 ± 0.0017. On the basis of the frequencies obtained in this work, it was also possible to exclude the assignment of several interstellar emissions to the sulfur dimer.     

Photorefractive performance of a CdSe/ZnS core/shell nanoparticle-sensitized polymer

We report the photorefractive performance of a polymer composite sensitized by CdSe/ZnS core/shell nanoparticles, and also comprising poly(N-vinylcarbazole) and an electro-optic chromophore. The nanoparticles are characterized by absorption and photoluminescence spectroscopy, elemental analysis, transmission electron microscopy, and powder x-ray diffraction. The electro-optic response of the composite is measured independently of the photorefractive effect by transmission ellipsometry. An asymmetric two-beam coupling gain of 30.6+/-0.4 cm(-1) is obtained, confirming photorefractivity. Degenerate four-wave mixing is used to assess photorefractive performance and, at a poling field of 70 V microm(-1), yields a diffraction efficiency of 4.21%+/-0.03%, a holographic contrast of 3.05 x 10(-4)+/-1 x 10(-6), a space-charge rise time of 25+/-2 s, and a sensitivity of 4.7 x 10(-5)+/-4 x 10(-6) cm3 J(-1). These results constitute a significant improvement on the performance of previous nanoparticle-sensitized photorefractive polymer composites.     

Polyferredoxin-based electrode materials

Electrochemical oxidation of the hydrosulfide cluster [Fe4S4(SH)4]2- on gold, platinum or vitreous carbon in a methyl cyanide electrolyte leads to the growth of a conducting film. Spectroscopic and other evidence suggests that the film has cubane centres, predominately in the [4Fe4S]3+ oxidation state, which are linked by disulfide ligands to give an anionic array of [Fe4S4(S approximately)4]n- units. X-ray data suggests some long-range order in the electrode material. The polyferredoxin binds redox active cations consistent with an anionic array.     

Synergic Binding of Carbon Monoxide and Cyanide to the FeMo Cofactor of Nitrogenase: Relic Chemistry of an Ancient Enzyme?

The first electrochemical and infra-red data on the binding of cyanide to the isolated iron-molybdenum cofactor of nitrogenase, FeMoco, is described. It is shown that cyanide stabilises a hitherto unrecognised, low-spin, EPR-active (S= 1/2), superoxidised form of FeMoco, and we provide the first evidence that carbon monoxide and cyanide bind synergically to the oxidised and semireduced states of the isolated cofactor, states which are unreactive to carbon monoxide alone.     

Design of a compound screening collection for use in high throughput screening

In this paper we introduce a quantitative model that relates chemical structural similarity to biological activity, and in particular to the activity of lead series of compounds in high-throughput assays. From this model we derive the optimal screening collection make up for a given fixed size of screening collection, and identify the conditions under which a diverse collection of compounds or a collection focusing on particular regions of chemical space are appropriate strategies. We derive from the model a diversity function that may be used to assess compounds for acquisition or libraries for combinatorial synthesis by their ability to complement an existing screening collection. The diversity function is linked directly through the model to the goal of more frequent discovery of lead series from high-throughput screening. We show how the model may also be used to derive relationships between collection size and probabilities of lead discovery in high-throughput screening, and to guide the judicious application of structural filters.