Surface properties of Hafnium diboride(0 0 0 1) as determined by X-ray photoelectron spectroscopy and scanning tunneling microscopy

The surface structure and properties of the HfB₂(0 0 0 1) (Hafnium diboride, HfB₂) surface have been investigated with X-ray photoelectron spectroscopy, low energy electron diffraction (LEED), and scanning tunneling microscopy (STM). Annealing temperatures above 1900°C produce a sharp (1×1) LEED pattern, which corresponds to STM images showing flat (0 0 0 1) terraces with a very low contamination level separated by steps 3.4 Å in height, corresponding to the separation of adjacent Hf planes in the HfB₂ bulk structure. For lower annealing temperatures, extra p(2×2) spots were observed with LEED, which correspond to intermediate terraces of a p(2×1) missing row structure as observed with STM.     

An SCF study of P4O6 and P4O10

The electronic structures of the oxides P₄O₆ and P₄O₁₀ are calculated by the self-consistent molecular orbital method including all valence electrons and the 3d orbitals on phosphorus. It is found that the former molecule appears to be virtually non-polar whilst in the latter, the P-O (terminal) bonds are highly polar. The bond order matrix shows that the internal P-P bonding in the P₄ unit is not marked.     

Enhanced ligand affinity for receptors in which components of the binding site are independently mobile

Using calmodulin antagonism as a model, it is demonstrated that, under circumstances in which binding sites are motionally independent, it is possible to create bifunctional ligands that bind with significant affinity enhancement over their monofunctional counterparts. Suitable head groups were identified by using a semiquantitative screen of monofunctional tryptophan analogs. Two bifunctional ligands, which contained two copies of the highest-affinity head group tethered by rigid linkers, were synthesized. The bifunctional ligands bound to calmodulin with a stoichiometry of 1:1 and with an affinity enhancement over their monofunctional counterparts; the latter bound with a stoichiometry of 2:1 ligand:protein. A lower limit to the effective concentrations of the domains of calmodulin relative to each other (0.2-2 mM) was determined. A comparable effective concentration was achieved for bifunctional ligands based on higher-affinity naphthalene sulphonamide derivatives.     

The use of poorly resolved gas chromatographic curves for the analysis of binary mixtures of petroleum fractions

Blends of petroleum products are usually made from fractions which contain preponderantly the same compounds. Only the relative abundances vary. A calculation of the contribution of each blended fraction is theoretically possible with the aid of the gas Chromatographic elution curve even though resolution is uniformly poor in such complex systems. An elementary mathematical analysis is made to show what conditions must maintain. Experimental evidence is presented to indicate that the necessary conditions can be realized for petroleum blends. Binary mixtures of complex fractions may be analyzed with an accuracy of better than 10% and only normal attention to detail need be observed.     

Calculation of the π-electronic structures of vinyl boron compounds by the free-electron Method

The free-electron model has been used to investigate the -electronic structures and spectra of two vinylboranes. It is concluded that none of the simple F. E. methods is satisfactory alone and agreement between calculated and observed spectral quantities is only obtained when electron interaction is explicitly included in the calculations.

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Zusammenfassung Das Elektronengasmodell wurde zur Untersuchung der -Elektronenstrukturen und Spektren von zwei Vinylboranen angewendet. Es wurde gefunden, daß keine der einfachen Elektronengasmethoden allein befriedigend ist und daß ein Übereinstimmen zwischen berechneten und beobachteten Spektralwerten nur dann erreicht werden kann, wenn die Elektronenwechselwirkung explizit berücksichtigt wird.

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Résumé Le modèle de l'électron libre a été utilisé pour étudier les niveaux d'énergie électronique et les bandes d'absorption de deux boranes vinyliques. C'est trouvé que les méthodes simples ne sont pas satisfaisantes et l'accord entre les spectres calculés et observés est obtenu seulement quand l'interaction électronique est comprise dans les calculs.

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The authors thank Dr. B. J. Duke (University Computing Laboratory) for invaluable help and the D. S. I. R. for a maintenance grant (to D. R. A.). We are also indebted to Prof. D. M. Ritter for supplying copies of spectra.     

Comparative molecular field analysis (CoMFA) model using a large diverse set of natural, synthetic and environmental chemicals for binding to the androgen receptor

A large number of natural, synthetic and environmental chemicals are capable of disrupting the endocrine systems of experimental animals, wildlife and humans. These so-called endocrine disrupting chemicals (EDCs), some mimic the functions of the endogenous androgens, have become a concern to the public health. Androgens play an important role in many physiological processes, including the development and maintenance of male sexual characteristics. A common mechanism for androgen to produce both normal and adverse effects is binding to the androgen receptor (AR). In this study, we used Comparative Molecular Field Analysis (CoMFA), a three-dimensional quantitative structure-activity relationship (3D-QSAR) technique, to examine AR-ligand binding affinities. A CoMFA model with r2 = 0.902 and q2 = 0.571 was developed using a large training data set containing 146 structurally diverse natural, synthetic, and environmental chemicals with a 10(6)-fold range of relative binding affinity (RBA). By comparing the binding characteristics derived from the CoMFA contour map with these observed in a human AR crystal structure, we found that the steric and electrostatic properties encoded in this training data set are necessary and sufficient to describe the RBA of AR ligands. Finally, the CoMFA model was challenged with an external test data set; the predicted results were close to the actual values with average difference of 0.637 logRBA. This study demonstrates the utility of this CoMFA model for real-world use in predicting the AR binding affinities of structurally diverse chemicals over a wide RBA range.     

The automation of a commercial Fourier transform mass spectrometer to provide a quick and robust method for determining exact mass for the synthetic chemist

Automation of a commercially available Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer for the routine analysis of the synthetic products from high-speed chemistry is described. The automation includes software written by the instrument manufacturer and in-house developed software; allowing electronic submission of samples from the chemist and e-mailing of results back to the chemist. The use of samples of relatively high concentration (ca 1 mg x mL(-1)) is possible due to the protocol that has been developed, which includes dilution by the autosampler during sample injection. Though high concentrations are used for speed and convenience the amount of sample consumed is still small ca 15 microg per injection. The results from this method have been shown to be both accurate (average error +/- 0.91 ppm) and precise (-0.70 ppm to 2.26 ppm). The system is capable of analysing up to 800 samples per 24 hours. As high speed chemistry becomes more highly utilised within discovery the number of samples requiring accurate mass analysis will rise, and the method we have described will prevent high resolution mass spectrometry becoming the bottleneck in new chemical entity production. The accuracy and precision demonstrated by this method allows high confidence levels in assigned molecular formulae for expected compounds and reduces the number of possible formulae to consider when working with a compound that is not the desired product of a given reaction.