Snapshots of dioxygen activation by copper: the structure of a 1:1 Cu/O(2) adduct and its use in syntheses of asymmetric Bis(mu-oxo) complexes

The X-ray structure of a 1:1 Cu/O(2) adduct revealed side-on (eta(2)) O(2) coordination. Density functional calculations corroborated the structure, indicated a significant contribution of a Cu(III)-(O(2)(2-)) resonance form, and provided insights into the key bonding interactions. Reaction of a 1:1 adduct supported by a slightly different beta-diketiminate ligand with Cu(I) reagents resulted in the formation of novel asymmetric bis(mu-oxo) complexes that were identified by EPR, UV-vis, and Raman spectroscopy, as well as by an X-ray structure in one instance.     

A simplified proof of a theorem about group representations

It is a standard theorem of group representation theory that the dimension of an irreducible representation is a divisor of the order of the group. This paper gives a new, relatively simple proof, intended to make the theorem understandable to readers unfamiliar with algebraic integers.     

Extension of a theorem of P. Wolfe on singular integral equations

The integral operator which sends f (ζ) into $$\int_{|\xi |< 1} {\tfrac{{f(\xi )}}{{|x - \xi |^{p - 1} }}} d\xi = g(x)(|x|< 1)$$ x and ζ ∈ R^P, is shown to map the space of functions f (ζ) on |ζ|<1, square integrable with respect to the weight (1-|ξ|²)^1/2 one to one onto the space of functions g (x) on |x|<1 which possess gradients δg(x) in the sense of distribution theory, with both g(x) and δg(x) being square integrable with respect to the weight (1-|x|²)^1/2. This extends to p≥3 a result of P. Wolfe's in the case p=2.     

Perturbation theory for the radial distribution function for simple polar fluids

The radial distribution function for a fluid whose molecules interact according to the Stockmayer potential was calculated by means of thermodynamic perturbation theory using two different approximations for the perturbation term and was compared with computer simulation results. The approximation based on the Percus-Yevick equation was found to be in much better agreement with the simulations than was the “simplified superposition approximation” to the perturbation term.     

Anharmonicity in rotational and vibrational excitation of H2 by Li+ collisions

Integral cross sections for pure rotational and vibrational-rotational excitation of H₂(X¹Σ⁺_g) by Li⁺(¹S) impact are computed by close-coupling methods at 0.2, 0.6, and 1.2 eV in the c.m. system using vibrational functions that are numerical solutions of the one-dimensional radial Schrödinger equation for harmonic, Morse, and adiabatically corrected Kolos-Wolniewicz (KW) potential functions. Comparison of results employing KW and Morse functions shows excellent agreement for all transitions studied. Findings using harmonic oscillator functions, however, differ noticeably from KW and Morse values for vibrational (0 → 1) and very large rotational (Δj = 10) transitions, but are satisfactory for lower order (0 → 2, 4, 6, 8) rotational transitions.     

Synthesis of reduced complex oxides of molybdenum by fused salt electrolysis

Fused salt electrolysis has been used to prepare a number of reduced oxides of molybdenum with lanthanum, neodymium, and yttrium in single crystal or oriented polycrystalline form. The average valence of molybdenum in the various compounds ranged from 5.67 to 3.50. Previously unreported compounds include La₅Mo₄O₁₆ (triclinica = 5.64 Å,b = 20.7 0Å,c = 5.64 Å, α = 86.55°, β = 90.0°, γ = 93.45°); La₂Mo₂O₇ (orthorhombic,a = 12.19 Å,b = 6.05 Å,c = 3.87 Å); LaMo₂O₅ (hexagonal,a = 8.378 Å,c = 19.26 Å). In addition, single crystal specimens have been prepared of Y₂MoO₅,Ln₅Mo₃O₁₆(Ln =La, Nd) and metal atom cluster compounds of theA₂Mo₃O₈ type (A = Mg, Co, Ni, Zn).     

Identification of a minimal subset of receptor conformations for improved multiple conformation docking and two-step scoring

Docking and scoring are critical issues in virtual drug screening methods. Fast and reliable methods are required for the prediction of binding affinity especially when applied to a large library of compounds. The implementation of receptor flexibility and refinement of scoring functions for this purpose are extremely challenging in terms of computational speed. Here we propose a knowledge-based multiple-conformation docking method that efficiently accommodates receptor flexibility thus permitting reliable virtual screening of large compound libraries. Starting with a small number of active compounds, a preliminary docking operation is conducted on a large ensemble of receptor conformations to select the minimal subset of receptor conformations that provides a strong correlation between the experimental binding affinity (e.g., Ki, IC50) and the docking score. Only this subset is used for subsequent multiple-conformation docking of the entire data set of library (test) compounds. In conjunction with the multiple-conformation docking procedure, a two-step scoring scheme is employed by which the optimal scoring geometries obtained from the multiple-conformation docking are re-scored by a molecular mechanics energy function including desolvation terms. To demonstrate the feasibility of this approach, we applied this integrated approach to the estrogen receptor alpha (ERalpha) system for which published binding affinity data were available for a series of structurally diverse chemicals. The statistical correlation between docking scores and experimental values was significantly improved from those of single-conformation dockings. This approach led to substantial enrichment of the virtual screening conducted on mixtures of active and inactive ERalpha compounds.     

Studies in the heterocyclic series. XI. Reactions of 2-Amino-3-hydroxypyridine with 2-Chloro-3-nitropyridine

The reactions of 2-amino-3-hydroxypyridine and 2-chloro-3-nitropyridine in various solvents and in the presence of certain catalysts were studied. A dilute acid-catalysed procedure led to a 45% yield of 3-hydroxy-3-nitro-2,2-dipyridylamine which was also obtained by refluxing in alcoholic potassium hydroxide for several hours. The diarylamine was converted to 1,9-diazaphenoxazine by base-catalysed intramolecular condensation in refluxing DMSO. The same diazaphenoxazine was obtained directly by prolonged base-catalysed reaction of the starting pyridine compounds in DMSO. From a study of the infrared spectrum of the diarylamine precursor, it was found that strong NHO hydrogen bonding is responsible for the failure of the cyclization step in either aqueous or alcoholic base. This problem was overcome by the use of DMSO as the reaction solvent. Structural assignments were made by a study of their ultraviolet, infrared, nmr and mass spectra and the mechanistic pathways were also discussed.     

A chemical inhibitor reveals the role of Raf kinase inhibitor protein in cell migration

Raf kinase inhibitor protein (RKIP) is a modulator of cell signaling that functions as an endogenous inhibitor of multiple kinases. We demonstrate here a positive role for RKIP in the regulation of cell locomotion. We discovered that RKIP is the relevant cellular target of locostatin, a cell migration inhibitor. Locostatin abrogates RKIP's ability to bind and inhibit Raf-1 kinase, and it acts by disrupting a protein-protein interaction, an uncommon mode of action for a small molecule. Small interfering RNA-mediated silencing of RKIP expression also reduces cell migration rate. Overexpression of RKIP converts epithelial cells to a highly migratory fibroblast-like phenotype, with dramatic reduction in the sensitivity of cells to locostatin. RKIP is therefore the compound's valid target and a key regulator of cell motility.     

Post-source decay in the analysis of polystyrene by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Various secondary series are observed in matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectra of polystyrene. The number and positions of the series depend on the choice of matrix and added cation. For a given treatment, series observed in linear mode are not necessarily observed in reflectron mode, and vice versa. Post-source decay analysis was used to determine that the secondary series arise at least in part from formation and decay of adducts of polystyrene with matrix species. There is some treatment-to-treatment variation, but adduct formation and decay were observed for all tested treatments. The multiplicity of secondary series makes it unclear whether post-source decay occurs for the main series (polystyrene + cation)⁺ ions under the conditions normally used for polystyrene analysis. Such ions do undergo post-source decay at laser fluences greater than normally used. Although only polystyrene was investigated in this work, other polymers may also produce adduct and decay series in MALDI analysis. Their presence can mask the presence of minor components in a sample, but at least as observed here, do not have a strong influence on molecular mass determinations.