Stereoselective syn epoxidation of the dihydrodiols of dibenz[a,h] anthracene and 7-methylbenz[a] anthracene

Epoxidation of the bay region dihydrodiols of the title hydrocarbons affords stereoselectively the corresponding syn diol epoxides rather than the anticipated isomeric anti diol epoxides, indicative of a dominant cis-directing effect of the benzylic vs the allylic axial hydroxyl groups.     

Crystal growth, defect structure and magnetism of new Li3N-derived lithium nitridocobaltates

New nitridocobaltates Li(3-x-y)Co(x)N are revealed to contain significant Li(+) vacancies (y approximately 0.45) disordered within lithium-nitrogen planes and to exist as partially delocalised spin systems as a result of increased covalency through infinite -N-(Li,Co)-N- chains.     

Inorganic salts in non-aqueous solvents: Absorption spectra of transition metal salts in dimethylformamide

Absorption spectra of Cr, Mn, Fe, Co, Ni and Cu salts have been determined in dimethylformamide. In most cases the spectra differed considerably from those in aqueous solutions. The absorption maxima and the molar absorptivities of these salts in dimethylformamide are tabulated. The spectra are strongly influenced by the presence of certain anions, the order of decreasing effect being Cl^-, Oac^-, NO₃^- and ClO₄^-.     

The SGB/NP hydration free energy model based on the surface generalized born solvent reaction field and novel nonpolar hydration free energy estimators

The development and parameterization of a solvent potential of mean force designed to reproduce the hydration thermodynamics of small molecules and macromolecules aimed toward applications in conformation prediction and ligand binding free energy prediction is presented. The model, named SGB/NP, is based on a parameterization of the Surface Generalized Born continuum dielectric electrostatic model using explicit solvent free energy perturbation calculations and a newly developed nonpolar hydration free energy estimator motivated by the results of explicit solvent simulations of the thermodynamics of hydration of hydrocarbons. The nonpolar model contains, in addition to the more commonly used solvent accessible surface area term, a component corresponding to the attractive solute-solvent interactions. This term is found to be important to improve the accuracy of the model, particularly for cyclic and hydrogen bonding compounds. The model is parameterized against the experimental hydration free energies of a set of small organic molecules. The model reproduces the experimental hydration free energies of small organic molecules with an accuracy comparable or superior to similar models employing more computationally demanding estimators and/or a more extensive set of parameters.     

Comment on the effect of internal energy on the rate of formation of NO+ by the reaction of O++N2

The effects of translational and vibrational energy on the rate of formation of NO⁺ are compared using the translational and vibrational excitation functions. The effects of simultaneous variation of translational, rotational and vibrational energy are assessed by comparing rates as a function of total reactant center of mass energy.     

Interpolation of cosine operator functions

Summary Using basic techniques from the theory of interpolation spaces equivalence theorems are established for the intermediate spaces between a given Banach space A and the domain D(^r) of the r-th power of the infinitesimal generator of a strongly continuous cosine operator function C. The results are applied to the study of second order evolution equations including regularity, order reduction and approximation by finite difference methods.     

Spatial distribution of upper-room germicidal UV radiation as measured with tubular actinometry as compared with spherical actinometry

Chemical actinometry of UV germicidal irradiation using sections of quartz tubing as compared with quartz spheres as irradiation vessels has been investigated . Vessels were either 3 mm inner diameter quartz tubing, 46 cm in length (tubular actinometry), or 1 cm quartz spheres (spherical actinometry). The vessels containing an iodide/iodate actinometric solution were suspended from the ceiling at 24 positions in a room (6 x 6 m) containing five germicidal lamp fixtures in the corners and in the center of the room. The lamp fixtures were louvered collimating the radiation in the horizontal (x, y) plane. Hence, the tubes, which span the depth of the radiation field, essentially integrate the radiation along the z-axis for a given x, y position. The pseudospatial average fluence rate obtained using tubular actinometry was 18 mW/cm(2) for the volume contained in the upper 46 cm (18 inch) of the room. Spherical actinometry, which measured the fluence rate in the center of the beam, provided an average value of 32 mW/cm(2) over the volume of the beam. A comparison of the fluence rates obtained by these two methods allowed the average depth of the beam to be estimated as 26 cm. It is concluded that tubular actinometry is more advantageous than spherical actinometry for this application.     

Adventures with azides of the fluorocarbon class

Mechanistic and synthetic highlights of out studies during the past twenty years on azides derived from fluorocarbon systems {alkenes ($\text{e.g.}$ CF₃CFCFN₃), aza-alkenes and -cycloalkenes [$\text{e.g.}$$\text{CF}{}_2\text{(CF}{}_2\text{)}{}_2\text{C(CF}{}_3\text{)NC}$(CF₃)N₃], arenes ($\text{e.g.}$ C₆F₅N₃), and heteroarenes($\text{e.g.}$ 4-N₃.C₅F₄N)} will be discussed with emphasis on recent results bearing on the synthesis of novel seven-membered $\text{N}$-heterocycles.     

Intramolecular dimers: a new strategy to fluorescence quenching in dual-labeled oligonucleotide probes

Many genomics assays use profluorescent oligonucleotide probes that are covalently labeled at the 5' end with a fluorophore and at the 3' end with a quencher. It is generally accepted that quenching in such probes without a stem structure occurs through F?rster resonance energy transfer (FRET or FET) and that the fluorophore and quencher should be chosen to maximize their spectral overlap. We have studied two dual-labeled probes with two different fluorophores, the same sequence and quencher, and with no stem structure: 5'Cy3.5-beta-actin-3'BHQ1 and 5'FAM-beta-actin-3'BHQ1. Analysis of their absorption spectra, relative fluorescence quantum yields, and fluorescence lifetimes shows that static quenching occurs in both of these dual-labeled probes and that it is the dominant quenching mechanism in the Cy3.5-BHQ1 probe. Absorption spectra are consistent with the formation of an excitonic dimer, an intramolecular heterodimer between the Cy3.5 fluorophore and the BHQ1 quencher.     

Opioid conformations: The remarkable effect of C-14 substituents on ring c conformations of 6α and 6β epimers of 6-substituted epoxymorphinan opioid ligands

High field ¹H nmr studies have shown that the nature of the C -14 substituents has a remarkable influence on ring C conformation of epoxymorphinan opioids which have a 6α-hydroxyl group. In sharp contrast to the ring C twist-boat conformation observed in those 6α-hydroxy compounds which also have a 14-hydroxyl group (α-naltrexol; α-oxymorphol), ring C exists predominantly as a chair conformer in 6α-hydroxy compounds which have a proton bound to C -14 (dihydromorphine; dihydrocodeine). The 6β-hydroxy compounds (β-naltrexol; β-oxymorphol) have a ring C chair conformation in agreement with earlier studies.