The enthalpy of formation of tungsten azide pentafluoride

The enthalpy of hydrolysis of solid tungsten azide pentafluoride in alkaline aqueous solution (1.O mol dm^?3 KOH; 298.2K) is ?578 kJ mol^?1. Hence its enthalpy of formation is ?1170 kJ mol^?1.     

Solvatochromism and piezochromism of metal→ligand chargetransfer bands of ternary diimine complexes of tungsten(0), molybdenum(0), and iron(II)

Summary The solvatochromic behaviour of W(CO)₄(LL), LL=a diazabutadiene or a pyridine Schiff base, and of Mo(CO)₄ (butane-2,3-dionedihydrazone) is described. Pressure effects on the charge-transfer spectra of these compounds, the [Mo(CO)₄(fz)]^2– anion {fz=ferrozine; 3-(2-pyridyl)-5, 6-bis-(4-sulphonatophenyl)-1,2,4-triazine}, and Fe(bipy)₂(CN)₂ are reported. Solvent sensitivities are discussed in terms of the nature of the ligands and of the central metal atom, and the idea of a correlation between these solvent sensitivities and piezochromic behaviour developed for these and related ternary irondiimine-cyanide species.Author to whom all correspondence should be directed.     

New, optically active phosphine oxazoline (JM-Phos) ligands: syntheses and applications in allylation reactions.

Three different syntheses of the phosphine oxazoline systems 1 are presented. Two of these approaches are divergent routes designed to involve an advanced intermediate that can be transformed into several different end-products. The third is a shorter route specifically designed to facilitate preparations of these systems on a larger scale using minimal functional group protection. Overall, eight different phosphine oxazolines were prepared. These were screened in several palladium-mediated allylation reactions. They proved to be most useful for asymmetric alkylation of 3-acetoxy-1,3-diphenylpropene and less suitable/effective for the more challenging substrates (a pentenyl derivative and a cyclohexenyl system). X-ray crystallographic analysis of the complex [(eta 3-PhCHCHCHPh)Pd(1a)][PF6] led to the conclusion that the origins of asymmetric induction in these systems might be indirectly attributed to interaction of the oxazoline-phenyl substituent with the palladium and with an allyl-phenyl substituent. Finally, data is presented for allylation of a silylenolate of an N-acyl oxazolidinone; excellent enantioselectivities and yields were obtained.     

Soft X-ray spectromicroscopy studies of pitting corrosion of reinforcing steel bar

Pitting corrosion of reinforcing steel bar (rebar) imbedded in concrete by chloride ions can cause concrete degradation. It is thus necessary to develop methods to mitigate concrete corrosion which could include using a protective polymer rebar coating. Corrosion studies of polyvinyl butyral-carbon black polymer-coated rebar using soft X-ray fluorescence (XRF) microprobe and micro-X-ray absorption near edge spectroscopy (μ-XANES) are reported in this study. After removal of the polyvinyl butyral-carbon black polymer coating, Fe Lα₁, Mn Lα₁, and O Kα₁ XRF maps were collected as well as Fe and Mn L₃-edge μ-XANES spectra from different regions across the whole rebar surface by collection of total electron yield (TEY) and partial XRF yield (PFY) spectra. The distribution of metallic Fe and Fe corrosion products was determined by analysis of the Fe XRF map. The μ-XANES spectra indicated a higher fraction of Fe (III) phases on the corroded rebar surface, while Fe (II/III) phases were the major corrosion products beneath the surface region. In addition, Mn (II) and Mn (III) were determined as the valence states of the manganese corrosion products.     

Metathesis for catalyst design: metacatalysis

Prior studies have shown an effective way to produce diverse ligand sets for catalyst discovery is by using mixtures of monodentate forms to generate catalysts in situ. Research described here was performed to illustrate that alkene-functionalized monodentate ligands could be used in this way and in another that increases the diversity of the ligand library in an interesting way. Specifically, we hypothesized that as well as being used as monomers, these alkenes could be cross metathesized in situ immediately before the catalysis step. This combination of metathesis to form ligands in situ, then catalysis is referred to here as metacatalysis. In the event, a library of quinidine and quinine alkaloid-derived phosphites were tested as mixtures of monomers and dimers formed via metathesis in situ. The data obtained illustrated that metacatalysis can be used to identify ligands that positively and negatively modulate enantioselectivities in iridium-mediated hydrogenations of α,β-unsaturated carboxylic acid derivatives, relative to the mixtures of the monomeric forms used.     

On the isomorphism problem for finite dimensional diagram algebras

somorphism problems for finite dimensional algebras can be computationally hard. When the algebras are monomial, it is shown, refining work of Shirayanagi, that there is a simple definitive combinatorial method. However, examples show that no such criterion is possible if the class of algebras is expanded to that of diagram algebras (in the sense of Fuller). The presentation of a diagram algebra is field independent but the existence of an isomorphism between two such is not. (Subject classes: 16G30, 16P10, 20M25).     

Synthesis of spirolactams and spiropiperidines as CCR4 receptor antagonists

The synthesis of racemic and non-racemic spirocyclic lactams that display high binding affinity toward CCR4 is described. Two distinct series of spirocycles were prepared from the common intermediate 9.     

Complete 1H and 13C assignments of fluorinated analogs of dehydroepiandrosterone

The complete assignments of all 1H and 13C chemical shifts were made for the fluorinated dehydroepiandrosterone (DHEA) analog fluasterone, 2, and two potential in vivo metabolites 3 and 4. The assignments were made using a combination of one- and two-dimensional NMR techniques (1H, 13C, gDQCOSY, gHSQC, gHMBC). Once the proton chemical shifts were assigned, the stereochemistry of the two hydroxylated analogs was determined using 2D ROESY experiments.     

Syntheses, photophysical properties, and application of through-bond energy-transfer cassettes for biotechnology

We have designed fluorescent "through-bond energy-transfer cassettes" that can harvest energy of a relatively short wavelength (e.g., 490 nm), and emit it at appreciably longer wavelengths without significant loss of intensity. Probes of this type could be particularly useful in biotechnology for multiplexing experiments in which several different outputs are to be observed from a single excitation source. Cassettes 1-4 were designed, prepared, and studied as model systems to achieve this end. They were synthesized through convergent routes that feature coupling of specially prepared fluorescein- and rhodamine-derived fragments. The four cassettes were shown to emit strongly, with highly efficient energy transfer. Their emission maxima cover a broad range of wavelengths (broader than the four dye cassettes currently used for most high-throughput DNA sequencing), and they exhibit faster energy-transfer rates than a similar through-space energy-transfer cassette. Specifically, energy-transfer rates in these cassettes is around 6-7 ps, in contrast to a similar through-space energy-transfer system shown to have a decay time of around 35 ps. Moreover, the cassettes are considerably more stable to photobleaching than fluorescein, even though they each contain fluorescein-derived donors. This was confirmed by bulk fluorescent measurements, and in single-molecule-detection studies. Modification of a commercial automated DNA-sequencing apparatus to detect the emissions of these four energy-transfer cassettes enabled single-color dye-primer sequencing.