Structural Mimics of Acetylene Hydratase: Tungsten Complexes Capable of Intramolecular Nucleophilic Attack on Acetylene

Bioinspired complexes employing the ligands 6-tert-butylpyridazine-3-thione (SPn) and pyridine-2-thione (SPy) were synthesized and fully characterized to mimic the tungstoenzyme acetylene hydratase (AH). The complexes [W(CO)(C₂H₂)(CHCH-SPy)(SPy)] ( 4 ) and [W(CO)(C₂H₂)(CHCH-SPn)(SPn)] ( 5 ) were formed by intramolecular nucleophilic attack of the nitrogen donors of the ligand on the coordinated C₂H₂ molecule. Labelling experiments using C₂D₂ with the SPy system revealed the insertion reaction proceeding via a bis-acetylene intermediate. The starting complex [W(CO)(C₂H₂)(SPy)₂] ( 6 ) for these studies was accessed by the new acetylene precursor mixture [W(CO)(C₂H₂)_n(MeCN)_3−nBr₂] (n=1 and 2; 7 ). All complexes represent rare examples in the field of W−C₂H₂ chemistry with 4 and 5 being the first of their kind. In the ongoing debate on the enzymatic mechanism, the findings support activation of acetylene by the tungsten center.     

Boolean constant degree functions on the slice are juntas

We show that a Boolean degree $d$ function on the “slice” $\left(\genfrac{}{}{0ex}{}{\left[n\right]}{k}\right)?\{(x_1,\dots ,x_n)\in \{0,1\}:{\sum }_{i=1}^n{x}_i=k\}$ is a junta (depends on a constant number $\gamma \left(d\right)$ of coordinates), assuming that $k,n?k$ are large enough. This generalizes a classical result of Nisan and Szegedy on the hypercube ${\{0,1\}}^n$. Moreover, we show that the maximum number of coordinates that a Boolean degree $d$ function can depend on is the same on the slice and on the hypercube.     

Near-Integrability and Recurrence in FPU Chains with Alternating Masses

Journal of Nonlinear Science - An important aspect of understanding FPU chains is the existence of invariant manifolds (called “bushes”) in FPU chains. We will focus on the classical...     

Preparation of <Superscript>95m</Superscript>Tc radiotracer

Several procedures for preparation of the ^95mTc radiotracer following irradiation of a thin Mo target with deuterons were tested. The procedures consisting of alkaline-oxidative fusion of the irradiated target in a mixture of Na₂O₂ + NaOH and subsequent liquid–liquid extraction with 2-butanone, and acid decomposition of the target in a mixture of H₂SO₄ + HNO₃ followed by extraction chromatography with PAN-Aliquat 336 composite material appeared suitable for the given purpose.     

The homologous series of 1,1'-ferrocenylenebisdihalophosphanes (C5H4PX2)2Fe (X = F, Cl, Br, I): precursors for the first metallocene bridged bisphosphaalkene

A facile synthetic access to the homologous series of 1,1'-ferrocenylene bisdihalophosphanes Fc'(PX2)2 (X = F, Cl, Br, I; Fc' = 1,1'-ferrocenediyl = ferrocenylene = -C5H4FeC5H4-) is reported. The 31P NMR spectroscopic data of this series suggest a similar electronic interaction of the -PX(2) unit with the ferrocene system as in monofunctional ferrocenyldihalophosphanes. Crystal structures for Fc'(PCl2)2 and Fc'(PBr2)2 reveal that the nature of the halogen atom within the phosphane unit strongly influences the twist angle of the ferrocene system, while leaving the other structural parameters mostly unaffected. Based on these bisdihalophosphanes, a synthetic access to the first metallocene bridged bisphosphaalkene ((C5H4P=C(t-Bu)OTMS)2Fe) is reported in which the tert-butyl substituents provide sufficient steric pressure to control the E/Z isomeric ratio which leads to the almost exclusive formation of the most stable Z,Z isomer out of the three possible isomers.     

Gaussian model for localized translational motion: application to incoherent neutron scattering

A simple model based on Gaussian statistics, aimed at describing localized diffusive translational motion in one, two, and three dimensions is presented and used to calculate the corresponding incoherent neutron scattering laws. In the time domain, these laws are closed form mathematical functions. In the frequency domain, some of these laws can be expressed as an infinite series depending on one single index. Owing to this relative simplicity, such a model can advantageously replace previous models such as diffusion on a segment, inside a circle and inside a sphere with an impermeable surface, to analyze neutron quasielastic scattering data associated with molecular motions in confined media. It may also be more realistic when the confinement is defined by soft, ill-defined boundaries.     

Singular and selfsimilar solutions for Euler equations with phase transitions

Riemann problems for the full set of Euler equations for two phases with phase transition are considered. Based on the assumptions across the phase boundary kinetic relations to describe the mass transfer between the phase are derived from the second law of thermodynamics. Self-similar as well as singular solutions can be constructed. For both cases the structure of the solution is discussed.     

A new class of metric divergences on probability spaces and its applicability in statistics

The classI _f β, βε(0, ∞], off-divergences investigated in this paper is defined in terms of a class of entropies introduced by Arimoto (1971,Information and Control,19, 181–194). It contains the squared Hellinger distance (for β=1/2), the sumI(Q ₁‖(Q ₁+Q ₂)/2)+I(Q ₂‖(Q ₁+Q ₂)/2) of Kullback-Leibler divergences (for β=1) and half of the variation distance (for β=∞) and continuously extends the class of squared perimeter-type distances introduced by Österreicher (1996,Kybernetika,32, 389–393) (for βε (1, ∞]). It is shown that\((I_{f_\beta } (Q_1 ,Q_2 ))^{\min (\beta ,1/2)}\) are distances of probability distributionsQ ₁,Q ₂ for β ε (0, ∞). The applicability of\(I_{f_\beta }\)-divergences in statistics is also considered. In particular, it is shown that the\(I_{f_\beta }\)-projections of appropriate empirical distributions to regular families define distribution estimates which are in the case of an i.i.d. sample of size'n consistent. The order of consistency is investigated as well.