Storable arylpalladium(II) reagents for alkene labeling in aqueous media

We show that arylpalladium(II) reagents linked to biotin and indocyanine dye residues can be prepared by decarboxylative palladation of appropriately substituted electron-rich benzoic acid derivatives. When prepared under the conditions described, these organometallic intermediates are tolerant of air and water, can be stored for several months in solution in dimethyl sulfoxide, and permit biotin- and indocyanine dye-labeling of functionally complex olefinic substrates in water by Heck-type coupling reactions.     

Temperature dependence of the crystal structure and g-values of trans-diaquabis(methoxyacetato)copper(II): evidence for a thermal equilibrium between complexes with tetragonally elongated and compressed geometries

The crystal structures of trans-diaquabis(methoxyacetato)copper(II) and the isostructural nickel(II) complex have been determined over a wide temperature range. In conjunction with the reported behavior of the g-values, the structural data suggest that the copper(II) compound exhibits a thermal equilibrium between three structural forms, two having orthorhombically distorted, tetragonally elongated geometries but with the long and intermediate bonds to different atoms, and the third with a tetragonally compressed geometry. This is apparently the first reported example of a copper(II) complex undergoing an equilibrium between tetragonally elongated and compressed forms. The optical spectrum of single crystals of the copper(II) compound is used to obtain metal-ligand bonding parameters which yield the g-values of the compressed form of the complex and hence the proportions of the complex in each structural form at every temperature. When combined with estimates of the Jahn-Teller distortions of the different forms, the latter produce excellent agreement with the observed temperature dependence of the bond lengths. The behavior of an infrared combination band is consistent with such a thermal equilibrium, as is the temperature dependence of the thermal ellipsoid parameters and the XAFS. The potential surfaces of the different forms of the copper(II) complex have been calculated by a model based upon Jahn-Teller coupling. It is suggested that cooperative effects may cause the development of the population of tetragonally compressed complexes, and the crystal packing is consistent with this hypothesis, though the present model may oversimplify the diversity of structural forms present at high temperature.     

Molecular dynamics studies of brittle fracture in vitreous silica: Review and recent progress

The dynamics of brittle fracture in vitreous silica has been a subject of many molecular dynamics (MD) simulations and experiments. A striking similarity between both simulations and experiments is the observation of nanoscale voids that eventually coalesce leading to failure. In this work, we review the above MD simulations and carry out further MD investigations using two variations of classical 2-body potentials. We study the effect of charge-transfer, an important aspect neglected by previous simulations. Further, we examine the growth of ‘critical’ voids and characterize regions surrounding the voids.     

A decomposition theorem on the scalar potential of a compressible BKZ fluid

Based on the existence of a caloric equation of state in the thermodynamic theory of a nonlinear viscoelastic fluid (Bernstein, Kearsley and Zapas, 1964), and the additional assumption that the local entropy production along any instantaneous deformation path is finite, we first show that such a fluid behaves as a perfectly elastic material whenever the deformation gradient suffers from a jump-type discontinuity. The nature of the apparently perfectly elastic material serving to interpret results in the instantaneous deformation depends on the previous historyonly through two parameters, namely, the density and the temperature of the fluid immediately prior to the jump. This result is then applied, in conjunction with the usual conditions of isotropy and objectivity as well as an application of Schur's Lemma on irreducible sets of matrices, to obtain a decomposition of the scalar potential of the compressible Bernstein-Kearsley-Zapas Fluid (abbrev. BKZ Fluid).

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Zusammenfassung Gegründet auf der Existenz einer kalorischen Zustandsgleichung in der thermodynamischen Theorie einer nichtlinearen viskoelastischen Flüssigkeit (Bernstein, Kearsley und Zapas, 1964) und der zusätzlichen Annahme, daß die örtliche Entropiezunahme entlang einer Deformationskurve endlich ist, zeigen wir zuerst, dass sich eine solche Flüssigkeit wie ein ideales elastisches Material verhält, wenn der Deformationsgradient eine sprunghafte Unstetigkeit aufweist. Die Eigenschaften des scheinbar idealen elastischen Materials, die dazu dienen, Ergebnisse der momentanen Deformation zu interpretieren, hängen von der Vorbehandlung nur durch Werte von zwei Parametern ab, nämlich der Dichte und Temperatur der Flüssigkeit direkt von der sprunghaften Veränderung. Das Ergebnis, zusammen mit den üblichen Bedingungen der Isotropie und Objektivität wie auch der Anwendung von Schurs Lemmas über nichtreduzierbare Gruppen von Matrizen, wird dann dazu verwendet, eine Zerlegung des skalaren Potentials einer verdichtbaren Bernstein-Kearsley-Zapas-Flüssigkeit (BKZ-Flüssigkeit) zu erzielen.

     

The essential nonlinearity ofN-level quantum thermodynamics

This paper explores the possibility that linear dynamical maps might be used to describe the energy-conserving, entropy-increasing motions which occur in closed thermodynamic systems as they approach canonical thermal equilibrium. ForN-level quantum systems withN>2, we prove that no such maps exist which are independent of the initial state.     

High performance liquid chromatographic analysis of six conjugated and unconjugated estrogens in serum.

Six estrogens-estrone, equilin, estradiol, sodium estrone sulphate, sodium equilin sulphate and sodium 17-alpha-dihydroequilin sulphate in dog serum were successfully separated and quantified by a high performance liquid chromatographic method developed in our laboratories. The mobile phase was optimized by studying the effects of an organic modifier (acetonitrile) and an ion pairing reagent (tetrabutylammonium hydroxide). The serum sample work-up procedure was designed to recover both conjugated and unconjugated estrogens. The optimum method involved acetonitrile to precipitate serum proteins/peptides and extract estrogens. Residues were reconstituted in 50% acetonitrile in water for injection. The detection limits for these six estrogens via UV detection ranged from 0.5 to 5 ng on-column with a signal-to-noise ratio (S/N) of 10 for a 20 microL injection and via fluorescence 0.1 ng on-column for 17-beta-estradiol. Validation data are included for all six estrogens.