Structure and properties of new mixed-valent [Mn(III)2Mn(IV)3Ln(III)5O5] complexes (Ln(III) = Tm(III), Lu(III), and Yb(III))

By using 2'-hydroxyacetophenoxime, a new family of complexes with an [Mn(III)(2)Mn(IV)(3)Ln(5)O(5)] core was obtained with Ln = Tm (1), Lu (2), and Yb (3). Heterometallic Mn/Tm and Mn/Lu combinations have had no precedence so far. Studies of the magnetic properties indicate the presence of intracomplex antiferromagnetic interactions in 1 and 3, as well as a dominating ferromagnetic interaction between Mn(III) and Mn(IV) spins in 2, leading to an S(T) = 5/2 ground state.     

A transferable ab initio based force field for aqueous ions

We present a new polarizable force field for aqueous ions (Li(+), Na(+), K(+), Rb(+), Cs(+), Mg(2 +), Ca(2 +), Sr(2 +), and Cl(-)) derived from condensed phase ab initio calculations. We use maximally localized Wannier functions together with a generalized force and dipole-matching procedure to determine the whole set of parameters. Experimental data are then used only for validation purposes and a good agreement is obtained for structural, dynamic, and thermodynamic properties. The same procedure applied to crystalline phases allows to parametrize the interaction between cations and the chloride anion. Finally, we illustrate the good transferability of the force field to other thermodynamic conditions by investigating concentrated solutions.     

Conductivity in nonpolar media: Experimental and numerical studies on sodium AOT-hexadecane, lecithin-hexadecane and aluminum(III)-3,5-diisopropyl salicylate-hexadecane systems

The conductivity behavior of doped hydrocarbon systems is studied by applying impedance spectroscopy. In the case of 3,5-diisopropyl salicylato aluminum (III) the charge carriers are formed by dissociation of the compound and their concentration is proportional to the square root of the solute concentration. In hydrocarbon systems that consist of micelle forming compounds (sodium AOT/ lecithin) a linear dependence of charge carrier concentration on solute concentration is observed in the concentration regime where micelles are present. The conduction mechanisms are studied by numerical solution of a Poisson-Nernst-Planck system that describes the charge transport. We follow two different approaches to extract the degree of micelle dissociation from the impedance data. Firstly, by computing the response of a linear approximation of the Poisson-Nernst-Planck model, and secondly by computing the fully nonlinear response from direct numerical simulations using finite elements. For high and moderate frequencies both approaches agree very well with the experimental data. For small frequencies the response becomes nonlinear and the concept of impedance fails. Furthermore, the numerically computed values for the degree of dissociation are of the same order of magnitude as the values obtained with classical formulas, but still differ by a factor of about 1/3. The direct numerical simulation allows new insight into the conduction mechanisms for different frequency regimes.     

Theoretical analysis of a non-contact spring with inclined permanent magnets for load-independent resonance frequency

In this paper a non-contact magnetic spring design is presented that uses inclined magnets to produce an adjustable relationship between load force and dynamic stiffness. With appropriate choice of parameters, the spring may either operate with a range of constant natural frequency against variable load forces, or a positive stiffness in one horizontal direction may be achieved in addition to having a positive vertical stiffness. Dynamic simulations are presented to assess the non-linear stability of a planar three degree of freedom version of the system; cross-coupling between horizontal and rotation motion is shown to compromise passive stability, in which case passive constraints or active control must be used to avoid instability. The design is scalable in that using larger magnets increases the load bearing capacity and decreases the natural frequency of the system.     

Zum massenspektrometrischen Fragmentierungsverhalten von Thiophen-Benzologen

The nine benzothiophenes investigated show rather similar fragmentation patterns after electron impact. There are variations only in the abundances of fragment ions originating from the loss of S or CS with or without a hydrogen. The possible modes of formation of these fragment ions are discussed.     

Komplement?re Quenchofluorimetrie mit Elektronen-Donoren und -Acceptoren in der Analytik polycyclischer aromatischer Kohlenwasserstoffe

Zusammenfassung Quenchofluorimetrie mit Elektronendonoren gestattet die selektive Erkennung und Bestimmung von alternierenden polycyclischen aromatischen Kohlenwasserstoffen (PAK) in Gegenwart nicht-alternierender PAK und ergänzt so die Quenchofluorimetrie mit Elektronenacceptoren. Komplementäre Quenchofluorimetrie mit Elektronendonoren und-acceptoren ist eine leistungsfähige Methode in der Analytik von PAK's.

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Complementary quenchofluorimetry with electron donors and acceptors in the analysis of polycyclic aromatic hydrocarbons

Summary Quenchofluorimetry with electron donors allows the selective detection and determination of alternant polycyclic aromatic hydrocarbons (PAH) in the presence of non-alternant PAH's, thus completing quenchofluorimetry with electron acceptors. Complementary quenchofluorimetry with electron donors and acceptors is an efficient method in the analysis of PAH's.

Der eine von uns (H. D.) dankt für die Förderung der Arbeit durch Forschungsmittel des Landes Niedersachsen.     

Electric susceptibility of unsolvated glycine-based peptides

The DC electric susceptibilities of unsolvated glycine-based peptides, WGn (W = tryptophan and G = glycine) with n = 1-5, have been measured by deflection of a molecular beam in an electric field. These are the first electric deflection measurements performed on peptides. At 300 K the susceptibilities are in the range of 200-400 A(3). By far the largest contribution to the susceptibilities is from the permanent dipole moment of the peptides. The results indicate that the peptides do not have rigid conformations with fixed dipoles. Instead the dipole is averaged as the peptides explore their energy landscape. For a given WGn peptide, all molecules have almost the same average dipole, which suggests that they all explore a similar energy landscape on the microsecond time scale of the measurement. The measured susceptibilities are in good overall agreement with values calculated from the average dipole moment deduced from Monte Carlo simulations.