Electrophorèse sur papier des cations minéraux en présence d'agents complexants

Résumé La migration des ions argent, plomb et mercure-II en présence d'acide,-diaminodiéthyléther-N,N-tétracétique, a été étudiée, en fonction du p_H. Les différences observées permettent des séparations dans le cas des mélanges binaires.

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Summary The migration of the silver-, lead-, and mercury(II) ions in the presence of ,-diaminodiethylether-N,N-tetraacetic acid has been studied as a function of p_H. The observed differences permit separations in the case of binary mixtures.

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Zusammenfassung Die p_H-Abhängigkeit der Wanderung von Silber-, Blei- und Quecksilber(II)-ionen in Gegenwart von,-Diaminodiäthyläther-N,N-tetraessigsäure wurde untersucht. Die beobachteten Verschiedenheiten ermöglichen die Trennung binärer Gemische.

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Dédié à l'occasion du 100^me anniversaire de la naissance deFriedrich Emich.     

Colorability of Planar Graphs with Isolated Nontriangular Faces

By a hole graph we mean a 2-connected planar graph where no two nontriangular faces have a vertex in common. We give necessary and sufficient conditions for a hole graph to be 3-colorable.Acknowledgments. This paper was prepared in framework of the exchange program between the Austrian and Slovak Academies of Sciences. The third author was active at Department of Mathematics, Vanderbilt University and Fakulta prírodných vied, ilinská univerzita v iline.Mathematics Subject Classification (1991): 05C15     

Mass-profile and instability-growth measurements for 300-wire Z-pinch implosions driven by 14-18 MA

We present the first comprehensive study of high wire-number, wire-array Z-pinch dynamics at 14-18 MA using x-ray backlighting and optical shadowgraphy diagnostics. The cylindrical arrays retain slowly expanding, dense wire cores at the initial position up to 60% of the total implosion time. Azimuthally correlated instabilities at the array edge appear during this stage which continue to grow in amplitude and wavelength after the start of bulk motion, resulting in measurable trailing mass that does not arrive on axis before peak x-ray emission.     

Towards rational syntheses of the elusive metallocarbohedrenes: density functional prescriptions for electronic and geometric structures

The metallocarbohedrenes are binary molecular clusters containing metal atoms linked by acetylenediide C(2) groups. Hundreds of these molecules have been generated, detected and reacted in the gas phase since the prototype, [Ti(8)(C(2))(6)], was reported in 1992, but none has yet been synthesised pure in bulk: the time gap between detection and preparation increasingly exceeds that of the fullerenes. We report here the results of density functional calculations of geometrical and electronic structure of more than 150 postulated metallocarbohedrenes, stabilised by terminal ligation, in order to recognise the more electronically favourable and less reactive targets. At least 38 metallocarbohedrenes have been identified as having a spin singlet ground state, with a relatively large (> 0.5 eV) energy gap between HOMO and LUMO, and an appropriate HOMO energy. In addition, a considerable number of electronically stable metallocarbohedrenes are predicted to have highly paramagnetic ground states, potentially useful in molecular magnetism. The geometrical principles for enclosing but unstrained coordination of metal sites by terminal ligands are outlined. Mechanisms for rational syntheses are considered in the context of reaction type and precursor selection, including issues of oxidation and reduction, and kinetic versus thermodynamic control. This leads to many diverse reactions suggested for the rational syntheses of metallocarbohedrenes. Some preliminary experimental results are presented.     

Distance Dependence of Bidirectional Concerted Proton–Electron Transfer in Phenol‐Ru(2,2′‐bipyridine)32+ Dyads

Proton‐coupled electron transfer (PCET) was investigated in three covalent donor–bridge–acceptor molecules with different bridge lengths. Upon photoexcitation of their Ru(bpy)₃²⁺ (bpy=2,2′‐bipyridine) photosensitizer in acetonitrile, intramolecular long‐range electron transfer from a phenolic unit to Ru(bpy)₃²⁺ occurs in concert with release of the phenolic proton to pyrrolidine base. The kinetics of this bidirectional concerted proton–electron transfer (CPET) reaction were studied as a function of phenol–Ru(bpy)₃²⁺ distance by increasing the number of bridging p‐xylene units. A distance decay constant (β) of 0.67±0.23 Å^?1 was determined. The distance dependence of the rates for CPET is thus not significantly steeper than that for ordinary (i.e., not proton coupled) electron transfer across the same bridges, despite the concerted motion of oppositely charged particles into different directions. Long‐range bidirectional CPET is an important reaction in many proteins and plays a key role in photosynthesis; our results are relevant in the context of photoinduced separation of protons and electrons as a means of light‐to‐chemical energy conversion. This is the first determination of β for a bidirectional CPET reaction.     

Morphospecific polymerization: Polyoxymethylene copolymers

Homopolymerization and copolymerization of trioxane by use of various catalysts have been investigated. When MoO₂(AcAc)₂ is employed, crystalline homopolymers and copolymers as formed from polymerization exhibit significantly higher melting points than corresponding polymers prepared by use of ordinary cationic catalysts. The higher melting points are attributed to different morphology of the polymer chains formed during polymerization. We now call this phenomenon morphospecific polymerization. This communication describes our results in the copolymerization of trioxane and 1,3-dioxolane and some outstanding properties of the copolymers. A polymerization mechanism is also proposed.     

Proton-coupled electron transfer from a luminescent excited state

A luminescent cationic iridium complex with a 2,2'-biimidazole ligand forms hydrogen-bonded 1 : 1 adducts with benzoate anions; photoexcitation of the metal complex in presence of 3,5-dinitrobenzoate triggers a proton-coupled electron transfer.     

Light‐Driven Electron Accumulation in a Molecular Pentad

Accumulation and temporary storage of redox equivalents with visible light as an energy input is of pivotal importance for artificial photosynthesis because key reactions, such as CO₂ reduction or water oxidation, require the transfer of multiple redox equivalents. We report on the first purely molecular system, in which a long‐lived charge‐separated state (τ≈870 ns) with two electrons accumulated on a suitable acceptor unit can be observed after excitation with visible light. Importantly, no sacrificial reagents were employed.