Mononuclear and Dinuclear Copper Complexes of Tridentate Redox-active Ligands with Tunable H-bonding Donors: Structure,Spectroscopy and H+/e− Reactivity

In this research article, we describe the synthesis and characterization of mononuclear and dinuclear Cu complexes bound by a family of tridentate redox-active ligands with tunable H-bonding donors. The mononuclear Cu-anion complexes were oxidized to the corresponding “high-valent” intermediates by oxidation of the redox-active ligand. These species were capable of oxidizing phenols with weak O−H bonds via H-atom abstraction. Thermodynamic analysis of the H-atom abstractions, which included reduction potential measurements, pK_a determination and kinetic studies, revealed that modification of the anion coordinated to the Cu and changes in the H-bonding donor did not lead to major differences in the reactivity of the “high-valent” CuY complexes (Y: hydroxide, phenolate and acetate), which indicated that the tridentate ligand scaffold acts as the H⁺ and e⁻ acceptor.     

Electron-transfer kinetics and activation barriers for the reductions of nitrosonium and nitronium ions in aprotic solvents

Using the cyclic voltammetry (CV), the electron-transfer kinetics for the reductions of NO⁺ and NO₂⁺ cations have been studied at the Pt electrode in nitromethane, sulfolane, and propylene carbonate. The heterogeneous rate constants have been determined by two independent procedures from the transfer coefficient α, the diffusion coefficient D, from a detailed examination of the CV-peak separations, and from an inspection of the values of the cathodic peak potentials at different scan rates. The results have been compared to those reported in the literature, and discussed. In the classical model, outer-sphere electron-transfer reactions are considered subject to an activation energy arising from solvent reorganization and bond reorganization processes. The solvent and molecular reorganizational barriers for these electroreductions have been assessed in aprotic media. The Marcus-Hush theory has been applied to the self-exchange reactions of the NO₂⁺/NO₂ and NO⁺/NO couples in an attempt to predict the rate of electron transfer. The findings indicate some improvement between theory and experiment. However, it should be noted that the experimental values of k_s found for the NO₂⁺ reduction in the solvents used are still too high in comparison with those determined theoretically. In view of the fairly strong coordination of the solvent molecule(s) as ligand(s) to NO₂⁺ and NO⁺ cations, we believe that such discrepancies should stem, to some extent, from the involvement of an inner-sphere pathway by generation of an activated complex on the surface of the Pt electrode. © 1993 John Wiley & Sons, Inc.     

New water-soluble calix[4]arene-based bipyridyl podands incorporating carboxylate groups

New calixarene-based bis-bipyridyl podands incorporating two sodium (4-oxo)-butanoate or four sodium carboxymethyl groups at the upper rim were synthesised and fully characterised. The (4-oxo)-butanoate derivative bearing unsubstituted bipyridyl arms was not soluble in water at neutral pH, while its 4,4′-dicarboxylate analogue was perfectly soluble, as were the carboxymethyl derivatives. The association of water solubility to the chelating behaviour of the bipyridyl subunits resulted in the ability to complex the unstable copper(I) cation in water, even in the presence of bovine serum albumin.     

Construction d'une paramétrixe pour des opérateurs différentiels hypoelliptiques marimaux sur un espace homogéne d'un groupe de Lie nilpotent gradué de rang 2

Soient G une alébre de Lie nilpotente stratifée de rang 2, une sous-algébre de G, _0, la représentation de G dans l'espace L ²( \ G) indiute par le caractére trivial C, P un opérateur homogène appartenant à l'algébre universelle enveloppante (complexifiée) U(G) tel que l'opérateur _0, (P) soit hypoelliptique maximal. Cet opérateur peut s'exprimer par une intégrale dépendant de la restriction du symbole p de P au sousensemble = G · décrit par les orbites des éléments de dans la représentation contragrédiente de G dans G ^*.Une algèbre de symboles définis sur est construite et permet de déterminer une paramétrixe de _0, (P); des résultats de réguralité de cet opérateur dans des espaces de Sobolev adaptés sont ensuite obtenus.     

Coprecipitation/accumulation/distribution of manganese and iron, and electrochemical characteristics of Mn in calcareous seawater

A study of managanese and iron associated with particulate matter in seawaters derived from the English Channel (and North Sea). Sequential extraction procedures have been used to identify geochemical processes that govern Mn and Fe coprecipitation/accumulation/distribution in different particulate phases (carbonate; Fe-Mn(hydr)oxides; organic matter and residual phase). The oxidation states of Mn and Fe, some mechanisms of bonding and the magnetic characteristics of particles have been investigated by Mössbauer spectroscopy, electron spin resonance(ESR) spectroscopy, and mass susceptibility balance. The effect of pH and redox potential on stability of different dissolved and particulate Mn species was also examined. In the these calcareous seawaters, manganese (II) is predominantly bound to the carbonate phase (calcite) in the form of Mn_xCa_1-xCO₃. However the persistent occurrence of Mn in oxidation states > 2 in these particles has suggested the existence of manganese(III) in the polymeric FeOOH structures as an intermediate entity during Mn(II) oxidation in the sea. The activity coefficient of the entity MnOOH in FeOOH has been evaluated and p-pH diagrams of Mn have been proposed under marine conditions.     

Modelisation of the Electric Field Linear Response of an Infinite Aggregate of All-Trans Hexatriene Chains by Electrostatic Interaction Model

A classical electrostatic polarization scheme using the additive distribution procedure has been applied to determine the longitudinal polarizability of an all-trans hexatriene molecule in an infinite stretched fiber. The parameters have been derived from ab initio CPHF/6-31G calculations and the electrostatic scheme has been validated via comparison with ab initio results on small clusters. Upon packing the polarizability of all-trans hexatriene increases by 7%. This small increase results from the balance between the enhancement of the polarizability due to collinear packing and the reduction associated with lateral packing.     

Synthesis of chiral α-substituted N-[((2S)-2-hydroxy-2-phenyl)-ethyl]-2-phenylglycine derivatives by diastereocontrolled alkylation of (6 R)-2,3,5,6-tetrahydro-3,6-diaryl-N-[(2′R)-(2′-methyl)phenyl-methyl]-4H-1,4-oxazin-2-ones

The synthesis of α-substituted N-[((2S)-2-hydroxy-2-phenyl)-ethyl]-2-phenylglycine derivatives is reported. The key step of the sequence is the highly diastereoselective alkylation of (6R)-2,3,5,6-tetrahydro-3,6-diaryl-N-[(2′R)-(2′-methyl)phenylmethyl]-4H-1,4-oxazin-2-ones after deprotonation with t-BuOK. Opening of the resulting oxazinone with ethanolic KOH, followed by hydrogenolysis of the corresponding N-[(2R)-(2-methyl)phenylmethyl] compound to furnish the expected 2-phenylglycine derivative, is also described.     

Chemical and electrochemical behaviour of nitric and nitrous acids in sulpholane

With a glass electrode filled with mercury as indicator electrode for hydrogen ions, the acidity constant of nitric acid and the stability constants of the complexes HA(-)(2) (A Cl(-), NO(-)(3)) in sulpholane at 303 K have been determined potentiometrically. The acidity constant of nitrous acid has also been determined in supholane medium because of the low stability of this acid in aprotic media. On the basis of the results, some aspects of the electrochemical and thermodynamic properties of oxygen-nitrogen compounds are discussed in order to explain the catalytic effect of NO(+) in aromatic nitration by N(2)O(4) and/or N(2)O(3) in aprotic solvents.