Spanning pairs of Rh2(acetate)4 units with Ru(II) complexes

A synthetic route to linear pairs of Rh2 "paddlewheel" dimers bridged by Ru(II) complexes is presented. A bis(4'-(4-carboxyphenyl)-terpyridine)Ru(II) complex spans two Rh2 dimers and displays a 26 A separation between the dimers. Increased electronic interaction is found for the dimer of dimers without the phenyl groups using bis(4'-(4-carboxy)-terpyridine)Ru(II) as the bridging complex.     

Unbounded sequences of stable limit cycles in the delayed Duffing equation: an exact analysis

Nonlinear Dynamics - The delayed Duffing equation $${\ddot{x}}(t)+x(t-T)+x^3(t)=0$$ is shown to possess an infinite and unbounded sequence of rapidly oscillating, asymptotically stable periodic...     

Connectivity and design of planar global attractors of Sturm type. II: Connection graphs

Based on a Morse-Smale structure we study planar global attractors Af of the scalar reaction-advection-diffusion equation ut=uxx+f(x,u,ux) in one space dimension. We assume Neumann boundary conditions on the unit interval, dissipativeness of f, and hyperbolicity of equilibria. We call Af Sturm attractor because our results strongly rely on nonlinear nodal properties of Sturm type.The planar Sturm attractor consists of equilibria of Morse index 0, 1, or 2, and their heteroclinic connecting orbits. The unique heteroclinic orbits between adjacent Morse levels define a plane graph Cf which we call the connection graph. Its 1-skeleton consists of the unstable manifolds (separatrices) of the index-1 Morse saddles.We present two results which completely characterize the connection graphs Cf and their 1-skeletons in purely graph theoretical terms. Connection graphs are characterized by the existence of pairs of Hamiltonian paths with certain chiral restrictions on face passages. Their 1-skeletons are characterized by the existence of cycle-free orientations with certain restrictions on their criticality. Such orientations are called bipolar in [H. de Fraysseix, P.O. de Mendez, P. Rosenstiehl, Bipolar orientations revisited, Discrete Appl. Math. 56 (1995) 157-179].In [B. Fiedler, C. Rocha, Connectivity and design of planar global attractors of Sturm type. I: Orientations and Hamiltonian paths, Crelle J. Reine Angew. Math. (2007), in press] we have shown the equivalence of the two characterizations. Moreover we have established that connection graphs of Sturm attractors indeed satisfy the required properties. In the present paper we show, conversely, how to design a planar Sturm attractor with prescribed plane connection graph or 1-skeleton of the required properties. In [B. Fiedler, C. Rocha, Connectivity and design of planar global attractors of Sturm type. III: Small and Platonic examples, 2007, submitted for publication] we describe all planar Sturm attractors with up to 11 equilibria. We also design planar Sturm attractors with prescribed Platonic 1-skeletons.     

Kinetic and Thermodynamic Control in Self-Assembly: Sequential Formation of Linear and Circular Helicates

NMR and MS analysis as a function of time has shown that the self-assembly of a linear ligand with Fe²⁺ or Ni²⁺, metal ions of octahedral coordination geometry, generates first a triple helicate and thereafter the circular helicate 1 as kinetic and thermodynamic products, respectively. The results provide insight into features of the energy hypersurface on which this self-assembly operates and point to the general role of kinetic and thermodynamic control in such processes.     

Homoclinic period blow-up in reversible and conservative systems

We show that in conservative systems each non-degenerate homoclinic orbit asymptotic to a hyperbolic equilibrium possesses an associated family of periodic orbits. The family is parametrized by the period, and the periodic orbits accumulate on the homoclinic orbit as the period tends to infinity. A similar result holds for symmetric homoclinic orbits in reversible systems. Our results extend earlier work by Devaney and Henrard, and provide a positive answer to a conjecture of Strömgren. We present a unified approach to both the conservative and the reversible case, based on a technique introduced recently by X.-B. Lin.Dedicated to Prof. Klaus Kirchgässner on the occasion of his sixtieth birthday     

Intramolecular Anion Effect in Polyoxometalate‐Based Organocatalysts: Reactivity Enhancement and Chirality Transfer by a Metal Oxide–Organic Cation Interaction

An α₁‐Dawson polyanion bearing a lateral side chain with a 4‐aminopyridine end group was synthesized. This organopolyoxometalate catalyzes the addition of indenyl allyl silanes to cinnamoyl fluorides. The polyanionic framework influences the organocatalyst activity and selectivity. A moderate but nonzero chirality transfer from the chiral inorganic framework to the organic substrate was observed.     

Identification of polyoxometalates as nanomolar noncompetitive inhibitors of protein kinase CK2

Protein kinase CK2 is a multifunctional kinase of medical importance that is dysregulated in many cancers. In this study, polyoxometalates were identified as original CK2 inhibitors. [P2Mo18O62](6-) has the most potent activity. It inhibits the kinase in the nanomolar range by targeting key structural elements located outside the ATP- and peptide substrate-binding sites. Several polyoxometalate derivatives exhibit strong inhibitory efficiency, with IC50 values < or = 10 nM. Furthermore, these inorganic compounds show a striking specificity for CK2 when tested in a panel of 29 kinases. Therefore, polyoxometalates are effective CK2 inhibitors in terms of both efficiency and selectivity and represent nonclassical kinase inhibitors that interact with CK2 in a unique way. This binding mode may provide an exploitable mechanism for developing potent drugs with desirable properties, such as enhanced selectivity relative to ATP-mimetic inhibitors.     

Amphiphilic Polyoxometalates for the Controlled Synthesis of Hybrid Polystyrene Particles with Surface Reactivity

Amphiphilic organo‐polyoxometalates (POMs) used in the radical emulsion polymerization of styrene allowed the preparation in aqueous medium of stable 50–100 nm polystyrene–POM composite latexes. Thanks to the presence of a trithiocarbonate group in the POM amphiphile, POMs could be covalently linked to the polymer particle surface. The chemical and catalytic integrity of the POMs was confirmed, and the POM‐mediated surface photoactivity of the latexes was demonstrated by the spatially controlled nucleation of silver nanoparticles at the periphery of the composites.