Activated scaling of classical and quantum spin glasses

A model for thermally activated dynamics in disordered systems shows that the linear and nonlinear susceptibility follows a generic exponential form with a "critical rounding," chi(1) proportional to chi(3) proportional to [T ln(t/tau(0)')/K](gamma/b phi) exp - [Tt(g)(phi b)ln(t/tau(0)'/K)](nu/b) (T=temperature, t=time, K=barrier constant, t(g) = 1 - T(SG)/T, and T(SG) = transition temperature; gamma>0 for chi(3) and <0 for chi(1)). This model, also valid in the presence of resonant tunneling states at energies K(0) < K [provided that K is replaced by K(0)+2T ln (1/Gamma(0)), where Gamma(0)(2) proportional, variant tunnel splitting of a spin S=1], is potentially applicable to a wide variety of systems opening the way for the study of thermally activated quantum phase transitions. The famous spin-glass system LiHo(x)Y(1-x) seems to follow this model.     

Bromine adsorption on Ge(001) surface: comparative study for coverages of 0.25, 0.5, 0.75 and 1 monolayer

We present theoretical analysis of bromine adsorption on the Ge(001)-p(1×2) surface. Bromine adsorbs dissociatively at the Ge(001) surface and the adlayer of bromine develops ordered structures of adatoms bound to substrate dimers. We analyse atomic configurations of the Ge(001) surface covered by 0.25, 0.5, 0.75 and 1 monolayer of bromine. Various stable surface structures, found in calculations, are presented and their energies are compared. Simulated STM images are also discussed for the considered configurations.      

Tetra­ethyl­ammonium bis­(N,N‐diethyl­dithio­carbamato‐κ2S,S′)iodo­cadmate(II)

The title compound, (C₈H₂₀N)[Cd(C₅H₁₀NS₂)₂I], containing a heteroleptic five‐coordinate mononuclear anionic cadmium complex, crystallizes in ortho­rhom­bic form in the space group Pnma. Both anion and cation lie about mirror planes. Unlike other known [Cd(dtc)₂X]‐type complexes (where dtc is dithio­carbamate and X is a halogen or pseudohalogen), the central CdS₄I core shows a square‐pyramidal configuration, with a basal plane defined by four S atoms from two chelating dithio­carbamate ligands related by a symmetry plane. The central Cd atom is displaced from the basal S₄ plane towards the apical I atom of the square pyramid.     

Mass spectrometric studies of 2-aryl-5-acetylthiazole derivatives

Electron ionisation mass spectrometry was usefully used to characterize structurally 2-aryl-5-acetylthiazole derivatives in the gas phase. The compounds show characteristic fragmentation pathways depending on the chemical nature of the substituent at position 2, consisting mainly in the cleavage of both the 1,2- and 3,4-bonds of the thiazole ring. Liquid secondary ion mass spectrometry was applied to study the effects of protonation on the gas-phase unimolecular reactions of this class of compound. Tandem mass spectrometric experiments, carried out on molecular and protonated molecular ions, and also on fragment ions produced in the source, allowed the elucidation of gas-phase decompositions of low-internal energy ions.     

Reversible guest-induced magnetic and structural single-crystal-to-single-crystal transformation in microporous coordination network {[Ni(cyclam)]3[W(CN)8]2}n

Planar honeycomb-like coordination network {[Ni(cyclam)]3[W(CN)8]2}n (cyclam = 1,4,8,11-tetraazacyclotetradecane) was obtained in the self-assembly reaction of [Ni(cyclam)]2+ and [W(CN)]83-. Its structure is characterized by void channels along the a axis. The compound shows reversible water adsorption in the temperature range of 25-40 degrees C with the formation of {[Ni(cyclam)]3[W(CN)8]2}n.16nH2O, accompanied by single-crystal-to-single-crystal transformation. The structural transformation significantly changes the character of intraplane magnetic exchange interactions.     

Vanadium and molybdenum peroxides: synthesis and catalytic activity in oxidation reactions

Catalysis by transition metal ions in oxidation reactions with hydrogen peroxide and alkyl hydroperoxides is a leading topic in the pursuit of more sustainable and selective processes, to obtain compounds with high added value. The most recent achievements concerning the synthesis and characterization, as well as the key aspects of reactivity, of V(V) and Mo(VI) peroxo complexes have been collected here.     

A photochemical activation scheme of inert dinitrogen by dinuclear Ru(II) and Fe(II) complexes

A general photochemical activation process of inert dinitrogen coordinated to two metal centers is presented on the basis of high-level DFT and ab initio calculations. The central feature of this activation process is the occupation of an antibonding pi* orbital upon electronic excitation from the singlet ground state S0 to the first excited singlet state S1. Populating the antibonding LUMO weakens the triple bond of dinitrogen. After a vertical excitation, the excited complex may structurally relax in the S1 state and approaches its minimum structure in the S1 state. This excited-state minimum structure features the dinitrogen bound in a diazenoid form, which exhibits a double bond and two lone pairs localized at the two nitrogen atoms, ready to be protonated. Reduction and de-excitation then yield the corresponding diazene complex; its generation represents the essential step in a nitrogen fixation and reduction protocol. The consecutive process of excitation, protonation, and reduction may be rearranged in any experimentally appropriate order. The protons needed for the reaction from dinitrogen to diazene can be provided by the ligand sphere of the complexes, which contains sulfur atoms acting as proton acceptors. These protonated thiolate functionalities bring protons close to the dinitrogen moiety. Because protonation does not change the pi*-antibonding character of the LUMO, the universal and well-directed character of the photochemical activation process makes it possible to protonate the dinitrogen complex before it is irradiated. The pi*-antibonding LUMO plays the central role in the activation process, since the diazenoid structure was obtained by excitation from various occupied orbitals as well as by a direct two-electron reduction (without photochemical activation) of the complex; that is, the important bending of N2 towards a diazenoid conformation can be achieved by populating the pi*-antibonding LUMO.     

Cellular responses to patterned poly(acrylic acid) brushes

We use patterned poly(acrylic acid) (PAA) polymer brushes to explore the effects of surface chemistry and topography on cell-surface interactions. Most past studies of surface topography effects on cell adhesion have focused on patterned feature sizes that are larger than the dimensions of a cell, and PAA brushes have been characterized as cell repellent. Here we report cell adhesion studies for RBL mast cells incubated on PAA brush surfaces patterned with a variety of different feature sizes. We find that when patterned at subcellular dimensions on silicon surfaces, PAA brushes that are 30 or 15 nm thick facilitate cell adhesion. This appears to be mediated by fibronectin, which is secreted by the cells, adsorbing to the brushes and then engaging cell-surface integrins. The result is detectable accumulation of plasma membrane within the brushes, and this involves cytoskeletal remodeling at the cell-surface interface. By decreasing brush thickness, we find that PAA can be 'tuned' to promote cell adhesion with down-modulated membrane accumulation. We exemplify the utility of patterned PAA brush arrays for spatially controlling the activation of cells by modifying brushes with ligands that specifically engage IgE bound to high-affinity receptors on mast cells.