The Role of Radical Bridges in Polynuclear Single-Molecule Magnets

Employing radical bridges between anisotropic metal ions has been a viable route to achieve high-performance single-molecule magnets (SMMs). While the bridges have been mainly considered for their ability to promote exchange interactions, the crystal-field effect arising from them has not been taken into account explicitly. This lack of consideration may distort the understanding and limit the development of the entire family. To shed light on this aspect, herein we report a theoretical investigation of a series of N -radical-bridged diterbium complexes. It is found that while promoting strong exchange coupling between the terbium ions, the N -radical induces a crystal field that interferes destructively with that of the outer ligands, and thus reduces the overall SMM behavior. Based on the theoretical results, we conclude that the SMM behavior in this series could be further maximized if the crystal field of the outer ligands is designed to be collinear with that of the radical bridge. This conclusion can be generalized to all exchange-coupled SMMs.     

Markov processes associated with L p -resolvents and applications to stochastic differential equations on Hilbert space

We give general conditions on a generator of a C₀-semigroup (resp. of a C₀-resolvent) on L^p(E,μ), p ≥ 1, where E is an arbitrary (Lusin) topological space and μ a σ-finite measure on its Borel σ-algebra, so that it generates a sufficiently regular Markov process on E. We present a general method how these conditions can be checked in many situations. Applications to solve stochastic differential equations on Hilbert space in the sense of a martingale problem are given. Dedicated to Giuseppe Da Prato on the occasion of his 70th birthday     

Hyperbranched polycyclocarbosiloxane

A new cross-linkable naphthalene-cyclocarbosiloxane was synthesised starting from bis[1,4-bis(methylhydrosiloxanyl)-dihydronaphthalene] via catalytic addition of the Si-H reactive groups to the unsaturated bond of triethoxyvinylsilane. Hyperbranched polycyclocarbosiloxane networks were formed by condensation of the alcoxyl groups in the presence of dibutyltin dilaurate as catalyst. The cross-linking process was studied in order to obtain information concerning the values of the reaction parameters and to determine the position of the gelation point relative to conversion.GPC analysis, IR, and 1H-NMR spectral analysis techniques were used to investigate the chemical structures of the intermediates and of the product.     

A tris(mu-hydroxy)tricopper(II) complex as a model of the native intermediate in laccase and its relationship to a binuclear analogue

The reaction of a copper(I) complex with a sterically demanding secondary diamine ligand and O2 yields a tris(mu-hydroxy)tricopper(II) complex. This complex is a structural model of the proposed native intermediate in multicopper oxidases, with interesting structural, magnetic, and solution properties.     

Mechanism of a strongly anisotropic MoIII-CN-MnII spin-spin coupling in molecular magnets based on the [Mo(CN)(7)](4-) heptacyanometalate: a new strategy for single-molecule magnets with high blocking temperatures

Unusual spin coupling between Mo(III) and Mn(II) cyano-bridged ions in bimetallic molecular magnets based on the [Mo(III)(CN)(7)](4-) heptacyanometalate is analyzed in terms of the superexchange theory. Due to the orbital degeneracy and strong spin-orbit coupling on Mo(III), the ground state of the pentagonal-bipyramidal [Mo(III)(CN)(7)](4-) complex corresponds to an anisotropic Kramers doublet. Using a specially adapted kinetic exchange model we have shown that the Mo(III)-CN-Mn(II) superexchange interaction is extremely anisotropic: it is described by an Ising-like spin Hamiltonian JS(z)(Mo) S(z)(Mn) for the apical pairs and by the J(z)S(z)(Mo) S(z)(Mn) + J(xy)(Sx(Mo) Sx(Mn) + Sy(Mo) Sy(Mn)) spin Hamiltonian for the equatorial pairs (in the latter case J(z) and J(xy) can have opposite signs). This anisotropy resulted from an interplay of several Ising-like (Sz(Mo) Sz(Mn)) and isotropic (S(Mo)S(Mn)) ferro- and antiferromagnetic contributions originating from metal-to-metal electron transfers through the pi and sigma orbitals of the cyano bridges. The Mo(III)-CN-Mn(II) exchange anisotropy is distinct from the anisotropy of the g-tensor of [Mo(III)(CN)(7)](4-); moreover, there is no correlation between the exchange anisotropy and g-tensor anisotropy. We indicate that highly anisotropic spin-spin couplings (such as the Ising-like JS(z)(Mo) S(z)(Mn)) combined with large exchange parameters represent a very important source of the global magnetic anisotropy of polyatomic molecular magnetic clusters. Since the total spin of such clusters is no longer a good quantum number, the spin spectrum pattern can differ considerably from the conventional scheme described by the zero-field splitting of the isotropic spin of the ground state. As a result, the spin reorientation barrier of the magnetic cluster may be considerably larger. This finding opens a new way in the strategy of designing single-molecule magnets (SMM) with unusually high blocking temperatures. The use of orbitally degenerate complexes with a strong spin-orbit coupling (such as [Mo(III)(CN)(7)](4-) or its 5d analogues) as building blocks is therefore very promising for these purposes.     

On Weyl structures

We characterize the relation between the geometrical properties of Weyl manifolds and the algebraic properties of the Weyl algebras (§1) and the deformation algebras associated to two conformal Weyl connections (§2). The last section is devoted to the study of the Weyl-Lyra algebras associated to a conformal Weyl connection and a conformal semisymmetric connection.     

Biosensors for phenol derivatives using biochemical signal amplification

Two different approaches, both exploiting two enzymes cooperative functioning, to enhance the sensitivity of tyrosinase (PPO) based biosensor for amperometric detection of phenols have been compared. For this purpose, one monoenzyme electrode (PPO) and two bienzyme electrodes (PPO and d-glucose dehydrogenase, GDH; PPO and horseradish peroxidase, HRP) were constructed using agar-agar gel as enzyme immobilization matrix. The biosensors responses for l-tyrosine detection were recorded at −50 mV versus saturated calomel electrode (SCE). The highest sensitivity (74 mA M⁻¹) was observed for the PPO-GDH couple, while that recorded for PPO-HRP couple system was only 32 times higher than that measured for monoenzyme electrode (0.01 mA M⁻¹). The ability of the PPO-, PPO-GDH-, PPO-HRP-based biosensors to assay phenols was demonstrated by quantitative determination of phenol, 1,2-dihydroxybenzene, 1,3-dihydroxybenzene, 1,4-dihydroxybenzene, 2-amino-3 (4-hydroxyphenyl) propanoic acid, 2-hydroxytoluene, 3-hydroxytoluene, 4-hydroxytoluene, 4-clorophenol, 3-clorophenol, 2-clorophenol, 4-hydroxybenzoic acid.     

Synthesis,characterization and spectroscopic studies of pyrazinamide metal complexes

The present paper deals with the synthesis and characterization of Schiff base complexes of pyrazinamide an antitubercular drug. Metals selected for complexation are copper, silver, gold, zinc, mercury, iron and cobalt. The complexes have been suitably synthesized and isolated in pure powdered form. Analytical data agrees with the compositions M(L), M′(L)₂ and M″(L)₂·2H₂O, respectively where M = Ag, M′ = Cu, Au, Zn and Hg and M″ = Fe and Co, ligand metal ratios were also confirmed by monovariation method and Job’s method of continuous variation. Molar conductance values suggest the non ionic nature of the complexes. The tentative structure assigned to the complexes on the basis of stoichiometry and analytical data were further supported by spectral studies viz; IR, NMR, magnetic susceptibility and electronic spectra. A preliminary attempt has also been made to compare the potencies of metal complexes with parent drug. The Cu and Ag complexes are giving encouraging results. Particle size studies further suggest that the drug molecule undergoes reduction in size on complexation.     

Active aeroelastic control of aircraft composite wings impacted by explosive blasts

In this paper, the dynamic aeroelastic response and the related robust control of aircraft swept wings exposed to gust and explosive type loads are examined. The structural model of the wing is in the form of a thin/thick-walled beam and incorporates a number of non-standard effects, such as transverse shear, material anisotropy, warping inhibition, the spanwise non-uniformity of the cross-section, and the rotatory inertias. The circumferentially asymmetric stiffness lay-up configuration is implemented to generate preferred elastic couplings, and in this context, the implications of the plunging–twist elastic coupling and of warping inhibition on the aeroelastic response are investigated. The unsteady incompressible aerodynamic theory adopted in this study is that by von-Kármán and Sears, applicable to arbitrary small motion in the time domain. The considered control methodology enabling one to enhance the aeroelastic response in the subcritical flight speed range and to suppress the occurrence of the flutter instability is based on a novel control approach that is aimed to improve the robustness to modeling uncertainties and external disturbances. To this end, a combined control based on Linear Quadratic Gaussian (LQG) controller coupled with the Sliding Mode Observer (SMO) is designed and its high efficiency is put into evidence.