Trinuclear copper(II) complexes derived from Schiff-base ligands based on a 6-amino-6-deoxyglucopyranoside: structural and magnetic characterization

The trinuclear copper(II) complexes ([CuL1)(mu-ac)Cu(mu-ac)CuL1) (1) and ([CuL2)(mu-ac)Cu(mu-ac)CuL2) (2) of the tridentate aminosaccharide-derived Schiff-base ligands H2L1 [6-N-(salicylidene)amino-6-deoxy-1,2,3-tri-O-methyl-alpha-D-glucopyranoside] and H2L2 [6-N-(3,5-di-tert-butylsalicylidene)amino-6-deoxy-1,2,3-tri-O-methyl-alpha-D-glucopyranoside] were synthesized and structurally characterized. The trinuclear complex units can be described as two terminal copper-ligand moieties bridged by a central copper acetate moiety, with the Cu centers arranged in a triangular fashion. IR and UV/vis spectroscopic studies strongly indicate that the trinuclear structure is maintained in a methanolic solution. The temperature dependence of the magnetic susceptibility of both complexes shows a moderate antiferromagnetic coupling and can be well interpreted by applying a symmetric Cua-Cub-Cua' model with linear spin topology. The fit of the magnetic data affords coupling constants J of -34 and -24 cm(-1) for 1 and 2, respectively [H = -J(SaSb + SbSa')]. For mu-alkoxo-mu-acetato-bridged copper(II) complexes with a large dihedral angle between the adjacent coordination planes, as found in 1 and 2, such an antiferromagnetic coupling is unusual. However, density functional theory calculations of 2 using BP86, B3LYP*, and B3LYP density functionals confirmed a symmetric doublet ground state.     

Mean values of multiplicative functions

Let f(n) be a totally multiplicative function such that | ƒ (n)|⪯ 1 for all n, and let F(s) = ∑ ∞ n=1 ƒ(n)n —∞ be the associated Dirichlet series. A variant of Halász"s method is developed, by means of which estimates for ∑ N n=1 ƒ(n)/n are obtained in terms of the size of | F(s) | for s near 1 with ℜs >1. The result obtained has a number of consequences, particularly concerning the zeros of the partial sum U N (s) =∑ N n=1 n-s s of the series for the Riemann zeta function.     

Nucleophilic addition to dimethylvinylphosphine sulfide as a convenient route to polydentate ligands containing the 2-dimethylphosphinoethyl unit

The synthesis of a range of new phosphine-containing polydentate ligands has been achieved by addition of sulfur and nitrogen nucleophiles to dimethylvinylphosphine sulfide, followed by reduction of the resulting phosphine sulfides with lithium aluminium hydride.     

Determination of 2,4-dichlorophenoxyacetic acid and silvex in water with high-performance liquid chromatography

The determination of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-(2,4,5-trichlorophenoxy) propionic acid (Silvex) in water at the μg l^-1 level is based on liquid/ liquid extraction and high-performance liquid chromatography. Sample preparation for water samples is simplified. The ranges of linear response are 50 ng to 60 μg for 2,4-D and 30 ng to 60 μg for Silvex. The average recoveries of 2,4-D at the 10 μg l^-1 and 1 μg l^-1 levels are 91% and 120%, respectively, while the average recoveries of Silvex at the 10 μg l^-1 and 1 μg l^-1 levels are 85% and 110%, respectively.     

New synthesis and insight into the structure of blue ultramarine pigments

A new and easy method for preparing blue sodalite pigments which involves high-temperature calcination of sodalite samples synthesized with aluminum sulfate and an organic template, is presented. Calcination generated the S(3)(-) and S(2)(-) radicals, and the effects of the Al/Si ratio and the calcination temperature on the nature and amounts of the radicals were examined. The radicals were characterized in detail by continuous wave and pulsed EPR at X- and W-band frequencies (approximately 9 and 95 GHz, respectively) complemented by UV-vis measurements. The high-field electron-paramagnetic resonance (EPR) measurements allowed us to clearly resolve the g anisotropy of S(3)(-) and W-band electron nuclear double resonance (ENDOR) measurements detected strong coupling with extra-framework (23)Na cations and weak coupling with framework (27)Al. On the basis of the spectroscopic results and density functional theory (DFT) calculations of the g-tensors of S(3)(-) and S(2)(-) radicals, the EPR signals were attributed to three different radicals, all with the open structure C(2v), that are located within the sodalite beta cages. While two of these radicals are well isolated, the third one is associated with an exchange-narrowed signal originating from S(3)(-) radicals in nearby sodalite cages.     

Parabolic quantitative structure-activity relationships and photodynamic therapy: application of a three-compartment model with clearance to the in vivo quantitative structure-activity relationships of a congeneric series of pyropheophorbide derivatives used as photosensitizers for photodynamic therapy

An open three-compartment pharmacokinetic model was applied to the in vivo quantitative structure-activity relationship (QSAR) data of a homologous series of pyropheophorbide photosensitizers for photodynamic therapy (PDT). The physical model was a lipid compartment sandwiched between two identical aqueous compartments. The first compartment was assumed to clear irreversibly at a rate K0. The measured octanol-water partition coefficients, P(i) (where i is the number of carbons in the alkyl chain) and the clearance rate K0 determined the clearance kinetics of the drugs. Solving the coupled differential equations of the three-compartment model produced clearance kinetics for each of the sensitizers in each of the compartments. The third compartment was found to contain the target of PDT. This series of compounds is quite lipophilic. Therefore these drugs are found mainly in the second compartment. The drug level in the third compartment represents a small fraction of the tissue level and is thus not accessible to direct measurement by extraction. The second compartment of the model accurately predicted the clearance from the serum of mice of the hexyl ether of pyropheophorbide a, one member of this series of compounds. The diffusion and clearance rate constants were those found by fitting the pharmacokinetics of the third compartment to the QSAR data. This result validated the magnitude and mechanistic significance of the rate constants used to model the QSAR data. The PDT response to dose theory was applied to the kinetic behavior of the target compartment drug concentration. This produced a pharmacokinetic-based function connecting PDT response to dose as a function of time postinjection. This mechanistic dose-response function was fitted to published, single time point QSAR data for the pheophorbides. As a result, the PDT target threshold dose together with the predicted QSAR as a function of time postinjection was found.     

Effect of sampler and skimmer orifice size on analyte and analyte oxide signals in inductively coupled plasma-mass spectrometry

The size of the orifice in the sampling cone of the interface in an inductively coupled plasma-mass spectrometer (ICP-MS) has a major impact on signal characteristics. In particular, for oxide forming elements, the MO⁺/M⁺ ratio is very dependent on orifice size. This is illustrated for a range of elements (La, Ho and Yb) as a function of nebulizer gas flow and for sampling cone orifice sizes ranging from 0.51 to 0.94 mm. In addition the size of the sampling orifice changes the shape of the signal vs nebulizer flow rate plot and this is illustrated. A curious and important observation is that the signal dependence on nebulizer flow rate is essentially identical for all analytes at any one orifice size if the analyte and analyte oxide (when observed) responses are summed. This indicates that the sampling orifice is the primary location of oxide formation in ICP-MS. Finally the effect of the skimmer orifice diameter on analyte signals is also illustrated for orifice diameters of 0.76, 0.89 and 1.0 mm in conjunction with sampling orifice sizes ranging from 0.51 to 0.94 mm.     

Plasticity induced by nanoparticle dispersions in bulk metallic glasses

We show room temperature plasticity in several ZrCu-based bulk metallic glasses (BMG) after dispersions of crystalline nanoparticles were generated prior to mechanical testing. BMGs are heated in synchrotron light in transmission such that annealing can be interrupted at the very first detection of nucleation of the crystallites. Effect of embedded nanocrystals on the mechanical properties of BMG-Composites was investigated by compressive testing. When nanocrystal dispersions were generated, zirconium-copper-based BMGs that initially showed no plastic deformation prior to fracture, exhibited ductile behavior in compression with about 10% deformation.     

Investigation of Fe structural environments in “leucite”-type framework silicates using a combination of Mössbauer and X-ray absorption spectroscopies

Synthetic iron-containing leucite-type phases have been studied using⁵⁷Fe Mössbauer spectroscopy in combination with X-ray absorption spectroscopy (XAFS and XANES). The Mössbauer and XAS data confirm that both Fe²⁺ and Fe³⁺ occupy tetrahedrally coordinated framework sites in the synthetic phases. In addition, information on Fe²⁺/Fe³⁺ ratios, cation site occupancies and first shell bond lengths has also been obtained.