New Copper(II) Complexes Containing 2-Furoic Hydrazide and 5-Nitro-2-Furoic Hydrazide Ligands: Synthesis,Thermal, Magnetic and Spectroscopic Characterization

Two new copper(II) complexes, [Cu₂(L¹)₄(H₂O)₂](SO₄)₄· 2H₂O and [Cu(L²)₂(H₂O)₂]SO₄, were isolated containing 2-furoic hydrazide and 5-nitro-2-furoic hydrazide ligands, respectively. The complexes were characterized by thermal, magnetic and spectroscopic techniques, showing a distorted tetragonal environment around the metal ion. Compound (1), containing 2-furoic hydrazide as the ligand, appears to be dimeric in the solid state, with substituted hydrazine acting as a bidentate bridging ligand. On the contrary, a monomeric species was observed with the 5-nitro-2-furoic hydrazide ligand, probably in the cis configuration, for compound (2). Magnetic measurements for the binuclear copper(II) complex (1) were carried out at low temperatures, in the 2–300 K range, and a magnetic field of 500 G, indicating that besides an intramolecular ferromagnetic interaction between the two Cu(II) centers, for which J/k = 1.07 K, further weak antiferromagnetic interactions between adjacent dimers, with Jz/k =–0.95 K, should be taken into account. However, in MeOH/H₂O solution, evidence of equilibria involving the dimer (1) and the corresponding mononuclear cis and trans species was obtained from e.p.r. spectra.     

Effects of applied voltage on water at a gold electrode interface from ab initio molecular dynamics

Electrode–water interfaces under voltage bias demonstrate anomalous electrostatic and structural properties that are influential in their catalytic and technological applications. Mean-field and empirical models of the electrical double layer (EDL) that forms in response to an applied potential do not capture the heterogeneity that polarizable, liquid-phase water molecules engender. To illustrate the inhomogeneous nature of the electrochemical interface, Born–Oppenheimer ab initio molecular dynamics calculations of electrified Au(111) slabs interfaced with liquid water were performed using a combined explicit–implicit solvent approach. The excess charges localized on the model electrode were held constant and the electrode potentials were computed at frequent simulation times. The electrode potential in each trajectory fluctuated with changes in the atomic structure, and the trajectory-averaged potentials converged and yielded a physically reasonable differential capacitance for the system. The effects of the average applied voltages, both positive and negative, on the structural, hydrogen bonding, dynamical, and vibrational properties of water were characterized and compared to literature where applicable. Controlled-potential simulations of the interfacial solvent dynamics provide a framework for further investigation of more complex or reactive species in the EDL and broadly for understanding electrochemical interfaces in situ.

Ab initio molecular dynamics of an aqueous electrode interface reveal the electrostatic, structural, and dynamic effects of quantifiable voltage biases on water.     

Simultaneous determination of caffeine, theobromine, and theophylline by high-performance liquid chromatography

This work relates the development of an analytical methodology to simultaneously determine three methylxanthines (caffeine, theobromine, and theophylline) in beverages and urine samples based on reversed-phase high-performance liquid chromatography. Separation is made with a Bondesil C18 column using methanol-water-acetic acid or ethanol-water-acetic acid (20:75:5, v/v/v) as the mobile phase at 0.7 mL/min. Identification is made by absorbance detection at 273 nm. Under optimized conditions, the detection limit of the HPLC method is 0.1 pg/mL for all three methylxanthines. This method is applied to urine and to 25 different beverage samples, which included coffee, tea, chocolate, and coconut water. The concentration ranges determined in the beverages and urine are: < 0.1 pg/mL to 350 microg/mL and 3.21 microg/mL to 71.2 microg/mL for caffeine; < 0.1 pg/mL to 32 microg mL and < 0.1 pg/mL to 13.2 microg/mL for theobromine; < 0.1 pg/mL to 47 microg/mL and < 0.1 pg/mL to 66.3 microg/mL for theophylline. The method proposed in this study is rapid and suitable for the simultaneous quantitation of methylxanthines in beverages and human urine samples and requires no extraction step or derivatization.     

Formal syntheses of (+/-)-pinnaic acid and (+/-)-halichlorine

[chemical reaction: see text]. Concise formal syntheses of marine alkaloids (+/-)-pinnaic acid (1) and (+/-)-halichlorine (2) have been accomplished from a common intermediate. The syntheses illustrate the utility of selective olefin cross metathesis methodologies for the elaboration of advanced synthetic intermediates in complex molecule synthesis.     

Thermal study of TiO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> yellow ceramic pigment obtained by the Pechini method

TiO₂–CeO₂ oxides for application as ceramic pigments were synthesized by the Pechini method. In the present work the polymeric network of the pigment precursor was studied using thermal analysis. Results obtained using TG and DTA showed the occurrence of three main mass loss stages and profiles associated to the decomposition of the organic matter and crystallization. The kinetics of the degradation was evaluated by means of TG applying different heating rates. The activation energies (E _a) and reaction order (n) for each stage were determined using Horowitz–Metzger, Coats–Redfern, Kissinger and Broido methods. Values of E _a varying between 257–267 kJ mol^–1 and n=0–1 were found. According to the kinetic analysis the decomposition reactions were diffusion controlled.     

Oligosaccharide synthesis with glycosyl phosphate and dithiophosphate triesters as glycosylating agents

Described is an efficient one-pot synthesis of alpha- and beta-glycosyl phosphate and dithiophosphate triesters from glycals via 1,2-anhydrosugars. Glycosyl phosphates function as versatile glycosylating agents for the synthesis of beta-glucosidic, beta-galactosidic, alpha-fucosidic, alpha-mannosidic, beta-glucuronic acid, and beta-glucosamine linkages upon activation with trimethylsilyl trifluoromethanesulfonate (TMSOTf). In addition to serving as efficient donors for O-glycosylations, glycosyl phosphates are effective in the preparation of S-glycosides and C-glycosides. Furthermore, the acid-catalyzed coupling of glycosyl phosphates with silylated acceptors is also discussed. Glycosyl dithiophosphates are synthesized and are also used as glycosyl donors. This alternate method offers compatibility with acceptors containing glycals to form beta-glycosides. To minimize protecting group manipulations, orthogonal and regioselective glycosylation strategies with glycosyl phosphates are reported. An orthogonal glycosylation method involving the activation of a glycosyl phosphate donor in the presence of a thioglycoside acceptor is described, as is an acceptor-mediated regioselective glycosylation strategy. Additionally, a unique glycosylation strategy exploiting the difference in reactivity of alpha- and beta-glycosyl phosphates is disclosed. The procedures outlined here provide the basis for the assembly of complex oligosaccharides in solution and by automated solid-phase synthesis with glycosyl phosphate building blocks exclusively or in concert with other donors.     

Crosslinked polyethylene foams, via EB radiation

Polyethylene foams, produced by radio-induced crosslinking, show a smooth and homogeneous surface, when compared to chemical crosslinking method using peroxide as crosslinking agent. This process fosters excellent adhesive and printability properties. Besides that, closed cells, intrinsic to theses foams, imparts opitmum mechanical, shocks and insulation resistance, indicating these foams to some markets segments as: automotive and transport; buoyancy, flotation and marine: building and insulation: packaging: domestic sports and leisure goods. We were in search of an ideal foam, by adding 5 to 15% of blowing agent in LDPE. A series of preliminary trials defined 203° C as the right blowing agent decomposition temperature. At a 22.7 kGy/dose ratio, the lowest dose for providing an efficient foam was 30 kGy, for a formulation comprising 10% of azodicarbonamide in LDPE, within a 10 minutes foaming time.     

Development and evaluation of a GC/FID method for the analysis of free amino acids in quince fruit and jam.

A GC/FID methodology for determination of twenty-one free amino acids in quince fruit (pulp and peel) and jam is described. The sample preparation was simple, involving a SCX Solid-Phase Extraction (SPE) purification step and a fast derivatization with ethyl chloroformate for gas chromatographic analysis. The chromatographic separation was achieved using a CP-Sil 19 CB wcot fused-silica capillary column. Under the chosen conditions, with temperature and pressure programming, this capillary column was able to separate all the amino acids not only in a short time but also with good separation. The GC/FID procedure is rapid, sensitive, reproducible and accurate. The detection limit values for amino acids were low, between 0.004 and 0.115 microg/mL, and the method was precise. As a general rule, the recovery values were high. Due to its rapidity and low cost, this technique can be useful in the quality control of quince products.     

Direct voltammetric determination of Mo(VI) in plants: the need for a multivariate study of interferences

A multivariate modelling procedure using a second order composite design showed that the adsorptive stripping voltammetry (AdSV) technique used for molybdenum determination in a N,N-dimethylformamide (DMF)-ethanol-water homogeneous ternary solvent system (HTSS) using α-benzoinoxime (αBO) as the complexing agent and a sodium acetate-acetic acid buffer as the supporting electrolyte is much more tolerant to the presence of phosphorous (as phosphate) and iron than it could be presumed. Instead of the concentration ratios of P/Mo=100 and Fe/Mo=500, determined by univariate experiments, these values were respectively raised to 97,500 and 4200 when the phosphate and Fe(III) levels are varied simultaneously from 0.625 to 2.500 and from 0.006 to 0.150 mg l⁻¹, respectively, in the voltammetric cell, keeping the molybdenum concentration constant at 3.00 μg l⁻¹. This allowed us to propose a straightforward AdSV-HTSS procedure for the determination of Mo(VI) in plants. The AdSV results compared favourably with those obtained by using graphite furnace atomic absorption spectrometry (GFAAS) and with the results of samples from the International Plant-Analytical Exchange (IPE) programme of Wageningen University (The Netherlands).     

Simultaneous spectrophotometric determination of nickel and iron in copper-base alloy with bromo-PADAP

The reaction of nickel (II) with Br-PADAP, in the presence of tergitol NPX surfactant, forms a complex with absorption peaks at 520 and 560 nm. The iron(II)-Br-PADAP system at the same conditions forms a chelate with absorption peaks at 560 and 748 nm. This allows the simultaneous spectrophotometric determination of nickel and iron by measuring the absorbance at 560 and 748 nm. The proposed method, at ph 4.0-5.7, shows a molar absorptivity of 1.22 x 10(5)l . mole(-1) . cm(-1) for nickel at 560 nm and 8.20 x 10(4)l . mole(-1) . cm(-1) at 560 nm and 3.35 x 10(4)l . mole(-1) . cm(-1) at 748 nm for iron(II). Beer's law is obeyed up to 0.40 mu/ml of nickel(II) and up to 0.65 mu/ml of iron(II). Thiosulphate as masking agent allows the simultaneous determination of iron and nickel in the presence of high concentrations of copper. The ethylene glycol 2-(2-amino-ethyl) tetracetic acid provides the elimination of many other interferences. The method has been applied successfully to the simultaneous determination of nickel and iron in reference samples.