Synthesis and spectroscopic properties of a new bipyridine-bipyrazoyl(pyridine)-thiocyanato-ruthenium(II) complex

The complex [Ru(II)(dcbpyH₂)(bdmpp)NCS](PF₆) (1) (where dcbpyH₂ is 2,2′-bipyridine-4,4′-dicarboxylic acid, bdmpp is 2,6-bis(3,5-dimethyl-N-pyrazoyl)pyridine,) is synthesized and characterized extensively by ¹H NMR and ¹³C NMR 1D and 2D, mass spectroscopy, cyclic voltammetry, electronic absorption spectroscopy and IR. The half-wave potential of the Ru(II)/Ru(III) redox couple was measured at E_1/2=+0.795 V versus Ag/AgCl in CH₃CN. The complex presents three intense metal-to-ligand charge transfer (MLCT) (d_M→π_L*) absorption bands centered at 383 (=21 300 M⁻¹ cm⁻¹), 432 (=22 400 M⁻¹ cm⁻¹) and 475 nm (=23 400 M⁻¹ cm⁻¹), respectively. The absorbance is extremely strong between 400 and 500 nm and even at 620 nm, the extinction coefficient is still high (=3768 M⁻¹ cm⁻¹). The strong π-acceptor property of the trans-isothiocyanate ligand compared with the Cl⁻ ligand is probably the cause of the blue-shift observed in complex 1. These properties make the complex potentially promising for the photosensitization process. The incorporation of TiO₂ photoelectrodes derivatized with this complex into a solar cell using a composite polymer/inorganic oxide solid-state electrolyte confirmed its sensitizing ability. Incident monochromatic photon-to-current conversion efficiency (IPCE) values of about 30% and overall energy conversion efficiency (η) of 1.7% were obtained.     

Performance of Pt/SnO2 catalyst in the gas phase hydrogenation of crotonaldehyde

Selective hydrogenation of crotonaldehyde was performed on 5% Pt/SnO₂ catalysts, in gaseous phase, at atmospheric pressure, at 353 K. Two types of catalyst were prepared using H₂PtCl₆ and Pt(NH₃)₄(NO₃)₂ as metallic precursors. Their performances were compared as a function of the reduction temperature and both catalysts were characterised by X-ray diffraction after different reduction treatments. Using the ex-chloride catalyst, the selectivity values to the unsaturated alcohol (UOL) resulted into a maximum of 45% while a selectivity as high as 70–77%, in 0–25% conversion range, was achieved by using ex-nitrate catalyst reduced at 443 K. The formation of Pt–Sn alloy on the metal particles of platinum was thought to be necessary to improve the activity and the selectivity on these catalysts. In the contrast, a presence of PtSn₂ formed at a reduction temperature higher than 473 K led to a decrease of activity and selectivity.     

Stationary-phase effects in gradient high-performance liquid chromatography

The type of the stationary phase for reversed-phase liquid chromatography significantly affects the sample polarity range that can be covered using gradients of organic solvents in water. The polarity range available for gradient separations of samples containing compounds differing in the lipophilic parts of the molecules can be characterized by "gradient lipophilic capacity", Pl, based on the retention of standard compounds with a repeat lipophilic structural unit, such as a methylene group. The gradient lipophilic capacity is also suitable to characterize the separation possibilities of the columns in non-aqueous reversed-phase gradient elution of strongly non-polar compounds, such as triacylglycerols. In the same way, the suitability of various columns for reversed-phase gradient separations of oligomers can be characterized by "gradient oligomer capacity", as demonstrated in the example of oligo(ethylene glycols). To enable a comparison of the properties of stationary phases independent of column efficiency and dimensions, the gradient lipophilic capacity or the gradient oligomer capacity should be normalized for a "standard" column plate number, gradient range and volume (in column hold-up volume units). The gradient lipophilic capacity or the gradient oligomer capacity and the number of compounds that can be resolved during a gradient run decrease as the initial concentration of the strong solvent in the mobile phase increases and (or) the gradient time decreases. These quantities can be used to select a suitable column and to adjust the optimum gradient profile (the initial composition of the mobile phase and the gradient steepness) with respect to the time of analysis and the number of oligomers or other compounds with regular repeat structural groups that can be resolved during the gradient run.     

Complexes derived from the general copper(II)/maleamic acid/N,N′,N′′-chelate reaction systems: Synthetic,reactivity, structural and spectroscopic studies

The synthetic investigation of the Cu^II/maleamate(−1) ion (HL⁻)/N,N′,N′′-chelate general reaction system has allowed access to compounds [Cu₂(HL)₂(bppy)₂](ClO₄)₂·H₂O (1·H₂O), [Cu(HL)(bppy)(ClO₄)] (2) and [Cu(HL)(terpy)(H₂O)](ClO₄) (4) (bppy = 2,6-bis(pyrazol-1-yl)pyridine, terpy = 2,2′;6′,2′′-terpyridine). In the absence of externally added hydroxides, compound [Cu₂(L′)₂(bppy)₂](ClO₄)₂ (3) was obtained from MeOH solutions; L′⁻ is the monomethyl maleate(−1) ligand which is formed in situ via the Cu^II-assisted HL⁻ → L′⁻ transformation. In the case of tptz-containing (tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine) reaction systems, the Cu^II-assisted hydrolysis of tptz to pyridine-2-carboxamide (L1) afforded complex [Cu(L1)₂(NO₃)₂] (5). The crystal structures of 1–5 are stabilized by intermolecular hydrogen bonding and π–π stacking interactions. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the ligands.     

Wavelet expansions and asymptotic behavior of distributions

We develop a distribution wavelet expansion theory for the space of highly time-frequency localized test functions over the real line S₀(R)⊂S(R) and its dual space , namely, the quotient of the space of tempered distributions modulo polynomials. We prove that the wavelet expansions of tempered distributions converge in . A characterization of boundedness and convergence in is obtained in terms of wavelet coefficients. Our results are then applied to study local and non-local asymptotic properties of Schwartz distributions via wavelet expansions. We provide Abelian and Tauberian type results relating the asymptotic behavior of tempered distributions with the asymptotics of wavelet coefficients.     

Raman studies and optical properties of some (PbO)x(Bi2O3)0.2(B2O3)0.8−x glasses

Five (PbO)_x(Bi₂O₃)_0.2(B₂O₃)_0.8−x glasses, where x = 0, 0.2, 0.3, 0.4 and 0.6, were prepared. The dilatometric glass transition temperature (T_g) was found in the region 470 (x = 0)≥ T_g ( °C) ≥ 347 (x = 0.6), and the density (ρ) varied within 4.57 (x = 0) ≤ ρ (g/cm³) ≤ 8.31 (x = 0.6). Raman spectra indicated the conversion of BO₃ to BO₄ entities for low x values but for x > 0.3, namely, for x → 0.6, back‐conversion occurred, most probably. From the measurements of the optical transmission on very thin bulk samples, the room temperature optical gap values (E_g) were determined to be in the range 4.03 (x = 0)≥ E_g (eV) ≥ 3.08 (x = 0.6). The temperature (T) dependence of the optical gap (E_g(T)) in the region 300 ≤ T(K) ≤ 600 was examined and approximated by a linear relationship of the form of E_g(T) = E_g(0)− γT, where γ × 10⁻⁴(eV/K) varied from 5.1 to 6.8. The non‐linear refractive index (n₂) was estimated from the optical gap values and it was found to correspond to the n₂ values calculated from the experimental third‐order non‐linear optical susceptibility taken from the literature. Copyright © 2008 John Wiley & Sons, Ltd.     

Evaluation of automated direct sample introduction with comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry for the screening analysis of dioxins in fish oil

An automated direct sample introduction technique coupled to comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (DSI-GC x GC/TOF-MS) was applied for the development of a relatively fast and easy analytical screening method for 17 polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and 4 non-ortho polychlorinated biphenyls (PCBs) in fish oil. Comparison of instrumental performance between DSI-GC x GC/TOF-MS and the traditional gas chromatographic high resolution mass spectrometric (GC-HRMS) method showed good agreement of results for standard solutions analyzed in blind fashion. Relatively high tolerance of the DSI technique for lipids in the final extracts enabled a streamlined sample preparation procedure that only required gel permeation chromatography (GPC) and solid-phase extraction (SPE) cleanup with graphitized carbon black. The sample size for the method was 2g of cod liver oil, which achieved limits of quantitation (LOQs) of 0.019-7.8 pg/g toxic equivalent quotients for the individual PCDD/Fs. Lower detection limits can be achieved by using larger sample size and scaling up the sample preparation procedure, but this adds to the labor, time, solvent consumption, and expense of the approach. However, the streamlined method yielded 0.94 pg/g and 2.3 pg/g LOQs for 2,3,7,8-tetrachloro dibenzofuran (TCDF) and 3,3',4,4',5-pentachloro biphenyl (CB126), which were sufficiently low for regulatory monitoring of 2g samples. Therefore, instead of congener specific analysis, this streamlined analytical screening method for TCDF and CB126 has the potential to monitor fish oil contaminated with dioxin and dioxin-like PCBs at or above current food safety limits. Acceptable recoveries for nearly all analytes at three different spiking levels in fish oil samples were achieved with good repeatability.