Structural and spectroscopic characterization of Al2−x Cr x O3 powders obtained by polymeric precursor method

Al₂O₃ and Al_2−x Cr _x O₃ (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL^*a^*b^* color data). The obtained results allow to identify the γ-Al₂O₃ to α-Al₂O₃ phase transition. The single-phase α-Al₂O₃ powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al_2−x Cr _x O₃ are related to the γ to α-Al₂O₃ phase transition and the temperature and time range for such transition depends on the chromium content.     

New alkyl-cobalt(III) complexes containing chiral centers in the chelating system

The complex mer-[Co(III)(L(1)Npy)(2)](+) (1') where the L(1)Npy(-) is the tridentate 3-[(2-pyridyl)methylimino]butan-2-one oximate ligand, gives alkyl-cobalt derivatives after reduction with NaBH(4)/Pd(2+) to the Co(I) and alkylation. The formation of the cobalt-carbon bond is accompanied by the reduction to the amino form of one or both imino ligands (depending on the experimental conditions) initially present in 1'. In one series of experiments, complexes of the type fac-[RCo(III)(L(1)Npy)(H-L(1)NHpy)](+) (R = Me, i-Pr, CH(2)Cl, CH(2)Br, CH(2)CF(3), and Bz) were obtained, in which only one of the two ligands was reduced to the amino form (H-L(1)NHpy). The saturation of one azomethine group causes the products to assume a fac configuration and induces the formation of one asymmetric carbon and one asymmetric nitrogen center in the chelating system. When an excess of reducing agent is used, both azomethine groups may be saturated, causing the introduction of one pair of chiral carbons and one pair of chiral nitrogens. Two isomers of the methyl derivative [MeCo(III)(L(1)NHpy)(H-L(1)NHpy)](+) were isolated. The X-ray analysis reveals that these isomers differ from one another in configuration of the C and N chiral centers. Possible reaction mechanisms leading to these different types of complexes are proposed.     

Determination of phenolic acids in olive oil by capillary electrophoresis

A CZE method for the separation and quantitation of phenolic acids (cinnamic, syringic, p-coumaric, vanillic, caffeic, 3,4-dihydroxyphenylacetic, protocatechuic), extracted from extra virgin olive oil, was developed. The sample preparation involved the LLE and SPE extraction methods. CE separation was performed in a fused silica capillary of I.D.= 50microm using as a BGE 40 mM borate buffer at pH=9.2. The separation voltage was 18kV with corresponding current of 27-28 microA. Detection was accomplished with UV-detector at lambda=200nm. The proposed method was fully validated. A good repeatability of migration time (RSD% ranged from 0.81 to 1.63) and of corrected peak area (RSD% from 2.89 to 5.77) was obtained. The linearity of detector response in the range from 5 to 50 ppm was checked, obtaining the correlation coefficient R2 values in the range: 0.9919-0.9997. Some phenolic acids in real oil samples were detected and quantified with the proposed method.     

On-line identification of sugarcane (Saccharum officinarum L.) methoxyflavones by liquid chromatography-UV detection using post-column derivatization and liquid chromatography-mass spectrometry

Sugarcane (Saccharum officinarum L., Gramineae) bagasse and leaves were investigated for their flavonoid content and transgenic sugarcane ("Bowman-Birk" and "Kunitz") was compared with non-modified ("control") plants. Analyses were carried out by high-performance liquid chromatography coupled to diode array UV detection (LC/UV), also using post-column addition of shift reagents, and tandem MS (atmospheric pressure chemical ionization-MS/MS and collision-induced dissociation-MS). On-line UV and MS data demonstrated the presence of methoxyflavone glycosides and aglycones in a total of seven compounds. Three naturally occurring flavones glycosides and two unusual erythro- and threo-diastereoisomeric flavolignan 7-O-glucosides were identified together with their aglycones.     

Atmospheric pressure ionization mass spectrometry of purine and pyrimidine markers of inherited metabolic disorders

Purines and pyrimidines are of interest owing to their significance in processes in living organisms. Mass spectrometry is a promising analytical tool utilized in their analysis. Two atmospheric pressure ionization (API) methods (electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI)) in both negative and positive modes applied to selected purine and pyrimidine metabolites (markers of inherited metabolic disorders) were studied. APCI is less sensitive to alkali metal cations present in a sample and offers higher response than ESI for studied compounds. Both of the techniques afford quasi-molecular ions, but fragmentation also occurs to a certain extent. However, the application of collision-induced dissociation of quasi-molecular ions is essential to confirm a certain metabolite in a sample. Fragmentation of both positive and negative ions was evaluated using multi-stage mass spectrometric experiments. Typical neutral losses correspond to molecules NH(3), H(2)O, HCN, CO, H(2)NCN, HNCO and CO(2). The ion [NCO](-) arises in the negative mode. The cleavage of the glycosidic C-N bond is characteristic for relevant metabolites. Other neutral losses (CH(2)O, C(2)H(4)O(2) and C(3)H(6)O(3)) originate from fragmentation of the glycosidic part of the molecules. In addition to fragmentation, the formation of adducts of some ions with applied solvents (H(2)O, CH(3)OH) was observed. The composition of the solution infused into the ion source affects the appearance of the mass spectra. Tandem mass spectra allow one to distinguish compounds with the same molecular mass (uridine-pseudouridine and adenosine-2'-deoxyguanosine). Flow injection analysis APCI-MS/MS was tested on model samples of human urines corresponding to adenosine deaminase deficiency and xanthine oxidase deficiency. In both cases, the results showed potential diagnostic usefulness.     

A neutral complex of an azino–DTDAF compound with TCNQ

In the crystal structure of the title 1:1 complex, ethyl 2‐{[5‐(ethoxy­carbonyl)‐2,3‐dihydro‐3,4‐di­methyl‐1,3‐thia­zol‐2‐yl­idene]­hydrazono}‐2,3‐di­hydro‐3,4‐di­methyl‐1,3‐thia­zole‐5‐carboxyl­ate–7,7,8,8‐tetra­cyano‐p‐quinodi­methane (1/1), C₁₆H₂₂N₄O₄S₂·C₁₂H₄N₄, the planar donor and tetra­cyano‐p‐quinodi­methane (TCNQ) mol­ecules are each located on inversion centres and are stacked alternately. The bond lengths indicate that, in this complex, the donor and acceptor are neutral, as confirmed by IR investigation.     

Reactivity of radicals generated on irradiation of trans-[Ru(NH3)4(NO2)P(OEt)3](PF6)

The electronic absorption spectrum of trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+) in aqueous solution is characterized by a strong absorption band at 334 nm (lambda(max) = 1800 mol(-1) L cm(-1)). On the basis of quantum mechanics calculations, this band has been assigned to a MLCT transition from the metal to the nitro ligand. Molecular orbital calculations also predict an LF transition at 406 nm, which is obscured by the intense MLCT transition. When trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+) in acetonitrile is irradiated with a 355 nm pulsed laser light, the absorption features are gradually shifted to represent those of the solventocomplex trans-[Ru(NH(3))(4)(solv)(P(OEt)(3)](2+) (lambda(max) = 316 nm, epsilon = 650 mol(-1) L cm(-1)), which was also detected by (31)P NMR spectroscopy. The net photoreaction under these conditions is a photoaquation of trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+), although, after photolysis, the presence of the nitric oxide was detected by differential pulse polarography. In phosphate buffer pH 9.0, after 15 min of photolysis, a thermal reaction resulted in the formation of a hydroxyl radical and a small amount of a paramagnetic species as detected by EPR spectroscopy. In the presence of trans-[Ru(NH(3))(4)(solv)P(OEt)(3)](2+), the hydroxyl radical initiated a chain reaction. On the basis of spectroscopic and electrochemical data, the role of the radicals produced is analyzed and a reaction sequence consistent with the experimental results is proposed. The 355 nm laser photolysis of trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+) in phosphate buffer pH 7.4 also gives nitric oxide, which is readily trapped by ferrihemeproteins (myoglobin, hemoglobin, and cytochrome C), giving rise to the formation of their nitrosylhemeproteins(II), (NO)Fe(II)hem.     

Oxidation of methanol at the network film of polyoxometallate-linked ruthenium-stabilized platinum nanoparticles

We explore here the ability of ruthenium hydroxo species to undergo spontaneous deposition on Pt nanoparticles and to form colloidal solutions of oxoruthenium-protected (-stabilized) nanoparticles of Pt. These particles can be spontaneously attracted to carbon substrates, and they form ultrathin self-assembled films. Fabrication of the multilayer network films on electrodes has been achieved by linking the positively charged oxoruthenium-covered Pt clusters with heteropolyanions of tungsten. By repeated alternate treatments in a solution of phosphododecatungstate (PW₁₂O₄₀^3–) and in a colloidal suspension of oxoruthenium-protected (-stabilized) Pt nanoparticles, the film thickness can be increased systematically (layer by layer) to form stable three-dimensional assemblies on carbon electrodes. It is apparent from cyclic voltammetric and chronoamperometric measurements (that were performed at 20 and 60 °C) that the resulting hybrid films show attractive properties towards the oxidation of methanol at fairly low potentials (0.25–0.4 V versus the saturated calomel electrode). With approximately the same loading of oxoruthenium-covered Pt nanoparticles and under analogous conditions, linking or derivatizing the nanoparticles with phosphotungstate leads to the systems higher electrocatalytic activity. It is possible that, in addition to ruthenium hydroxo species, PW₁₂O₄₀^3– exhibits an activating effect on dispersed Pt particles. An alternative explanation may involve the possibility of different morphologies of the catalytic films in the presence and absence of phosphotungstate anions.Dedicated to Zbigniew Galus on the occation of his 70th birthday     

Studies on the Flash Vacuum Thermolysis of Thiones of Selected N‐, O‐, and S‐Heterocycles

Thermal decomposition of thiones of selected N‐, O‐ and S‐heterocycles under flash vacuum thermolysis conditions was investigated. In the case of six‐membered 4H‐3,1‐benzoxathiin‐4‐thione 6 , the course of the reaction depended on the substitution pattern at C(2) (Scheme 3). Thus, the 2‐unsubstituted derivative 6a led to the unstable product 2 , which upon treatment with MeOH was converted quantitatively into methyl 2‐mercaptobenzoate ( 7 ). The analogous thermolysis of the 2,2‐dimethyl derivative 6b yielded 2‐methyl‐4H‐1‐benzothiopyran‐4‐thione ( 8 ) as a sole product. In the case of thiophthalide derivatives 15 , a thermal rearrangement in the gas phase leading to the corresponding benzo[c]thiophen‐1(3H)‐ones 16 in high yields was observed (Scheme 6). Unexpectedly, thionation of 1,3‐oxathiolan‐5‐one 17 with Lawesson's reagent under standard conditions led to 1,2‐dithietane derivative 19 , which, after the gas‐phase thermolysis, underwent a ring enlargement to yield 3H‐1,2‐dithiole 20 (Scheme 7). The six‐membered 4H‐1,3‐benzothiazine‐4‐thione 21 was shown to give three products: phenanthro[9,10‐c]‐1,2‐dithiete ( 22 ), 3H‐1,3‐benzodithiole‐3‐thione ( 23 ), and N‐(3H‐1,2‐benzodithiol‐3‐ylidene)prop‐2‐en‐1‐amine ( 24 ) (Scheme 8). The latter is the product of the initial reaction, whereas 22 and 23 are postulated to be formed as secondary products of the conversion of the intermediate 6‐(thioxomethylene)cyclohexa‐2,4‐diene‐1‐thione ( 26 ) (Schemes 9 and 10).