Thermal and spectroscopic investigation of new binuclear Pt(II) complexes with carboxylic acids

The thermal decomposition of the binuclear Pt(II) complexes with acetate, propionate, valerate and izovalerate ligands were studied by TG and DTA techniques. The Pt(II) complex with acetic acid (PtAA) was stable up to 343.15 K, Pt(II) complex with propionic acid (PtPrA) was stable up to 323.15 K, Pt(II) complex with valeric acid (PtVA) was stable up to T=313.15 K and Pt(II) complex with isovaleric acid (PtIvA) was stable up to 408.15 K. The PtAA complex was investigated again after a year by thermogravimetric analysis. After the thermal decomposition of the Pt(II) complexes with carboxylic acids, only in the PtVA complex and PtAA complex (investigated after a year) the final residue contains only platinum, while in the rest complexes the solid residue was a mixture of platinum and platinum carbides (PtC₂, Pt₂C₃).     

Palladium(II) complexes with 5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione

Two new palladium(II) complexes with 5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione(mpyh) were synthesized: cis-[Pd(mpyh)₂Cl₂]·H₂O and cis-[Pd(mpyh)₂Br₂]·2H₂O. The molecular formulae of the complexes were confirmed by elemental analysis, IR, ¹H NMR spectra and DTA study. The ligand is coordinated to the palladium ion with N-atom of the pyridine ring. The spectroscopic data indicate a square planar geometry with two N-pyridine atoms and two halogene anions in cis position. The final product of the thermal decomposition of cis-[Pd(mpyh)₂Cl₂]·H₂O is metallic Pd, whereas for cis-[Pd(mpyh)₂Br₂]·2H₂O the residue consists of metallic Pd and C. The cytotoxic effects of the complexes were examined in vitro on some human tumor cell lines. The cis-[Pd(mpyh)₂Cl₂]·H₂O proved to be more active as compared to the cis-[Pd(mpyh)₂Br₂]·2H₂O.     

A matrix-assisted laser desorption/ionization mass spectrometry approach to the lipid A from Mesorhizobium loti

The isolation, purification and analysis of the lipid A obtained from Mesorhizobium loti Ayac 1 BII strain is presented. Analysis of the carbohydrate moiety after acid hydrolysis by high-pH anion-exchange chromatography with pulse amperometric detection (HPAEC-PAD) showed the presence of glucosamine and galacturonic acid as the only sugar components. Gas chromatographic (GC) and GC/mass spectrometric (MS) analysis of the fatty acids revealed the presence of 3-OH-C12:0; 3-OH-C13:0; 3-OH-C20:0 and 27-OH-C28:0 among the major hydroxylated species. In addition, C16:0, C17:0, C18:0 and C 20:0 were shown as main saturated fatty acids. Different polyacylated species were evidenced by thin layer chromatography of lipid A, allowing the purification of two fractions. Ultraviolet matrix-assisted laser desorption/ionization time-of-flight (UV-MALDI-TOF) MS analysis with different matrices, in the positive- and negative-ion mode, was performed. The fast moving component revealed the presence of hexa-acylated species, varying in the fatty acid composition. Species containing three 3-OH fatty acids and a 27-OH-C28:0 fatty acid were observed. Individual ions within this family differ by +/-14 mass units. The slow moving component was enriched mainly in penta-acylated species. Among them, three subgroups were detected: the major one compatible with the sugar core bearing two 3-OH 20:0 fatty acids, a 3-OH 13:0 or a 3-OH 12:0 fatty acid, a 27-OH 28:0 fatty acid and one saturated fatty acid. Each signal differs in a C18:0 acyl unit from the corresponding hexa-acylated family. On the other hand, a subgroup bearing one 3-OH 20:0 fatty acid, one 27-OH 28:0 fatty acid and two non-polar fatty acids was shown. A minor subgroup compatible with structures containing two hydroxylated and three non-polar fatty acids was also detected. The results obtained showed that nor-harmane was an excellent matrix for charged lipid A structural studies in both, positive and negative ion modes.     

Quinone-sensitized steady-state photolysis of acetophenone oximes under aerobic conditions: kinetics and product studies

Oxidation of oximes via photosensitized electron transfer (PET) results in the formation of the corresponding ketones as the major product via oxime radical cations and iminoxyl radicals. The influence of electron-releasing and electron-accepting substituents on these reactions was studied. The observed substituent effect strongly supports formation of iminoxyl radicals from the oximes via an electron transfer-proton transfer sequence rather than direct hydrogen atom abstraction. Correlation of the relative conversion of the oximes with Hammett parameters shows that radical effects dominate for the meta-substituted acetophenone oximes (rho(rad)/rho(pol) = 5.4; r2 = 0.93), whereas the para-substituted oximes are influenced almost equally by radical and ionic effects (rho(rad)/rho(pol) = -1.1; r2 = 0.98). From these data sets we conclude that the follow-up reactions proceed through a number of intermediates with both radical and ionic character. This was confirmed by product studies with the use of an isotopically labeled nucleophile. In addition to the major oxidation product (ketone), a chlorine-containing product was often identified as well. Studies on the formation of this product show that the most likely pathway is either via a direct nucleophilic addition in a complex formed between the oxime radical cation and the chloranil radical anion or via a radical substitution (SH2) mechanism. These studies show that with the increasing use of oximes as drugs and pesticides, intake of these chemicals followed by enzymatic oxidation may result in the formation of a variety of reactive intermediates, which may lead to cell and tissue damage.     

Determination of phenol, resorcinol and hydroquinone in air samples by synchronous fluorescence using partial least-squares (PLS)

The determination of phenolic compounds is of great importance owing to their high toxicity. Some of them are present in tobacco smoke and it is important for their monitoring in air of closed room. A simple, rapid and sensitive method was developed for simultaneous determination of hydroquinone, resorcinol and phenol in this kind of samples. Synchronous fluorescence technique was used and the data were processed by using the partial least-squares (PLS) chemometric algorithm. The concentrations for experimental calibration matrix were varied between 0.02 and 0.2 mg L⁻¹ for hydroquinone, between 0.05 and 0.6 mg L⁻¹ for resorcinol and between 0.05 and 0.4 mg L⁻¹ for phenol in accordance with the national legislation. The cross-validation method was used to select the number of factors. To check the accuracy of the proposed method a recovery study on real samples was carried out.     

Simultaneous separation of five fluoroquinolone antibiotics by capillary zone electrophoresis

A chiral separation method for glycidol enantiomers determination by normal-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry was developed. Two chiral stationary phases, amylose tris-(3,5-dimethylphenylcarbamate) (Chiralpak AD-H) and (S)-indoline-2-carboxylic acid and (R)-1-(α-naphthyl) ethylamine (SUMICHIRAL OA-4900) have been investigated. The effects of the mobile phase composition, elution program and column temperature were also studied. Under the best conditions: Chiralpak AD-H column, mobile phase composition n-hexane:ethanol (70:30, v/v), flow rate of 0.8 mL/min and 40 °C column temperature, a good resolution (Rs = 1.6) for both enantiomers has been achieved with an analysis time of 16 min. The method was found to be linear in the range from 100 to 500 ppm for both glycidol enantiomers with a good determination coefficient (r² higher than 0.99) and good precision. Limits of detection of 31 and 50 ppm for (R)-(+)-glycidol and (S)-(−)-glycidol, respectively, were obtained. The method was applied to the determination of the enantiomeric excess and yield obtained in a asymmetric epoxidation process of allyl alcohol with a chiral titanium-tartrate complex as catalyst.     

The correlation-consistent composite approach: application to the G3/99 test set

The correlation-consistent composite approach (ccCA), an ab initio composite technique for computing atomic and molecular energies, recently has been shown to successfully reproduce experimental data for a number of systems. The ccCA is applied to the G3/99 test set, which includes 223 enthalpies of formation, 88 adiabatic ionization potentials, 58 adiabatic electron affinities, and 8 adiabatic proton affinities. Improvements on the original ccCA formalism include replacing the small basis set quadratic configuration interaction computation with a coupled cluster computation, employing a correction for scalar relativistic effects, utilizing the tight-d forms of the second-row correlation-consistent basis sets, and revisiting the basis set chosen for geometry optimization. With two types of complete basis set extrapolation of MP2 energies, ccCA results in an almost zero mean deviation for the G3/99 set (with a best value of -0.10 kcal mol(-1)), and a 0.96 kcal mol(-1) mean absolute deviation, which is equivalent to the accuracy of the G3X model chemistry. There are no optimized or empirical parameters included in the computation of ccCA energies. Except for a few systems to be discussed, ccCA performs as well as or better than Gn methods for most systems containing first-row atoms, while for systems containing second-row atoms, ccCA is an improvement over Gn model chemistries.     

From 1-homogeneous supremal functionals to difference quotients: relaxation and Γ-convergence

In this paper we consider positively 1-homogeneous supremal functionals of the type . We prove that the relaxation $\bar{F}$ is a difference quotient, that is where is a geodesic distance associated to F. Moreover we prove that the closure of the class of 1-homogeneous supremal functionals with respect to Γ-convergence is given exactly by the class of difference quotients associated to geodesic distances. This class strictly contains supremal functionals, as the class of geodesic distances strictly contains intrinsic distances. Mathematics Subject Classification (2000) 47J20, 58B20, 49J45     

A novel convenient synthesis of benzoquinazolines

[reaction: see text] A novel synthetic pathway to benzoquinazolines from naphthylamines is reported. Benzoquinazoline nucleus was cyclized in good yield from N-protected naphthylamines using hexamethylenetetramine in TFA and potassium ferricyanide in aqueous ethanolic KOH. This method is efficient and convenient with respect to previously reported synthetic pathways.     

Optimization of parameters of sampling and determination of reduced sulfur compounds using cryogenic capture and gas chromatography in tropical urban atmosphere

Reduced sulfur compounds, RSCs (H₂S, COS, CH₃SH, CH₃SCH₃, CS₂ and CH₃S₂CH₃) play a role in global cycle and acid rain formation. At trace levels RSCs in air are difficult to collect, store and analyze because of their highly adsorptive and reactive properties. This work optimizes parameters of sampling and instrumental determination of RSCs for urban measurements. The method used is based on cryogenic sampling and gas chromatography provided with a cryofocusing trap and flame photometric detection.Greater sampling efficiency was obtained with liquid argon as freezing fluid and air flow rate of 150 mL min^? 1 for two hours. Best results have been obtained with preconcentration for 3 min and injection volume of 3 ml. For H₂S, CH₃SH and CH₃S₂CH₃ the method showed a precision of 89%, limit of detection of 0.10 µg m^? 3 and limit of quantification 0.3 µg m^? 3. For CH₃SCH₃ and CS₂ the corresponding values were 89%, 0.15 µg m^? 3 and 0.5 µg m^? 3 and for COS were 75%, 0.18 µg m^? 3 and 0.8 µg m^? 3 respectively. Sampling efficiency varied between 70–80% for all the RSCs. Accuracy of H₂S from field measurements obtained with parallel measurements using a continuous monitor varied between 88 and 98%. The optimized methodology proved to be suitable for field measurements in urban tropical atmospheres with different characteristics.