Determination of organophosphate esters in air samples by dynamic sonication-assisted solvent extraction coupled on-line with large-volume injection gas chromatography utilizing a programmed-temperature vaporizer

An on-line method for the determination of airborne organophosphate esters based on dynamic sonication-assisted solvent extraction and large-volume injection (LVI) gas chromatography with nitrogen-phosphorous detection is introduced. The LVI is performed with a programmed-temperature vaporizer. The entire extracted fraction of 800 microl (hexane-methyl-tert.-butyl ether, 7:3, v/v) is introduced directly into the GC system without any clean-up step following extraction. The extraction and analysis step were completed in less than 15 min. The limit of detection of the investigated organophosphate esters was established to be in the range of 5-32 pg/filter. The correlation coefficients (r2) were investigated in the linear range study of the entire system and established to be approximately 0.9900 for all the investigated organophosphates esters. Applications of the method was demonstrated with the extraction of air samples collected onto glass fiber filters from different indoor environments. Six organophosphate esters were found at the levels 0.4-138 ng/m3.     

Excited-state dynamics of fac-[ReI(L)(CO)3(phen)]+ and fac-[ReI(L)(CO)3(5-NO2-phen)]+ (L = imidazole, 4-ethylpyridine; phen = 1,10-phenanthroline) complexes

The nature and dynamics of the lowest excited states of fac-[Re(I)(L)(CO)(3)(phen)](+) and fac-[Re(I)(L)(CO)(3)(5-NO(2)-phen)](+) [L = Cl(-), 4-ethyl-pyridine (4-Etpy), imidazole (imH); phen = 1,10-phenanthroline] have been investigated by picosecond visible and IR transient absorption spectroscopy in aqueous (L = imH), acetonitrile (L = 4-Etpy, imH), and MeOH (L = imH) solutions. The phen complexes have long-lived Re(I) --> phen (3)MLCT excited states, characterized by CO stretching frequencies that are upshifted relative to their ground-state values and by widely split IR bands due to the out-of-phase A'(2) and A"nu(CO) vibrations. The lowest excited states of the 5-NO(2)-phen complexes also have (3)MLCT character; the larger upward nu(CO) shifts accord with much more extensive charge transfer from the Re(I)(CO)(3) unit to 5-NO(2)-phen in these states. Transient visible absorption spectra indicate that the excited electron is delocalized over the 5-NO(2)-phen ligand, which acquires radical anionic character. Similarly, involvement of the -NO(2) group in the Franck-Condon MLCT transition is manifested by the presence of an enhanced nu(NO(2)) band in the preresonance Raman spectrum of [Re(I)(4-Etpy)(CO)(3)(5-NO(2)-phen)](+). The Re(I) --> 5-NO(2)-phen (3)MLCT excited states are very short-lived: 7.6, 170, and 43 ps for L = Cl(-), 4-Etpy, and imH, respectively, in CH(3)CN solutions. The (3)MLCT excited state of [Re(I)(imH)(CO)(3)(5-NO(2)-phen)](+) is even shorter-lived in MeOH (15 ps) and H(2)O (1.3 ps). In addition to (3)MLCT, excitation of [Re(I)(imH)(CO)(3)(5-NO(2)-phen)](+) populates a (3)LLCT (imH --> 5-NO(2)-phen) excited state. Most of the (3)LLCT population decays to the ground state (time constants of 19 (H(2)O), 50 (MeOH), and 72 ps (CH(3)CN)); in a small fraction, however, deprotonation of the imH.+ ligand occurs, producing a long-lived species, [Re(I)(im.)(CO)(3)(5-NO(2)-phen).-]+.     

Controlled Double-Bond Migration in Palladium-Catalyzed Intramolecular Arylation of Enamidines

Palladium-catalyzed intramolecular cyclization of N-(N'-tert-butylformimidoyl)-6-[2-(2-iodophenyl)ethyl]-1,2,3,4-tetrahydropyridine (1a) and N-(N'-tert-butylformimidoyl)-6-[3-(2-iodophenyl)propyl]-1,2,3,4-tetrahydropyridine (1b) respectively results in formation of spiro compounds 1'-(N-tert-butylformimidoyl)-3',4'-dihydrospiro[indan-1,2'(1'H)-pyridine] (4a), 1'-(N-tert-butylformimidoyl)-1',6'-dihydrospiro[indan-1,2'(3'H)-pyridine] (5a), and 1'-(N-tert-butylformimidoyl)-5',6'-dihydrospiro[indan-1,2'(1'H)-pyridine] (6a) and 1'-(N-tert-butylformimidoyl)-3,3',4,4'-tetrahydrospiro[naphthalene-1(2H),2'(1'H)-pyridine] (4b), 1'-(N-tert-butylformimidoyl)-1',3,4,6'-tetrahydrospiro[naphthalene-1(2H),2'(3'H)-pyridine] (5b), and 1'-(N-tert-butylformimidoyl)-3,4,5',6'-tetrahydrospiro[naphthalene-1(2H),2'(1'H)-pyridine] (6b). The double-bond migration process can be controlled, and any of the three double-bond isomers can be prepared by employing proper ligands. A combination of BINAP and the amidine function was required to obtain the isomers 5a and 5b with the double bond in the homoallylic position relative to the aryl group. An electrospray ionization mass spectrometric study was conducted to support suggested reaction intermediates.     

Development of quantitative vitellogenin-ELISAs for fish test species used in endocrine disruptor screening

The yolk protein precursor vitellogenin (Vtg) in plasma has proved to be a simple and sensitive biomarker for assessing exposure of fish to environmental estrogens. Within international bodies such as the Organization for Economic Cooperation and Development (OECD) work is ongoing to develop screening and testing programmes for endocrine disrupting effects of new chemicals, and in the focus of this development are the fish test species common carp (Cyprinus carpio), fathead minnow (Pimephales promelas), zebrafish (Danio rerio) and Japanese medaka (Oryzias latipes). In this study we have developed quantitative enzyme linked immunosorbent assays (ELISAs) for Vtg in common carp/fathead minnow, zebrafish and Japanese medaka. The assays were developed using a combination of monoclonal and polyclonal fish Vtg antibodies in a sandwich format, using stabilized Vtg from the test species as a standard. The carp Vtg ELISA has a working range of 1–63 ng/mL, a minimal detection limit of 0.6 ng/mL, and may also be used for quantification of Vtg in fathead minnow. In fathead minnow whole-body homogenate samples, the practical detection limit is 400 ng/mL due to the matrix effect. The zebrafish Vtg ELISA has a working range of 0.5–63 ng/mL, a minimal detection limit of 0.4 ng/mL, and a practical detection limit of 200 ng/mL in whole-body homogenate samples. The medaka Vtg ELISA has a working range of 0.25–16 ng/mL, a minimal detection limit of 0.1 ng/mL, and a practical detection limit of 125 ng/mL in whole-body homogenate samples. The intra- and inter-assay variations were below 20% for all assays. The assays were evaluated with sets of representative samples spanning the wide dynamic range of Vtg-levels found in fish exposed to environmental estrogens, and all three assays are currently undergoing international inter-laboratory validation.     

Synthesis,crystal structure,and magnetic properties of mu-hydroxo-bis[pentakis(acetonitrile)chromium(III)] tetrafluoroborate: an acetonitrile analogue to "acid rhodo"

The reaction of [Cr(NCCH(3))(6)](2+) with dioxygen in acetonitrile (MeCN) solution acidified with HBF(4) gave red crystals of the binuclear complex [(CH(3)CN)(5)Cr(OH)Cr(NCCH(3))(5)](BF(4))(5) (1). From the X-ray crystal structure of 1, the Cr-O-Cr angle was found to be 147.5(2) degrees. Magnetic susceptibility measurements of 1 showed an antiferromagnetic coupling between the two chromium(III) centers with a triplet energy J = 35.9(1) cm(-1). On redissolution of 1 in MeCN, the hydroxo bridge was deprotonated, and a green solution of the complex [(CH(3)CN)(5)CrOCr(NCCH(3))(5)](4+) formed. The electronic absorption spectrum of this solution is very similar to the spectrum of the classical complex [(H(3)N)(5)CrOCr(NH(3))(5)](4+) with intense bands in the UV and near-UV region. From the temperature dependence of the absorption spectrum near 12900 cm(-1), the triplet energy J was found to be 1067(19) cm(-1). The acidity of the hydroxo bridge in 1 is very high with an acid dissociation constant K(a) > 1 M.     

Determination of stability constants of chelate complexes: Part II. Applications

The proposed simplified method for calculating the stability constants of chelate complexes from pH and pM measurements (Part I) is applied to two systems. On the basis of data reported by Österberg, the stability constants of copper o-phosphorylserylglutamic acid are calculated and good agreement is achieved. In addition, the stability constants of the mononuclear, binuclear and trinuclear silver complexes of TTHA (triethylenetetraminehexaacetic acid) were calculated from potentiometric pAg data. These calculations yielded the following values of the cumulative constants: log β_AgL=8.7, log β_AgHL= 17.6, log β_AgH2L= 23.8, log β_Ag2L= 14.0, log β_Ag2HL = 20.5, log β_Ag2H2L = 25.6, log β_Ag2L =17.0.     

Dynamic microwave-assisted extraction coupled on-line with solid-phase extraction: determination of polycyclic aromatic hydrocarbons in sediment and soil

This paper describes a new extraction tool for the determination of polycyclic aromatic hydrocarbons (PAHs) in soil and sediment samples, using dynamic microwave-assisted extraction combined with solid-phase extraction (DMAE-SPE). The critical variables for DMAE-SPE are investigated and optimized in an experimental design. The technique proved to be fast, accurate and able to yield quantitative extraction of PAHs from naturally contaminated sediment and soil samples. The set-up is fully automated and features monitored extraction, which facilitates rapid optimization of the method. In addition, only small quantities of solvent and sample are required.     

Theoretical study on solvation effects in chemical reactions: A vibrational coupling model

A vibrational coupling model to treat the solvation effects in chemical reaction rate calculations is proposed and applied to the intramolecular hydrogen transfer reaction CH₃O· → ·CH₂OH in the condensed phase. The effect of solvation is taken into account in two ways: (1) the solvent effect on the activation energy of the reaction is simulated by including 39 surrounding water molecules, represented by fractional charges at the assumed atomic positions, in the potential energy surface calculation; and (2) the vibrational couplings between the 10 nearest solvent molecules and the molecules constituting the reaction system are explicitly included in a vibrational frequency calculation. RRKM theory with Miller's tunneling correction included is employed to calculate the rate constants. The effect of solvation causes a significant change in the chemical reaction rate, mainly through a lowering of the activation energy. The vibrational coupling causes a slight increase of the rate constant in the tunneling region by perturbing the vibrational frequencies of the reactant and transition states, which appear in the rate-constant expression, but has little effect at higher temperatures.     

Synthesis of 5-alkylidene-2,5-dihydropyrrol-2-ones and their ring-transformation into 5,6-dihydrobenzo[h]chromones, 5,6,7,8-tetrahydrochromones and pyran-4-ones

Acid-mediated ring-transformations of 5-alkylidene-2,5-dihydropyrrol-2-ones, available by cyclization of 1,3-diketone dianions with bis(imidoyl) dichlorides of oxalic acid, resulted in formation of functionalized pyran-4-ones, such as 5,6-dihydrobenzo[h]chromones and 5,6,7,8-tetrahydrochromones.