Application of new high-performance liquid chromatography and solid-phase extraction materials to the analysis of pesticides in human urine

A method for the simultaneous determination of diuron and linuron pesticides in human urine was developed, using both solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) phases made in our own laboratory. These materials were prepared by sorption of polysiloxanes onto a silica surface, followed by immobilization. The HPLC columns were prepared from poly(methyloctylsiloxane), PMOS, immobilized onto silica with microwave radiation while the SPE cartridges where made with poly(methyloctadecylsiloxane), immobilized thermally. Method validation was performed for diuron and linuron for three fortification levels. The recoveries obtained were 85-103%, the inter- and intra-assay precisions were less than 1.6 and 1.8%, respectively. The limits of quantitation and detection for diuron were 2.4 and 8.0 microg/l and for linuron were 5.0 and 12 microg/l, respectively.     

New evidence on the regiochemistry of the tert-butyldiphenylsilylcupration of allene using the silylcuprate or silylcopper reagent

The regiochemistry in the tert-butyldiphenylsilylcupration of the allene depends on the temperature and also on the nature of the electrophile. Thus, the intermediate generated by addition of the silylcuprate at −78°C reacted with electrophiles to give allylsilanes, except with oxo compounds which afforded vinylsilanes. On the other hand, the silylcopper reagent was added at −40°C leading, in all cases, to the corresponding allylsilanes. When enones were used as electrophile the vinylsilanes were the 1,2-addition products and the allylsilanes those from 1,4-addition. These functionalized vinyl or allyl tert-butyldiphenylsilanes are interesting synthons for the preparation of conjugated tert-butyldiphenylsilyltrienes and functionalized exocyclic alkylidenecyclopentenes.     

Formation of substituted N-oxide hydroxyquinolines from o-nitrophenyl Baylis-Hillman adduct: a new key intermediate intercepted by ESI-(+)-MS(/MS) monitoring

A new mechanistic proposal on the formation of N-oxide hydroxyquinolines from BH adducts based on the interception by electrospray ionization mass spectrometry of a new key o-trifluoroacetylated intermediate.     

Energy decompositions according to physical space partitioning schemes

This work describes simple decompositions of the energy of molecular systems according to schemes that partition the three-dimensional space. The components of those decompositions depend on one and two atomic domains thus providing a meaningful chemical information about the nature of different bondings among the atoms which compose the system. Our algorithms can be applied at any level of theory (correlated or uncorrelated wave functions). The results reported here, obtained at the Hartree-Fock level in selected molecules, show a good agreement with the chemical picture of molecules and require a low computational cost in comparison with other previously reported decompositions.     

Templated conversion of a crown ether-containing macrobicycle into [2]rotaxanes

A crown ether-containing macrobicycle was used as the wheel component in a templated synthesis of a [2]rotaxane with an acetal-containing axle. The molecular structures of the macrobicycle and the [2]rotaxane were characterized by NMR spectroscopy and X-ray crystallography. The chloride-binding ability of the macrobicycle, either free in solution or when it is part of a [2]rotaxane, is quite weak as determined by NMR titration experiments. A second analogous [2]rotaxane, with a longer axle, was synthesized, and its solvent-dependent co-conformation was characterized by 2D NMR spectroscopy. The position of the wheel along the axle can be controlled by the solvent polarity, however, attempts to use metal cations such as Na(+), K(+), Ba(2+), and Ag(+) to switch the wheel position in polar solvents were unsuccessful.     

On the global lifting of meromorphic forms

We characterize the existence of global liftings of local data of meromorphic forms, satisfying a family of compatibility conditions on their polar sets, in terms of obstructions belonging to the cohomology H^.(X, ^.), where X is the ambient manifold. These obstructions are constructed canonically, using residue-principal value operators.     

Regioselectivity in aromatic Claisen rearrangements

Theoretical calculations and the isomeric product composition for a series of eight meta-substituted allyl aryl ethers confirm the reliability of a new (1)H NMR methodology used to predict aromatic Claisen regioselectivity from ground-state conformational preference of the reactant allyloxy group. Frontier HOMO-LUMO intramolecular orbital interactions, a classical approach in predicting reactivity and selectivity for Claisen rearrangements of allyl vinyl ethers, is shown to fail to mimic transition-state orbital interactions for aromatic Claisen rearrangements of meta-substituted allyl aryl ethers. B3LYP/6-31G(d,p) calculations on reactants and transition states are shown, however, to correctly predict the outcome of such aromatic Claisen rearrangements from either the preferential reactant ground-state conformation (theoretical predictions that agree with the NMR measurements) or the less energetic transition state, or both.     

Reactivity of 3-amino-, 3-halogeno-, and 3-nitro-2-pyrones and thiopyrones

Substituted pyrrole and furan-2-carboxylic acids were obtained from 3-amino- and 3-halogeno-2-pyrones. The reactions of several substituted 2-pyrones and thiopyrones with different amines and carbonyl reagents were studied.     

Hydrogen/chlorine exchange reactions of gaseous carbanions

Gas-phase reactions of three typical carbanions CH(2)NO(2)(-), CH(2)CN(-), and CH(2)S(O)CH(3)(-) with the chloromethanes CH(2)Cl(2), CHCl(3), and CCl(4), examined by tandem mass spectrometry, show a novel hydrogen/chlorine exchange reaction. For example, reaction between the nitromethyl anion CH(2)NO(2)(-) and carbon tetrachloride CCl(4) forms the ion CHClNO(2)(-). The suggested reaction mechanism involves nucleophilic attack by CH(2)NO(2)(-) at the chlorine of CCl(4) followed by proton transfer within the resulting complex [CH(2)ClNO(2) + CCl(3)(-)] to form CHClNO(2)(-) and CHCl(3). Two other carbanions CH(2)CN(-) and CH(2)S(O)CH(3)(-) also undergo the novel hydrogen/chlorine exchange reactions with CCl(4) but to a much smaller extent, their higher nucleophilicities favoring competitive nucleophilic attack reactions. Proton abstraction is the exclusive pathway in the reactions of these carbanions with CHCl(3). While CH(2)CN(-) and CH(2)S(O)CH(3)(-) promote mainly proton abstraction and nucleophilic displacement in reactions with CH(2)Cl(2), CH(2)NO(2)(-) does not react.     

A Pre-Concentration Procedure Using Cloud Point Extraction for the Determination of Manganese in Saline Effluents of a Petroleum Refinery by Flame Atomic Absorption Spectrometry

This paper describes the development of a cloud point extraction procedure for the determination of manganese in saline effluents by flame atomic absorption spectrometry (FAAS). The optimization step was performed using the Doehlert matrix involving the following variables: buffer concentration, pH and centrifugation time. The validation process was assessed as: parameters of the analytical curve, precision, effect of other ions in the proposed procedure, robustness test and accuracy. The proposed procedure allows the determination of manganese with a detection limit (3δ/S) of 0.60 μg L⁻¹, and a precision expressed as relative standard deviation (RSD) of 2.2 (n = 8) and 1.5% (n = 8) for a manganese concentration of 1 and 5 μg L⁻¹, respectively. The pre-concentration factor obtained was 84. The recovery achieved for the determination of manganese in the presence of several other metal ions demonstrated that this procedure could be satisfactorily applied to the analysis of environmental samples. The accuracy was confirmed by the analysis of CRM trace elements in water (NIST 1643d). This procedure was applied to the determination of manganese in saline effluents of a petroleum refinery. For three analyzed samples the manganese content varied between 44.9 and 67.9 μg L⁻¹.