Screening and determination of pesticides in soil using continuous subcritical water extraction and gas chromatography-mass spectrometry

In the present work the efficiency of water under subcritical conditions for the extraction of pesticides having a broad spectrum of polarities from soils was evaluated. The pesticides under study were carbofuran, hexachlorobenzene, dimethoate, simazine, atrazine, lindane, diazinon, methylparathion, alachlor, aldrin-R, metholachlor, chlorpyrifos, heptachlor epoxide, dieldrin, endrin, 4,4-DDT and metoxichlor. Optimization studies were carried out using a blank soil (Non-Polluted Soil 1, CLN-1, RTC) and a real soil which were previously spiked with the pesticide mixture and aged for 60 days. A laboratory-made aluminum oven with controlled temperature was used to carry out the leaching process with subcritical water, where it is placed a pre-heater and the extraction cell. The following variables were studied, keeping the pressure controlled about 1200 p.s.i.: the extraction temperature, the time of static and dynamic extraction and the flow-rate of water (1 p.s.i. = 6894.76 Pa). The extraction efficiency of the pesticides increases with the temperature trending to the quantitative extraction at temperatures near to 300 degrees C. After the extraction process, the analytes were transferred quantitatively to 5 ml dichloromethane, before the determination by GC-MS. The results indicate that under the optimized conditions mostly of the analytes are extracted quantitatively in 90 min with recoveries quite similar to those obtained by the standard Soxhlet extraction procedure. Alternatively, by using an extraction time of 25 min, the method can be used as screening for all the pesticides, with recoveries depending on their polarity.     

Synthesis of 4-hydroxy-6,9-difluorobenz[g]isoquinoline-5,10-diones and conversions to 4-hydroxy-6,9-bis[(aminoalkyl)amino]-benz[g]isoquinoline-5,10-diones

Synthetic procedures have been developed which lead to 4-hydroxy-6,9-difluorobenz[g]isoquinoline-5,10-dione ( 4a ) and its 3-methyl analogue 4b . Attempts to displace the fluorides from 4a with N,N-dimethylethylenediamine were unsuccessful. Analogue 4a on treatment with N-(t-butoxycarbonyl)ethylene diamine led to 15 , formed from addition of the nucleophilic amine to C-3. On the other hand, analogue 4b , on treatment with N,N-dimethylethylenediamine led to the anticipated difluoride displacement product 3c . The protection of the hydroxy group of 4a by benzylation with phenyldiazomethane led to 4c which on treatment with N-(t-butoxycarbonyl)ethylene diamine or N,N-dimethylethylenediamine led to the corresponding 6,9-bis-substituted analogues 18a and 18b , respectively. Reductive debenzylations of 18a and 18b by hydrogenation over Pearlman's catalyst also effected partial reductions of the quinone. However, air oxidation of the over reduced products led to 3a and 3b , respectively. Treatment of 3a with hydrogen chloride gas led to the hydrochloride salt of 3d . Addition of O-p-Methoxybenzyl-N,N'-diisopropylurea to 4a led to the p-methoxybenzyl analogue 4d . Treatment of 4d with N,N-dimethylethylene diamine or N-(t-butoxycarbonyl)ethylene diamine led to displacements of the fluorides to yield 18c and 18d , respectively. Deprotection of 18c to 3b was accomplished using methanesulfonic acid. Treatment of 18d with trifluoroacetic acid followed by addition of maleic acid led to dimaleate salt of 3d .     

Synthesis of regioisomeric 6,9-(chlorofluoro)-substituted benzo[g]quinoline-5,10-diones,benzo[g] isoquinoline-5,10-diones and 6-chloro-9-fluorobenzo[g]quinoxaline-5,10-dione

Treatment of difluoro or chloro fluoro-substituted benzyl bromides 5a-c with zinc dust in tetrahydro-furan leads to the corresponding benzylic zinc bromides 6a-c. These organometallics on treatment with chlorosubstituted heterocyclic esters 4A and 4B mediated by nickel catalysis undergo couplings to yield dihalobenzyl substituted heterocyclic esters 7Aa-c and 7Ba-c. Treatment of 4c with 6c under Pd catalysis leads to 7Cc. The acids 8, prepared by hydrolysis of these esters, with treatment of fuming sulfuric acid undergo cyclizations and oxidations to yield the desired regioisomeric dihalo-substituted heterocyclic quinones 2.     

Adsorption of human serum albumin (HSA) onto colloidal TiO2 particles, Part I

The adsorption of human serum albumin (HSA) onto colloidal TiO2 (P25 Degussa) particles was studied in NaCl electrolyte at different solution pH and ionic strength. The HSA-TiO2 interactions were studied using adsorption isotherms and the electrokinetic properties of HSA-covered TiO2 particles were monitored by electrophoretic mobility measurements. The adsorption behavior shows a remarkable dependence of the maximum coverage degree on pH and was almost independent of the ionic strength. Other characteristic features such as maximum adsorption values at the protein isoelectric point (IEP approximately 4.7) and low-affinity isotherms that showed surface saturation even under unfavorable electrostatic conditions (at pH values far away from the HSA IEP and TiO2 PZC) were observed. Structural and electrostatic effects can explain the diminution of HSA adsorption under these conditions, assuming that protein molecules behave as soft particles. Adsorption reactions are discussed, taking into account acid-base functional groups of the protein and the surface oxide in different pH ranges, considering various types of interactions.     

Bonding in benzene methylene isomers: Modern VB study using spin-coupled theory

The electronic structure of the benzene methylene isomers fulvene, dimethylenecyclobutene, and trimethylenecyclopropene is studied using spin-coupled theory. It is shown that the three isomers all possess three noninteracting π-bonds and very low resonance energies. This is to be contrasted with benzene, where the symmetric coupling of the π-electron spins around the ring provides a considerable larger resonance energy. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 319–327, 1999     

Copolymerization of styrene with (Z)-1,3-pentadiene in the presence of a syndiotactic-specific catalyst

Copolymerization of styrene with (Z)-1,3-pentadiene affords copolymers mostly containing 1,2 pentadiene units. Both the styrene and the pentadiene units are in syndiotactic arrangement but the comonomer sequence distribution is far from bernoullian. Interestingly, the behavior of (Z)-1,3-pentadiene does not change much when polymerization temperature raises from −20 to +20°C, notwithstanding that (Z)-1,3-pentadiene affords a 1,2-syndiotactic homopolymer at −20°C but a prevailingly 1,4 cis homopolymer at +20°C. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2697–2702, 1997     

A generalized Langevin dynamics approach to model solvent dynamics effects on proteins via a solvent-accessible surface. The carboxypeptidase A inhibitor protein as a model

A generalized Langevin dynamics (GLD) scheme is derived for (bio)macromolecules having internal structure, arbitrary shapes and a size larger than solvent molecules (i.e. proteins). The concept of solvent-accessible surface area (SASA) is used to incorporate solvent effects via external forces thereby avoiding its explicit molecular representation. A simulation algorithm is implemented in the GROMOS molecular dynamics (MD) program including random forces and memory effects, while solvation effects enter via derivatives of the surface area. The potato carboxypeptidase inhibitor (PCI), a small protein, is used to numerically test the approach. This molecule has N- and C-terminal tails whose structure and fluctuations are solvent dependent. A 1-ns MD trajectory was analyzed in depth. X-ray and NMR structures are used in conjunction with MD simulations with and without explicit solvent to gauge the quality of the results. All the analyses showed that the GLD simulation approached the results obtained for the MD simulation with explicit simple-point-charge-model water molecules. The SASAs of the polar atoms show a natural exposure towards the solvent direction. A FLS solvent simulation was completed in order to sense memory effects. The approach and results presented here could be of great value for developing alternatives to the use of explicit solvent molecules in the MD simulation of proteins, expanding its use and the time-scale explored. Received: 2 February 2000 / Revised: 12 March 2000 / Accepted: 26 May 2000 / Published online: 2 November 2000     

Transition states in modern valence-bond theory: application to the Cope rearrangement

Modern valence-bond theory, in its spin-coupled form, is used to study the electronic structure of the transition structures in the Cope rearrangement. It is found that the transition structure described by a “chair” geometry with a “6-in-6” CASSCF/6-31G^* wave function is clearly aromatic while the CASSCF/6-31G^*“boat” transition structure corresponds more closely to two weakly interacting allyl radicals. Moreover, there is a striking resemblance between the CASSCF chair transition structure and the benzene molecule, arising from the modern valence-bond analysis in terms of Rumer spin functions. In agreement with previous works, dynamical correlated wave functions show shorter interallylic distances in the optimized transitions structures. The use of spin-coupled wave functions on the latter geometries results in diradical and aromatic character for the chair and boat transition structures, respectively. Received: 13 October 1998 / Accepted: 30 December 1998 / Published online: 7 June 1999     

The use of ab initio quantum molecular self-similarity measures to analyze electronic charge density distributions

Exact quantum molecular overlaplike and Coulomb-like self-similarity measures are studied in a selected series of molecules with the same number of electrons. It is found that quantum molecular overlap self-similarity measures can be used to estimate the concentration of electronic charge in molecules. A good linear relationship between the overlap self-similarity measure and the volume is found for molecules with the same number of electrons when the atoms of the systems being compared belong to the same row of the periodic table. Finally, an upper bound for the quantum molecular overlap self-similarity measure of molecules with a number of electrons up to 54 is given from the atomic quantum self-similarity measures obtained using Slater-type functions. © 1996 John Wiley & Sons, Inc.     

4-Alkoxycarbonyl, 4-alkylthiocarbonyl and 5-alkoxycarbonyloxy derivatives of 1-substituted-3-methylpyrazol-5-ones

The reaction of 1-substituted-3-methylpyrazol-5-ones 1 with alkyl chloroformates and calcium hydroxide in dioxane have been studied. With 1-phenyl-3-methylpyrazol-5-one, the isolated product was alkyl 3-methyl-5-oxo-1-phenylpyrazole-4-carboxylate 2 but with 1-alkyl-3-methylpyrazol-5-one formation of 1-alkyl-5-alkoxycarbonyloxy-3-methylpyrazole 3 was observed. Replacement of alkyl chloroformate by bis(alkoxythiocarbonyl) sulfide results in the formation of 4-alkoxythiocarbonyl derivatives 4 in low yield with both 1-substituted-3-methylpyrazol-5-ones.