Search results for "residue"
showing 10 items of 390 documents
Analytical utility of quadrupole time-of-flight mass spectrometry for the determination of pesticide residues in comparison with an optimized column …
2009
Abstract A multiresidue method for the analysis of 30 pesticides with different physicochemical properties in fruits and vegetables was developed. The method involves a rapid and small-scale extraction procedure based on matrix solid-phase dispersion using octadecylsilyl (C18) as the dispersant and dichloromethane as the eluent. The target pesticides were determined using column high-performance liquid chromatography/triple quadrupole-tandem mass spectrometry (LC/QqQ-MS/MS). The method was validated for sensitivity, linearity, reproducibility, and accuracy. A recovery study was conducted at 3 different levels, and the average ranged from 74 to 99 for all of the studied compounds, with relat…
A phosphonamidate containing aromatic N-terminal amino group as inhibitor of leucine aminopeptidase-design, synthesis and stability.
2006
Fully deprotected phosphonamidate dipeptides, predicted as effective inhibitors of cytosolic leucine aminopeptidase, showed unexpected instability in water solution at pH below 12. Their hydrolysis rate was strictly correlated with basicity of the N-terminal amino group. To improve this feature a phosphonamidate analogue containing less basic, aromatic 2-aminophenylphosphonate residue in P1 position of the inhibitor was designed. The target compound was synthesised starting from diethyl 2-nitrophosphonate in several step procedure. The decrease in basicity of the terminal amino moiety of the modified analogue in fact resulted in satisfactory improvement of hydrolytic stability of the P–N bo…
Evaluation of Organophosphorus Pesticide Residues in Citrus Fruits from the Valencian Community (Spain)
1997
Abstract Approximately 200 citrus samples from markets of the Valencian Community (Spain) were analyzed to establish their residue levels in 12 organophosphorus pesticide residues during the 1994-1995 campaign. The organophosphorus pesticides carbophenothion, chlorpyriphos, chlorfenvinphos, diazinon, ethion, fenitrothion, malathion, methidation, methylparathion, phosmet, quinalphos, and tetradifon were simultaneously extracted by matrix solidphase dispersion and determined by gas chromatography- mass spectrometry using selected ion monitoring mode. A total of 32.25% contained pesticide residues and 6.9% exceeded the European Union Maximum Residue Levels (MRLs). The pesticides found in the s…
Monitoring of five postharvest fungicides in fruit and vegetables by matrix solid-phase dispersion and liquid chromatography/mass spectrometry
2002
Abstract A method was developed for monitoring dichloran, flutriafol, o-phenylphenol, prochloraz, and tolclofos-methyl in fruits and vegetables, using matrix solid-phase dispersion and liquid chromatography with mass spectrometry detection. The method was used to determine fungicide content in 200 samples of chards, onions, peppers, bananas, lemons, and oranges. Of the samples examined, 54% contained o-phenylphenol with concentrations ranging from 0.005 to 3.34 mg/kg and 35% showed prochloraz in the range of 0.06–1.95 mg/kg. Dichloran, flutriafol, and tolclofos-methyl were detected only occasionally. Only 4% of the samples exceeded the European Union maximum residue limits. The pesticides i…
Pentapeptides containing two dehydrophenylalanine residues - synthesis, structural studies and evaluation of their activity towards cathepsin C
2008
Synthesis, structural and biological studies of pentapeptides containing two Delta Phe residues (Z and E isomers) in position 2 and 4 in peptide chain were performed. All the investigated peptides adopted bent conformation and majority of them could exist as two different. conformers in solution. Only pentapeptides. containing free N-termini appeared to act as weak inhibitors of cathepsin C with the slow-binding, competitive mechanism of inhibition. free acids being bound slightly better than their methyl esters. Results of Molecular modeling suggested significant difference between peptides, depending of the type of amino acid residue in position 5 in peptide chain. Dehydropeptides contain…
Novel cleavable cell-penetrating peptide-drug conjugates: synthesis and characterization
2014
We report the first drug conjugate with a negatively charged amphipathic cell-penetrating peptide. Furthermore, we compare two different doxorubicin cell-penetrating peptide conjugates, which are both unique in their properties, due to their net charge at physiological pH, namely the positively charged octaarginine and the negatively charged proline-rich amphipathic peptide. These conjugates were prepared exploiting a novel heterobifunctional crosslinker to join the N-terminal cysteine residue of the peptides with the aliphatic ketone of doxorubicin. This small linker contains an activated thiol as well as aminooxy functionality, capable of generating a stable oxime bond with the C-13 carbo…
Il riconoscimento reciproco del maschile e del femminile nella prospettiva della pedagogia fondamentale
2017
Il saggio descrive i dati fenomenologici elementari delle identità dei generi, la genitalità anatomica e il gender. Questo secondo reperto si presenta come l’aspetto malleabile della sessualità umana; la variabilità non è però assoluta: il corpo non può essere annullato e con esso le proprietà del corpo femminile e di quello maschile, congegni atti a generare una nuova vita della specie umana. Questi rilievi sono visti nella prospettiva dell’azione educativa, qui intesa come relazionalità riconoscente. Ora, una tale prospettiva consente di definire le identità dei generi come un’esistenziale, intenzionalità situata e desituante legate da un’unità originaria che ha la sua condizione di possi…
Conformational preferences and synthesis of isomersZandEof oxazole-dehydrophenylalanine
2016
Dehydrophenylalanine, ΔPhe, is the most commonly studied α,β-dehydroamino acid. In nature, further modifications of the α,β-dehydroamino acids were found, for example, replacement of the C-terminal amide group by oxazole ring. The conformational properties of oxazole-dehydrophenylalanine residue (ΔPhe-Ozl), both isomers Z and E, were investigated. To determine all possible conformations, theoretical calculations were performed using Ac-(Z/E)-ΔPhe-Ozl(4-Me) model compounds at M06-2X/6-31++G(d,p) level of theory. Ac-(Z/E)-ΔPhe-Ozl-4-COOEt compounds were synthesized and the conformational preferences of each isomer, Z and E, were investigated using FTIR and NMR-NOE in solutions of increasing p…
Experimental Study on Diflubenzuron: Degradation in Freshwater and Bioconcentration in Mosquitofish Following Chronic Exposure
2013
ISSN: 2152-2197 ; ESSN: 2152-2219. Editeur commercial : Scientific Research Publishing; International audience; Diflubenzuron (DFB, trade name dimilin® 25 WP) is a chitin synthesis inhibitor widely used against forest insect pests in Algeria. Prior to implementation of these products as chemical agents for mosquito control, knowledge on their potential effects on non-target organisms and its behaviour in water are needed. Therefore, the present study was focused on DFB and aimed to use an HPLC procedure developed previously in order to obtain information on its degradation in freshwater and its bioconcentration in adult females of the fish Gambusia affinis (Cyprinodondiformes, Poeciliidae),…
Clean-up and confirmation procedures for gas chromatographic determination of pesticide residues in contaminated waters. Part I
1993
The effects of sulphuric acid, potassium hydroxide and chromic acid on eleven organochlorine and ten organophosphorus pesticides were investigated. The treatments destroy some pesticides totally or partially, leave others unaltered and have a clean-up effect. These reactions can be used to confirm the presence of an identified pesticide. The clean-up extracts in the environmental samples facilitate the identification of the organochlorine and organophosphorus pesticides and their quantitative analysis. The results obtained for contaminated surface waters show the usefulness of these methods for multi-residue capillary gas chromatography without the need for other additional separative chrom…