Inhibition of AChE by malathion and some structurally similar compounds

Inhibition of bovine erythrocyte acetylcholinesterase (free and immobilized on controlled pore glass) by separate and simultaneous exposure to malathion and malathion transformation products which are generally formed during storage or through natural or photochemical degradation was investigated. Increasing concentrations of malathion, its oxidation product malaoxon, and its isomerisation product isomalathion inhibited free and immobilized AChE in a concentration-dependent manner. K-I, the dissociation constant for the initial reversible enzyme inhibitor-complex, and k(3), the first order rate constant for the conversion of the reversible complex into the irreversibly inhibited enzyme, were determined from the progressive development of inhibition produced by reaction of native AChE with malathion, malaoxon and isomalathion. KI values of 1.3 x 10(-4) M-1, 5.6 x 10(-6) M-1 and 7.2 x 10(-6) M-1 were obtained for malathion, malaoxon and isomalathion, respectively. The IC50 values for free/immobilized AChE, (3.7 +/- 0.2)10(-4) M/(1.6 +/- 0.1)10(-4), (2.4 +/- 0.3)10(-6)/(3.4 +/- 0.1)10(-6) M and (3.2 +/- 0.3)10(-6) M/(2.7 +/- 0.2)10(-6) M, were obtained from the inhibition curves induced by malathion, malaoxon and isomalathion, respectively. However, the products formed due to photoinduced degradation, phosphorodithioic O,O,S-trimethyl ester and O,O-dimethyl thiophosphate, did not noticeably affect enzymatic activity, while diethyl maleate inhibited AChE activity at concentrations GT 10 mM. Inhibition of acetylcholinesterase increased with the time of exposure to malathion and its inhibiting by-products within the interval from 0 to 5 minutes. Through simultaneous exposure of the enzyme to malaoxon and isomalathion, an additive effect was achieved for lower concentrations of the inhibitors (in the presence of malaoxon/isomalathion at concentrations 2 x 10(-7) M/2 x 10(-7) M, 2 x 10(-7) M/3 x 10(-7) M and 2 x 10(-7) M/4.5 x 10(-7)M), while an antagonistic effect was obtained for all higher concentrations of inhibitors. The presence of a non-inhibitory degradation product (phosphorodithioic O,O,S-trimethyl ester) did not affect the inhibition efficiencies of the malathion by-products, malaoxon and isomalathion

Protolytic equilibria and photodegradation of quercetin in aqueous solution

Studies of protolytic equilibria and investigations of stability of flavonoids at different acidities are necessary to better understand their antioxidant efficiencies and autoxidation characteristics. The protonation constant of carbonyl group and dissociation constants of OH groups of quercetin in aqueous solutions were determined spectrophotometrically. The distribution diagram of ionic species in aqueous solutions of various acidities was calculated. Study of the effects of UV irradiation on quercetin at pH 5.00, 7.50 and 10.00 indicated that UV irradiation accelerated quercetin autoxidation via the formation of the oxidation product. The stability of quercetin and oxidation product was investigated as a function of irradiation time by using spectrophotometric and HPLC techniques. The apparent pseudo-first-order rate constants for quercetin degradation and oxidation product formation were calculated and discussed

Photodegradation of pesticides and application of bioanalytical methods for their detection.

2005 IUPACPhotodegradation oC coumaphos and azinphos-methyl in lhe air, in oxygen, and in nitrogen atmosphere (quartz reactor eyuipped with six 18-W lamps with the maximum emission intensity al 310 nm) was sludied. The faslest reaclion occurred with coumaphos in nitrogen almosphere (complete decomposilion in 10 min), where the formation of a new compound was also detected by high-performance liquid chromatography (HPLC). In lhe case of azinphos-methyl, no additional signals in HPLC chromalogram were observed. The rearrangement mechanism, involving a triplet-state activation complex and the formation of an acetylcholinesterase (AChE)-inhibiting oxo analog of coumaphos was verihed and con[irmed by laser flash photolysis. The suitability of bioanalytical flow-injection analysis (FIA) systems, based on AChE inhibition and speclrophotometric or thermal lens spectrometric deteclion for rapid and sensitive screening in food qualily control was demonstrated. Owing to the high sensitivity of thermal lens speclrometry (TLS), several steps in sample preparation can be avoided (preconcentration, purilication, isolation) and incubation times reduced. High sample throughpuls (10 h-I) are, however, also achievable for medium toxic oxo organophosphorus (OP) pesticides using spectrophotomelric detection providing limits of detection (LODs) al lhe level of 10 ppb malaoxon equivalents, which is still about 50 times below maximal residue levels. Testing of the melhod for practical application on a set of 60 samples gave no false negalive results and a level of 1.7 % false positives

Photocatalytic degradation of dimethoate using LbL fabricated TiO2/polymer hybrid films

Degradation of dimethoate under UV irradiation using TiO2/polymer films prepared by the layer-by-layer (LbL) method was investigated. The thin films were fabricated on glass slides and the surface morphology and roughness of the thin films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effect of lamp intensity, catalyst loading in the layers, number of bilayers, pH and initial dimethoate concentration on the degradation of dimethoate was systematically studied. The degradation was monitored using high performance liquid chromatography (HPLC) analysis and total organic carbon (TOC) measurements as a function of irradiation time, to see the change in concentration of dimethoate and mineralization, respectively. Complete degradation of dimethoate was achieved under TiO2 optimum loading of 4 g/L at an UV irradiation time of 180 min. Increase in the lamp intensity, catalyst loading and number of bilayers increased the rate of degradation. At a pH of 4.62, complete degradation of dimethoate was observed. The degradation efficiency decreased with increase in initial dimethoate concentration. The degradation byproducts were analyzed and confirmed by gas chromatography-mass spectra (GC-MS). Toxicity of the irradiated samples was measured using the luminescence of bacteria Vibrio fischeri after 30 min of incubation and the results showed more toxicity than the parent compound. Catalyst reusability studies revealed that the fabricated thin films could be repeatedly used for up to ten times without affecting the photocatalytic activity of the films. The findings of the present study are very useful for the treatment of wastewaters contaminated with pesticides. (C) 2011 Elsevier B.V. All rights reserved