Major Photodegradation Products Research Articles

Phototransformation of halobenzoquinones in aqueous solution under the simulate sunlight: Kinetics, mechanism and products

Halobenzoquinones (HBQs) are a novel family of unregulated disinfection byproducts (DBPs). Little is known about their phototransformation activities in natural water. Here, five HBQs with various halogenated substituent types, numbers, and structures positions were selected to investigate the kinetics of degradation in aqueous solutions at various concentrations and in the presence of common environmental variables (Cl−, NO2−, and humic acid). The results indicated that dichloride and dibromo-substituted HBQs were photolyzed, whereas tetrachloro-substituted HBQs showed little degradation. The photolysis rate constant (k) of HBQs decreased with increasing initial concentration. The presence of NO2− and Cl− promoted the degradation of HBQs mainly through the formation of hydroxyl radical (•OH), which were confirmed by electron paramagnetic resonance (EPR). In contrast, humic acid played a negative role on HBQs transformation due to the adsorption and quenching reactions. Possible conversion pathways for HBQs were proposed based on the identification of two major photodegradation products, hydroxylated HBQs and halogenated-benzenetriol, as well as reactive free radicals. This study provided meaningful insights into the environmental fates and risk assessments of HBQs in natural aquatic system.

Stability-Indicating Quantification of Ciprofloxacin in the Presence of Its Main Photo-Degradation Product by CZE and UPLC: A Comparative Study

Active pharmaceutical ingredients (APIs) can be assured to be safe and effective with the help of stability-indicating procedures. An accurate comparison comprising the utilization of capillary zone electrophoresis (CZE) and ultra-performance liquid chromatography (UPLC) for the sensitive and accurate measurement of ciprofloxacin (CPF) in the presence of its major photo-degradation product was conducted. The CZE and UPLC working conditions were optimized to obtain the best pattern of separation for CPF and its photo-degradant. The linearity range of the cited techniques was confirmed to be 0.5 to 50 µg/mL. A thorough validation scheme according to the ICH-Q2B criteria was performed, including linearity, accuracy, precision, robustness, detection, and quantification limits. Selective quantification of CPF in the presence of up to 90% of its main photo-degradant was carried out using the proposed methods. For the analysis of CPF in tablet and intravenous (I.V.) solution forms, the CZE and UPLC procedures were applied. The suggested methods can be applied to keep an eye on the safety and efficacy of CPF in either bulk or dosage forms.

Initial Excited State Dynamics of Lumichrome upon Ultraviolet Excitation.

Lumichrome (LC) is the major photodegradation product of biologically important flavin cofactors. Since LC serves as a structural comparison with the flavins; understanding excited states of LC is fundamentally important to establish a connection with photophysics of different flavins, such as lumiflavin (LF), riboflavin (RF), flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Herein, we deduce the initial excited state structural dynamics of LC using UV resonance Raman (UVRR) intensity analysis. The UVRR spectra at wavelengths across the 260 nm absorption band of LC were measured and resulting Raman excitation profiles and absorption spectrum were self-consistently simulated using a time-dependent wave packet formalism to extract the initial excited state structural and solvent broadening parameters. These results are compared with those obtained for other flavins following UV excitations. We find that LC undergoes a very distinct instantaneous charge redistribution than flavins, which is attributed to the extended π-conjugation present in flavins but missing in LC. The homogeneous broadening linewidth of LC appears to be lower than that of LF, while the inhomogeneous broadening values are comparable, indicating greater solvent interaction with excited flavin on ultrafast timescale compared with LC, whereas on longer timescale these interactions are almost similar.

Photocatalytic degradation of profenofos using silver-platinum doped zeolite

Organophosphate insecticides are persistent organic pollutants that have a variety of adverse impacts in several environmental compartments. The photo-degradation of organophosphate profenofos was researched in the presence and absence of silver-platinum-doped zeolite in (Ag-Pt-Zeolite) upon irradiation with ultraviolet light at wavelengths of 302 and 254 nm. Photo-degradation of profenofos at 302 nm and in the presence of Ag-Pt-Zeolite was 73 % complete in 60 min. GC/MS analysis indicated the formation of two major photo-degradation products upon irradiation with 302 nm in the presence of the catalyst. Moreover, four products were identified for the irradiation with 254 nm in the presence of the catalyst and for the uncatalyzed irradiated profenofos samples. The toxicity of the degradation products was assessed by exposure experiments using Drosophila melanogaster. These experiments showed that degradation resulted in overall less toxic products within the first 30 min of degradation, followed by an overall increase in toxicity after 30 min of UV exposure. The present work provides a treatment technique for the adequate removal of profenofos from water sources in order to mitigate its detrimental effects on the environment.

HPLC method for simultaneous analysis of ticagrelor and its organic impurities and identification of two major photodegradation products

A simple, fast and sensitive analytical method by high-performance liquid chromatography (HPLC) was developed and validated for the simultaneous determination of ticagrelor and two synthesis impurities. The HPLC method was established using an Agilent 1200 Series equipment coupled to photodiode array detector (PDA) at 270nm with a Zorbax Plus C8 column (150×4.6mm, 5.0μm), injection volume of 20μL, and a constant temperature of 25°C. The mobile phase consisted of acetonitrile: ammonium acetate 50mM (57:43, v/v) and pH adjusted to 8.2 with ammonium hydroxide 6M, at a flow rate of 0.7mL/min. No interference peaks from excipients and diluent system indicated the specificity of the method. The calibration curves showed determination coefficients (r2)>0.99, calculated by linear regression. The limit of quantitation (LOQ) for impurities 1 and 2 were 2.0 and 0.2μg/mL, respectively. Intra and interday relative standard deviations (RSDs) were <2% for ticagrelor and <6% for the impurities, proving the precision of the method. Besides, two mayor degradation products formed when sample solutions of ticagrelor were exposed to UVC radiation were elucidated and the mechanisms involved in the photolytic degradation of ticagrelor were proposed.

Liquid chromatographic–mass spectrometric monitoring of photodegradation of diphenylamine using experimental design methodology

Abstract Diphenylamine (DPA) photodegradation was studied by applying the optimal response surface design methodology to the chromatographic data from pollutant solutions exposed to stressing irradiation. The procedure consisted of data analysis of aliquots collected at different reaction times and injected to a high-performance liquid chromatography coupled to diode array detection-mass spectrometry (HPLC–DAD–MS). The variables considered for the process optimization were irradiation power, irradiation time and pH of solution, for a solution with DPA concentration of 100 mg L −1 . This methodology allowed assessing and identifying the effects of different factors studied and their interactions in the process response. An appropriate quadratic model was developed in order to plot the response surface and contour curves and to perform the process optimization. The results obtained revealed that DPA photodegradation is strongly dependent on the solution pH and irradiation power. Under the optimal conditions (i.e., pH of 10, irradiation power of 2 × 15 W lamp and irradiation time of 150 min), it was possible to achieve an almost complete photodegradation of DPA. The process was found to follow a pseudo-first-order kinetic model. Mass spectrometric analysis allowed the identification of carbazole (CB) as the major photodegradation product. A possible pathway for the photodegradation of DPA was suggested. The optimized methodology was applied to preparation and separation of CB, as an important mediator in fine chemistry and pharmacy, from DPA by thin layer chromatography.

Photodegradation kinetics of lodenafil carbonate, structure elucidation of two major degradation products using UPLC-MS/MS and in vitro cytotoxicity

The photostability of lodenafil carbonate was studied and some degradation products were observed. A stability-indicating liquid chromatography method for the determination of lodenafil carbonate was used to determine the kinetics of photodegradation. The identification of two major photodegradation products was performed by an isocratic ultra performance liquid chromatography-tandem mass spectrometry method (UPLC-MS/MS). UPLC-MS/MS was carried out on a Waters® Acquity Ultra Performance LC system coupled to a Micromass® Quadrupole Time of Flight tandem mass spectrometer equipped with an electrospray ionization interface in positive ion mode. The column applied was Acquity UPLC® BEH C18; the mobile phase consisted of a mixture of methanol–formic acid 0.1% pH 4.0 (55 : 45, v/v) at a flow-rate of 0.4 mL min−1 and UV detection at 290 nm. The photodegradation of lodenafil carbonate followed first-order reaction kinetics and the kinetic parameters of degradation rate constant and t90% were calculated. Under photodegradation conditions, ion products were detected at m/z 393 (DP-1) and at m/z 377 (DP-2). The product DP-1 is 4-ethoxy-3-(1-methyl-7-oxo-3-propyl-6,7-dihydro-1H-pyrazolo [4,3-d]pyrimidin-5-yl)-benzenesulfonic acid and DP-2 probably is 4-ethoxy-3-(1-methyl-7-oxo-3-propyl-6,7-dihydro-1H-pyrazolo [4,3-d]pyrimidin-5-yl) benzenesulfinic acid. The degraded samples of lodenafil carbonate were also evaluated in order to determine the in vitro cytotoxicity against mononuclear cells.

Captopril and its dimer captopril disulfide: Photodegradation, aerobic biodegradation and identification of transformation products by HPLC–UV and LC–ion trap-MSn

In some countries effluents from hospitals and households are directly emitted into open ditches without any further treatment and with very little dilution. Under such circumstances photo- and biodegradation in the environment can occur. However, these processes do not necessarily end up with the complete mineralization of a chemical. Therefore, the biodegradability of photoproduct(s) by environmental bacteria is of interest.Cardiovascular diseases are the number one cause of death globally. Captopril (CP) is used in this study as it is widely used in Egypt and stated as one of the essential drugs in Egypt for hypertension. Three tests from the OECD series were used for biodegradation testing: Closed Bottle test (CBT; OECD 301 D), Manometric Respirometry test (MRT; OECD 301 F) and the modified Zahn–Wellens test (ZWT; OECD 302 B). Photodegradation (150W medium-pressure Hg-lamp) of CP was studied. Also CBT was performed for captopril disulfide (CPDS) and samples received after 64min and 512min of photolysis.The primary elimination of CP and CPDS was monitored by LC–UV at 210nm and structures of photoproducts were assessed by LC–UV–MS/MS (ion trap). Analysis of photodegradation samples by LC–MS/MS revealed CP sulfonic acid as the major photodegradation product of CP. No biodegradation was observed for CP, CPDS and of the mixture resulting from photo-treatment after 64min in CBT. Partial biodegradation in the CBT and MRT was observed in samples taken after 512min photolysis and for CP itself in MRT. Complete biodegradation and mineralization of CP occurred in the ZWT.

Isolation and structure elucidation of the major photodegradation products of seratrodast

Photodegradation of seratrodast ([±]-7-(3,5,6-trimethyl-1,4-benzoquinone-2-yl)-7-phenyl-heptanoic acid, SD), a p-benzoquinone anti-asthmatic drug, has been investigated in different solutions. HPLC analysis showed that SD was degradated under UV irradiation at 254 nm to afford three major products (SD1, SD2 and SD3) in methanol and in acetonitrile/H 2O solutions, while only two of them (SD2 and SD3) could be detected in acetonitrile solution. Furthermore, SD1 was unstable even when the samples were protected from light, so the acetylated SD1 (Ace-SD1) together with SD2 and SD3 were isolated by semi-preparative reversed-phase HPLC. The structures were elucidated as 6-(2,5-diacetoxy-3,4,6-trimethyl-phenyl)-7-phenyl-hept-6-enoic acid (Ace-SD1), 7-phenyl-6-(2,4,5-trimethyl-3,6-dioxo-cyclohexa-1,4-dienyl)-hept-6-enoic acid (SD2) and 5-(5-hydroxy-4,6,7-trimethyl-2-phenyl-benzofuran-3-yl)-pentanoic acid (SD3) based on the spectral data of MS, UV spectrum, IR spectrum and NMR spectrum. Meanwhile, a possible route for the formation of these photoproducts was proposed, which might explain the generation procedure of SD1, SD2 and SD3 during UV irradiation.

Improved photostability indicating ion-pair chromatography method for pergolide analysis in tablets and in the presence of cyclodextrins

Pergolide (PG) a semi-synthetic ergot alkaloid derivative used mainly for the treatment of Parkinson's disease is known to be a photosensitive drug substance. The major photodegradation products are PG sulphoxide (SX) and PG sulphone (SN), which are also the main impurities of the bulk drug substance. It is widely metabolized to more than 10 metabolites including SX and SN. In this work an improved photostability indicating ion-pair chromatography method for PG mesilate was developed. The method can be applied in the determination of PG and impurities in aqueous solutions and in tablets for routine analysis. This new method is appropriate for the quantitative determination of PG in the presence of its impurities and photodegradation products and can also be used for PG complexes with cyclodextrins (commonly used as photostabilizing agents). Furthermore it is suitable for the quantitation of its impurities and its thermal or photo-induced decomposition products. Separation was achieved on a ThermoQuest C 18 BDS column and Sodium octanosulphonate was used as ion-pairing agent. Analysis was performed at 223 nm. Validation parameters included: specificity, linearity, precision and accuracy, limit of quantitation and suitability. The method was found to be specific and linear for PG, as well as for SX and, SN impurities. The recovery was 100.83 ± 0.46% for PG, 99.86 ± 0.33% for SX and 99.77 ± 1.84% for SN. Finally the photodegradation profile of PG mesilate was studied in different initial sample concentration. The obtained result revealed that: PG photolysis is catalyzed by its degradation products and that decrease of initial sample concentration reduces the rate of PG photoinduced degradation.

Pyrene—p-tert-butylcalixarenes inclusion complexes formation: a surface photochemistry study

Diffuse reflectance and luminescence techniques were used to study the photophysics and photochemistry of pyrene within p-tert-butylcalix[n]arenes with n = 4, 6, and 8, and to study their ability to form inclusion complexes in heterogeneous media. Evidences for inclusion complex formation were found for the three hosts under study. Ground state diffuse reflectance results have shown the formation of ground state dimers of pyrene inside the cavity of calix[6]arene and calix[8]arene, with this feature much more evident for calix[6]arene. For calix[4]arene, only a monomer fits inside the cavity and the presence of pyrene microcrystals outside the cavity was detected. A luminescence lifetime distribution analysis was performed, revealing the presence of prompt emissions from the pyrene microcrystals outside the cavity in the case of calix[4]arene and from the constrained dimers inside the cavities of calix[6]arene and calix[8]arene. Transient absorption results have shown the presence of pyrene radical cation and also of trapped electrons for the three hosts under study. The formation of the phenoxyl radical of the calixarene following the laser pulsed excitation of pyrene at 355 nm is increased for calix[6]arene and calix[8]arene. This feature is particularly relevant for calix[6]arene, suggesting a very favourable situation for the hydrogen atom abstraction to occur. The analysis of the degradation products revealed the presence of hydroxypyrene as a major photodegradation product for the three hosts. Dihydro-hydroxypyrene was also formed in the case of calix[6]arene and calix[8]arene. The formation of the calixarene's phenoxyl radical and subsequent hydrogen abstraction is consistent with the formation of dihydro-dihydroxypyrene.

Aquatic Photochemistry of Nitrofuran Antibiotics

The aquatic photochemical degradation of a class of pharmaceuticals known as the nitrofuran antibiotics (furaltadone, furazolidone, and nitrofurantoin) was investigated. Direct photolysis is the dominant photodegradation pathway for these compounds with the formation of a photostationary state between the syn and the anti isomers occurring during the first minutes of photolysis. The direct photolysis rate constant and quantum yield were calculated for each of the three nitrofurans. Reaction rate constants with reactive oxygen species (ROS), 102 and *OH, were also measured, and half-lives were calculated using environmentally relevant ROS concentrations. Half-lives calculated for reaction with 1O2 and *OH are in the ranges of 120-1900 and 74-82 h, respectively. When compared to the direct photolysis half-lives, 0.080-0.44 h in mid-summer at 45 degrees N latitude, it is clear that indirect photochemical processes cannot compete with direct photolysis. The major photodegradation product of the nitrofurans was found to be nitrofuraldehyde, which is also photolabile. Upon photolysis, nitrofuraldehyde produces NO, which is easily oxidized to nitrous acid. The acid produced further catalyzes the photodegradation of the parent nitrofuran antibiotics, leading to autocatalytic behavior. Natural waters were found to buffer the acid formation.

Iron-catalyzed photochemical transformation of benzoic acid in atmospheric liquids: Product identification and reaction mechanisms

This study investigated iron-catalyzed photochemical oxidation of benzoic acid (BA), one of the major photodegradation products of petroleum hydrocarbons, under sunlight or monochromatic light irradiation in a wavelength range of 254–419 nm. The photochemical degradation of BA in the absence of iron (III) occurred at irradiation wavelengths below 300 nm. The photochemical transformation of BA in the presence Fe(III) was observed at both 254, 350, 419 nm and under solar irradiation. The half-life for the photodegradation of BA (100 μM) was 160±20 min in the presence of 20 μM Fe(III) at pH 3.20 on sunny August days at noon time. The degradation rate increased with increasing concentration of Fe(III). The reaction products were separated and identified using capillary electrophoresis (CE), gas chromatography/mass spectrometry (GC/MS) and UV-Visible spectrophotometry. The major reaction products were 2-hydroxybenzoic, 3-hydroxybenzoic and 4-hydroxybenzoic acids. Hydrogen peroxide (H 2O 2) and Fe(II) species were also formed during the photochemical reactions. The proposed reaction mechanisms include the photoexcitation of Fe(III) hydroxide complexes to form Fe(II) ions and hydroxyl radicals (OH ) that attack ortho, meta and para positions of BA to form corresponding monohydroxybenzoic acids and H 2O 2. The monohydroxybenzoic acids formed further react with hydroxyl and surperoxide radicals (HO 2 − /O 2 − ) to yield dihydroxybenzoic acids in atmospheric water droplets.

Photochemistry of benzophenone on Ti-MCM-41 surfaces

Diffuse reflectance and chromatography techniques were used to study three Ti-MCM-41 solid powders, containing 1%, 2.5% and 8% of Ti, and to investigate the photochemistry of benzophenone adsorbed on their surfaces. The observed ground state absorption, luminescence and transient absorption spectra depend on the Ti content of the solid support. The luminescence intensity of the pure powders and of the solids with adsorbed benzophenone decreases with the Ti content. The benzophenone triplet emission was detected in all solids but its half-lives decrease with the Ti content of the support. Hydrogen-bonded excited benzophenone luminescence is also quenched but was detected only on supports with low Ti percentage. Transient absorption reveals the formation of trapped electrons and the presence of ligand-to-metal charge transfer in the pure solids, under 266 nm excitation. Ti aggregates are present in all used solid supports. Triplet–triplet absorption of benzophenone was observed in all solids under argon atmosphere. Transient absorption due to the OH–benzophenone radical was detected in all conditions and increases with the Ti content of the powder. 2-Hydroxybenzophenone and benzoic acid are the major photodegradation products in air-equilibrated conditions.

Acute enantioselective toxicity of fipronil and its desulfinyl photoproduct to Ceriodaphnia dubia

Fipronil is a phenylpyrazole insecticide increasingly used in applications such as rice culture, turf grass management, and residential pest control, with a high probability to contaminate aquatic environments. As a chiral pesticide, fipronil is released to the environment as a racemic mixture (equal amounts of optical isomers called enantiomers). Enantiomers can have different toxicological and biological activity; however, information on these differences, which is necessary for accurate risk assessment of chiral pesticides, is limited. Here we examine the acute toxicity of fipronil enantiomers, the racemate, and its photoproduct (desulfinyl fipronil) to Ceriodaphnia dubia. The 48-h median lethal concentration (LC50) values based on measured concentrations of each compound indicate the (+) enantiomer (LC50 = 10.3 +/- 1.1 microg/L, mean +/- standard error [SE]) was significantly more toxic to C. dubia than either the (-) enantiomer (LC50 = 31.9 +/- 2.2 microg/L) or racemate (LC50 = 17.7 +/- 1.3 microg/L). To account for any potential loss of fipronil through photolysis, tests were performed under light (fluorescent) and dark exposure conditions, and no significant differences in toxicity were observed. Desulfinyl fipronil, the major photodegradation product, which is not chiral, was detected at < 1% of each parent compound in test solutions after 48 h. Separate toxicity tests with desulfinyl fipronil found a > 20-fold higher LC50 (355 +/- 9.3 microg/L) compared to the fipronil racemate, suggesting lower adverse effects to C. dubia as a result of fipronil photolysis. The present results suggest selection of the (-) enantiomer in fipronil production for lower impacts to C. dubia; however, the consistency and relevancy of fipronil's enantiomer-specific activity at both acute and chronic levels of concern to additional target and nontarget species needs further consideration.

Photochemistry of benzophenone adsorbed on MCM-41 surface

The photochemistry of benzophenone adsorbed on a channel-type solid support MCM-41 was studied by the use of diffuse reflectance and chromatographic techniques. For comparison purposes parallel studies were also conducted on silicalite and H-ZSM-5. The observed ground state absorption, luminescence and transient absorption spectra and photoproduct distribution strongly depend on the substrate under study. Triplet state luminescence was observed in all solids, hydrogen-bonded excited benzophenone emission was detected on MCM-41 while protonated excited benzophenone luminescence was observed only on H-ZSM-5. Transient absorption showed the triplet state in all solids and formation of the OH benzophenone adduct on MCM-41 and H-ZSM-5. Ketyl radical formation occurs after 355 nm irradiation but is a minor degradation pathway. The formation of transients resulting from the reaction of benzophenone with molecular oxygen was also detected on MCM-41, in air-equilibrated conditions and benzoic acid is the main degradation product. 2-Hydroxybenzophenone is one of the major photodegradation products on MCM-41 and H-ZSM-5. Products resulting from the α-cleavage were also detected under 266 nm irradiation. Benzophenone was found to be very stable in silicalite under all used conditions.

Effect of Titanium Dioxide on Photostability of Solid-State Mequitazine

TiO(2) has been widely used in pharmaceutical products, and it also has been used as a photocatalyst. In this study, the influence of photocatalytic activity on the stability of solid-state mequitazine, an H(1)-blocker, was investigated. The photo-degradation of mequitazine with TiO(2) occurred under irradiation with both light sources. The degree of degradation of mequitazine with anatase was higher than that of rutile. The degradation was significantly enhanced with increasing relative humidity. The relationship between the apparent degradation rate constant and water vapor pressure could be clearly described by a simple power law. The major photo-degradation products of mequitazine, resulting from photocatalytic activity of TiO(2), were mequitazine-S-oxide and mequitazine-sulphone. A remarkable degradation of mequitadine occurred with addition of TiO(2), and its photocatalytic activity was controlled by water vapor pressure. The photo-degradation of mequitazine with TiO(2) is a different process from mequitazine without TiO(2), because mequitazine-S-oxide and mequitazine-sulphone are not formed with normal photo-degradation of mequitazine.

Identification of photoproducts from imazosulfuron by HPLC.

Photolysis of imazosulfuron was studied in aqueous solution under UV light. The reaction followed a pseudo-first-order kinetic with significant correlation coefficient. The major photodegradation products of imazosulfuron after irradiation under UV light were separated and tentatively identified by HPLC-MS analysis as (4,6-dimethoxypyrimidine-2-yl)aminocarbonylsulfamic acid, 4,6-dimethoxy-2-ureidopyrimidine and 2,2'-dichloro-[3,3'] bi [imidazo[1,2-a] pyridinyl]. The results indicate that different reaction pathways are followed: (1) cleavage of the sulfonylurea bridge; (2) desulfonylation, which can proceed either by a carbon-sulfur cleavage or a nitrogen-sulfur cleavage. A mechanism for the formation of the photoproducts is proposed.

Isolation and structure elucidation of the major photodegradation products of loteprednol etabonate

Photodegradation of loteprednol etabonate ( 5), a steroid anti-inflammatory drug, in the solid state, in aqueous suspension, and in aqueous acetonitrile solution has been investigated. Analysis by HPLC showed that the profile of photodegradation products in the solid state was qualitatively similar to that in the aqueous suspension, although the profile in the aqueous acetonitrile solution was considerably different. The major photodegradation products were isolated from the aqueous suspension and the aqueous acetonitrile solution by using preparative reversed-phase HPLC and their structures were elucidated on the basis of spectroscopic data. Photolysis in the solid state and in aqueous suspension yielded three rearrangement products, chloromethyl 17α-ethoxycarbonyloxy-11β-hydroxy-5α-methyl-2-oxo-19-norandrosta-1(10),3-diene-17β-carboxylate ( 8), chloromethyl 17α-ethoxycarbonyloxy-11β-hydroxy-1-methyl-3-oxo-6(5→10α)- abeo-19-norandrosta-1,4-diene-17β-carboxylate ( 9), and chloromethyl 1β,11β-epoxy-17α-ethoxycarbonyloxy-2-oxo-10α-androsta-4-ene-17β-carboxylate ( 10). In aqueous acetonitrile solution, 10 was the major product, however, 8 and 9 were not obtained. Pathways for the formation of these compounds from loteprednol etabonate ( 5) are proposed.

Aqueous photochemistry of pesticides triadimefon and triadimenol

The photochemistry of pesticides triadimefon and triadimenol was studied in aqueous solution and in methanol/water mixtures, in controlled and natural conditions. The photodegradation kinetics and product distribution are strongly dependent on the solvent and on the irradiation wavelength. The degradation rates are faster at 254 nm than at 313 nm. The kinetics is faster in water than methanol. Direct photoreaction is an important dissipation pathway of triadimefon in natural water systems while triadimenol is stable in these conditions. 1,2,4-Triazole and 4-chlorophenol are two of the major photodegradation products. The formation of the 4-chlorophenoxyl radical was detected for both pesticides in methanol and methanol/water mixtures. In methanol/water mixtures the reaction of both pesticides also occurs with 4-chlorophenolate formation, which increases with the water content. The photochemical studies of pesticides and other pollutants should be made in conditions as similar as possible to those observed in environmental systems.