Ultraviolet photodegradation of folic acid

The vitamin folate is vital for all living creatures. Scientists have suggested that ultraviolet degradation of folate in vivo played a role in the evolution of mankind. In order to better understand the photodegradation of folate, we have provided a spectroscopic study of the ultraviolet photodegradation of aqueous folic acid under aerobic conditions. We found strong indications that the folic acid molecule is cleaved into p-aminobenzoyl-L-glutamic acid and 6-formyl pterin when exposed to ultraviolet radiation. When the irradiation continues, 6-formyl pterin is degraded to pterin-6-carboxylic acid. The photodegradation of folic acid is divided into three phases. In the first phase, the formation of photoproducts follows a zero order rate law. In the second phase the presence of photoproducts sensitizes the degradation of folic acid and the degradation process is accelerated. In the third phase the degradation of 6-formyl pterin to pterin-6-carboxylic acid is the dominating process. This reaction follows a first order rate law. We show that both 6-formyl pterin and pterin-6-carboxylic acid sensitize the photodegradation of folic acid. However, experiments performed in heavy water indicate that generation of singlet oxygen is probably not the explanation for the photosensitizing of folic acid.     

The phototransformation of 4-chloro-2-methylphenoxyacetic acid under KrCl and XeBr excilamps irradiation in water

The effect of UV radiation of a KrCl and a XeBr on the photodegradation of 4-chloro-2-methylphenoxyacetic acid (MCPA) was studied. The main photoproducts were identified by gas chromatograph/mass spectrometry (GC/MS). The variation of chlorine-ion and active chlorine in MCPA aqueous solution exposed to excilamp radiation was also defined by analytical methods. Irradiation of MCPA solution with a KrCl excilamp emitting mainly at 222 nm yield 2-methylhydroquinone and lactone of 2-hydroxy-3-methyl-5-chlorophenoxyacetic acid as the main photoproducts. Irradiation of MCPA solution with a XeBr excilamp emitting mainly at 283 nm yield 2-methylhydroquinone as the main photoproduct. Biological processes are not suitable for MCPA removal due to low or total absence of biodegradability of this class of pollutants. Estimation of biodegradability of phototreated MCPA solution was carried out according to ratios of biological oxygen demand (BOD₅) to chemical oxygen demand (COD). The biodegradability of MCPA solutions increased after irradiation.     

Effect of light intensity and wavelengths on photodegradation reactions of riboflavin in aqueous solution

A study of the effect of light intensity and wavelengths on photodegradation reactions of riboflavin (RF) solutions in the presence of phosphate buffer using three UV and visible radiation sources has been made. The rates and magnitude of the two major photodegradation reactions of riboflavin in phosphate buffer (i.e., photoaddition and photoreduction) depend on light intensity as well as the wavelengths of irradiation. Photoaddition is facilitated by UV radiation and yields cyclodehydroriboflavin (CDRF) whereas photoreduction results from normal photolysis yielding lumichrome (LC) and lumiflavin (LF). The ratios of the photoproducts of the two reactions at 2.0 M phosphate concentration, CDRF/RF (0.09-0.22) and CDRF/LC (0.54-1.75), vary with the radiation source and are higher with UV radiation than those of the visible radiation. On the contrary, the ratios of LF/LC (0.15-0.25) increase on changing the radiation source from UV to visible. The rate is much faster with UV radiation causing 25% degradation of a 10(-5) M riboflavin solution in 7.5 min compared to that of visible radiations in 150-330 min.     

On-fiber photodegradation after solid-phase microextraction of p,p'-DDT and two of its major photoproducts,p,p'-DDE and p,p'-DDD

The potential of performing photochemical studies in solid phase microextraction (SPME) fibers, "photo-SPME", to study the photodegradation of p,p'-DDT and two of its major degradation products, p,p'-DDE and p,p'-DDD, is shown. Analyses were carried out by gas chromatography mass spectroscopy detection. DDT was extracted from aqueous solutions using five different commercial coatings. The fibers were then exposed to UV light emitted by a low-pressure mercury lamp. After 30 min of irradiation, the degradation of DDT only occurred in polydimethylsiloxane fibers. The on-fiber degradation kinetics of p,p'-DDT was studied from 2 to 60 min. A large number of photoproducts were generated and their kinetic behavior was studied. In order to clarify the possible photoreaction pathways for DDT, individual water solutions containing p,p'-DDD or p.p'-DDE were prepared and photo-SPME was performed for each compound at different irradiation times. On the basis of the photoproducts identified, some photodegradation pathways are proposed. Finally, aqueous photodegradation studies followed by SPME were performed and compared to the photo-SPME. This work will show the enormous potential of photo-SPME to perform photodegradation studies.     

Reactive oxygen species formation by UV-A irradiation of urocanic acid and the role of trace metals in this chemistry

We have extended our study of the decomposition of urocanic acid (UCA) with ultraviolet A radiation (UV-A) by the self-sensitized generation of singlet oxygen (see Photochem. Photobiol. 75, 565 [2002]). The chemistry has been found to be partially dependent on the presence of trace metal, most likely iron. Rigorous removal of metal impurities from the reaction mixture, using Chelex, retarded (but did not eliminate) the UV-A-initiated UCA degradation. The addition of small amounts of ferric chloride to the Chelex-treated solutions restored reactivity. Chelex treatment had a modest effect on the previously reported ability of UCA photoproducts to photonick supercoiled plasmid DNA. Also, photoinactivation of Sindbis virus on irradiation with the UCA photoproducts is now reported. Inactivation of the virus by a photoproduct mixture derived from a UCA solution that had been pretreated with Chelex was less rapid and gave better behaved time-course plots than was observed for photoproducts from non-Chelex treated solutions. These results are particularly noteworthy in light of the ubiquitous presence of both UCA and iron in the skin.     

Effect of binary and ternary polyethyleneglycol and/or beta-cyclodextrin complexes on the photochemical and photosensitizing properties of Naproxen

The effect of the polyethylene glycol and/or beta-cyclodextrin on the photolability of aqueous solutions of the anti-inflammatory drug Naproxen was studied. In all systems studied, the photodegradation process followed zero-order kinetics, leading to the same photoproducts as in the absence of these additives. Kinetic studies revealed that the presence of polyethylene glycol (PEG) reduced drug photodegradation (phi=0.11 in water and phi=0.045 in the presence of 1% of PEG). By contrast, the binary inclusion complex, Naproxen:beta-CD, did not protect the drug from degradation, phi=0.11. However, the ternary complex, Naproxen:beta-CD:PEG, reduced the efficiency of the photodegradative process to a considerable extent, with phi=0.022 in this system. In all cases the presence of the different additives elicited a change in the photomixture composition, the alcoholic derivative being the major photoproduct formed. Nevertheless, the change in the efficiency of the process and the amount of the photoproducts formed in the different systems were not related with the biodamage produced by the drug. In this sense, the presence of free Naproxen clearly sensitized the photoperoxidation of linoleic acid. The photosensitizing effect decreased as the PEG concentration increased and was completely abolished by both the binary (Naproxen:beta-CD) and ternary (Naproxen:beta-CD:PEG) complexes. In light of these observations, it is possible to speculate that in these systems the prevention of biodamage would be due to a decrease in the contact between the short-lived species generated during Naproxen photodegradation and biological structures, rather than to the nature or amount of the photoproducts.     

PHOTOSENSITIZATION BY METHOTREXATE PHOTOPRODUCTS

Abstract— Photoproducts induced upon excitation of methotrexate by UV light have been separated by ion exchange chromatography. They include 2,4-diamino-6-pteridinecarboxylic acid, 2,4-diamino-6-pteridine-carboxaldehyde and other unidentified pteridine derivatives. The same photoproducts can be also formed upon photodynamic reaction using hematoporphyrin as photosensitizer. In oxygen saturated aqueous solutions (pH∼7), methotrexate photoproducts sensitize the oxidation of histidine and tryptophan by UV light by a process involving singlet oxygen. In aqueous solutions containing albumin or in human serum, the same photoproducts are formed from free methotrexate but not from albumin-bound methotrexate. In the latter case the results may suggest that methotrexate covalently binds to albumin upon excitation with UV light either in absence or in presence of oxygen. These results could explain the photosensitization accompanying cancer chemotherapy with high dose methotrexate and also the synergistic effects of PUVA + low dose methotrexate in psoriasis therapy.     

Photolysis of thin films of cypermethrin using in situ FTIR monitoring: Products, rates and quantum yields

Cypermethrin is a synthetic pyrethroid insecticide commonly used both indoors and outdoors. Following its application, cypermethrin residues are exposed to atmospheric oxidants, such as ozone and OH radicals, as well as to solar radiation. The current work focuses on the photochemical degradation of cypermethrin under 254 nm, 310 nm, and solar radiation; including kinetic analysis, quantum yields, and identification of volatile and non-volatile products. The investigation was done using a combined FTIR set-up for parallel analysis of condensed and gas phases. Complementary GC–MS analysis was conducted on the pesticide’s residues. Quantum yields of 0.41 and 0.25 were obtained under 254 and 310 nm, respectively. These values are in agreement with outdoor studies and are higher than the known yields for aqueous solution. The values obtained under all tested conditions suggest that photodegradation of adsorbed cypermethrin is a major outdoor degradation pathway. Oxygen presence was found to increase degradation rate and quantum yield.The identified photoproducts include 3-phenoxybenzaldehyde, 3-phenoxybenzoic acid, acetonitrile (m-phenoxyphenyl), and cypermethrin isomers on the surface and formic acid, CO₂ and CO in the gas phase. The condensed phase products are more polar than the parent molecule, suggesting that they may be susceptible to a greater leaching rate in soils.     

A Laser Flash Photolysis Study on Fenofibric Acid

Fenofibric acid (FA) is a photosensitizing drug used in the treatment of hyperlipidemia. This compound follows two different photodegradation pathways: the free acid exhibits the typical benzophenone photoreactivity, while its sodium salt undergoes photodecarboxylation via a triplet biradical, that undergoes intramolecular electron transfer to form a carbanion, or cyclization to give an intramolecular light-absorbing transient (LAT). The obtained photoproducts are explained as the result of pro-tonation of the carbanion, ring opening of the LAT with rearrangement or oxygen trapping of any of the triplet intermediates. The above mechanism is supported by direct detection of the triplet state of FA and two long-lived intermediates in laser flash photolysis experiments. The triplet lifetime of the carboxylate form in methanol is 0.06 μ.s; by contrast, in the case of the free acid, it is 10 times longer. The benzophenone moiety is clearly the key chromophore involved in the photobehavior of FA.     

Photochemistry of riboflavin derivatives in methanolic solutions

Light-induced degradation of the riboflavin derivatives is reported, including 5-deaza-riboflavin, iso-6,7-riboflavin, 3-methyl-tetra-acetyl-riboflavin (3MeTARF), and 3-benzyl-lumiflavin. The studied compounds undergo photolytic processes with considerable quantum yields in methanolic solutions (φ ≈ 10(-3)-10(-4) mol einst(-1)). Photolysis in anaerobic conditions is more efficient than that in the presence of oxygen. Experiments show that triplet excited state of flavin molecules is involved in the reactions. The main photoproducts are the respective alloxazinic and isoalloxazinic derivatives of the substrates. 3MeTARF reveals higher photostability than riboflavin. The values of photodegradation quantum yields were estimated for the four studied derivatives.     

β-Cyclodextrin as a photostabilizer of the plant growth regulator 2-(1-naphthyl) acetamide in aqueous solution

The plant growth regulator 2-(1-naphthyl) acetamide (NAAm) is susceptible to degradation by sunlight and UV light in aqueous solution. Its inclusion complex with β-cyclodextrin (β-CD) was characterized by absorption and fluorescence spectroscopy and its photodegradation was compared with that of aqueous solutions of NAAm. The complex was formed with a stoichiometric ratio of 1:1 with a binding constant of 651 M^?1. The photodegradation behavior of NAAm in the inclusion complex NAAm:β-CD was investigated using both UV (λ = 254 nm) and simulated solar light (Suntest) irradiation. It was found that the NAAm:β-CD complex increases NAAm photostability towards photochemical degradation markedly. In addition, an influence of β-CD concentration was also observed on NAAm degradation rate: higher β-CD concentrations lead to a slower photoinduced transformation. Moreover, some differences were found in the photoproducts in the presence and absence of the cyclodextrin, indicating inhibition of some of the mechanistic pathways. β-CD stabilizes NAAm photodegradation towards sunlight and UV irradiation, enhancing its efficient application on formulations for the treatment of fruits and vegetables.     

Study of the photoinduced degradation of polycyclic musk compounds by solid-phase microextraction and gas chromatography/mass spectrometry

Polycyclic musks are widely used synthetic fragrances that have been identified during the last few years in biota samples and environmental matrices. Nevertheless, there is a lack of information concerning the photodegradation behavior of these compounds. In this work, the photoinduced degradation of six polycyclic musk compounds (Cashmeran, Celestolide, Phantolide, Galaxolide, Traseolide and Tonalide) was studied using a solid-phase microextraction (SPME) fiber as support. Musk fragrances were extracted from aqueous solutions using SPME fibers that were subsequently exposed to ultraviolet (UV) irradiation for different times. To study the degradation kinetics and to tentatively identify the photoproducts generated, gas chromatography coupled to ion trap mass spectrometry was used. Aqueous photodegradation studies were also performed. The on-fiber photodegradation approach avoids the need for further extraction processes and makes the identification of photoproducts easier, due to their higher concentration on the fibers. All musk compounds were easily photodegraded, suggesting that UV irradiation could work as a decontamination tool for these musks.     

Investigation of photodegradation products generated after UV-irradiation of five polybrominated diphenyl ethers using photo solid-phase microextraction

In this study, the photoinduced degradation of five polybrominated diphenyl ethers (PBDEs), BDE-47, BDE-100, BDE-99, BDE-154 and BDE-153, is studied using solid-phase microextraction polydimethylsiloxane fibers as photolytic support. PBDEs are extracted from aqueous solutions using SPME fibers that are subsequently exposed to UV irradiation for different times (from 2 to 60 min). Photodegradation kinetics of the five PBDEs, tentative identification and photochemical behavior of the generated photoproducts, as well as photodegradation pathways, have been studied employing this on-fiber approach technique (photo-SPME) followed by gas chromatography-mass spectrometry analysis. Aqueous photodegradation studies have also been performed and compared with photo-SPME. All the photoproducts detected in the aqueous experiments were previously found in the photo-SPME experiments. In this study, reductive debromination by successive losses of bromine atoms is confirmed as the main photodegradation pathway of PBDEs. A large number of PBDEs were obtained as photoproducts of the five target analytes. Other mechanism of photodegradation observed was intramolecular cyclization from the homolytic dissociation of the C-Br bond; thus, polybromo-dibenzofurans were generated. This work contributes to the study of the photodegradation of PBDEs and shows the potential of photo-SPME to evaluate the photo-transformation of organic pollutants.     

Photo-oxidation of phenol over titania pillared zirconium phosphate and titanium phosphate

The photodegradation of phenol was studied in the aqueous solutions over titania pillared zirconium phosphate and titanium phosphate under solar radiation and compared with that of the UV-radiation (6 W low pressure Hg vapor lamp). This reaction was studied by varying different parameters such as catalyst dose, initial phenol concentration, pH of solution and irradiation time. The degradation rate of phenol was favourable under neutral pH condition. The degradation process approximately obeyed first-order kinetics with apparent rate of degradation constant increasing with decreasing the initial phenol concentration.     

UV light induced photodegradation of liposome encapsulated fluoroquinolones: An MS study

Fluoroquinolone antibacterial agents are among the drugs most commonly causing phototoxic side effects. The phototoxicity may be originated in formation of reactive oxygen species upon ultraviolet exposure. Researches aiming the liposomal encapsulation of fluoroquinolones, expecting an increase in their therapeutic index, enhance the importance of studies on physicochemical properties and photostability of liposomal preparations. We studied the photodegradation of ciprofloxacin, ofloxacin and lomefloxacin by mass spectrometry upon various doses of UV irradiation. Lomefloxacin, the most phototoxic fluoroquinolone among them, was encapsulated into small unilamellar and multilamellar liposomes. Impact of vesicle structure and lipid composition – the presence of unsaturated fatty acid containing dioleoyl-phosphatidylcholine in dipalmitoyl-phosphatidylcholine liposomes – on the lomefloxacin photolysis was investigated; the structure of the main photoproducts was identified by mass spectrometry. It was found that the presence and type of lipids influence the ways of photodegradation process.     

A new on-line solid phase extraction high performance liquid chromatography tandem mass spectrometry method to study the sun light photodegradation of mono-chloroanilines in river water

The study investigates the natural photodegradation pathway of mono-chloroanilines in river waters, with the aim to identify the predominant photoproducts formed. At this purpose a new sensitive on-line SPE HPLC–MS/MS method has been developed with LOQ values equal or lower than the legal threshold concentration levels allowed for mono-chloroanilines in waters. The degradation processes of o-, m- and p-chloroaniline have been investigated subjecting their solutions, prepared both in ultrapure and in river water, to sun light irradiation simulated by a solar box system. The SPE HPLC–MS/MS methodology allowed to evaluate the degradation kinetics, to identify the predominant photodegradation products and to propose the chemical structures. Two photoproducts (aniline and 3-aminophenol), for which standards are available, have also been quantified.     

Application of solid-phase microextraction to the study of the photochemical behaviour of five priority pesticides: "on-fiber" and aqueous photodegradation

Solid-phase microextraction (SPME) is applied to study the photochemical degradation of five priority pesticides: atrazine, alachlor, aldrin, dieldrin, endrin. Analyses were carried out by gas chromatography-mass spectrometry. The possibility of studying the photochemical degradation of the target compounds in solid-phase microextraction fibers, "photo-SPME", is evaluated employing different SPME coatings. The target analytes were extracted from aqueous solutions using different commercial coatings and then, the fibers were exposed to UV light. Results indicated that on-fiber photodegradation takes place in a considerably major extent using PDMS coating for an irradiation time of 30min. On-fiber photodegradation kinetics of each analyte were determined by UV irradiation of the PDMS for different times. A large number of photoproducts were generated and they were tentatively identified by means of their mass spectra and with the aid of literature. In this way, main photodegradation mechanisms could be postulated. Aqueous photodegradation studies followed by SPME were performed and compared with photo-SPME. All the photoproducts detected in the aqueous experiments were previously found in the photo-SPME experiments. This study shows the potential of photo-SPME to evaluate the photo-transformation of organic pollutants.     

Further research on the photo-SPME of triclosan

In this study the photoinduced degradation of triclosan has been investigated by photo-solid-phase microextraction (photo-SPME). In photo-SPME, photodegradation is carried out on the SPME fibre containing the target compound. Triclosan was extracted from aqueous solutions by use of polydimethylsiloxane SPME fibres and these were subsequently exposed to UV irradiation (power 8 W, wavelength 254 nm) for different times (from 2 to 60 min). The photodegradation kinetics of triclosan were investigated, the photoproducts generated were tentatively identified, and the photochemical behaviour of these products was studied by use of this on-fibre approach followed by gas chromatographic–mass spectrometric analysis. Eight photoproducts were tentatively identified, including chlorinated phenols, chlorohydroxydiphenyl ethers, 2,8-dichlorodibenzo-p-dioxin, and a possible dichlorodibenzodioxin isomer or dichlorohydroxydibenzofuran. The main photodegradation mechanisms were postulated and photodegradation pathways proposed. The effect of pH on triclosan degradation and on triclosan-to-dioxin conversion was also investigated. Triclosan degradation occurred, and generation of 2,8-dichlorodibenzo-p-dioxin was confirmed, throughout the pH range studied (from 3 to 9).      

Photochemical behavior of sitafloxacin, fluoroquinolone antibiotic, in an aqueous solution

Sitafloxacin (STFX) hydrate, an antimicrobial agent, is photo-labile in aqueous solutions. The photodegradation rates (k) in neutral solutions were higher than those observed in acidic and alkaline solutions and maximum at the maximum absorption wavelength of STFX. The structures of photodegradation products were elucidated as 7-[7-amino-5-azaspiro[2.4]heptan-5-yl]-6-fluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid and 1-(1-amino-2-[16-fluoro-1-(2-fluoro-1-cyclopropyl)-1,4-dihydro-4-oxo-3-quinolin-7-yl]-amino]ethyl)cyclopropanecarbaldehyde. This implies that dechlorination is the key step in the photodegradation of STFX. The effect of halide ions on the photodegradation of STFX was estimated by observing the increments in the photostability of STFX with the addition of chloride ions. In contrast, in the presence of bromide ions, instead of increased photostability of the STFX rate, a new photodegradation product in the presence of bromide ion was observed. The structure of this new photodegradation product was an 8-bromo form of STFX, which was substituted for chlorine at the 8-position, so the dissociation of C-Cl bond at the 8-position of STFX was the rate-limiting step in the initial process of the photodegradation. STFX generated .C (carbon centered radical) and .OH (hydroxyl radical) in the process of photodegradation in a pH 4.0 buffer. On the contrary, STFX did not generate C in the presence of chloride ion in a pH 4.0 buffer. The .C was generated and then degraded into the above degradation products by photoirradiation in the absence of chloride ion, but the .C immediately reacted with chloride when it was present. As a result, the C-Cl bond was recovered leading to a possible increase in the apparent photostability.     

Inhibited degradation of nylon 66 in presence of nitrogen dioxide,ozone, air,and near—ultraviolet radiation

Degradation of nylon 66 films of different morphologies was studied in the presence of nitrogen dioxide, ozone, oxygen, and near-ultraviolet radiation (λ > 2900 Å). Films cast from formic acid solution showed normal random degradation, whereas films cast from benzyl alcohol solutions and dried at elevated temperatures under nitrogen showed very strongly inhibited random degradation. This inhibition may be due to protection of peptide groups by hydrogen bonding with benzaldehyde or benzoic acid or even to their chemical reactions at elevated temperatures. Oxygen was not rigorously excluded during preparation of the films. Degradation of nylon 66 films cast from formic acid solutions at room temperature containing benzaldehyde or benzoic acid, respectively, is also inhibited. The energy of activation for inhibited degradation in presence of nitrogen dioxide is relatively small, indicating that the process is either controlled by diffusion of polymer radicals from medium cages or by diffusion of gases into the polymer. The degradation kinetics can be expressed by “weak”-link random degradation. The weak links are in the present case unprotected peptide groups. The functional relationship between chain scission rate constants and NO₂ pressure is linear.