Epoxiconazole degradation in water samples: a comparative study of Fenton, photo-Fenton, solar photo-Fenton, and solar photolysis processes.

Epoxiconazole (EPO) is classified as a persistent organic pollutant due to its ability to persist in the environment for prolonged periods. Its degradation is pivotal in mitigating its environmental impact. This investigation focuses on assessing the degradation of EPO using various methodologies, namely Fenton, photo-Fenton, solar photo-Fenton, and solar photolysis, conducted in both Milli-Q water and groundwater. These experiments encompassed evaluations at both the standard pH typically used in photo-Fenton reactions and the natural pH levels inherent to the respective aqueous environments. Additionally, EPO degradation products were analyzed after a 60-min reaction. Notably, in systems utilizing groundwater, the inclusion of additional iron was unnecessary, as the naturally occurring iron content in the groundwater facilitated the intended processes. Specifically, in Milli-Q water, solar photo-Fenton demonstrated an EPO degradation efficiency of 97%. Furthermore, the substitution of Milli-Q water with groundwater in Fenton-like processes did not significantly affect the efficacy of EPO degradation. These findings underscore the potential of solar photo-Fenton as an economically viable and environmentally sustainable strategy for EPO degradation.

A novel eco-friendly polymeric photosensitizer based on chitosan and flavin mononucleotide.

Flavin mononucleotide (FMN) is a dye belonging to the flavin family. These dyes produce photosensitized degradation of organic compounds via reaction with the excited states of the dye or with reactive oxygen species photogenerated from the triplet of the dye. This article presents a new polymeric dye (FMN-CS) composed of the photosensitizer FMN covalently bonded to chitosan polysaccharide (CS). FMN-CS obtained has a molecular weight of 230 × 103 g mol-1 and a deacetylation degree of 74.8%. The polymeric dye is an environmentally friendly polymer with spectroscopic and physicochemical properties similar to those of FMN and CS, respectively. Moreover, under sunlight, it is capable of generating 1O2 with a quantum yield of 0.31. FMN-CS, like CS, is insoluble in basic media. This allows easy recovery of the polymeric dye once the photosensitized process has been carried out and makes FMN-CS a suitable photosensitizer for the degradation of pollutants in contaminated waters. To evaluate whether FMN-CS may be used for pollutant degradation, the photosensitized degradation of two trihydroxybenzenes by FMN-CS was studied.

Oregano Essential Oil Interactions with Photogenerated Singlet Molecular Oxygen.

Essential oils are a mixture of volatile compounds, products of the secondary metabolism of plants. Once extracted, they can be deteriorated losing their organoleptic and therapeutic properties due to various environmental factors, being light exposure in aerobic conditions the main cause. In this work, the oregano essential oil extraction and characterization from Origanum vulgare plants grown in the experimental field of the FTU-UNSL and its photodegradation in MeOH:H2 O 60:40 v/v solvent were studied. Characterization by EIMS and NIST Mass Spectrometry indicates the main compounds of oregano essential oil, quantified in the extracted oil by GC-MS, are carvacrol (7.14%) and thymol (47.37%). Degradation of essential oil and its two major components can be caused by reactive oxygen species photogenerated from endogenous sensitizers as riboflavin. Our results suggest degradation occurs involving singlet molecular oxygen. Interaction of carvacrol and thymol with singlet oxygen is mainly a physical process, while essential oil has an important reactive component, which indicates there might be other constituents which could contribute to reactive photoprotection. The effect of simultaneous presence of oregano essential oil and tryptophan amino acid-used as a photooxidizable model under riboflavin-photosensitizing conditions-was studied in order to evaluate the possible photoprotection exerted by the essential oil.

Experimental and Theoretical Study of the Stability of the Complex Fisetin-Cu(II) and A Comparative Study of Free Ligand and Complex Interaction with Molecular Singlet Oxygen.

In this work, the flavonol fisetin was selected in order to study its reactivity against Cu(II), a metal ion of interest in biological media and industry. The stoichiometry and apparent formation constant of the complex in ethanolic medium at 25°C were evaluated using spectrophotometric techniques. The resulting stoichiometry was a 1:1 ligand:metal complex, and a log K = 5.17 ± 0.12 was determined. Since two possible chelation sites can be proposed for the complex formation, quantum chemistry calculations were performed on these structures. Calculations suggest that the hydroxyl-keto site is more stable for the complex formation than the catechol site. Flavonoids could exert protection against oxidative damage caused by reactive oxygen species, and this biological activity could be affected by chelation with metal ions. This led us to perform a study on the interaction of both, free flavonoid and complex, with reactive oxygen species. Our results showed both compounds quench molecular singlet oxygen photogenerated with visible light, mainly in a physical fashion. In order to analyze a possible protective effect of flavonoid and its complex against oxidative damage in biological environments, the amino acid tryptophan was selected as a model oxidation system. Free flavonoid does not have a marked protective effect, whereas its complex showed a relevant protective effect.

Photo-Fenton and Riboflavin-photosensitized Processes of the Isoxaflutole Herbicide.

The proherbicide Isoxaflutole (IXF) hydrolyzes spontaneously to diketonitrile (DKN) a phytotoxic compound with herbicidal activity. In this work, the sensitized degradation of IXF using Riboflavin (Rf), a typical environmentally friendly sensitizer, Fenton and photo-Fenton processes has been studied. The results indicate that only the photo-Fenton process produces a significant degradation of the IXF. Photolysis experiments of IXF sensitized by Riboflavin is not a meaningful process, IXF quenches the Rf excited triplet (3 Rf*) state with a quenching rate constant of 1.5 · 107  m-1  s-1 and no reaction is observed with the species O2 (1 Δg ) or O 2 · - generated from 3 Rf*. The Fenton reaction produces no changes in the IXF concentration. While the photo-Fenton process of the IXF, under typical conditions, it produces a degradation of 99% and a mineralization to CO2 and H2 O of 88%. A rate constant value of 1.0 × 109  m-1  s-1 was determined for the reaction between IXF and HO˙. The photo-Fenton process degradation products were identified by UHPLC-MS/MS analysis.

Effect of Cu(2+)-complexation on the scavenging ability of chrysin towards photogenerated singlet molecular oxygen (O2((1)Δg)). Possible biological implications.

Visible-light irradiation of aqueous-ethanolic solutions of Riboflavin (Rf) in the individual presence of the flavone chrysin (Chr) and its complex with Cu(2+) ([Chr2Cu]; 2:1 L:M) generates singlet molecular oxygen O2((1)Δg), that concomitantly interact with both flavone derivatives. Overall (kt) and reactive (kr) rate constants in the order of 10(7)M(-1)s(-1) were determined for the process. Metal chelation greatly enhances the scavenging ability of [Chr2Cu] towards O2((1)Δg) through a mechanism dominated, in >80%, by the physical component. In this way, practically all O2((1)Δg) is deactivated by the complex without significant loss of the quencher. The isolated flavone quenches O2((1)Δg) in a prevailing reactive fashion. The very low value exhibited by [Chr2Cu] for the kr/kt ratio constitutes a positive quality for antioxidative protectors in biological media, where elevated local concentration and high reactivity of significant molecules make them initial targets for O2((1)Δg) aggression. Finally, two interesting properties in the field of free radicals scavenging by [Chr2Cu] must be mentioned. In first place metal chelation itself, in the obvious sense of free metal ion withdrawal from the oxidizable medium, prevents the initiation of a free radical-mediated oxidation processes through mechanisms of Fenton or lipid peroxidation. In addition, the incorporation of Cu adds to [Chr2Cu] the ability of a free radical scavenger, already described for similar Cu-chelate compounds. This collection of beneficial properties positions the complex as a remarkably promising bioprotector towards ROS-mediated oxidation. A quantification of the efficiency on the initial anti-oxidative effect exerted by Chr and [Chr2Cu] towards tryptophan was carried out. The amino acid is an archetypal molecular model, commonly employed to monitor oxidative degradation of proteinaceous media. It was efficiently photoprotected against O2((1)Δg)-mediated photooxidation by [Chr2Cu].

Scavenging of photogenerated ROS by Oxicams. Possible biological and environmental implications.

The profusely employed drugs Piroxicam (Piro), Tenoxicam (Teno) and Meloxicam (Melo) belonging to the non-steroidal antiinflammatory drug (NSAID) family of the Oxicams (Oxis) were studied in the frame of two specific conditions: (a) their ROS scavenging ability, in relation to a possible biological antioxidant action and (b) their photodegradability under environmental conditions, in the context of Oxi-contaminated waters. Singlet molecular oxygen (O2((1)Δg)) and superoxide radical anion (O2(-)) were photogenerated through Riboflavin (Rf, vitamin B2)-photosensitization in aqueous and aqueous-methanolic solutions in the presence of Oxi concentrations in the range 50-500 µM. The visible-light absorber vitamin is currently present in all types of natural waters and constitutes the most frequent endogenous photosensitizer in mammals. Hence, it was employed in order to mimic both natural sceneries of interest. All three Oxis quench O2((1)Δg) with rate constants in the order of 10(8)M(-1)s(-1) showing a significant photodegradation efficiency given by a dominant reactive fashion for deactivation of the oxidative species. Although this is not a desirable property in the context of photoprotection upon prolonged photoirradiation, constitutes in fact a promissory aspect for the degradation NSAIDs, in waste waters. Indirect evidence indicates that Melo is also oxidized through a O2(-)-mediated component. The simultaneous presence of Piro plus tryptophan or tyrosine under Rf-photosensitizing conditions, which has taken the amino acids as photooxidizable model residues in a proteinaceous environment, indicates that the NSAID induces a protection of the biomolecules against photodynamic degradation.

On the photooxidation of the multifunctional drug niclosamide. A kinetic study in the presence of vitamin B2 and visible light.

OBJECTIVES: The multifunctional drug niclosamide (NSD), extensively employed therapeutically, is a frequent pollutant of surface waters. Considering the environmental importance of photodegradative processes for this type of contaminant, the kinetic and mechanistic aspects of the possible visible-light-mediated photooxidation of NSD were studied under naturalistic conditions. METHODS: The visible-light absorber riboflavin (vitamin B2) was employed as a photosensitizer. The vitamin can usually be found in natural waters and is the most common endogenous photosensitizer in mammals. The interaction of NSD with electronically excited states of Rf and with photogenerated reactive oxygen species (ROS) was evaluated through conventional UV spectroscopy, laser flash photolysis, time-resolved phosphorescence detection of singlet molecular oxygen (O2((1)Δg)), and polarographic dosage of dissolved oxygen. RESULTS: Ground state NSD quenched the long-lived triplet excited state of Rf ((3)Rf*) and the photogenerated ROS (O2((1)Δg)) and superoxide radical anion (O2•−). As a result, NSD was photooxidized. The rate constants for the interaction NSD-O2((1)Δg) are particularly low, in the order of 10(6)/M/s, although the whole interaction is attributable to a pure reactive process. The O2((1)Δg) quenching was faster in alkaline medium, favored by the ionization of the NSD phenolic group. Under Rf-photosensitization, NSD was degraded very much more rapidly than phenol, the latter being considered a paradigmatic water-contaminant model compound. NSD may behave as an antioxidant in bio-environments, as demonstrated employing the photooxidizable amino acid tryptophan as a relevant biological target. DISCUSSION: The results indicate that a O2•−-mediated process is the main route for the Rf-sensitized photooxidation of NSD. Photodegradation of the biocide in the presence and absence of phenol and tryptophan was quantitatively evaluated, discussed, and interpreted in terms of competitive quenching processes of (3)Rf*, O2((1)Δg), and O2•− by the substrates.

The NSAIDs indomethacin and diflunisal as scavengers of photogenerated reactive oxygen species.

Diflunisal (DFNS) and Indomethacin (IMTC) are two profusely employed NSAIDs that provide anti-inflammatory and analgesic effects in humans. The scavenging of reactive oxygen species (ROS) by both NSAIDs was systematically studied in pH 7 aqueous solution. The ROS O2 ((1)Δg), O2(•-) and H2O2, generated by visible light irradiation of Riboflavin (Rf) in the presence of DFNS and IMTC, are deactivated by the NSAIDs. The ROS scavenging action by both NSAIDs constitutes an interesting result and adds one more positive aspect to the beneficial actions attributed to these drugs. Nevertheless it should be taken into account that several NSAIDs, in particular IMTC, have been connected to the pathogenesis of gastric mucosal lesions, which in some cases includes ROS generating-ability. DFNS quenches ROS in a dominant physical fashion. It constitutes an excellent protective-antioxidant provided that is practically not destroyed/oxidized after the ROS scavenging action. IMTC, being also an efficient interceptor of ROS, belong to the so-called group of sacrificial-ROS quenchers: It is easily degraded by the oxidative species in the scavenging action. Although this property is negative in the context of prolonged ROS elimination, exhibits a promissory aspect for the degradation of pharmaceutical contaminants, such as NSAIDs, in waste waters.

On the generation and quenching of reactive-oxygen-species by aqueous vitamin B2 and serotonin under visible-light irradiation.

It is well known that endogenous daylight-absorbing compounds produce the sensitized photodegradation of biologically relevant substrates. In this context the photostability of a mixture of the indole neurotransmitter serotonin (Sero) and vitamin B2 (riboflavin, Rf) upon visible-light irradiation and the possible role of Sero and related compounds as generators or deactivators of reactive oxygen species (ROS) was investigated through a kinetic and mechanistic study. The work was done at pH 7 and under experimental conditions in which only the vitamin absorbs photoirradiation. Tryptamine (Trpa) and 5-hydroxyindole (OHIn) were included in the study as model compounds for the neurotransmitter. The visible light irradiation of aqueous Rf in the individual presence of Sero, Trpa and 5-OHIn, under aerobic conditions, induce degradative processes on the indole derivatives (In-der). At least two different mechanisms operate. Our analysis shows that the main reaction pathway is an electron-transfer-mediated quenching of triplet excited Rf ((3)Rf(*)) by the In-der. It produces the species Rf(-)/RfH() and the In-der radical cation that could react to form phenoxy and α-amino radicals. In a further reaction step the species O(2)(-) and OH() could be produced. In parallel, energy transfer from (3)Rf(*) to dissolved oxygen would generate O(2)((1)Δ(g)). Within the frame of the proposed mechanism, results suggest that Rf-sensitized degradation of Sero occurs via the mentioned ROS and non-oxygenated radical-mediated processes. The indole compound quenches O(2)((1)Δ(g)) in a dominant physical fashion. This fact constitutes a desirable property in antioxidants, provided that the quenching process practically does not eliminate the scavenger. Sero exerts a photoprotective effect towards tryptophan through the combined quenching of O(2)((1)Δ(g)) and (3)Rf(*), the latter excited species responsible for the generation of ROS. The amino acid can be taken as a target model of oxidizable biological substrates, particularly proteins.

Photostability and spectral properties of fluorinated fluoresceins and their biarsenical derivatives: a combined experimental and theoretical study.

New fluorinated biarsenical derivatives with improved optical properties based on highly photostable analogs of fluorescein were recently introduced. The photophysical parameters of the triplet excited states as well as photosensitized oxidation reactions of these dyes were determined in order to investigate the influence of molecular structure on the exceptional photostability of these fluorophores. The lack of correspondence between triplet quantum yields and lifetimes with the photobleaching rates of some of the fluorophores of the series suggests that differential reactivities of the excited states with ground state oxygen accounts for the different photodegradation resistances. The UV-visible absorption and emission spectra of the fluorinated fluoresceins and their biarsenical derivatives were evaluated using a TD-DFT/BP86/6-31G** approach, taking bulk solvent effects into account by means of the polarizable continuum model. The calculated properties are in good agreement with experimental data. The S0-->S1 vertical excitation energies in the gas phase and in water were obtained with the optimized geometries of the excited states. This type of calculation could be used in the rational design of new dyes.

Sensitized photooxidation of thyroidal hormones. Evidence for heavy atom effect on singlet molecular oxygen [O2(1Deltag)]-mediated photoreactions.

Thyronine derivatives are essential indicators of thyroid gland diseases in clinical diagnosis and are currently used as standards for developing ordinary biochemical assays. Photooxidation of gland hormones of the thyronine (TN) family and structurally related compounds (TN, 3,5-diiodothyronine,3,3',5-triiodothyronine and 3,3',5,5'-tetraiodothyronine or thyroxine) was studied using rose bengal, eosin and perinaphthenone (PN) as dye sensitizers. Tyrosine (Tyr) and two iodinated derivatives (3-iodotyrosine and 3,5-diiodotyrosine) were also included in the study for comparative purposes. Irradiation of aqueous solutions of substrates containing xanthene dyes with visible light triggers a complex series of competitive interactions, which include the triplet excited state of the dye (3Xdye*) and singlet molecular oxygen [O2(1Deltag)]-mediated and superoxide ion-mediated reactions. Rate constants for interaction with the 3Xdye*, attributed to an electron transfer process, are in the order of 10(8)-10(9) M-1 s-1 depending on the dye and the particular substrate. The photosensitization using PN follows a pure Type-II (O2(1Deltag) mediated) mechanism. The presence of the phenolic group in Tyr, TN and iodinated derivatives dominates the kinetics of photooxidation of these compounds. The reactive rate constants, k(r), and the quotient between reactive and overall rate constants (k(r)/k(t) values, in the range of 0.7-0.06) behave in an opposite fashion compared with the overall rate constants and oxidation potentials. This apparent inconsistency was interpreted on the basis of an internal heavy atom effect, favoring the intersystem-crossing deactivation route within the encounter complex with the concomitant reduction of effective photooxidation.

On the antioxidant properties of therapeutic drugs: quenching of singlet molecular oxygen by aminosalicylic acids.

The ability of the widely employed therapeutic drugs 4-aminosalicylic acid and 5-aminosalicylic acid to act as singlet molecular oxygen (O(2)((1)delta(g))) scavengers was investigated at pH 7 and pH 12. The isomer 3-aminosalicylic acid was also included in the study for comparative purposes. All three compounds quench photochemically generated O(2)((1)delta(g)) with rate constants in the range of 10(7)-10(8) x M(-1)s(-1), depending on the experimental conditions. No chemical reaction (oxidation of the aminosalicylic acids) was detected at the neutral pH, whereas at pH 12 both chemical and physical interactions with O(2)((1)delta(g)) operated. The physical process implies the de-activation of the oxidant species without destruction of the aminosalicylic acid. The quotients between the overall and reactive rate constants for O(2)((1)delta(g)) quenching at pH 12 (k(r)/k(t) ratios), which account for the actual effectiveness of photodegradation, were relatively low (0.22, 0.04, and 0.06 for 3-, 4- and 5-aminosalicylic acids, respectively). This indicates that the drugs, particularly the 4- and 5-amino derivatives, de-activate the excited oxygen species, at both pH values studied, mainly in a physical fashion, preventing its photodegradation and providing an antioxidative protection for possible photo-oxidizable biological targets in the surroundings.