Effect of organic co-solvents in the evaluation of the hydroxyl radical scavenging activity by the 2-deoxyribose degradation assay: The paradigmatic case of α-lipoic acid

Preparation, characterization, and evaluation of antioxidant activity and bioavailability of a self-nanoemulsifying drug delivery system (SNEDDS) for buckwheat flavonoids

The self-nanoemulsifying drug delivery system has shown many advantages in drug delivery. In this study, a self-nanoemulsifying drug delivery system of buckwheat flavonoids was prepared for enhancing its antioxidant activity and oral bioavailability. A nanoemulsion of buckwheat flavonoids was developed and characterized, and its antioxidant, in vitro release, and in vivo bioavailability were determined. The nanoemulsion was optimized by the central composite design response surface experiment, and its particle size, polymer dispersity index (PDI), zeta potential, morphology, encapsulation efficiency, and stability were evaluated. The antioxidant activity was tested by measuring its 2,2-diphenyl-1-picrylhydrazyl scavenging activity, hydroxyl radical scavenging activity, and superoxide anion scavenging ability. In vitro release of buckwheat flavonoids nanoemulsion showed a higher cumulative release than the suspension, and the release fitting model followed the Ritger-Peppas and Weibull models. The effective concentration of the nanoemulsion was evaluated in vivo using a Wistar rat model, and the area under the plasma concentration-time curve of the buckwheat flavonoids nanoemulsion was 2.2-fold higher than that of the buckwheat flavonoid suspension. The Cmax of the nanoemulsion was 2.6-fold greater than that of the suspension. These results indicate that the nanoemulsion is a promising oral drug delivery system that can improve the oral bioavailability to satisfy the clinical requirements.

Relevance of N-nitrosation reactions for secondary amines in nitrate-rich wastewater under UV-C treatment

This study investigated the transformation of secondary amine pharmaceuticals in UV-C/NO₃^- and in nitrate-rich wastewater at 254 nm by taking diclofenac, diphenylamine, mefenamic acid and furosemide as probe compounds. The degradation of targeted compounds were positively related to nitrate concentration and mainly caused by the formation of peroxynitrite and related reactive nitrogen species (e.g., nitrogen oxide and nitrogen dioxide radicals). Major transformation products were identified to provide fundamental understanding of the selective oxidation of secondary amine with reactive nitrogen species. UV photolysis, hydroxyl radical oxidation, nitration and nitrosation processes were found to be the most significant transformation pathways. In case of diphenylamine, for which most of the identified intermediates were available as standard, the relative significance of each transformation route could be established, highlighting for the first time the important role of N-nitrosation processes in UV/NO₃^- treatment followed by the decomposition of the resulting N-nitroso compounds by an alpha hydroxylation mechanism. This specific transformation pathway was of concern because it constitutes the molecular basis of N-nitrosamine carcinogenicity and may contribute to the increase in effluent genotoxicity under UV-C treatment in addition to the formation of nitrophenols. Hydrogenocarbonate ions at concentration values higher than 300 mg/L appeared to be a protective specie against nitrosation processes due to the formation of carbamate adducts but H₂O₂ in UV-C/H₂O₂ could be responsible for an exacerbation of the N-nitrosation pathway due to an addition source of hydroxyl radical in the system. The occurrence of major transformation products of diclofenac was confirmed in nitrate-rich wastewater under UV-C treatment at pilot-scale operation.

Fluorene oxidation by solar-driven photo-Fenton process: toward mild pH conditions

Polycyclic aromatic hydrocarbons (PAHs) are on the list of priority pollutants to be eliminated from the environment due to their carcinogenic and mutagenic action, chemical stability, and resistance to biodegradation. The aim of this study was to evaluate the degradation of fluorene, a well-known PAH, in aqueous solutions (0.03 and 0.08 mg L^-1), by means of a solar-driven conventional (PF) and modified photo-Fenton mediated by ferrioxalate complexes (PFF). Photolysis was also employed for comparison purposes. PF reaction was evaluated at different pH values (2.8, 3.5, and 4.0) and iron concentrations (2, 5, 10, and 20 mg L^-1). On the other hand, PFF studies were conducted at mild pH conditions (4.0, 5.0, and 6.0) and iron content of 2 mg L^-1, keeping initial iron/oxalate molar ratio at 1:3. In both PF and PFF, the initial hydrogen peroxide/iron molar ratio was maintained at 5. In the presence of methanol as cosolvent for fluorene dissolution, the PF reaction was hampered and no consumption of H₂O₂ was observed during the reaction carried out at constant pH (2.8). This led to low degradation rates, similar to those achieved by photolysis. Under the same pH but using acetonitrile as cosolvent for fluorene dissolution, fluorene degradation was found to be proportional to the iron content used in the PF experiments. On the other hand, at an invariable iron concentration of 5 mg Fe²⁺ L^-1, the increase in pH was accompanied by a decrease in the molar fraction of the most photoactive iron complex (FeOH²⁺) and ferric hydroxides precipitation, leading to a reduction in the fluorene degradation rate. With regard to the PFF tests, similar fluorene degradation performance was achieved at pH 4 and 5, while at pH 6 iron precipitation became relevant and the degradation rate was slightly slower. PFF has shown to be more efficient than the PF under the same pH (4) and iron concentration (2 mg L^-1). Moreover, even at near neutral pH (6), fluorine degradation was shown to be feasible by using ferrioxalate complexes.

Ozone initiated inactivation of Escherichia coli and Staphylococcus aureus in water: Influence of selected organic solvents prevalent in wastewaters

Absorption, stability and reactivity of ozone in water are critical parameters to determine its efficiency in microbial inactivation. In this study, the influence of four water-soluble organic solvents commonly discharged from industrial lines into wastewater systems, namely; ethanol, methanol, ethyl acetate and dimethyl sulfoxide (DMSO) on the ozone-facilitated inactivation of Escherichia coli and Staphylococcus aureus in water was investigated. Ozone absorption (up to 12 min) as a function of ozone aeration time, and the decomposition rate were spectrophotometrically monitored in the presence of 2.5% and 5% concentrations of each organic solvent. Their consequent effect on bacterial inactivation was determined. The inactivation kinetics were described using the efficiency factor Hom model. Residual concentrations of absorbed ozone in solutions with ethyl acetate or DMSO were relatively higher than those in methanol or ethanol-containing solutions. DMSO and ethyl acetate enhanced the stability of ozone in water, characterised by a lower decomposition rate constant in DMSO (k_d = 3.81 × 10^-2 M^-1 s^-1) and ethyl acetate (k_d = 4.45 × 10^-2 M^-1 s^-1) solutions, in contrast with that in methanol (k_d = 1.13 × 10^-1 M^-1 s^-1), where the decomposition rate was higher. The faster absorption and stability of ozone in ethyl acetate and DMSO corresponded with an observed increase in the log inactivation of E. coli and S. aureus by approximately 2-fold relative to that in methanol.

Antioxidant activity of nanomaterials

Nanomaterials represent one of the most promising frontiers in the research for improved antioxidants. Some nanomaterials, including organic (i.e. melanin, lignin) metal oxides (i.e. cerium oxide) or metal (i.e. gold, platinum) based nanoparticles, exhibit intrinsic redox activity that is often associated with radical trapping and/or with superoxide dismutase-like and catalase-like activities. Redox inactive nanomaterials can be transformed into antioxidants by grafting low molecular weight antioxidants on them. Herein, we propose a classification of nanoantioxidants based on their mechanism of action, and we review the chemical methods used to measure antioxidant activity by providing a rationale of the chemistry behind them.

Criegee Chemistry on Aqueous Organic Surfaces

In the troposphere, the fate of gas-phase Criegee intermediates (CIs) is deemed to be determined by their reactions with water molecules. Here it is shown that CIs produced in situ on the surface of water/acetonitrile (W/AN) solutions react competitively with millimolar carboxylic acids. Present experiments probe, via online electrospray mass spectrometry, CIs' chemistry on the surface of α-humulene and β-caryophyllene in W/AN microjets exposed to O₃(g) for <10 μs. Mass-specific identification lets us establish the progeny of products and intermediates generated in the early stages of CIs' reactions with H₂O, D₂O, H₂¹⁸O, and n-alkyl-COOH (n = 1-7). It is found that n-alkyl-COOH competes for CIs with interfacial water, their competitiveness being an increasing function of n. Present findings demonstrate that CIs can react with species other than H₂O on the surface of aqueous organic aerosols due to the low water concentrations prevalent in the outermost interfacial layers.