Revisiting Mg solubility in CuO nanorods: limit probed by neutron diffraction and effect on the particle toxicity towards bacteria in water.

Both nanometer-sized CuO and MgO particles exhibit bactericidal activities against Staphylococcus aureus and Escherichia coli, two bacteria causing healthcare-associated infections. The solid solution Cu1-xMgxO is potentially interesting for biomedical applications as one of the compositions could have a much higher bactericidal activity than the parent CuO and MgO oxides considered separately. But, to date, no Vegard's law proves the real existence of such a solid solution. This study was aimed at shedding light on the solubility of Mg2+ ions in CuO nanoparticles and its impact on the free oxygen radicals they produce, the quantity of which determines their bactericidal performance. The solid solution Cu1-xMgxO does exist and particles were synthesized as nanorods of 50-60 nm length by thermally decomposing at 400 °C the single source precursors Cu1-xMgx(OH)2. Vegard's laws exist only in the compositional range 0 ≤ x ≤ 0.1, due to the low capacity of the distorted NaCl-type structure to accommodate regular coordination [MgO6] octahedra. Only neutron diffraction allowed the detection of the small amount of MgO nanoparticles present as impurity in a 10 g sample beyond the solubility limit of x = 0.1. In this series, CuO nanorods remain the most active against E. coli and S. aureus with reduction in viability of 99.998% and 98.7% after 180 min in water, respectively. Our synthesis route has significantly increased the activity of pure CuO nanoparticles beyond the values reported so far, especially against E. coli. The bactericidal performances of CuO and the magnesium-substituted counterparts (i.e. Cu1-xMgxO) are not linked to cupric ions they release in water since their mass concentrations after 180 min are much lower than minimal concentrations inhibiting the growth of E. coli and S. aureus. These CuO nanorods kill bacteria in water because they produce a large quantity of free oxygen radicals in the presence of H2O2 only, the majority of which are highly toxic HO˙ radicals. Mg2+ ions have a detrimental effect on this production, thus explaining the lowest bactericidal performance of Cu1-xMgxO nanorods. Definitive knowledge of the toxicity of Cu1-xMgxO nanoparticles towards bacteria in water is now available.

Understanding the bactericidal mechanism of Cu(OH)2 nanorods in water through Mg-substitution: high production of toxic hydroxyl radicals by non-soluble particles.

To date, there is still a lack of definite knowledge regarding the toxicity of Cu(OH)2 nanoparticles towards bacteria. This study was aimed at shedding light on the role played by released cupric ions in the toxicity of nanoparticles. To address this issue, the bactericidal activity of Cu(OH)2 was at first evaluated in sterile water, a medium in which particles are not soluble. In parallel, an isovalent substitution of cupric ions by Mg2+ was attempted in the crystal structure of Cu(OH)2 nanoparticles to increase their solubility and determine the impact on the bactericidal activity. For the first time, mixed Cu1-xMgx(OH)2 nanorods (x ≤ 0.1) of about 15 nm in diameter and a few hundred nanometers in length were successfully prepared by a simple co-precipitation at room temperature in mixed alkaline (NaOH/Na2CO3) medium. For E. coli, 100% reduction of one million CFU per mL (6 log10) occurs after only 180 min on contact with both Cu(OH)2 and Cu0.9Mg0.1(OH)2 nanorods. The entire initial inoculum of S. aureus is also killed by Cu(OH)2 after 180 min (100% or 6 log10 reduction), while 0.01% of these bacteria stay alive on contact with Cu0.9Mg0.1(OH)2 (99.99% or 4 log10 reduction). The bactericidal performances of Cu(OH)2 and the magnesium-substituted counterparts (i.e. Cu1-xMgx(OH)2) are not linked to cupric ions they release in water since their mass concentrations after 180 min are much lower than minimal concentrations inhibiting the growth of E. coli and S. aureus. Finally, an EPR spin trapping study reveals how these nanorods kill bacteria in water: only the presence of hydrogen peroxide, a by-product of the normal metabolism of oxygen in aerobic bacteria, allows the Cu(OH)2 and its magnesium-substituted counterparts to produce a lethal amount of free radicals, the majority of which are the highly toxic HO˙.

Azacalixphyrins as an innovative alternative for the free-radical photopolymerization under visible and NIR irradiation without the need of co-initiators.

Azacalixphyrins are unique aromatic macrocycles featuring strong absorption from the visible to the near-infrared (NIR) spectral ranges. This work demonstrates through EPR spin-trapping experiments that the N-alkyl tetrasubstituted azacalixphyrin (ACP) can lead to the formation of carbon-centered radicals initiating for the free-radical photopolymerization (FRP) of bio-based acrylate monomer upon the irradiation of several light emitting diodes, which emissions range from 455 to 660 nm. Compared to other previously reported systems, the tremendous advantage of the ACP photoinitiating system is its ability to promote photopolymerization on its own, avoiding the introduction of co-initiators. A new potential application of this promising photoinitiator is highlighted through the fabrication of well-defined microstructures under NIR laser diode irradiation at λ = 800 nm.

EPR Study of KO2 as a Source of Superoxide and •BMPO-OH/OOH Radical That Cleaves Plasmid DNA and Detects Radical Interaction with H2S and Se-Derivatives.

Superoxide radical anion (O2•-) and its derivatives regulate numerous physiological and pathological processes, which are extensively studied. The aim of our work was to utilize KO2 as a source of O2•- and the electron paramagnetic resonance (EPR) spin trapping 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide (BMPO) technique for the preparation of •BMPO-OOH and/or •BMPO-OH radicals in water solution without DMSO. The method distinguishes the interactions of various compounds with •BMPO-OOH and/or •BMPO-OH radicals over time. Here, we show that the addition of a buffered BMPO-HCl mixture to powdered KO2 formed relatively stable •BMPO-OOH and •BMPO-OH radicals and H2O2, where the •BMPO-OOH/OH ratio depended on the pH. At a final pH of ~6.5-8.0, the concentration of •BMPO-OOH radicals was ≥20 times higher than that of •BMPO-OH, whereas at pH 9.0-10.0, the •BMPO-OH radicals prevailed. The •BMPO-OOH/OH radicals effectively cleaved the plasmid DNA. H2S decreased the concentration of •BMPO-OOH/OH radicals, whereas the selenium derivatives 1-methyl-4-(3-(phenylselanyl) propyl) piperazine and 1-methyl-4-(4-(phenylselanyl) butyl) piperazine increased the proportion of •BMPO-OH over the •BMPO-OOH radicals. In conclusion, the presented approach of using KO2 as a source of O2•-/H2O2 and EPR spin trap BMPO for the preparation of •BMPO-OOH/OH radicals in a physiological solution could be useful to study the biological effects of radicals and their interactions with compounds.

Lawsone Derivatives as Efficient Photopolymerizable Initiators for Free-Radical, Cationic Photopolymerizations, and Thiol-Ene Reactions.

Two new photopolymerizable vinyl (2-(allyloxy) 1,4-naphthoquinone, HNQA) and epoxy (2-(oxiran-2yl methoxy) 1,4-naphthoquinone, HNQE) photoinitiators derived from lawsone were designed in this paper. These new photoinitiators can be used as one-component photoinitiating systems for the free-radical photopolymerization of acrylate bio-based monomer without the addition of any co-initiators. As highlighted by the electron paramagnetic resonance (EPR) spin-trapping results, the formation of carbon-centered radicals from an intermolecular H abstraction reaction was evidenced and can act as initiating species. Interestingly, the introduction of iodonium salt (Iod) used as a co-initiator has led to (1) the cationic photopolymerization of epoxy monomer with high final conversions and (2) an increase of the rates of free-radical polymerization of the acrylate bio-based monomer; we also demonstrated the concomitant thiol-ene reaction and cationic photopolymerizations of a limonene 1,2 epoxide/thiol blend mixture with the HNQA/Iod photoinitiating system.

Hydration and bactericidal activity of nanometer- and micrometer-sized particles of rock salt-type Mg1-xCuxO oxides.

Copper substitution together with nano-structuring are applied with the aim to increase the bactericidal performances of the rocksalt-type MgO oxide. The partial substitution of magnesium ions with Cu2+ has been successfully achieved in both micrometer- and nanometer-sized particles of MgO up to 20 mol% in increments of 5 mol%. Microstructural analyses using the Integral Breadth method revealed that the thermal decomposition of the single source precursor Mg1-xCux(OH)2-2y(CO3)y.zH2O at 400 °C creates numerous defects in 10-20 nm-sized particles of Mg1-xCuxO thus obtained. These defects make the surface of nanoparticles highly reactive towards the sorption of water molecules, to the extent that the cubic cell a parameter in as-prepared Mg1-xCuxO expands by +0.24% as soon as the nanoparticles are exposed to ambient air (60% RH). The hydration of Mg1-xCuxO particles in liquid water is based on a conventional dissolution-precipitation mechanism. Particles of a few microns in size dissolve all the more slowly the higher the copper content and only Mg(OH)2 starts precipitating after 3 h. In contrast, the dissolution of all 10-20 nm-sized Mg1-xCuxO particles is complete over a 3 h period and water suspension only contains 4-12 nm-sized Mg1-xCux(OH)2 particles after 3 h. Thereby, the bactericidal activity reported for water suspension of Mg1-xCuxO nanoparticles depends on the speed at which these nanoparticles dissolve and Mg1-xCux(OH)2 nanoparticles precipitate in the first 3 h. Only 10 mol% of cupric ions in MgO nanoparticles are sufficient to kill both E. coli and S. aureus with a bactericidal kinetics faster and reductions in viability at 3 h (6.5 Log10 and 2.7 Log10, respectively) higher than the conventional antibacterial agent CuO (4.7 Log10 and 2 Log10 under the same conditions). EPR spin trapping study reveals that "hydroxylated" Mg0.9Cu0.1O as well as Mg0.9Cu0.1(OH)2 nanoparticles produce more spin-adducts with highly toxic hydroxyl radicals than their copper-free counterparts. The rapid mass adsorption of Mg0.9Cu0.1(OH)2 nanoparticles onto the cell envelopes following their precipitation together with their ability to produce Reactive Oxygen Species are responsible for the exceptionally high bactericidal activity measured in the course of the hydroxylation of Mg0.9Cu0.1O nanoparticles.

Polyradical PROXYL/TEMPO Conjugates Connected by Ester/Amide Bridges: Synthesis, Physicochemical Studies, and DFT Calculations.

A series of di-/trinitroxide esters and amides featuring PROXYL and/or TEMPO radicals connected with alicyclic bridges were prepared in 61-92 % yields and their properties were analysed by using multiple experimental techniques. The examination of EPR spectra of radicals in organic solvents augmented with DFT calculations brought valuable information on the conformational dynamics and spin exchange mechanisms. Cyclic voltammetry investigations revealed (quasi)reversible electrochemical behaviour of studied nitroxides with their half-wave potentials ranging from -51 to -17 mV. SQUID measurements of selected radicals revealed that the magnetism of di- and trinitroxides is significantly different, since antiferromagnetic coupling in biradicals is notably larger than in triradicals. The single-crystal X-ray analysis of selected biradicals revealed the existence of 3D supramolecular networks of molecules linked through hydrogen-bonding interactions. These polynitroxide radicals can serve as promising bridging or chelating ligands in the synthesis of transition-metal-based molecular magnets.

•BMPO-OOH Spin-Adduct as a Model for Study of Decomposition of Organic Hydroperoxides and the Effects of Sulfide/Selenite Derivatives. An EPR Spin-Trapping Approach.

Lipid hydroperoxides play an important role in various pathophysiological processes. Therefore, a simple model for organic hydroperoxides could be helpful to monitor the biologic effects of endogenous and exogenous compounds. The electron paramagnetic resonance (EPR) spin-trapping technique is a useful method to study superoxide (O2•-) and hydroxyl radicals. The aim of our work was to use EPR with the spin trap 5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO), which, by trapping O2•- produces relatively stable •BMPO-OOH spin-adduct, a valuable model for organic hydroperoxides. We used this experimental setup to investigate the effects of selected sulfur/selenium compounds on •BMPO-OOH and to evaluate the antioxidant potential of these compounds. Second, using the simulation of time-dependent individual BMPO adducts in the experimental EPR spectra, the ratio of •BMPO-OH/•BMPO-OOH-which is proportional to the transformation/decomposition of •BMPO-OOH-was evaluated. The order of potency of the studied compounds to alter •BMPO-OOH concentration estimated from the time-dependent •BMPO-OH/•BMPO-OOH ratio was as follows: Na2S4 > Na2S4/SeO32- > H2S/SeO32- > Na2S2 ~Na2S2/SeO32- ~H2S > SeO32- ~SeO42- ~control. In conclusion, the presented approach of the EPR measurement of the time-dependent ratio of •BMPO-OH/•BMPO-OOH could be useful to study the impact of compounds to influence the transformation of •BMPO-OOH.

Graphitic Carbon Nitride for Photocatalytic Air Treatment.

Graphitic carbon nitride (g-C3N4) is a conjugated polymer, which recently drew a lot of attention as a metal-free and UV and visible light responsive photocatalyst in the field of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability and earth-abundant nature. In the present work, bulk g-C3N4 was synthesized by thermal decomposition of melamine. This material was further exfoliated by thermal treatment. S-doped samples were prepared from thiourea or further treatment of exfoliated g-C3N4 by mesylchloride. Synthesized materials were applied for photocatalytic removal of air pollutants (acetaldehyde and NOx) according to the ISO 22197 and ISO 22197-1 methodology. The efficiency of acetaldehyde removal under UV irradiation was negligible for all g-C3N4 samples. This can be explained by the fact that g-C3N4 under irradiation does not directly form hydroxyl radicals, which are the primary oxidation species in acetaldehyde oxidation. It was proved by electron paramagnetic resonance (EPR) spectroscopy that the dominant species formed on the irradiated surface of g-C3N4 was the superoxide radical. Its production was responsible for a very high NOx removal efficiency not only under UV irradiation (which was comparable with that of TiO2), but also under visible irradiation.

Evaluation of phototoxic and cytotoxic potential of TiO2 nanosheets in a 3D reconstructed human skin model.

Despite a continuous increase of commercial products containing nanoparticles, only few materials are currently used in such large amounts, forms and sizes as titanium dioxide - TiO2. Besides its use in cosmetics, food industry and biomedicine, TiO2 nanoparticles (NPs) are also used as highly efficient photocatalysts due to their unique ability to convert complex organic materials to carbon dioxide, water and simple mineral acids via complex radical and electron transfer reactions. The main objective of the current project was to assess the potential dermal effect (phototoxicity and skin toxicity) of TiO2 nanosheets (TIG-800) synthesized from the lyophilized aqueous colloids of peroxo-titanic acid by high-temperature treatment. The effect was examined on reconstructed human skin model EpiDerm in the test pre-validated by ECVAM and adopted into the ICH S10 guidelines for the preclinical photo-safety assessment of drugs. In addition, two further commercial samples of nanocrystalline TiO2, namely Aeroxide P25 and Eusolex T-2000, and six benchmark materials from pre-validation studies were tested. None of the TiO2 NPs tested in the study caused acute phototoxicity or cytotoxicity in the reconstructed 3D tissues up to the highest concentration tested. The prediction of photo-irritation potency for the benchmark chemicals was comparable to previous studies. For some of the tested materials, we identified reasons for false negative results or variability in previously published datasets by improved dosing, conditions of irradiation, and choice of suitable solvents. The method proved its suitability for photo-irritation assessment of topically applied materials.

Highly Virulent Bactericidal Effects of Curcumin-Based µ-Cages Fabricated by Two-Photon Polymerization.

A new antibacterial strategy is reported based on two-photon fabrication of three-dimensional curcumin-embedded µ-cages. Such devices were designed to entrap and kill Staphylococcus aureus bacteria upon visible light irradiation. The proposed concept mainly relies on the pivotal role of curcumin, which is sequentially used as a two-photon active free radical initiator and as a photogenerator of reactive oxygen species within the cage µ-volumes. We show that these µ-cages exhibit extremely high antimicrobial properties, leading to 95% bacteria mortality after only 10 min visible irradiation. A preconcentration mechanism of photogenerated oxygen species is proposed to account for this highly performing bactericidal effect whose virulence can be strikingly switched on by increasing the light exposure time from 5 to 10 min.

Products of Sulfide/Selenite Interaction Possess Antioxidant Properties, Scavenge Superoxide-Derived Radicals, React with DNA, and Modulate Blood Pressure and Tension of Isolated Thoracic Aorta.

Selenium (Se), an essential trace element, and hydrogen sulfide (H2S), an endogenously produced signalling molecule, affect many physiological and pathological processes. However, the biological effects of their mutual interaction have not yet been investigated. Herein, we have studied the biological and antioxidant effects of the products of the H2S (Na2S)/selenite (Na2SeO3) interaction. As detected by the UV-VIS and EPR spectroscopy, the product(s) of the H2S-Na2SeO3 and H2S-SeCl4 interaction scavenged superoxide-derived radicals and reduced ·cPTIO radical depending on the molar ratio and the preincubation time of the applied interaction mixture. The results confirmed that the transient species are formed rapidly during the interaction and exhibit a noteworthy biological activity. In contrast to H2S or selenite acting on their own, the H2S/selenite mixture cleaved DNA in a bell-shaped manner. Interestingly, selenite protected DNA from the cleavage induced by the products of H2S/H2O2 interaction. The relaxation effect of H2S on isolated thoracic aorta was eliminated when the H2S/selenite mixture was applied. The mixture inhibited the H2S biphasic effect on rat systolic and pulse blood pressure. The results point to the antioxidant properties of products of the H2S/selenite interaction and their effect to react with DNA and influence cardiovascular homeostasis. The effects of the products may contribute to explain some of the biological effects of H2S and/or selenite, and they may imply that a suitable H2S/selenite supplement might have a beneficial effect in pathological conditions arisen, e.g., from oxidative stress.

Photoactive Polyoxometalate/DASA Covalent Hybrids for Photopolymerization in the Visible Range.

The synthesis of TBA-DASA-POM-DASA, the first photoactive covalent hybrid polyoxometalate (POM) incorporating a donor-acceptor Stenhouse adduct (DASA) reverse photochrome, is presented. It has been evidenced that in solution the equilibrium between the colorless cyclopentenone and the highly colored triene conformers is strongly dependent not only on the nature of the solvent but also the countercations, allowing to tune its optical properties. This complex has been further associated to photochromic spironaphtoxazine cations, resulting in a material which can be activated by two distinct optical stimuli. Moreover, when combined with N-methyldiethanolamine, TBA-DASA-POM-DASA constitutes a performing photoinitiating system for polyethylene glycol diacrylate polymerization and under visible light irradiation, a promising result in a domain scarcely developed in POM chemistry.

Synthesis and Anticancer Activity of Novel 9-O-Substituted Berberine Derivatives.

Berberine is a bioactive isoquinoline alkaloid derived from many plants. Although berberine has been shown to inhibit growth and induce apoptosis of several tumor cell lines, its poor absorption and moderate activity hamper its full therapeutic potential. Here, we describe the synthesis of a series of 9-O-substituted berberine derivatives with improved antiproliferative and apoptosis-inducing activities. An analysis of novel berberine derivatives by EPR spectroscopy confirmed their similar photosensitivity and analogous behavior upon UVA irradiation as berberine, supporting their potential to generate ROS. Improved antitumor activity of novel berberine derivatives was revealed by MTT assay, by flow cytometry and by detection of apoptotic DNA fragmentation and caspase-3 activation, respectively. We showed that novel berberine derivatives are potent inhibitors of growth of HeLa and HL-60 tumor cell lines with IC50 values ranging from 0.7 to 16.7 µM for HL-60 cells and 36 to >200 µM for HeLa cells after 48 h treatment. Further cell cycle analysis showed that the observed inhibition of growth of HL-60 cells treated with berberine derivatives was due to arresting these cells in the G2/M and S phases. Most strikingly, we found that berberine derivative 3 (9-(3-bromopropoxy)-10-methoxy-5,6-dihydro-[1,3]dioxolo[4,5-g]isoquino[3,2-a] isoquinolin-7-ylium bromide) possesses 30-fold superior antiproliferative activity with an IC50 value of 0.7 µM and 6-fold higher apoptosis-inducing activity in HL-60 leukemia cells compared to berberine. Therefore, further studies are merited of the antitumor activity in leukemia cells of this berberine derivative.

Sulfide (Na2S) and Polysulfide (Na2S2) Interacting with Doxycycline Produce/Scavenge Superoxide and Hydroxyl Radicals and Induce/Inhibit DNA Cleavage.

Doxycycline (DOXY) is an antibiotic routinely prescribed in human and veterinary medicine for antibacterial treatment, but it has also numerous side effects that include oxidative stress, inflammation, cancer or hypoxia-induced injury. Endogenously produced hydrogen sulfide (H2S) and polysulfides affect similar biological processes, in which reactive oxygen species (ROS) play a role. Herein, we have studied the interaction of DOXY with H2S (Na2S) or polysulfides (Na2S2, Na2S3 and Na2S4) to gain insights into the biological effects of intermediates/products that they generate. To achieve this, UV-VIS, EPR spectroscopy and plasmid DNA (pDNA) cleavage assay were employed. Na2S or Na2S2 in a mixture with DOXY, depending on ratio, concentration and time, displayed bell-shape kinetics in terms of producing/scavenging superoxide and hydroxyl radicals and decomposing hydrogen peroxide. In contrast, the effects of individual compounds (except for Na2S2) were hardly observable. In addition, DOXY, as well as oxytetracycline and tetracycline, interacting with Na2S or other studied polysulfides reduced the •cPTIO radical. Tetracyclines induced pDNA cleavage in the presence of Na2S. Interestingly, they inhibited pDNA cleavage induced by other polysulfides. In conclusion, sulfide and polysulfides interacting with tetracyclines produce/scavenge free radicals, indicating a consequence for free radical biology under conditions of ROS production and tetracyclines administration.

Copper(II) Thiosemicarbazone Complexes and Their Proligands upon UVA Irradiation: An EPR and Spectrophotometric Steady-State Study.

X- and Q-band electron paramagnetic resonance (EPR) spectroscopy was used to characterize polycrystalline Cu(II) complexes that contained sodium 5-sulfonate salicylaldehyde thiosemicarbazones possessing a hydrogen, methyl, ethyl, or phenyl substituent at the terminal nitrogen. The ability of thiosemicarbazone proligands to generate superoxide radical anions and hydroxyl radicals upon their exposure to UVA irradiation in aerated aqueous solutions was evidenced by the EPR spin trapping technique. The UVA irradiation of proligands in neutral or alkaline solutions and dimethylsulfoxide (DMSO) caused a significant decrease in the absorption bands of aldimine and phenolic chromophores. Mixing of proligand solutions with the equimolar amount of copper(II) ions resulted in the formation of 1:1 Cu(II)-to-ligand complex, with the EPR and UV-Vis spectra fully compatible with those obtained for the dissolved Cu(II) thiosemicarbazone complexes. The formation of the complexes fully inhibited the photoinduced generation of reactive oxygen species, and only subtle changes were found in the electronic absorption spectra of the complexes in aqueous and DMSO solutions upon UVA steady-state irradiation. The dark redox activity of copper(II) complexes and proligand/Cu(II) aqueous solutions towards hydrogen peroxide which resulted in the generation of hydroxyl radicals, was confirmed by spin trapping experiments.

Polysulfides and products of H2S/S-nitrosoglutathione in comparison to H2S, glutathione and antioxidant Trolox are potent scavengers of superoxide anion radical and produce hydroxyl radical by decomposition of H2O2.

Exogenous and endogenously produced sulfide derivatives, such as H2S/HS-/S2-, polysulfides and products of the H2S/S-nitrosoglutathione interaction (S/GSNO), affect numerous biological processes in which superoxide anion (O2-) and hydroxyl (OH) radicals play an important role. Their cytoprotective-antioxidant and contrasting pro-oxidant-toxic effects have been reported. Therefore, the aim of our work was to contribute to resolving this apparent inconsistency by studying sulfide derivatives/free radical interactions and their consequent biological effects compared to the antioxidants glutathione (GSH) and Trolox. Using the electron paramagnetic resonance (EPR) spin trapping technique and O2-, we found that a polysulfide (Na2S4) and S/GSNO were potent scavengers of O2- and cPTIO radicals compared to H2S (Na2S), GSH and Trolox, and S/GSNO scavenged the DEPMPO-OH radical. As detected by the EPR spectra of DEPMPO-OH, the formation of OH in physiological solution by S/GSNO was suggested. All the studied sulfide derivatives, but not Trolox or GSH, had a bell-shaped potency to decompose H2O2 and produced OH in the following order: S/GSNO > Na2S4 ≥ Na2S > GSH = Trolox = 0, but they scavenged OH at higher concentrations. In studies of the biological consequences of these sulfide derivatives/H2O2 properties, we found the following: (i) S/GSNO alone and all sulfide derivatives in the presence of H2O2 cleaved plasmid DNA; (ii) S/GSNO interfered with viral replication and consequently decreased the infectivity of viruses; (iii) the sulfide derivatives induced apoptosis in A2780 cells but inhibited apoptosis induced by H2O2; and (iv) Na2S4 modulated intracellular calcium in A87MG cells, which depended on the order of Na2S4/H2O2 application. We suggest that the apparent inconsistency of the cytoprotective-antioxidant and contrasting pro-oxidant-toxic biological effects of sulfide derivatives results from their time- and concentration-dependent radical production/scavenging properties and their interactions with O2-, OH and H2O2. The results imply a direct involvement of sulfide derivatives in O2- and H2O2/OH free radical pathways modulating antioxidant/toxic biological processes.

Protective role of quercetin against copper(II)-induced oxidative stress: A spectroscopic, theoretical and DNA damage study.

The radical scavenging and metal chelating properties of flavonoids indicate that they may play a protective role in diseases with perturbed metal homeostasis such as Alzheimer's disease. In this work we investigated the effect of the coordination of quercetin to copper(II) in view of the formation of ROS in Cu-catalyzed Fenton reaction. ABTS and DPPH assays confirmed that the copper(II)-quercetin complex exhibits a stronger radical scavenging activity than does quercetin alone. EPR spin trapping experiments have shown that chelation of quercetin to copper significantly suppressed the formation of hydroxyl radicals in the Cu(II)-Fenton reaction. DNA damage experiments revealed a protective effect for quercetin, but only at higher stoichiometric ratios of quercetin relative to copper. DNA protective effect of quercetin against ROS attack was described by two mechanisms. The first mechanism lies in suppressed formation of ROS due to the decreased catalytic action of copper in the Fenton reaction, as a consequence of its chelation and direct scavenging of ROS by free quercetin. Since the Cu-quercetin complex intercalates into DNA, the second mechanism was attributed to a suppressed intercalating ability of the Cu-quercetin complex due to the mildly intercalating free quercetin into DNA, thus creating a protective wall against stronger intercalators.

Polyradical PROXYL/TEMPO-Derived Amides: Synthesis, Physicochemical Studies, DFT Calculations, and Antimicrobial Activity.

A series of polynitroxide amides possessing 2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PROXYL) and/or 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) units connected through various bridges were synthesized and their properties were analyzed. EPR spectroscopy provided detailed insight into their paramagnetic character and related properties. A thorough examination of the EPR spectra of dinitroxides in organic solvents provided valuable information on the intramolecular motions, thermodynamics, and spin-exchange mechanisms. Analysis of low-temperature X- and Q-band EPR spectra of the dissolved dinitroxides provided spin-spin distances that were comparable with the theoretical values obtained by DFT. Cyclic voltammetry investigations revealed (quasi)reversible electrochemical behavior for PROXYL-derived biradicals, whereas significant loss of the reversibility was found for TEMPO-containing bi- and polyradicals. The inhibitory activities of the nitroxides against model bacteria, yeasts, and filamentous fungi were assessed.

Protonation and electronic structure of 2,6-dichlorophenolindophenolate during reduction. A theoretical study including explicit solvent.

Protonation in the two-electron/two-proton reduction processes of 2,6-dichlorophenolindophenolate (DCIP) is investigated combining density functional theory (DFT) and molecular dynamics (MD) methods. DCIP (anion), DCIP•- (radical anion), and DCIP2- (dianion) are considered, including the electronic structure analysis from the prospective of quantum theory of atoms and molecules (QTAIM). It is shown that oxygen on the indophenolate moiety and nitrogen are the first and/or the second proton acceptor sites and their energetic order depends on the total charge of the system. MD simulations of differently charged species interacting with the solvent molecules have been performed for methanol, water, and oxonium cation (H3O+). Methanol and water molecules are found to form only hydrogen bonds with the solute irrespective of its charge. The calculated pKa values show that the imino group of DCIPH- is a weaker acid than water. While in the case of DCIP (and DCIP•-) plus oxonium cation, proton transfer from the solvent to the solute was evidenced for both aforementioned acceptor sites. In addition, MD simulations of bulks containing 15 and 43 molecules of water around the DCIP molecule have been performed, revealing the formation of 2-4 hydrogen bonds. Graphical Abstract 2,6-Dichlorophenolindophenolate interacts with solvent molecules (water, oxonium cation and methanol). Hydrogen transfer and electronic structure are studied by DFT and molecular dynamics methods.