Diazene sulphonates are readily available compounds which are soluble in water and polar solvents. They strongly absorb the UV-VIS light and they decompose under UV irradiation via radical or ionic intermediates. These properties render them valuable, e.g. for analytical purposes and for photo-printing. In this presentation, it will be demonstrated that polymers with a pendant diazene sulphonate function as cross-linking agents and with pendant aromatic amines as hole-transporters can be considered as useful materials for organic light-emitting device (OLED) technology.

Application of TiO2 photocatalytic systems for water purification and remediation is based on the generation of short-lived reactive oxygen species able to destroy a variety of contaminants, upon the ultra-bandgap irradiation of TiO2 particles in the aerated aqueous media. However the recently more profound presence of inorganic nitrogen compounds can affect these processes due to the complex photochemical behavior of the nitrite and nitrate in aqueous solutions. The effect of the nitrite present in the titanium dioxide suspensions was monitored via the reactive radical intermediates detected by EPR spin trapping technique. Various spin trapping agents were applied to follow the changes in the behavior of the system caused by the nitrite upon UVA irradiation and the limits of the spin trapping technique itself were also considered. The competition reaction of the photo-generated holes and hydroxyl radicals with the nitrite was revealed as the dominant process occurring in the studied systems.

The metallisation of surfaces would be technologically very simple if it were possible to use the properties of the substances that decompose upon UV irradiation and produce species with a strong redox potential. In this work, diazene sulphonates are presented as possible reducing agents for Ag+ in aqueous solutions and in thin solid layers. The photo-formation of Agm+n clusters in the presence of diazene sulphonates in solutions was investigated via UV-VIS spectroscopy. Significant differences were observed in the electrical properties of surfaces after photo reduction; these occurred without any additional reducing agent.

Cyclic voltammetric and EPR/UV-vis-NIR spectroelectrochemical studies were performed to examine the cathodic reduction of 2,6-dichlorophenolindophenolate (DCIP) in proton-donating aqueous and methanol solutions, as well as in aprotic dimethylsulfoxide (DMSO), and to characterize the paramagnetic species generated upon the DCIP reduction. In situ EPR and UV-vis-NIR spectroelectrochemistry confirmed the formation of the radical anion DCIP •– in DMSO and methanol. The same radical anion was found also in the reaction system consisting of KO 2 mixed under argon with DCIP in DMSO or methanol, evidencing the electron transfer from superoxide radical anion to DCIP. The expected radical anion DCIP •– was not detected in the photoexcited suspensions DCIP/TiO 2 /DMSO under argon, which indicates fast consecutive reactions of photogenerated DCIP •– in the vicinity of TiO 2 surface. The reduction of blue-color DCIP to the final colorless product DCIPH 2 can be realized in multiple reaction pathways determined mainly by the proton-donating capacity of the solvent. Following the calculated total DFT energies, the oxygen on the indophenol moiety represents the first proton acceptor site for DCIP, DCIP •– , as well as for DCIP 2– species.

The chemical interaction of sodium sulfide (Na2S) with the NO-donor S-nitrosoglutathione (GSNO) has been described to generate new reaction products, including polysulfides and nitrosopersulfide (SSNO-) via intermediacy of thionitrous acid (HSNO). The aim of the present work was to investigate the vascular effects of the longer-lived products of the Sulfide/GSNO interaction. Here we show that the products of this reaction relax precontracted isolated rings of rat thoracic aorta and mesenteric artery (but to a lesser degree rat uterus) with a >2-fold potency compared with the starting material, GSNO (50 nM), whereas Na2S and polysulfides have little effect at 1-5 mu M. The onset of vasorelaxation of the reaction products was 7-10 times faster in aorta and mesenteric arteries compared with GSNO. Relaxation to GSNO (100-500 nM) was blocked by an inhibitor of soluble guanylyl cyclase, ODQ (0.1 and 10 mu M), and by the NO scavenger cPTIO (100 mu M), but less affected by prior acidification (pH 2-4), and unaffected by N-acetylcysteine (1 mM) or methemoglobin (20 mu M heme). By contrast, relaxation to the Sulfide/GSNO reaction products (100-500 nM based on the starting material) was inhibited to a lesser extent by ODQ only slightly decreased by cPTIO, more markedly inhibited by methemoglobin and N-acetylcysteine, and abolished by acidification before addition to the organ bath. The reaction mixture was found to generate NO as detected by EPR spectroscopy using N-(dithiocarboxy)-N-methyl-D-glucamine (MGD(2))-Fe2+ as spin trap. In conclusion, the Sufide/GSNO reaction products are faster and more pronounced vasorelaxants than GSNO itself. We conclude that in addition to NO formation from SSNO-, reaction products other than polysulfides may give rise to nitroxyl (HNO) and be involved in the pronounced relaxation induced by the Sulfide/GSNO cross-talk. (C) 2014 Elsevier Inc. All rights reserved.

Newly synthesized derivatives of 6-oxo-6,9-dihydro[1,2,5] selenadiazolo[3,4-h]quinoline variously substituted at position 7 are witnessed in solution in the N-9-deprotonated and protonated oxo tautomeric forms depending on the pH using UV/vis and NMR spectroscopy. Upon the anodic oxidation selenadiazoloquinolones produce paramagnetic species observed by EPR spectroscopy.

A simple method for isolation of luteolin-7-O-β-d-glucoside (cynaroside) from a short-lived perennial plant Anthriscus sylvestris (L.) Hoffm. is described. Cynaroside was isolated in high purity as documented by high-performance liquid chromatography (HPLC), thermal, and nuclear magnetic resonance (NMR) analyses. Isolated cynaroside shows biological activity especially against Gram-negative bacteria, exhibits antimutagenic activity, suppresses biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus, and increases frequency of mutations leading to ciprofloxacin resistance in Salmonella typhimurium. Additionally, electron paramagnetic resonance (EPR) spectroscopy and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) assay confirmed its antioxidant and radical scavenging activity. In situ EPR and ultraviolet–visible (UV–Vis) spectroelectrochemical experiments were performed to follow the oxidation reactions of cynaroside in dimethyl sulfoxide solutions. The primary oxidation step takes place on the 1,2-dihydroxybenzene subunit leading to an unstable semiquinone anion radical as proved by EPR spectroscopy and quantum chemical calculations. Spectroelectrochemical and antioxidant studies indicate an important role of the deprotonated form of cynaroside in its redox and antioxidant behavior.

The ability of 2,1,3-benzoselena(thia)diazole derivatives to generate paramagnetic intermediates upon monochromatic excitation (λ max = 365 nm) under different experimental conditions was monitored via EPR spin trapping. The photoinduced activation of molecular oxygen leading to the production of superoxide radical anions, along with other oxygen-, carbon-, or nitrogen-centered radicals originating from the solvent or the solute was evidenced via the identification of the corresponding spin adducts.

H2S signaling pathways interact with NO signaling pathways. To contribute to the understanding of the cross-talk between these pathways, we studied H2S induced NO release from nitroso-compounds in vitro and the biological effects of the reaction products. It was observed that H2S released NO from brain homogenate or cultured cells, indicating that biological systems contain nitroso-compounds from which H2S can induce NO release. In an in vitro model, the H2S donor Na2S decomposes S-nitrosoglutation (GSNO), which results in the formation of polysulfides Sn2- and (SSNO−). Bolus application of a Sn2- and H2S mixture at microM concentrations had significantly pronounced effect in vivo on rat hemodynamic parameters compared to H2S alone. In ex-vivo models, SSNO− relaxed phenylephrine induced aortic and mesenteric ring contraction. Its effect was faster and more pronounced in comparison to GSNO. As detected by spin trap EPR technique, SSNO− released NO faster than GSNO and scavenged the cPTIO radical. Sn2- and SSNO− both modulated the activities of calcium RyR2 and chloride channels. In conclusion, the exogenously produced products of H2S-GSNO interaction, Sn2- and SSNO−, had biological effects in vivo, ex-vivo and in vitro. However, detection of possible endogenous products of H2S-GSNO interactions is a challenge for future research. This work was supported by APVV-0074-11 and VEGA 2/0050/13.

The cathodic reduction of 10-ethyl-7H,10H-pyrido[2,3-f]quinoxalin-7-one (1a) and ethyl 10-ethyl-7-oxo-7H,10H-pyrido[2,3-f]quinoxaline-8-carboxylate (2a), as well as their 2,3-R,R-substituted derivatives (R = CH3 or C6H5), represents a reversible one-electron process coupled with the generation of corresponding radical monoanions as evidenced by in situ electron paramagnetic resonance (EPR)/UV–vis-near-infrared (NIR) cyclovoltammetric experiments in N,N-dimethylformamide. The detected radical monoanions are characterized by electronic absorption bands in the vis-NIR regions, and their EPR spectra show a dominant interaction of the unpaired electron with the nitrogen and hydrogen nuclei of the pyrazine ring. The reduction behavior of 10-ethyl-7-oxo-7H,10H-pyrido[2,3-f]quinoxaline-8-carboxylic acid (3a) and its 2,3-dimethyl or 2,3-diphenyl derivatives is more complex, revealing an irreversible first reduction peak, followed by a second reversible reduction step. Based on the results of the in situ EPR/UV–vis-NIR spectroelectrochemical measurements for quinoxaline carboxylic acids, the first irreversible reduction peak was assigned to a reduction process on the pyridone ring, followed by a second reversible reduction process on the π-electron deficient pyrazine moiety, generating the radical monoanions detected by EPR spectroscopy.

The generation of paramagnetic intermediates upon photoinduced reduction of substituted nitroquinolones 1-6 in dimethylsulfoxide/methanol titania suspensions was investigated by in situ EPR spectroscopy. The assignment of the primary photogenerated paramagnetic signals was based on the results of cyclic voltammetry, amperostatic in situ spectroelectrochemistry and in situ EPR/UV-Vis spectroelectrochemistry in aprotic dimethylsulfoxide and dimethylsulfoxide/methanol mixed solvent. The primary reduction step in the cathodically- or in the photocatalytically-induced electron transfer process represents the formation of radical monoanion, the stability of which is crucially influenced by the 1-ethyl substitution at the nitrogen of the 4-pyridone ring of quinolone. 1-Ethyl 6-nitroquinolones typically form stable radical anions with well-resolved EPR spectra, with detailed interpretation of hyperfine coupling constants (hfcc) supported by theoretical calculations. On the other hand, the radical anions of nitroquinolones with amino hydrogen at nitrogen of the enaminone system (N-C=C-C=O) convert rapidly to diamagnetic sigma-dimer dianions, reduced in the second reversible reduction step to paramagnetic sigma-dimer radical trianions. The EPR spectra obtained upon prolonged irradiation of 1-ethyl nitroquinolones in titania suspensions were assigned to the R-(NOH)-H-center dot intermediates produced via nitro group reduction. Experiments with deuterated methanol unambiguously confirmed the photoinduced reduction of the nitro group, including the interaction with hydrogen from the hydroxyl group of methanol. The generation of reactive radicals formed via methanol and dimethylsulfoxide oxidation in irradiated titania suspensions was investigated by EPR spin trapping technique.

4-Oxoquinoline derivatives (quinolones) represent heterocyclic compounds with a variety of biological activities, along with interesting chemical reactivity. The quinolone derivatives possessing secondary amino hydrogen at the nitrogen of the enaminone system are oxidized with 3-chloroperbenzoic acid to nitroxide radicals in the primary step while maintaining their 4-pyridone ring. Otherwise, N-methyl substituted quinolones also form nitroxide radicals coupled with the opening of the 4-pyridone ring in a gradual oxidation of the methyl group via the nitrone-nitroxide spin-adduct cycle. This was confirmed in an analogous oxidation using N,N-dimethylaniline as a model compound. N-Ethyl quinolones in contrast to its N-methyl analog form only one nitroxide radical without a further degradation.

Photoinduced reactions of 9‐oxo‐6,9‐dihydro[1,2,5]selenadiazolo[3,4‐f]quinoline‐8‐carboxylic acid (SeQCA) were investigated in alkaline media (aqueous NaOH solutions) by electron paramagnetic resonance (EPR) spectroscopy, following the in situ formation of paramagnetic species. According to UV–Vis and nuclear magnetic resonance investigations, protonation (pH ≈ 11) and deprotonation (pH ≈ 13) of the imino hydrogen of the 4‐pyridone moiety has to be considered, reflected also in the different EPR spectra observed upon irradiation. Photoinduced generation of radicals was found only for carboxylate substituted SeQCA; other studied selenadiazoloquinolone derivatives, together with those substituted at the C(8) position (R = H, COOCH2CH3, COOCH3, COCH3 or CN), did not generate paramagnetic species during exposure. Consequently, photodecarboxylation was suggested as the decisive step, accompanied by the decomposition of the selenadiazole ring, resulting in the formation of ortho‐hydroxylate anions. EPR parameters elucidated from experimental EPR spectra obtained at pH ≈ 11 and pH ≈ 13 indicate the formation of oxygen‐centered radicals at the decarboxylated 4‐pyridone ring. EPR spin trapping experiments with nitromethane confirmed a very effective photoinduced electron transfer from all the selenadiazoloquinolones investigated. Copyright © 2011 John Wiley & Sons, Ltd.

The redox behavior of the series of 7-substituted 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-h]quinolines and 8-substituted 9-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-f]quinolines with R(7), R(8) = H, COOC(2)H(5), COOCH(3), COOH, COCH(3), and CN has been studied by in situ EPR and EPR/UV-vis spectroelectrochemistry in dimethylsulfoxide. All selenadiazoloquinolones undergo a one-electron reduction process to form the corresponding radical anions. Their stability strongly depends on substitution at the nitrogen atom of the 4-pyridone ring. The primary generated radical anions from N-ethyl-substituted quinolones are stable, whereas for the quinolones with imino hydrogen, the initial radical anions rapidly dimerize to produce unusually stable sigma-dimer (σ-dimer) dianions. These are reversibly oxidized to the initial compounds at potentials considerably less negative than the original reduction process in the back voltammetric scan. The dimer dianion can be further reduced to the stable paramagnetic dimer radical trianion in the region of the second reversible reduction step. The proposed complex reaction mechanism was confirmed by in situ EPR/UV-vis cyclovoltammetric experiments. The site of the dimerization in the σ-dimer and the mapping of the unpaired spin density both for radical anions and σ-dimer radical trianions with unusual unpaired spin distribution have been assigned by means of density functional theory calculations.

In situ spectroelectrochemistry brings new dimensions into a conventional electrochemical experiment. Quinolone derivatives are for many years well known and important group of drugs. Two groups of novel quinolone derivatives with various structure and substituents were studied by spectroelectrochemical techniques in order to better understand their redox behavior. ESR spectroscopy provides valuable information about paramagnetic species (radical ions) generated upon electrochemical oxidation/reduction. On the basis of spectral and electrochemical data we proposed the mechanism of electrochemical reduction of presented quinolone derivatives.

Newly synthesized derivatives of 6‐oxo‐6,9‐dihydro[1,2,5]selenadiazolo[3,4‐ h ]quinoline variously substituted at position 7 (R = H, COOH, COCH 3 , CN, COOC 2 H 5 and COOCH 3 ) are established in strongly alkaline aqueous solutions (0.1 M NaOH; pH ∼ 13) as N(9)‐deprotonated structures, but in less alkaline solutions (0.001 M NaOH; pH ∼ 11) the N(9)‐protonated oxo tautomeric forms dominate. Upon their anodic oxidation in alkaline solutions, the selenadiazole ring is replaced, forming instead the paramagnetic species analogous to the ortho semiquinone radical anions as monitored by in situ EPR spectroscopy. The quantum chemical calculations for two representative selenadiazoloquinolones (R = H and COOH) and their anodic oxidation products presented are in agreement with experiments. Copyright © 2011 John Wiley & Sons, Ltd.

Derivatives of 1,4-dihydro-4-oxoquinoline substituted at 4-pyridone or/and benzene moieties were synthesized (Q1-Q17), and characterized by UV/vis and FT-IR spectroscopy. In dimethylsulfoxide and acetonitrile solvents a significant influence of the substituent's character and position on the quinolone skeleton was observed on the absorption bands in the UVA region (315-400 nm). Electron-withdrawing substituents (nitro, cyano, acetyl or trifluoroacetyl) caused a red shift, resulting in the effective absorption of UVA light. Photoinduced generation of superoxide radical anion and singlet oxygen upon UVA irradiation was followed by EPR spectroscopy using in situ spin trapping technique; 4-hydroxy-2,2,6,6-piperidine (TMP) served for singlet oxygen (O-1(2)) detection. An efficient generation of superoxide radical anions and singlet oxygen was observed predominantly for nitro-substituted quinolones. The effect of quinolones on proliferation of HL-60 cells was monitored, and the values of IC50 evidenced the highest inhibition in the presence of ethyl 1,4-dihydro-6-fluoro-8-nitro-4-oxoquinoline-3-carboxylate (Q17) and ethyl 1,4-dihydro-8-nitro-4-oxoquinoline-3-carboxylate (Q5). (C) 2011 Elsevier BM. All rights reserved.

Novel 7-substituted 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-h] quinoline (SeQ(1-6)) and 8-substituted 9-oxo-6,9-dihydro[1,2,5] selenadiazolo[3,4-f]quinoline derivatives (SeQN(1-5)) with R-7, R-8 = H, COOC2H5, COOCH3, COOH, COCH3 or CN were synthesized and their spectral characteristics were obtained by UV/Vis spectroscopy. Ultraviolet A photoexcitation of the selenadiazoloquinolones in dimethylsulfoxide or acetonitrile resulted in the formation of paramagnetic species coupled with molecular oxygen activation generating the superoxide radical anion or singlet oxygen, evidenced by electron paramagnetic resonance spectroscopy. The cytotoxic/photocytotoxic impact of selenadiazoloquinolones on murine and human cancer cell lines was demonstrated using the derivative SeQ5 (with R-7 = COCH3).

Thermal decomposition of transannular peroxide of anthracene (POA) (or 9,10-epidioxido anthracene) was studied by means of electron paramagnetic resonance spectroscopy (EPR) in the solid as well as in the liquid phases. Decomposition process proceeds via cleavage of the O-O bridge of the POA molecule, generating thus an alcoxy intermediate radical. Its concentration increases to a certain equilibrium stage during the time scale of the experiment. EPR spectra in the solid state were of the singlet type at the temperatures over 350 K, a doublet like anisotropic spectra were measured at the room temperature, both having g-value 2.0033. EPR spectrum from POA decomposed in benzene indicates four protons with higher (2aH = 0.305 mT, 2aH = 0.335 mT) and four protons with a lower (2aH = 0.075 mT, 2aH = 0.105 mT) splitting constants, corresponding well the radical expected after cleavage of O-O bridge.

Antioxidant properties of commercially-available ground and instant coffees were investigated by means of electron paramagnetic resonance (EPR) using as oxidants 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH), 4-hydroxy-2,2,6,6-tetramethylpiperidine N-oxyl (TEMPOL) and thermally decomposed K2S2O8. Only moderate differences were found in the antioxidant capacities of individual samples (expressed as trolox equivalent antioxidant capacity TEAC) with TEACABTS=0.22±0.02mmolg−1 for ground and TEACABTS=0.71±0.07mmolg−1 for instant coffees. Two coffee components (caffeic acid and caffeine) were investigated using moderate hydrogen/electron scavengers ABTS+ and DPPH, and a powerful oxidant OH radical (photochemically generated from H2O2). Caffeine is inert to ABTS+ and DPPH oxidants, but effective in the scavenging of OH radicals, with a bimolecular rate constant k=2.6×109M−1s−1. Caffeic acid is a very effective antioxidant in all oxidant systems, with k=9.4×109M−1s−1 in the bimolecular reaction with OH radicals. From the evaluated correlation matrix, a good linear relationship was found for the ground coffees between TEACABTS and TEACDPPH values (rTEACABTS/TEACDPPH=0.859) and also between the phenolics content expressed in gallic acid equivalents (GAE) and TEAC antioxidant capacities (rGAE/TEACABTS=0.729andrGAE/TEACDPPH=0.922).