Reactions of nitric oxide and nitrogen dioxide with coenzyme Q: involvement of the isoprenic chain.

The formation of a di-tert-alkyl nitroxide has been observed by Electron Spin Resonance during the exposure of coenzyme CoQ(10), in both the oxidized and reduced forms, to nitrogen dioxide (˙NO(2)) or to nitric oxide (˙NO) in the presence of oxygen. The same kind of nitroxide has been observed also with CoQ(1), CoQ(3) or with 1-phenyl-3-methyl-2-butene, chosen as model compounds. In all cases, the formation of the nitroxide may be justified only by admitting the involvement of the isoprenic chain of the coenzymes and in particular the addition of ˙NO(2) to the double bond. A mechanism which accounts for the formation of the nitroxide as well as the other compounds observed in the reactions is proposed and confirmed by a spectroscopic investigation (FT-IR, (1)H NMR, X-ray analysis) and by ESI-MS.

4-Nitro-phenyl 2-bromo-2-methyl-propano-ate.

In the title compound, C(10)H(10)BrNO(4), the planes of the carboxyl-ate and nitro groups are rotated by 60.53 (13) and 6.4 (3)°, respectively, to the benzene ring. In the crystal, inter-molecular C-H⋯O hydrogen bonds link the mol-ecules into zigzag chains parallel to the c axis.

The reaction of spiro[indoline-naphthopyrans] with nitrogen oxides. Not a case of biradical double trapping.

The reactions of six differently substituted photochromic spiro[indoline-naphtopyrans] with .NO or .NO(2) under normal daylight conditions have been investigated by means of EPR spectroscopy along with those of three structurally related spiro[indoline-benzopyrans]. The spectra due to cyclic oxynitroxides originating from double trapping of biradicals by .NO were observed with the three latter derivatives, this finding being in agreement with previous results. Similar signals were also observed with the six former compounds, but in this case they were responsible for just a minor component of the spectra, the main spectral signals being due to hitherto unreported paramagnetic species that on the basis of their spectral parameters are identified as iminoxy radicals. DFT calculations at the B3LYP/6-31G* level carried out on a variety of radicals support this assignment.

3-Benzyl-3-hy-droxy-2-phenyl-3H-indole 1-oxide.

The asymmetric unit of the title compound, C(21)H(17)NO(2), contains two crystallographically independent mol-ecules of similar geometry. The indole ring systems form dihedral angles of 8.30 (5) and 9.58 (5)° with the attached phenyl rings, and 56.96 (5) and 57.68 (5)° with the aromatic rings of the respective benzyl groups. The mol-ecular conformations are stabilized by intra-molecular C-H⋯O hydrogen bonds. In the crystal structure, centrosymmetrically related pairs of mol-ecules are linked into dimers through pairs of inter-molecular O-H⋯O hydrogen bonds, generating 12-membered rings with R(2) (2)(12) motifs. The dimers are further linked into a three-dimensional network by C-H⋯O inter-actions.

Nitroxides are more efficient inhibitors of oxidative damage to calf skin collagen than antioxidant vitamins.

Reactive oxygen species generated upon UV-A exposure appear to play a major role in dermal connective tissue transformations including degradation of skin collagen. Here we investigate on oxidative damage to collagen achieved by exposure to (i) UV-A irradiation and to (ii) AAPH-derived radicals and on its possible prevention using synthetic and natural antioxidants. Oxidative damage was identified through SDS-PAGE, circular dichroism spectroscopy and quantification of protein carbonyl residues. Collagen (2 mg/ml) exposed to UV-A and to AAPH-derived radicals was degraded in a time- and dose-dependent manner. Upon UV-A exposure, maximum damage was observable at 730 kJ/m2 UV-A, found to be equivalent to roughly 2 h of sunshine, while exposure to 5 mM AAPH for 2 h at 50 degrees C lead to maximum collagen degradation. In both cases, dose-dependent protection was achieved by incubation with muM concentrations of nitroxide radicals, where the extent of protection was shown to be dictated by their structural differences whereas the vitamins E and C proved less efficient inhibitors of collagen damage. These results suggest that nitroxide radicals may be able to prevent oxidative injury to dermal tissues in vivo alternatively to commonly used natural antioxidants.

Rottlerin inhibits ROS formation and prevents NFkappaB activation in MCF-7 and HT-29 cells.

Rottlerin, a polyphenol isolated from Mallotus Philippinensis, has been recently used as a selective inhibitor of PKC delta, although it can inhibit many kinases and has several biological effects. Among them, we recently found that Rottlerin inhibits the Nuclear Factor kappaB (NFkappaB), activated by either phorbol esters or H(2)O(2). Because of the redox sensitivity of NFkappaB and on the basis of Rottlerin antioxidant property, we hypothesized that Rottlerin could prevent NFkappaB activation acting as a free radicals scavenger, as other natural polyphenols. The current study confirms the antioxidant property of Rottlerin against the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) in vitro and against oxidative stress induced by H(2)O(2) and by menadione in culture cells. We also demonstrate that Rottlerin prevents TNFalpha-dependent NFkappaB activation in MCF-7 cells and in HT-29 cells transfected with the NFkappaB-driven plasmid pBIIX-LUC, suggesting that Rottlerin can inhibit NFkappaB via several pathways and in several cell types.

1-[2-(2,4-Dichloro-phenyl)-pent-yl]-1H-1,2,4-triazole.

The title compound, C(13)H(15)Cl(2)N(3), also known as penconazole, crystallizes as a racemate. The dihedral angle between the benzene and triazole rings is 24.96 (13)°. In the crystal structure, mol-ecules are linked into chains running parallel to the c axis by inter-molecular C-H⋯N hydrogen-bonding inter-actions.

2,2-Diphenyl-benzo[c]quinoline-1-ox-yl.

In the title compound, C(25)H(18)NO, a stable phenanthridinic nitroxide, the ring containing the nitroxide function assumes a twist-boat conformation and the dihedral angle formed by adjacent benzene rings is 21.78 (5)°. The phenyl substituents at position 2 are approximately orthogonal to each other, forming a dihedral angle of 81.04 (4)°. The crystal structure is stabilized by an intra-molecular C-H⋯O hydrogen bond and by C-H⋯π inter-actions.

Reaction of endogenous Coenzyme Q10 with nitrogen monoxide and its metabolite nitrogen dioxide.

Objectives: Coenzyme Q10, incorporated in DOPC lyposomes or naturally present in liver bovine mitochondria or in human blood plasma, was reacted with nitrogen dioxide •NO2 or with a •NO/•NO2 mixture. Methods and Results: The reaction course was monitored by Electron Paramagnetic Resonance (EPR) spectroscopy and in all cases the formation of a di-tert-alkyl nitroxide was observed, deriving from the addition of •NO2 to one of the double bonds, most likely the terminal one, of the isoprenic chain. The rate constant for nitroxide formation was also determined by EPR spectroscopy and an initial rate of ca. 7 × 10-8 M s-1 was obtained.

Sunscreens cause coral bleaching by promoting viral infections.

BACKGROUND: Coral bleaching (i.e., the release of coral symbiotic zooxanthellae) has negative impacts on biodiversity and functioning of reef ecosystems and their production of goods and services. This increasing world-wide phenomenon is associated with temperature anomalies, high irradiance, pollution, and bacterial diseases. Recently, it has been demonstrated that personal care products, including sunscreens, have an impact on aquatic organisms similar to that of other contaminants. OBJECTIVES: Our goal was to evaluate the potential impact of sunscreen ingredients on hard corals and their symbiotic algae. METHODS: In situ and laboratory experiments were conducted in several tropical regions (the Atlantic, Indian, and Pacific Oceans, and the Red Sea) by supplementing coral branches with aliquots of sunscreens and common ultraviolet filters contained in sunscreen formula. Zooxanthellae were checked for viral infection by epifluorescence and transmission electron microscopy analyses. RESULTS: Sunscreens cause the rapid and complete bleaching of hard corals, even at extremely low concentrations. The effect of sunscreens is due to organic ultraviolet filters, which are able to induce the lytic viral cycle in symbiotic zooxanthellae with latent infections. CONCLUSIONS: We conclude that sunscreens, by promoting viral infection, potentially play an important role in coral bleaching in areas prone to high levels of recreational use by humans.

UV-Filter combinations under UV-A exposure: concomitant quantification of over-all spectral stability and molecular integrity.

Efficient UV-absorbing molecules are designed to protect against UV-light over-exposure. However, upon UV exposure they may change spectral performance or act as photooxidants via generation of free radicals and reactive oxygen species alone or in combination with others. Therefore, information about their photointegrity which comprises (i) stable absorbance and (ii) absence of UV-induced molecular breakdown, is fundamental. In this study, seven commonly used UV-A, UV-B and broad spectrum UV-AB filters and their combinations, were incorporated into phosphatidylcholine (PC)-based liposomes and exposed to UV-A (275 kJ/m(2)). Spectral integrity, evaluated by recording UV-absorbance spectra of the extracted filter molecules and molecular integrity, assessed indirectly via quantification of UV-A induced PC peroxidation, revealed that spectral stability of filter molecules alone or in combination (e.g. trianilino p-carboxyethylhexyl triazine, EHT plus ethylhexyl p-methoxycinnamate, OMC) does not necessarily imply absence of radical generation and that spectral lability does not necessarily have to lead to radical generation and molecular decay (e.g. OMC). This simple system capable of discriminating between essentially photostable and photounstable UV-absorbing molecules alone and in mixtures, might be useful for determining the influence of UV-protection as well as of photostability of UV-absorbers with regard to UV-induced genotoxic/phototoxic and photoageing-related, radical-based processes.

An Unconventional Approach to Photomobile Composite Polymer Films.

Photomobile polymer (Pmp) films are fabricated by using a cheap and fast process. The working mechanism of the Pmp-film motion under illumination is explained. Details concerning the film structure and formation are given. Two related applications regarding light-induced caterpillar-miming motion and photocontrolled electrical switches are proposed.

Synthesis and application of a novel sunscreen-antioxidant.

Background information on the inefficacy of sunscreens to provide free radical protection in skin, despite their usefulness in preventing sunburn/erythema, prompted us to synthesize a compound which would display in the same molecule both UV-absorbing and antioxidant capacities. For this purpose, the UVB absorber, 2-ethylhexyl-4-methoxycinnamate (OMC) was combined with the piperidine nitroxide TEMPOL, which has antioxidant properties. The spectral properties of the new nitroxide-based sunscreen (MC-NO) as well as its efficacy to prevent photo-oxidative damage to lipids induced by UVA, natural sunlight and 4-tert-butyl-4-methoxydibenzoylmethane (BMDBM), a photo-unstable sunscreen which generates free radicals upon UV radiation, was studied. The results obtained demonstrate that MC-NO: (a) absorbs in the UVB region even after UVA irradiation; (b) acts as free radical scavenger as demonstrated by EPR experiments; (c) strongly reduces both UVA-, sunlight- and BMDBM-induced lipid peroxidation in liposomes, measured as reduced TBARS levels; and (d) has comparable antioxidant activity to that of commonly used vitamin E and BHT in skin care formulations. These results suggest that the use of the novel sunscreen-antioxidant or of other nitroxide-based sunscreens in formulations aimed at reducing photoinduced skin damage may be envisaged.

Changes in ultraviolet absorbance and hence in protective efficacy against lipid peroxidation of organic sunscreens after UVA irradiation.

Owing to the spectral distribution of solar UV, the UVA component of sunlight is now believed to be the main cause of photoaging and photocarcinogenesis and is much more effective than UVB in inducing peroxidative damage. Consequently, most skin care cosmetic products now include UVA filters in their formulations along with UVB filters. These modern sunscreens should provide and maintain their initial absorbance, hence protection, throughout the entire period of exposure to sunlight. However, not all UVA and UVB filters are sufficiently photostable. In this study, we examine the correlation between the photochemical degradation of sunscreen agents under UVA irradiation, with particular reference to the UVA-absorber 4-tert-butyl-4'-methoxydibenzoylmethane, alone and in combination with other organic UV filters (2-ethylhexyl 4 methoxycinnamate and 2-ethylhexyl 2-cyano-3,3-diphenylacrylate) and their ability to prevent UVA-induced lipid peroxidation. Since antioxidants are also added to formulations to deactivate free radicals generated during UVA exposure, vitamin E and the synthetic antioxidant, bis(2,2,6,6-tetramethyl-1-oxyl-piperidine-4-yl)sebacate, a nitroxide derivative, were also included in this study. By using simple in vitro tests, the results show that a decrease in spectral absorbance of the UV filters correlates in most cases with increased UVA-induced lipid peroxidation; this depends on the specific UV absorber analysed and also on whether they are alone or in combination. Furthermore, the combined presence or absence of antioxidants has a profound effect on this oxidative event. In particular, the nitroxide appears to be a more efficient photo-antioxidant than vitamin E. Similar experiments were also performed under natural sunlight and the results obtained did not differ substantially from those performed under UVA. The results presented and discussed in this work may help in understanding the effects of UVA/UVB absorbers and antioxidants upon the level of UV-induced ROS generated under UVA exposure and in natural sunlight which could be relevant for improving the photoprotection and efficacy of skin care cosmetic formulations.

Spin trapping of nitrogen dioxide and of radicals generated from nitrous acid.

Spin trapping of nitrogen dioxide radical by several nitrones has been studied. The reaction results in the formation of persistent acyl nitroxides, after the oxidation of the intermediate spin adducts having an -ONO group on C-2 atom. The intermediate is effectively detected when DEPMPO is used as the spin trap. The reaction between PBN or 5,7-di-tert-butyl-3,3-dimethyl indoline N-oxide with nitrous acid gives the corresponding acyl nitroxide only when oxygen is present in the reaction milieu. On the other hand, nitroso spin traps do not trap *NO2 confirming that the unpaired electron of nitrogen dioxide is localized on the oxygen atom.

Aromatic and aliphatic mono- and bis-nitroxides: a study on their radical scavenging abilities.

Nitroxide radicals are an emerging class of interesting compounds with versatile antioxidant and radioprotective properties. All literature studies have so far concentrated on compounds bearing only one nitroxide function. Here, we now investigate and compare the radical scavenging behaviour and antioxidant activity of aromatic indolinonic and aliphatic piperidine bis-nitroxides, i.e compounds bearing two nitroxide functions. Their corresponding mono-derivatives were also studied for comparison. Radical scavenging activity was investigated using EPR and UV-Vis spectroscopy by following spectral changes in acetonitrile of the nitroxides in the presence of alkyl and peroxyl radicals generated, respectively, under anoxic or aerobic conditions from thermal decomposition of AMVN [2,2'-azobis(2,4-di-methylvaleronitrile)]. Antioxidant activity of the nitroxides was evaluated by monitoring conjugated dienes (CD) formation during methyl linoleate micelles peroxidation and by measuring carbonyl content in oxidized bovine serum albumin (BSA). The results show that: (a) each nitroxide moiety in bis-nitroxides scavenges radicals independent of each other; (b) aliphatic nitroxides do not scavenge peroxyl radicals, at least under the experimental conditions used here, whereas indolinonic aromatic ones do: their stoichiometric number is 1.14 and 2.17, respectively, for mono- and bis-derivatives; (c) bis-nitroxides are roughly twice more efficient at inhibiting lipid peroxidation compared to their corresponding mono-derivatives. Although this study provides only comparative information on the relative radical-scavenging abilities of mono- and bis-nitroxides, it helps in understanding further the interesting reactivity of these compounds especially with regards to peroxyl radicals where many controversies in the literature exist.

Effect of complexation with randomly methylated beta-cyclodextrin on the aqueous solubility, photostability and antioxidant activity of an indolinonic nitroxide radical.

The interaction between the hydrophobic indolinonic nitroxide radical, 1,2-dihydro-2-methyl-2-phenyl-3H-indole-3-one-1-oxyl and hydrophilic alpha-, beta- and gamma-cyclodextrin derivatives was investigated in water by phase-solubility analysis. Among the studied cyclodextrins, random methyl-beta-cyclodextrin (RM-beta-CD) had the greatest solubilizing activity (1312-fold increase in. the intrinsic aqueous solubility). Solid complexes were prepared by the freeze-drying method and characterized by powder X-ray diffractometry and thermal analysis. Complexation of the nitroxide with RM-beta-CD was also confirmed in solution by electron paramagnetic resonance (EPR) spectroscopy. Photodegradation of the nitroxide was reduced by complexation with RM-beta-CD, this effect being more pronounced in the solid-state (the extent of degradation was 28.0% for the complex vs. 78.8% for uncomplexed nitroxide) than in solution (41.2 vs. 69.1% for uncomplexed nitroxide). The antioxidant activity of the complex was also investigated on the peroxidation of methyl linoleate micelles and on protein oxidation induced by free radical generators, and in both systems the free form of the nitroxide as well as its complex with RM-beta-CD, showed essentially the same degree of protection. Moreover, EPR experiments showed a time-dependent decrease in the EPR signal of both the complexed and uncomplexed nitroxides with the free-radical generators. Therefore, RM-beta-CD complexation of the nitroxide represents an effective strategy to improve its aqueous solubility and photostability, which is essential for certain biological applications, while it does not interfere with its radical scavenging efficiency.

The effects of derivatives of the nitroxide tempol on UVA-mediated in vitro lipid and protein oxidation.

Derivatives of tetramethylpiperidines are extensively employed in polymers to prevent photooxidation, and their stabilizing effect is attributed to the activity of the nitroxide radical derived from the parent amine. In this study, we examined the photoprotective effect of a commercial polymer photostabilizer, HALS-1, its corresponding nitroxide, bis(2,2,6,6-tetramethyl-piperidine-1-oxyl-4-yl)sebacate (TINO), and two derivatives of the piperidine nitroxide TEMPOL, 2,2,6,6-tetramethyl-piperidin-4-acetyloxy-1-oxyl (TEMP2) and 2,2,6,6-tetramethyl-piperidin-4-octanoyloxy-1-oxyl (TEMP8) synthesized by us, in liposomes exposed to ultraviolet A (UVA) radiation. For comparison, the UVA-absorber, 4-tert-butyl-4'-methoxydibenzoylmethane (Parsol 1789) used in many suncream formulations, was also included. The nitroxide TINO resulted extremely efficient at inhibiting aldehydic breakdown products deriving from 30 min exposure of liposomes to UVA and the protection was dose-dependent (10-100 microM). The corresponding amine HALS-1 was the least efficient while protection increased in the order: TEMP2 < Parsol 1789 < TEMP 8. HALS-1, TINO, and the two TEMPOL derivatives were also tested in a simple protein system consisting of bovine serum albumin (BSA) exposed to UVA. In this case, these compounds did not inhibit nor enhance UVA-mediated protein carbonyl formation in BSA. The differences in protection between the compounds are discussed in relation to their chemical reactivity, UVA-absorbing capacities, and their molecular structure. Overall, the results obtained envisage the potential use of nitroxide compounds as topical antioxidants.

Reduction of 1,4-quinone and ubiquinones by hydrogen atom transfer under UVA irradiation.

1,4-Benzoquinone, coenzyme Q0 and Q10 were reacted with a series of hydrogen donors in the ESR cavity in the presence or absence of UVA irradiation. The signals of the radicals generated from the hydrogen donors or of those of the semiquinones were detected. The reaction mechanism was interpreted by a hydrogen atom transfer instead of the usual electron transfer mechanism on the basis of the redox potentials of the reactants and the Marcus theory. The hydrogen atom transfer is explained by the excited triplet state of quinones, which, on the basis of quantum mechanic calculations, may be reached even under visible light. In some cases, hydrogen atom transfer was also observed without irradiation, although to a lesser extent.

Comparison of antioxidant activity between aromatic indolinonic nitroxides and natural and synthetic antioxidants.

In view of the possible employment of nitroxide compounds in various fields, it is important to know how they compare with other synthetic antioxidant compounds currently used in several industries and with naturally occurring antioxidants. To address this issue, the antioxidant activity of two aromatic indolinonic nitroxides synthesized by us was compared with both commercial phenolic antioxidants (BHT and BHA) and with natural phenolic antioxidants (alpha-hydroxytyrosol, tyrosol, caffeic acid, alpha-tocopherol). DPPH radical scavenging ability and the inhibition of both lipid and protein oxidation induced by the peroxyl-radical generator, AAPH, were evaluated. The results obtained show that overall: (i) the reduced forms of the nitroxide compounds are better scavengers of DPPH radical than butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BLT) but less efficient than the natural compounds; (ii) the nitroxides inhibit both linolenic acid micelles and bovine serum albumin (BSA) oxidation to similar extents as most of the other compounds in a concentration-dependent fashion. Since the aromatic nitroxides tested in this study are less toxic than BHT, these compounds may be regarded as potential, alternative sources for several applications. The mechanisms underlying the antioxidant activity of nitroxides were further confirmed by UV-Vis absorption spectroscopy experiments and macroscale reactions in the presence of radicals generated by thermolabile azo-compounds. Distribution coefficients in octanol/buffer of the nitroxides and the other compounds were also determined as a measure of lipophilicity.