Photochemical Initiation and Reactions of Thiyl Radicals Studied with SH2' Radical Traps.

A radical trapping method based on an SH2' homolytic substitution reaction was applied to study the mechanism of a photochemical spirocyclisation of indole-ynones in the presence of thiols. Starting material, products and a range of trapped radical intermediates were simultaneously detected in reaction mixtures by mass spectrometry (MS). The trapped intermediates included both initiating and main chain propagating radicals. These data made it possible to propose a self-initiation mechanism consistent with the originally postulated photoexcitation of an intramolecular electron donor-acceptor complex of the substrate. The effect of thiol structure on the MS peak intensity of the reaction components was rationalised in terms of the relative stability of the radical intermediates. The results were compared to a simpler related reaction, a photochemical thiol-ene addition where reagents, products and trapped intermediate radicals were also detected by MS. Relative MS peak intensities were again explained by a combination of electronic and steric effects on the stability of intermediate radicals. Overall, SH2' radical trapping was demonstrated to be a powerful experimental technique for providing mechanistic evidence on photochemical and other organic radical reactions.

Enhanced Mechanistic Understanding Through the Detection of Radical Intermediates in Organic Reactions.

Two applications of a radical trap based on a homolytic substitution reaction (SH2') are presented for the trapping of short-lived radical intermediates in organic reactions. The first example is a photochemical cyanomethylation catalyzed by a Ru complex. Two intermediate radicals in the radical chain propagation have been trapped and detected using mass spectrometry (MS), along with the starting materials, products and catalyst degradation fragments. Although qualitative, these results helped to elucidate the reaction mechanism. In the second example, the trapping method was applied to study the radical initiation catalyzed by a triethylboronoxygen mixture. In this case, the concentration of trapped radicals was sufficiently high to enable their detection by nuclear magnetic resonance (NMR). Quantitative measurements made it possible to characterize the radical flux in the system under different reaction conditions (including variations of solvent, temperature and concentration) where modelling was complicated by chain reactions and heterogeneous mass transfer.

Denitrative Hydroxylation of Unactivated Nitroarenes.

A one-step method for the conversion of nitroarenes into phenols under operationally simple, transition-metal-free conditions is described. This denitrative functionalization protocol provides a concise and economical alternative to conventional three-step synthetic sequences. Experimental and computational studies suggest that nitroarenes may be substituted by an electron-catalysed radical-nucleophilic substitution (SRN 1) chain mechanism.

The Role of Polyphenolic Antioxidants from Tea and Rosemary in the Hydroxyl Radical Oxidation of N-Acetyl Alanine.

In dead biological tissues such as human hair, the ability of antioxidants to minimise autoxidation is determined by their chemical reactions with reactive oxygen species. In order to improve our understanding of factors determining such antioxidant properties, the mechanistic chemistry of four phenolic antioxidants found in tea and rosemary extracts (epicatechin, epigallocatechin gallate, rosmarinic and carnosic acids) has been investigated. The degradation of N-acetyl alanine by photochemically generated hydroxyl radicals was used as a model system. A relatively high concentration of the antioxidants (0.1 equivalent with respect to the substrate) tested the ability of the antioxidants to intercept both initiating hydroxyl radicals (preventive action) and propagating peroxyl radicals (chain-breaking action). LC-MS data showed the formation of hydroxylated derivatives, quinones and hydroperoxides of the antioxidants. The structure of the assignment was aided by deuterium exchange experiments. Tea polyphenolics (epicatechin and epigallocatechin gallate) outperformed the rosemary compounds in preventing substrate degradation and were particularly effective in capturing the initiating radicals. Carnosic acid was suggested to act mostly as a chain-breaking antioxidant. All of the antioxidants except for rosmarinic acid generated hydroperoxides which was tentatively ascribed to the insufficient lability of the benzylic C-H bond of rosmarinic acid.

The key phytochemistry of rosemary (Salvia rosmarinus) contributing to hair protection against UV.

Extracts from rosemary (Salvia Rosmarinus) are analysed for their phytochemistry using LC-MS and the phytochemistry identified. The same extracts were tested for their efficacy to act as antioxidants by both hydrogen-atom transfer (ORAC) and single electron transfer (FRAP). A correlation analysis was performed to identify the key phytochemistry responsible for antioxidant efficacy. The top performing extracts were then tested in a peptide model and in hair with the presence of UV to measure ability to protect against UV-induced peptide and protein damage. Polyphenols (e.g. rosmarinic acid, glycosides of selgin) and abietane diterpenes (e.g. carnosic acid) in rosemary were identified as the principal compounds which enables the extracts to protect hair from UV. OBJECTIVE: The objective of this work was to correlate the phytochemistry of rosemary (Salvia rosmarinus), a botanical with known antioxidant properties, to a UV protection benefit in hair. These data will give insights into mechanisms of UV damage, the ROS formed and their reactivity. METHODS: LC-MS was used to compare the compounds in 10 commercial extracts of rosemary. ORAC (oxygen radical antioxidant capacity) and FRAP (ferric reducing antioxidant power) were used to measure the antioxidant capacity of the rosemary extracts. The ORAC assay measures ability of an antioxidant to react with a peroxyl radical via hydrogen atom extraction and FRAP measures electron transfer through reduction of ferric iron (Fe3+ ) to ferrous iron (Fe2+ ) by antioxidants present in the samples. Correlation of extract composition with antioxidant measures was performed using principal component analysis. Selected extracts were assessed for their ability to protect hair from UV damage in a model peptide system and on hair. In addition, the same methods were used to test rosmarinic acid and carnosic acid, key phytochemistries in the rosemary extracts. The model system was a peptide and its decomposition on exposure to UV was monitored by LC-MS in the absence and presence of the rosemary extracts. Hair degradation in the presence of UV was measured by exposure of UV in an Atlas weatherometer followed by extraction of degraded protein in water. A fragment of the S100A3 protein was used as a marker of UV damage (m/z = 1278) and quantified via LC-MS. RESULTS: Ten rosemary extracts were assessed for antioxidant performance and correlated with their compositions. The phytochemistry in each extract varied widely with a total of 33 individual compounds identified. The differences were most likely driven by the solvent and extraction method used by the supplier with extracts varying in the proportion of polar or non-polar compounds. This did influence their reactivity in the ORAC and FRAP assays and their efficacy in preventing protein damage. Two of the key compounds identified were rosmarinic acid and carnosic acid, with rosmarinic acid dominating in extracts with mainly polar compounds and carnosic acid dominating in extracts with mainly nonpolar compounds. Extracts with higher rosmarinic acid correlated with ORAC and FRAP scores, with UV protection on hair and in the peptide model system. The extracts chosen for hair experiments showed hair protection. UV protection was also measured for rosmarinic and carnosic acid. CONCLUSIONS: Despite the variation in the profile of phytochemistries in the 10 rosemary extracts, likely driven by the chosen extraction method, all rosemary extracts had antioxidant activity measured. This study suggests that the polyphenols (e.g. rosmarinic acid, glycosides of selgin) and abietane diterpenes (e.g. carnosic acid) are the principal compounds which enables the extracts to protect hair from UV.

INTRODUCTION: Les extraits de romarin (Salvia Rosmarinus) sont analysés par LC-MS pour établir et identifier leur profil phytochimique. Les mêmes extraits ont été testés pour leur efficacité à agir comme antioxydants à la fois par transfert d'atome d'hydrogène (ORAC) et par transfert d'électrons uniques (FRAP). Une analyse de corrélation a été réalisée pour identifier les propriétés phytochimiques clés responsables de l'efficacité antioxydante. Les extraits les plus performants ont ensuite été testés dans un modèle peptidique et sur les cheveux en présences d'UV pour mesurer la capacité à protéger contre les dommages induits par les UV su les peptides et protéines. Les polyphénols (par ex. acide rosmarinique, glycosides de selgin) et les diterpènes d'abiétine (par ex. acide carnosique) dans le romarin ont été identifiés comme les principaux composés permettant aux extraits de protéger les cheveux des UV. OBJECTIF: L'objectif de ce travail était de mettre en corrélation la phytochimie du romarin (Salvia rosmarinus), une plante aux propriétés antioxydantes connues, et les bénéfices d'une protection contre les UV dans les cheveux. Ces données fourniront des informations sur les mécanismes des dommages causés par les UV, la formation du ROS et leur réactivité. MÉTHODES: La LC-MS a été utilisée pour comparer les composés de 10 extraits commerciaux de romarin. L'ORAC (Oxygen Radical Antioxidant Capacity/Capacité d'absorption des radicaux d'oxygène) et la FRAP (Ferric Reduction Antioxidant Power/Pouvoir antioxydant de réduction ferrique) ont été utilisés pour mesurer la capacité antioxydante des extraits de romarin. Le dosage ORAC mesure la capacité d'un antioxydant à réagir avec un radical peroxyl par extraction d'atome d'hydrogène et la FRAP mesure le transfert d'électrons par réduction du fer ferrique (Fe3+ ) en fer ferreux (Fe2+ ) par les antioxydants présents dans les échantillons. La corrélation entre la composition de l'extrait et les mesures des antioxydants a été effectuée en analysant les composants principaux. Les extraits sélectionnés ont été évalués pour leur capacité à protéger les cheveux des dommages causés par les UV dans un modèle de système peptidique et sur les cheveux. En outre, les mêmes méthodes ont été utilisées pour tester l'acide rosmarinique et l'acide carnosique, principales caractéristiques phytochimiques dans les extraits de romarin. Le système modèle était un peptide et sa décomposition à l'exposition aux UV a été suivie par LC-MS en l'absence et en présence des extraits de romarin. La dégradation des cheveux en présence d'UV a été mesurée par l'exposition aux UV dans un indicateur de désagrégation Atlas suivi de l'extraction de protéines dégradées dans l'eau. Un fragment de la protéine S100A3 a été utilisé comme marqueur de dommage UV (m/z = 1278) et quantifié par LC-MS. RÉSULTATS: Dix extraits de romarin ont été évalués en termes de performance antioxydante et mis en corrélation avec leurs compositions. La phytochimie de chaque extrait variait considérablement, avec un total de 33 composés individuels identifiés. Les différences étaient très probablement dues à la méthode du solvant et de l'extraction utilisée par le fournisseur avec des extraits variant dans la proportion de composés polaires ou non polaires. Cela a effectivement influencé leur réactivité dans les dosages ORAC et FRAP et leur efficacité dans la prévention des dommages protéiques. Deux des composés clés identifiés étaient l'acide rosmarinique et l'acide carnosique, l'acide rosmarinique dominant dans les extraits contenant principalement des composés polaires et l'acide carnosique dominant dans les extraits contenant principalement des composés non polaires. Les extraits avec un taux d'acide rosmarinique plus élevé étaient mis en corrélation avec les scores ORAC et FRAP, avec une protection UV sur les cheveux et dans le système de modèle peptidique. Les extraits choisis pour les expériences sur les cheveux ont montré une protection des cheveux. La protection contre les UV a également été mesurée pour l'acide rosmarinique et l'acide carnosique. CONCLUSIONS: Malgré la variation des profils phytochimiques dans les dix extraits de romarin, probablement induite par la méthode d'extraction choisie, l'activité antioxydante de tous les extraits de romarin a été mesurée. Les polyphénols (par ex. acide rosmarinique, glycosides de selgin) et les diterpènes d'abiétane (par ex. acide carnosique) dans le romarin ont été identifiés comme les principaux composés permettant aux extraits de protéger les cheveux contre les UV.

New Approach to the Detection of Short-Lived Radical Intermediates.

We report a new general method for trapping short-lived radicals, based on a homolytic substitution reaction SH2'. This departure from conventional radical trapping by addition or radical-radical cross-coupling results in high sensitivity, detailed structural information, and general applicability of the new approach. The radical traps in this method are terminal alkenes possessing a nitroxide leaving group (e.g., allyl-TEMPO derivatives). The trapping process thus yields stable products which can be stored and subsequently analyzed by mass spectrometry (MS) supported by well-established techniques such as isotope exchange, tandem MS, and high-performance liquid chromatography-MS. The new method was applied to a range of model radical reactions in both liquid and gas phases including a photoredox-catalyzed thiol-ene reaction and alkene ozonolysis. An unprecedented range of radical intermediates was observed in complex reaction mixtures, offering new mechanistic insights. Gas-phase radicals can be detected at concentrations relevant to atmospheric chemistry.

Molecular environment and reactivity in gels and colloidal solutions under identical conditions.

A PEG-Tyr block copolymer forms a kinetically stable colloidal solution in water at room temperature which undergoes an irreversible conversion to a gel phase upon heating. A micellar solution and a gel can therefore be studied under identical experimental conditions. This made it possible to compare physical properties and chemical reactivity of micelles and gels in identical chemical environments and under identical conditions. EPR spectra of the spin-labelled copolymer showed that tyrosine mobility in gels was slightly reduced compared to micelles. Chemical reactivity was studied using photochemical degradation of tyrosine and tyrosine dimerization, in the absence and in the presence of an Fe(iii) salt. The reactivity trends were explained by reduced tyrosine mobility in the gel environment. The largest reactivity difference in gels and micelles was observed for bimolecular dityrosine formation which was also attributed to the reduction in molecular mobility.

Non-Thermal Plasma in Contact with Water: The Origin of Species.

Non-thermal atmospheric pressure plasma has attracted considerable attention in recent years due to its potential for biomedical applications. Determining the mechanism of the formation of reactive species in liquid treated with plasma is thus of paramount importance for both fundamental and applied research. In this work, the origin of reactive species in plasma-treated aqueous solutions was investigated by using spin-trapping, hydrogen and oxygen isotopic labelling and electron paramagnetic resonance (EPR) spectroscopy. The species originating from molecules in the liquid phase and those introduced with the feed gas were differentiated by EPR and 1 H NMR analysis of liquid samples. The effects of water vapour and oxygen admixtures in the feed gas were investigated. All the reactive species detected in the liquid samples were shown to be formed largely in the plasma gas phase. It is suggested that hydrogen peroxide (determined by UV/Vis analysis) is formed primarily in the plasma tube, whereas the radical species ⋅OOH, ⋅OH and ⋅H are proposed to originate from the region between the plasma nozzle and the liquid sample.

Magnetic and Electrochemical Properties of a TEMPO-Substituted Disulfide Diradical in Solution, in the Crystal, and on a Surface.

A study of the magnetic and electrochemical properties of a TEMPO-substituted disulfide diradical in three different environments was carried out: in solution, in the crystal, and as a self-assembled monolayer (SAM) on an Au(111) substrate, and the relationship between them was explored. In solution, this flexible diradical shows a strong spin-exchange interaction between the two nitroxide functions that depends on the temperature and solvent. Structural, dynamic, and thermodynamic information has been extracted from the EPR spectra of this dinitroxide. The magnetic interactions in the crystal include intra- and intermolecular contributions, which have been studied separately and shown to be antiferromagnetic in both cases. Finally, we demonstrate that both the magnetic and electrochemical properties are preserved upon chemisorption of the diradical on a gold surface. The resulting SAM displayed anisotropic magnetic properties, and angle-resolved EPR spectra of the monocrystal allowed a rough determination of the orientation of the molecules in the SAM.

Ion exchange in alginate gels--dynamic behaviour revealed by electron paramagnetic resonance.

The formation of alginate gel from low molecular weight alginate and very low molecular weight alginate in the presence of divalent cations was investigated using Electron Paramagnetic Resonance (EPR) spectroscopy. The transition from sol to gel in the presence of divalent cations was monitored by the changes in the dynamics of spin labelled alginate. The immobilisation of the spin labelled alginate in the gel reflects the strength of interaction between the cation and alginate chain. Diffusion experiments showed that both the cation and alginate polyanion in the gel fibres can exchange with molecules in solution. In particular, we showed that dissolved alginate polyanions can replace alginates in the gel fibres, which can hence diffuse through the bulk of the gel. This illustrates the surprisingly highly dynamic nature of these gels and opens up the possibility of preparing multicomponent alginate gels via polyanion exchange process.

Structural basis for DNA recognition and loading into a viral packaging motor.

Genome packaging into preformed viral procapsids is driven by powerful molecular motors. The small terminase protein is essential for the initial recognition of viral DNA and regulates the motor's ATPase and nuclease activities during DNA translocation. The crystal structure of a full-length small terminase protein from the Siphoviridae bacteriophage SF6, comprising the N-terminal DNA binding, the oligomerization core, and the C-terminal ß-barrel domains, reveals a nine-subunit circular assembly in which the DNA-binding domains are arranged around the oligomerization core in a highly flexible manner. Mass spectrometry analysis and four further crystal structures show that, although the full-length protein exclusively forms nine-subunit assemblies, protein constructs missing the C-terminal ß-barrel form both nine-subunit and ten-subunit assemblies, indicating the importance of the C terminus for defining the oligomeric state. The mechanism by which a ring-shaped small terminase oligomer binds viral DNA has not previously been elucidated. Here, we probed binding in vitro by using EPR and surface plasmon resonance experiments, which indicated that interaction with DNA is mediated exclusively by the DNA-binding domains and suggested a nucleosome-like model in which DNA binds around the outside of the protein oligomer.

Using EPR spectroscopy as a unique probe of molecular-scale reorganization and solvation in self-assembled gel-phase materials.

We describe the synthesis of spin-labeled bis-ureas which coassemble with bis-urea gelators and report on self-assembly as detected using electron paramagnetic resonance spectroscopy (EPR). Specifically, EPR detects the gel-sol transition and allows us to quantify how much spin-label is immobilized within the gel fibers and how much is present in mobile solvent pools-as controlled by temperature, gelator structure, and thermal history. EPR is also able to report on the initial self-assembly processes below the gelation threshold which are not macroscopically visible and appears to be more sensitive than NMR to intermediate-sized nongelating oligomeric species. By studying dilute solutions of gelator molecules and using either single or double spin-labels, EPR allows quantification of the initial steps of the hierarchical self-assembly process in terms of cooperativity and association constant. Finally, EPR enables us to estimate the degree of gel-fiber solvation by probing the distances between spin-labels. Comparison of experimental data against the predicted distances assuming the nanofibers are only composed of gelator molecules indicates a significant difference, which can be assigned to the presence of a quantifiable number of explicit solvent molecules. In summary, EPR provides unique data and yields powerful insight into how molecular-scale mobility and solvation impact on assembly of supramolecular gels.

Properties of polyethylene glycol/cyclodextrin hydrogels revealed by spin probes and spin labelling methods.

The properties of a gel consisting of a covalent network formed by the reaction of isocyanate end-capped polyethylene glycol (PEG) with ß-cyclodextrin, were investigated by EPR spectroscopy. Spin-labelled cyclodextrin was incorporated into the cross-link points of the gel and at the chain ends. The dynamics of the gel fibres as reported by the spin label, was found to be sensitive to the H-bonding ability of the solvent, density of cross-links and temperature. Addition of spin probes (e.g., TEMPO and adamantane-TEMPO) to the unlabelled gel made it possible to characterise the solvent pools in the gel. While TEMPO was uniformly distributed throughout the solvent pools, the adamantane derivative was located at the gel fibre-solvent pool interface; these two probes thus reported on the different locations in the solvent pools. At low temperature, the gels were shown to prevent ice crystallisation in the solvent pools resulting in the formation of supercooled water. Both probes showed that the water froze at ca. 250 K, thus suggesting that the properties of the supercooled water are uniform across the solvent pools.

Functional magnetic nanoparticles for protein delivery applications: understanding protein-nanoparticle interactions.

Iron oxide nanoparticles (IONPs) surface functionalised with thermo-responsive polymers can encapsulate therapeutic proteins and release them upon heating with an alternating magnetic field above the lower critical solution temperature (LCST). In order to make this delivery system clinically-relevant, we prepared IONPs coated with poly-N-isopropylmethacrylamide (PNIPMAM), a polymer with LCST above human body temperature. The optimal polymer chain length and nanoparticle size to achieve LCST of ca. 45 °C were 19 kDa PNIPMAM and 16 nm IONPs. The PNIPMAM-coated IONPs could encapsulate a range of proteins which were released upon heating above LCST in the presence of a competitor protein or serum. A small amount of encapsulated protein leakage was observed below LCST. The efficiency of protein encapsulation and release was correlated with molecular weight and glycosylation state of the proteins. Magnetic heating resulted in a faster protein release as compared to conventional heating without significant temperature increase of the bulk solution.

Sorption of metal ions by poly(ethylene glycol)/ß-CD hydrogels leads to gel-embedded metal nanoparticles.

Inorganic nanoparticles can be embedded within gels by selectively preloading them with suitable molecular precursors followed by reduction or another suitable reaction. Here, we exploit the selective sorption properties of cross-linked ß-cyclodextrin/poly(ethylene glycol) hydrogels, in analogy with polyurethane foams, to preconcentrate metal salts (HAuCl4 and K2[Co(SCN)4]) and subsequently generate gel-embedded metal nanoparticles (10-50 nm). The nanoparticles are shown to be immobilized within the gel network as a consequence of their large dimensions in comparison to the gel network pore size. We suggest this is a useful approach for the generalized synthesis of hybrid soft-hard nanomaterials.

Differential Effects of Betacyanin and Betaxanthin Pigments on Oxidative Stress and Inflammatory Response in Murine Macrophages.

SCOPE: Betalain pigments are increasingly highlighted for their bioactive and anti-inflammatory properties, although research is lacking to demonstrate contributions of individual betalains. The work herein aimed to compare effects of four main betalains on inflammatory and cell-protective markers and to highlight potential structure-related relationships of the two main subgroups: betacyanins vs betaxanthins. METHODS AND RESULTS: Murine RAW 264.7 macrophages were stimulated with bacterial lipopolysaccharide following incubation with betacyanins (betanin, neobetanin) and betaxanthins (indicaxanthin, vulgaxanthin I) in concentrations from 1 to 100 µM. All betalains suppressed expression of pro-inflammatory markers IL-6, IL-1ß, iNOS, and COX-2 with tendency for stronger effects of betacyanins compared to betaxanthins. In contrast, HO-1 and gGCS showed mixed and only moderate induction, while more emphasized effects were observed for betacyanins. While all betalains suppressed mRNA levels of NADPH oxidase 2 (NOX-2), a superoxide generating enzyme, only betacyanins were able to counteract hydrogen peroxide induced reactive oxygen species (ROS) generation, in alignment with their radical scavenging potential. Furthermore, betaxanthins exerted pro-oxidant properties, elevating ROS production beyond hydrogen peroxide stimulation. CONCLUSION: In summary, all betalains display anti-inflammatory properties, although only betacyanins demonstrate radical scavenging capacities, indicating potential differing responses under oxidative stress conditions, which requires further research.

Predictive Removal of Interfacial Defect-Induced Trap States between Titanium Dioxide Nanoparticles via Sub-Monolayer Zirconium Coating.

First principles modeling of anatase TiO2 surfaces and their interfacial contacts shows that defect-induced trap states within the band gap arise from intrinsic structural distortions, and these can be corrected by modification with Zr(IV) ions. Experimental testing of these predictions has been undertaken using anatase nanocrystals modified with a range of Zr precursors and characterized using structural and spectroscopic methods. Continuous-wave electron paramagnetic resonance (EPR) spectroscopy revealed that under illumination, nanoparticle-nanoparticle interfacial hole trap states dominate, which are significantly reduced after optimizing the Zr doping. Fabrication of nanoporous films of these materials and charge injection using electrochemical methods shows that Zr doping also leads to improved electron conductivity and mobility in these nanocrystalline systems. The simple methodology described here to reduce the concentration of interfacial defects may have wider application to improving the efficiency of systems incorporating metal oxide powders and films including photocatalysts, photovoltaics, fuel cells, and related energy applications.

Distance measurements in Au nanoparticles functionalized with nitroxide radicals and Gd(3+)-DTPA chelate complexes.

Nanosized gold particles were functionalised with two types of paramagnetic surface tags, one having a nitroxide radical and the other one carrying a DTPA complex loaded with Gd(3+). Selective measurements of nitroxide-nitroxide, Gd(3+)-nitroxide and Gd(3+)-Gd(3+) distances were performed on this system and information on the distance distribution in the three types of spin pairs was obtained. A numerical analysis of the dipolar frequency distributions is presented for Gd(3+) centres with moderate magnitudes of zero-field splitting, in the range of detection frequencies and resonance fields where the high-field approximation is only roughly valid. The dipolar frequency analysis confirms the applicability of DEER for distance measurements in such complexes and gives an estimate for the magnitudes of possible systematic errors due to the non-ideality of the measurement of the dipole-dipole interaction.

Uptake and Immunomodulatory Properties of Betanin, Vulgaxanthin I and Indicaxanthin towards Caco-2 Intestinal Cells.

The present study aimed to compare the absorption and transport patterns of three main betalains, betanin, vulgaxanthin I and indicaxanthin, into intestinal epithelial cells and to assess their distinct molecular effects on inflammatory and redox-related cell signalling in association with their radial scavenging potencies. All three betalains showed anti-inflammatory effects (5-80 µM), reflected by attenuated transcription of pro-inflammatory mediators such as cyclooxygenase-2 and inducible NO-synthase. Concomitant increases in antioxidant enzymes such as heme oxygenase-1 were only observed for betanin. Moreover, betanin uniquely demonstrated a potent dose-dependent radical scavenging activity in EPR and cell-based assays. Results also indicated overall low permeability for the three betalains with Papp of 4.2-8.9 × 10-7 cm s-1. Higher absorption intensities of vulgaxanthin and indicaxanthin may be attributed to smaller molecular sizes and greater lipophilicity. In conclusion, betanin, vulgaxanthin I and indicaxanthin have differentially contributed to lowering inflammatory markers and mitigating oxidative stress, implying the potential to ameliorate inflammatory intestinal disease. Compared with two betaxanthins, the greater efficacy of betanin in scavenging radical and promoting antioxidant response might, to some extent, compensate for its poorer absorption efficiency, as demonstrated by the Caco-2 cell model.

Aging of gold nanoparticles: ligand exchange with disulfides.

Aging of thiolate protected gold nanoparticles (AuNPs) results in reduced reactivity in the disulfide exchange as monitored by electron paramagnetic resonance (EPR) spectroscopy with a bisnitroxide disulfide incoming ligand. Factors determining the reactivity of the aged particles were investigated. The presence of different binding sites on the surface of AuNPs and a surface reorganization process during aging can explain observed reactivity trends.