Search

A profluorescent nitroxide was used to evaluate the oxidative potential of pollution derived from a compression ignition engine fuelled with biodiesel. The reaction products responsible for the observed fluorescence increase when a DMSO solution of nitroxide was exposed to biodiesel exhaust were determined by using HPLC/MS. The main fluorescent species was identified as a methanesulfonamide adduct arising from the reaction of the nitroxide with DMSO-derived sulfoxyl radicals.

A range of varying chromophore nitroxide free radicals and their nonradical methoxyamine analogues were synthesized and their linear photophysical properties examined. The presence of the proximate free radical masks the chromophore's usual fluorescence emission, and these species are described as profluorescent. Two nitroxides incorporating anthracene and fluorescein chromophores (compounds 7 and 19, respectively) exhibited two-photon absorption (2PA) cross sections of approximately 400 G.M. when excited at wavelengths greater than 800 nm. Both of these profluorescent nitroxides demonstrated low cytotoxicity toward Chinese hamster ovary (CHO) cells. Imaging colocalization experiments with the commercially available CellROX Deep Red oxidative stress monitor demonstrated good cellular uptake of the nitroxide probes. Sensitivity of the nitroxide probes to H(2)O(2)-induced damage was also demonstrated by both one- and two-photon fluorescence microscopy. These profluorescent nitroxide probes are potentially powerful tools for imaging oxidative stress in biological systems, and they essentially "light up" in the presence of certain species generated from oxidative stress. The high ratio of the fluorescence quantum yield between the profluorescent nitroxide species and their nonradical adducts provides the sensitivity required for measuring a range of cellular redox environments. Furthermore, their reasonable 2PA cross sections provide for the option of using two-photon fluorescence microscopy, which circumvents commonly encountered disadvantages associated with one-photon imaging such as photobleaching and poor tissue penetration.

Oxidative stress caused by generation of free radicals and related reactive oxygen species (ROS) at the sites of deposition has been proposed as a mechanism for many of the adverse health outcomes associated with exposure to particulate matter (PM). Recently, a new profluorescent nitroxide molecular probe (BPEAnit) developed at QUT was applied in an entirely novel, rapid and non-cell based assay for assessing the oxidative potential of particles (i.e. potential of particles to induce oxidative stress). The technique was applied on particles produced by several combustion sources, namely cigarette smoke, diesel exhaust and wood smoke. One of the main findings from the initial studies undertaken at QUT was that the oxidative potential per PM mass significantly varies for different combustion sources as well as the type of fuel used and combustion conditions. However, possibly the most important finding from our studies was that there was a strong correlation between the organic fraction of particles and the oxidative potential measured by the PFN assay, which clearly highlights the importance of organic species in particle-induced toxicity.

Background Type 1 Neurofibromatosis (NF1) is a genetic disorder linked to mutations of the NF1 gene. Clinical symptoms are varied, but hallmark features of the disease include skin pigmentation anomalies (cafe au lait macules, skinfold freckling) and dermal neurofibromas. Method These dermal manifestations of NF1 have previously been reported in a mouse model where Nf1+/− mice are topically treated with dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA). We adopted this mouse model to test the protective effects of a nitroxide antioxidant, 5-carboxy-1,1,3,3-tetramethylisoindolin-2-yloxyl (CTMIO). Antioxidants have previously been shown to increase longevity in nf1-deficient fruitflies. Doses of 4 μM and 40 μM CTMIO provided ad libitum in drinking water were given to Nf1-deficient mice. Results Consistent with previous reports, Nf1-deficient mice showed a 4.7-fold increase in papilloma formation (P < 0.036). However, neither dose of CTMIO had any significant affect on papilloma formation. A non-significant decrease in skin pigmentation abnormalities was seen with 4 μM but not 40 μM CTMIO. Subsequent analysis of genomic DNA isolated from papillomas indicated that DMBA/TPA induced tumors did not exhibit a local loss of heterozygosity (LOH) at the Nf1 locus. Conclusion These data reveal that oral antioxidant therapy with CTMIO does not reduce tumor formation in a multistage cancer model, but also that this model does not feature LOH for Nf1.

Alternative fuels and injection technologies are a necessary component of particulate emission reduction strategies for compression ignition engines. Consequently, this study undertakes a physicochemical characterization of diesel particulate matter (DPM) for engines equipped with alternative injection technologies (direct injection and common rail) and alternative fuels (ultra low sulfur diesel, a 20% biodiesel blend, and a synthetic diesel). Particle physical properties were addressed by measuring particle number size distributions, and particle chemical properties were addressed by measuring polycyclic aromatic hydrocarbons (PAHs) and reactive oxygen species (ROS). Particle volatility was determined by passing the polydisperse size distribution through a thermodenuder set to 300 °C. The results from this study, conducted over a four point test cycle, showed that both fuel type and injection technology have an impact on particle emissions, but injection technology was the more important factor. Significant particle number emission (54%-84%) reductions were achieved at half load operation (1% increase-43% decrease at full load) with the common rail injection system; however, the particles had a significantly higher PAH fraction (by a factor of 2 to 4) and ROS concentrations (by a factor of 6 to 16) both expressed on a test-cycle averaged basis. The results of this study have significant implications for the health effects of DPM emissions from both direct injection and common rail engines utilizing various alternative fuels. © 2011 American Chemical Society.

A series of new spin-labeled porphyrin containing isoindoline nitroxide moieties were synthesized and characterized as potential free radical fluorescence sensors. Fluorescence-suppression was observed in the free-base monoradical porphyrins, whilst the free-base biradical porphyrins exhibited highly suppressed fluorescence about three times greater than the monoradical porphyrins. The observed fluorescence-suppression was attributed to enhanced intersystem crossing resulting from electronexchange between the doublet nitroxide and the excited porphyrin fluorophore. Notably, fluorescencesuppression was not as strong in the related metalated porphyrins, possibly due to insufficient spin coupling between the nitroxide and the porphyrin. Continuous wave EPR spectroscopy of the diradical porphyrins in fluid solution suggests that the nitroxyl-nitroxyl interspin distance is long enough and tumbling is fast enough not to detect dipolar coupling.

A direct interrogation, portable analysis technique (portable FT-IR) and a novel environment-monitoring profluorescent sensor for studying aircraft coating degradation have been developed. For the direct interrogation approach, a standard military aircraft paint: 459-line Anzothane flexible polyurethane (lead free) has been used to illustrate a new potential field technique to evaluate coating service lifetime, portable FT-IR. This technique allows direct analysis of chemical changes within the degrading coatings and has the potential to evaluate service lifetime when coupled with advanced statistical analysis methods (chemometrics). The degradation environment monitoring sensors are embodied in a profluorescent environment-sensitive witness patch that may be analysed in-service by a field-deployable fluorescence spectrometer. Accelerated ageing for both the paint and the witness patches has been undertaken and their capabilities as aircraft paint degradation monitors assessed.

Reactive oxygen species (ROS) and related free radicals are considered to be key factors underpinning the various adverse health effects associated with exposure to ambient particulate matter. Therefore, measurement of ROS is a crucial factor for assessing the potential toxicity of particles. In this work, a novel profluorescent nitroxide, BPEAnit, was investigated as a probe for detecting particle-derived ROS. BPEAnit has a very low fluorescence emission due to inherent quenching by the nitroxide group, but upon radical trapping or redox activity, a strong fluorescence is observed. BPEAnit was tested for detection of ROS present in mainstream and sidestream cigarette smoke. In the case of mainstream cigarette smoke, there was a linear increase in fluorescence intensity with an increasing number of cigarette puffs, equivalent to an average of 101 nmol ROS per cigarette based on the number of moles of the probe reacted. Sidestream cigarette smoke sampled from an environmental chamber exposed BPEAnit to much lower concentrations of particles, but still resulted in a clearly detectible increase in fluorescence intensity with sampling time. It was calculated that the amount of ROS was equivalent to 50 ± 2 nmol per mg of particulate matter; however, this value decreased with ageing of the particles in the chamber. Overall, BPEAnit was shown to provide a sensitive response related to the oxidative capacity of the particulate matter. These findings present a good basis for employing the new BPEAnit probe for the investigation of particle-related ROS generated from cigarette smoke as well as from other combustion sources.

The aim of this work was to immobilize short melanocyte-stimulating hormone (MSH) anti-inflammatory peptide sequences onto a model surface using resorcinarenes, which are known to attach to a wide variety of hydrophilic materials. The first stage comprised the biological evaluation of a synthetic MSH peptide attached to different linking tethers (poly(ethylene glycol), PEG 350, octanoic acid or cholesterol) for the ability to inhibit inflammatory signaling. Findings showed that a glycinelysine-proline-D-valine sequence inhibited inflammatory signaling most effectively when attached to a PEG 350 tether. This molecule was selected for a second stage which comprised of synthesizing the MSH peptide attached to resorcinarene groups via a PEG tether and immobilizing it onto glass coverslips. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF–SIMS) indicated the presence of a surface attached peptide. The ability of the immobilized peptide to inhibit inflammatory signaling was then determined by culturing RN22 Schwann neuronal cells and human dermal fibroblast cells on functional surfaces and measuring NF-kB/p65 inflammatory transcription factor activation. Significant inhibition of inflammatory signaling was observed in cells cultured on functional surfaces. In conclusion, we therefore describe the development of a new approach enabling the rapid immobilization of short biologically active peptides. This work has potential for generating a ‘‘dip-and-dry’’ approach for altering the surface properties of biomaterial and medical devices. Many implantable medical devices can initiate an acute inflammatory response which in turn is detrimental to the function of the device. This can be triggered either by the initial implantation injury or by the biomaterial itself. Examples of this include coronary restenosis after stent implantation, the ‘stress cracking’ of pacemakers and the failure of peripheral nerve guides. Inflammation can be treated by steroids or non-steroidal anti-inflammatories (NSAIDs). However, these compounds frequently lack sensitivity or a specific targeted site of action, leading to side effects. Therefore the development of more specific and localized forms of treatment is important for controlling inflammation associated with biomaterials. Previous work has investigated modifying the material surface chemistry or immobilizing non-bio-fouling molecules, such as PEG. However, these techniques are not always appropriate because they do not specifically target inflammatory signaling. An alternative approach is through the exploitation of naturally occurring peptides to reduce inflammation. One potential peptide is a-MSH which has multiple roles in the body including the control of inflammation. An analogue of a-MSH, NleDPhe-a-MSH, has already been shown to increase allograft survival when injected into rats. Previous research has shown that the minimal sequence required for anti-inflammatory biology is a tripeptide at the carboxyl terminal consisting of lysine-proline-valine (KPV). This tripeptide mimics the anti-inflammatory effect of the full-length peptide, but is more specific as it does not exhibit melanotropic activity or stimulate dopa oxidase activity. This peptide has the ability to inhibit nuclear factor-kB (NF-kB) activation when stimulated by a wide range of proinflammatory agents, reducing the production of proinflammatory cytokines under its control. KPV can stimulate the direct production of the anti-inflammatory cytokine interleukin-10 (IL-10) and inhibit inflammation in vivo. Additionally, the peptide has been demonstrated to possess antimicrobial properties in vitro. The short tripeptide sequence makes it amenable for straightforward laboratory synthesis and this, in combination with its pharmacological potency, makes it an attractive candidate for immobilization on to medical device surfaces for creating a localized anti-inflammatory effect. a-MSH and its analogues have previously been immobilized using polyelectrolyte films and also as an analogue of the tripeptide (GKP-D-V), where it was attached to polystyrene beads. Both techniques demonstrated that the peptide retained anti-inflammatory properties when immobilized in vitro. Prostheses of titanium beads coated with polyelectrolyte multilayer films functionalized with a-MSH also retained the ability to inhibit inflammation when implanted into rats. The D-Val substitution in KP-D-V leads to greater anti-inflammatory properties than the KPV peptide and the parent molecule, a-MSH, probably due to reduced degradation. The present work describes a new methodology for immobilization of the tripeptide analogue GKP-D-V using resorcinarene group molecules. Resorcinarenes can be immobilized through hydrogen bonding of the hydroxylated bowl to hydrophilic materials through simple immersion of the material into a solution of the resorcinarene compound. This forms a new surface on that material, the properties of which then depend on the nature of the group covalently attached to the resorcinarene. Previous research has investigated the use of attaching alkyl chains and

Tissue damage resulting from the extracellular production of HOCl (hypochlorous acid) by the MPO (myeloperoxidase)-hydrogen peroxide-chloride system of activated phagocytes is implicated as a key event in the progression of a number of human inflammatory diseases. Consequently, there is considerable interest in the development of therapeutically useful MPO inhibitors. Nitroxides are well established antioxidant compounds of low toxicity that can attenuate oxidative damage in animal models of inflammatory disease. They are believed to exert protective effects principally by acting as superoxide dismutase mimetics or radical scavengers. However, we show here that nitroxides can also potently inhibit MPO-mediated HOCl production, with the nitroxide 4-aminoTEMPO inhibiting HOCl production by MPO and by neutrophils with IC50 values of approx. 1 and 6 μM respectively. Structure–activity relationships were determined for a range of aliphatic and aromatic nitroxides, and inhibition of oxidative damage to two biologically-important protein targets (albumin and perlecan) are demonstrated. Inhibition was shown to involve one-electron oxidation of the nitroxides by the compound I form of MPO and accumulation of compound II. Haem destruction was also observed with some nitroxides. Inhibition of neutrophil HOCl production by nitroxides was antagonized by neutrophil-derived superoxide, with this attributed to superoxide-mediated reduction of compound II. This effect was marginal with 4-aminoTEMPO, probably due to the efficient superoxide dismutase-mimetic activity of this nitroxide. Overall, these data indicate that nitroxides have considerable promise as therapeutic agents for the inhibition of MPO-mediated damage in inflammatory diseases.

A range of novel tetramethyl- and tetraethylisoindolinenitroxides, possessing aryl-linked carboxylic acids, amines, alcohols and phosphonic acids were prepared. Notably, the chemistry established for the aromatic dibromination of the tetramethylisoindolines was not easily transferred to the corresponding tetraethylisoindoline system. Instead, various tetraethylisoindoline analogues were accessed by the oxidation of methyl groups attached to the aromatic ring to give the carboxylic acids. The increased steric bulk of the tetraethyl structures should limit bio-reduction and these compounds may have potential as antioxidants.

New profluorescent mono- and di-isoindoline nitroxides (5, 11, 16 and 19) containing 9,10-diphenylanthracene and 9,10-bis(phenylethynyl)anthracene structural cores were synthesised by palladium-catalysed Suzuki and Sonogashira couplings. These nitroxide-fluorophore probes possess strongly suppressed fluorescence, even in the presence of only one nitroxide radical. Upon reduction, or reaction with other radicals, normal fluorescence emission is returned. The significant difference in fluorescence output between the nitroxides and their corresponding diamagnetic analogues makes these probes ideal tools for imaging polymer degradation using fluorescence microscopy. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Free-radical processes underpin the thermo-oxidative degradation of polyolefins. Thus, to extend the lifetime of these polymers, stabilizers are generally added during processing to scavenge the free radicals formed as the polymer degrades. Nitroxide radical precursors, such as hindered amine stabilizers (HAS),1,2 are common polypropylene additives as the nitroxide moiety is a potent scavenger of polymer alkyl radicals (R¥). Oxidation of HAS by radicals formed during polypropylene degradation yields nitroxide radicals (RRNO¥), which rapidly trap the polymer degradation species to produce alkoxyamines, thus retarding oxidative polymer degradation. This increase in polymer stability is demonstrated by a lengthening of the “induction period” of the polymer (the time prior to a sharp rise in the oxidation of the polymer). Instrumental techniques such as chemiluminescence or infrared spectroscopy are somewhat limited in detecting changes in the polymer during the initial stages of degradation. Therefore, other methods for observing polymer degradation have been sought as the useful life of a polymer does not extend far beyond its “induction period”

We previously showed that soluble nitroxides (nitric oxide analogues) mimicked the well-established ability of nitric oxide to cause biofilm dispersal and further showed that these compounds could prevent biofilm formation. Here, we investigated the effect of the nitroxide carboxy-TEMPO in combination with sub μg/ml concentrations of ciprofloxacin on pre-formed flow cell biofilms formed by Gram-negative bacteria. Combination therapy led to substantial eradication of existing biofilms formed by Pseudomonas aeruginosa PA14 (99.3%) and Escherichia coli O157 (93%).

International audience; The current study reports the synthesis and properties of a novel isoindoline nitroxide containing a benzophenone chromophore fused into the carbon framework. When exposed to UV light, rather than undergoing traditional benzophenone photochemical pathways, the presence of the nitroxide enables an energy transfer process whereby the nitroxide enters an excited state which induces an efficient hydrogen atom transfer from unactivated alkanes.

International audience; The combination of thermally-and photochemically-induced polymerization using light sensitive alkoxy-amines was investigated. The thermally driven polymerizations were performed via the cleavage of the alkoxyamine functionality, whereas the photochemically-induced polymerizations were carried out either by nitroxide mediated photo-polymerization (NMP2) or by a classical type II mechanism, depending on the structure of the light-sensitive alkoxyamine employed. Once the potential of the various structures as initiators of thermally-and photo-induced polymerizations was established, their use in combination for block copolymer syntheses was investigated. With each alkoxyamine investigated, block copolymers were successfully obtained and the system was applied to the post-modification of polymer coatings for application in patterning and photografting.

The persistent radical effect (PRE) established in the presence of a nitroxide has been widely investigated for the preparation of macromolecules with narrow molar mass distribution through radical polymerization (both in a bi-molecular fashion employing a nitroxide and radical initiator, and uni-molecularly using a thermally unstable alkoxyamine to supply both fragments). This chapter examines synthetic techniques available for designing both nitroxide free radicals as well alkoxyamines—the key mediating species in uni-molecular, nitroxide mediated polymerization. In both sections, a number of literature examples will be highlighted, with the aim being to provide the reader with a workable selection of design tools for the modification of both nitroxide and R-group moieties.

The methoxyamine group represents an ideal protecting group for the nitroxide moiety. It can be easily and selectively introduced in high yield (typically >90%) to a range of functionalised nitroxides using FeSO4·7H2O and H2O2 in DMSO. Its removal is readily achieved under mild conditions in high yield (70–90%) using mCPBA in a Cope-type elimination process.

Two novel dehydrating reagents 3 and 4, based on a phosphonium anhydride and an oxyphosphonium triflate respectively, were prepared by reaction of the corresponding polymer-supported phosphine oxides with triflic anhydride. Reagent 3, based on the novel phosphorus heterocycle 1,1,3,3-tetraphenyl-2-oxa-1,3-diphospholanium bis(trifluoromethanesulfonate), was found to be a useful reagent for ester and amide formation. A wide range ofcoupling/dehydration-type reactions, such as ester, amide, anhydride, peptide, ether and nitrile formation, were performed in high yield using the more readily prepared polymer-supported triphenylphosphine ditriflate 4, which was easily recovered and re-used several times without loss of efficiency. With primary alcohols, both reagents 3 and 4 provide an alternative to the Mitsunobu reaction, where the use of azodicarboxylates and chromatography to remove the phosphine oxide by-product can be avoided. The use of 4-dimethylaminopyridine allowed the esterification of secondary alcohols with 4 to proceed in high yield but with retention of configuration.

The orientational distribution of a set of stable nitroxide radicals in aligned liquid crystals 5CB (nematic) and 8CB (smectic A) was studied in detail by numerical simulation of EPR spectra. The order parameters up to the 10th rank were measured. The directions of the principal orientation axes of the radicals were determined. It was shown that the ordering of the probe molecules is controlled by their interaction with the matrix molecules more than the inherent geometry of the probes themselves. The rigid fused phenanthrene-based (A5) and 2-azaphenalene (A4) nitroxides as well as the rigid core elongated C11 and 5α-cholestane (CLS) nitroxides were found to be most sensitive to the orientation of the liquid crystal matrixes.

The methoxyamine group represents an ideal protecting group for the nitroxide moiety. It can be easily and selectively introduced in high yield (typically >90%) to a range of functionalised nitroxides using FeSO4·7H2O and H2O2 in DMSO. Its removal is readily achieved under mild conditions in high yield (70–90%) using mCPBA in a Cope-type elimination process.

A new and scalable method for the title reaction is developed and affords cleanly the di-iodo compounds in high yields and the mono-iodo compounds in modest yields.

The title compound, C24H26N2O8, is a derivative of neihumicin, a cytotoxic antibiotic from Micromonospora neihuensis. The compound crystallizes as discrete molecules with crystallographic inversion symmetry. Intermolecular N-HO hydrogen bonds yield polymeric chains along the c axis. The trimethoxyphenylmethylene side chain is found to be in a Z configuration about the C=C double bond.

Generally, the magnitude of pollutant emissions from diesel engines running on biodiesel fuel is ultimately coupled to the structure of the fuel's constituent molecules. Previous studies demonstrated the relationship between the organic fraction of particulate matter (PM) and its oxidative potential. Herein, emissions from a diesel engine running on different biofuels were analyzed in more detail to explore the role that different organic fractions play in the measured oxidative potential. In this work, a more detailed chemical analysis of biofuel PM was undertaken using a compact time of flight aerosol mass spectrometer (c-ToF AMS). This enabled a better identification of the different organic fractions that contribute to the overall measured oxidative potentials. The concentration of reactive oxygen species (ROS) was measured using a profluorescent nitroxide molecular probe 9-(1,1,3,3- tetramethylisoindolin-2-yloxyl-5-ethynyl)-10-(phenylethynyl)anthracene (BPEAnit). Therefore, the oxidative potential of the PM, measured through the ROS content, although proportional to the total organic content in certain cases, shows a much higher correlation with the oxygenated organic fraction as measured by the c-ToF AMS. This highlights the importance of knowing the surface chemistry of particles for assessing their health impacts. It also sheds light onto new aspects of particulate emissions that should be taken into account when establishing relevant metrics for assessing health implications of replacing diesel with alternative fuels. © 2013 American Chemical Society.

This study undertook a physicochemical characterization of particle emissions from a single compression ignition engine operated at one test mode with 3 biodiesel fuels made from 3 different feedstocks (i.e., soy, tallow, and canola) at 4 different blend percentages (20%, 40%, 60%, and 80%) to gain insights into their particle-related health effects. Particle physical properties were inferred by measuring particle number size distributions both with and without heating within a thermodenuder (TD) and also by measuring particulate matter (PM) emission factors with an aerodynamic diameter less than 10 μm (PM10). The chemical properties of particulates were investigated by measuring particle and vapor phase Polycyclic Aromatic Hydrocarbons (PAHs) and also Reactive Oxygen Species (ROS) concentrations. The particle number size distributions showed strong dependency on feedstock and blend percentage with some fuel types showing increased particle number emissions, while others showed particle number reductions. In addition, the median particle diameter decreased as the blend percentage was increased. Particle and vapor phase PAHs were generally reduced with biodiesel, with the results being relatively independent of the blend percentage. The ROS concentrations increased monotonically with biodiesel blend percentage but did not exhibit strong feedstock variability. Furthermore, the ROS concentrations correlated quite well with the organic volume percentage of particles - a quantity which increased with increasing blend percentage. At higher blend percentages, the particle surface area was significantly reduced, but the particles were internally mixed with a greater organic volume percentage (containing ROS) which has implications for using surface area as a regulatory metric for diesel particulate matter (DPM) emissions. © 2011 American Chemical Society.

This paper presents a review on the use of tethered nitroxide–fluorophore molecules as probes of oxidative change and free radical generation and reaction. The proximity of the nitroxide free radical to the fluorophore suppresses the normal fluorescence emission process. Nitroxide free radical scavenging, metabolism or redox chemistry return the system to its natural fluorescent state and so these tethered nitroxide–fluorophore molecules are described as being profluorescent. A survey of profluorescent nitroxides found in the literature is provided as well as background on the mechanism of action and applications of these compounds as fluorometric probes within the fields of biological, materials and environmental sciences.

This study reports the potential toxicological impact of particles produced during biomass combustion by an automatic pellet boiler and a traditional logwood stove under various combustion conditions using a novel profluorescent nitroxide probe, BPEAnit. This probe is weakly fluorescent but yields strong fluorescence emission upon radical trapping or redox activity. Samples were collected by bubbling aerosol through an impinger containing BPEAnit solution, followed by fluorescence measurement. The fluorescence of BPEAnit was measured for particles produced during various combustion phases: at the beginning of burning (cold start), stable combustion after refilling with the fuel (warm start), and poor burning conditions. For particles produced by the logwood stove under cold-start conditions, significantly higher amounts of reactive species per unit of particulate mass were observed compared to emissions produced during a warm start. In addition, sampling of logwood burning emissions after passing through a thermodenuder at 250 degrees C resulted in an 80-100% reduction of the fluorescence signal of the BPEAnit probe, indicating that the majority of reactive species were semivolatile. Moreover, the amount of reactive species showed a strong correlation with the amount of particulate organic material. This indicates the importance of semivolatile organics in particle-related toxicity. Particle emissions from the pellet boiler, although of similar mass concentration, were not observed to lead to an increase in fluorescence signal during any of the combustion phases.

A series of novel acetylene-substituted isoindoline nitroxides were synthesised viapalladium-catalysed copper-free Sonogashira coupling. These results demonstrate that the Sonogashira reaction is suitable for the generation of a wide range of aryl nitroxides of expanded structural variety. The novel aryl-iodide containing nitroxide, 5-iodo-1,1,3,3-tetramethylisoindolin-2-yloxyl, 3, was a key intermediate for this coupling, giving acetylene-substituted isoindoline nitroxides in high yield. Subsequent reaction of the deprotected ethynyl nitroxide 12 with iodinated polyaromatics furnished novel aromatic nitroxides with extended-conjugation. Such nitroxides have been described as profluorescent, as their quantum yields are significantly lower than those of the corresponding diamagnetic derivatives. The quantum yields of the naphthyl- and phenanthryl-acetylene isoindoline nitroxides (13 and 14) were found to be ∼200-fold and ∼65-fold less than the non-radical methoxyamine derivatives (23 and 24). Ethyne- and butadiyne-linked nitroxide dimers could also be synthesised by this cross coupling methodology.

Novel nitroxide-aspirin conjugates were synthesized and tested using human lung cancer cell lines. Previously, cyclooxygenase (COX2) was found to be elevated in lung cancer biopsy specimens relative to normal tissue (He et al., 2012; PlosOne 7:e31087). Lung cancer cellular proliferation is inhibited by nonsteroidal anti-inflamatory drugs (NSAIDs) such as indomethacin and aspirin (Hida et al., 1998; Anticancer Res. 18: 775). Dithiolethione-valproate conjugates inhibit COX-2 activity, increase E-cadherin expression and decrease the proliferation of non-small cell lung cancer (NSCLC) cells (Moody et al., 2010, Lung Cancer 68: 154). Here the effects of nitroxide-aspirin conjugates were investigated on NSCLC cells. 1KT121A, a 4-carboxy Tempo-aspirin conjugate, inhibited the proliferation of NCI-H1299 or A549 cells with IC50 values of 125 uM using the MTT assay whereas aspirin and tempol had IC50 values of 750 and >1000 uM, respectively. 1KT121A, which has an ester link, was approximately 5-fold more potent at inhibiting NSCLC cellular proliferation than aspirin plus tempol or 2KT106A, which is a Tempo-aspirin conjugate with an amide link. 1KT121A was more potent than 2KT106A or tempol plus aspirin at reducing prostaglandin E2 levels in A549 cells. Similar results were obtained if the nitroxide moiety was changed from 4-carboxy Tempo to 3-carboxy proxyl or 5-carboxy-1,1,3,3-tetramethylisoindolin-yloxyl (CTMIO). 1KT121A potentiated the ability of gefitinib, an EGF receptor tyrosine kinase inhibitor, to kill NSCLC cells. Because 1KT121A increased E-cadherin and reduced vimentin, it may impair epithelial-mesenchymal transitions of NSCLC cells. All of the nitoxide analogues were antioxidants based on the ability to inhibit reactive oxygen species in NSCLC cells treated with hydrogen peroxide. Nitroxide-aspirin conjugates represent a novel class of NSAIDs which are antioxidants that inhibit NSCLC proliferation. Citation Format: Terry W. Moody, Robert T. Jensen, Komba Thomas, Kathryn E. Fairfull-Smith, Steven E. Bottle, Lisa Ridnour, David A. Wink. Nitroxide-aspirin conjugates: A new class of NSAIDs. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4539. doi:10.1158/1538-7445.AM2015-4539

We describe a novel and facile approach to covalently graft molecules containing stable free radicals onto carbon surfaces including graphene, carbon nanotubes, glassy carbon and carbon fibres. The new technique employs a stable aryl nitroxide radical diazonium tetrafluoroborate salt. The salt may be isolated and added to carbon surfaces in solution, suspension or electrochemically and represents a convenient, versatile and highly efficient means to adorn graphitic materials with large numbers of free radical spin systems.

The tetraalkylation of N-benzylphthalimide is the major yield limiting step in the common synthetic route to isoindoline nitroxides. The progress of this reaction was found to be limited by the formation of previously unobserved mono- and dialkyl side products that do not lead to the desired product. The yield for the tetraalkylation of N-benzylphthalimide with ethylmagnesium iodide could be increased (60 % over two steps) when a stepwise addition sequence was employed. The new two-step synthesis offers a practical preparative scale alternative to the current approach.

A novel antioxidant for the potential treatment of ischaemia was designed by incorporating an isoindoline nitroxide into the framework of the free radical scavenger edaravone. 5-(3-Methyl-pyrazol-5-ol-1-yl)-1,1,3,3-tetramethylisoindolin-2-yloxyl 7 was prepared by N-arylation of 3-methyl-5-pyrazolone with 5-iodo-1,1,3,3-tetramethylisoindoline-2-yloxyl 8 in the presence of catalytic copper(I)iodide. Evaluation of 7, its methoxyamine derivative 10 and 5-carboxy-1,1,3,3-tetramethylisoindolin-2-yloxyl (CTMIO) against edaravone 1 in ischaemic rat atrial cardiomyocytes revealed significant decreases in cell death after prolonged ischaemia for each agent; however the protective effect of the novel antioxidant 7 (showing greater than 85% reduction in cell death at 100 μM) was significantly enhanced over that of edaravone 1 alone. Furthermore, the activity for 7 was found to be equal to or greater than the potent cardioprotective agent N6-cyclopentyladenosine (CPA). The methoxyamine adduct 10 and edaravone 1 showed no difference between the extent of reduction in cell death whilst CTMIO had only a modest protective effect.

This paper presents a review on the use of tethered nitroxide–fluorophore molecules as probes of oxidative change and free radical generation and reaction. The proximity of the nitroxide free radical to the fluorophore suppresses the normal fluorescence emission process. Nitroxide free radical scavenging, metabolism or redox chemistry return the system to its natural fluorescent state and so these tethered nitroxide–fluorophore molecules are described as being profluorescent. A survey of profluorescent nitroxides found in the literature is provided as well as background on the mechanism of action and applications of these compounds as fluorometric probes within the fields of biological, materials and environmental sciences.

A novel nitroxide‐mediated polymerization (NMP) control agent; 1,1,3,3‐tetramethyl‐2,3‐dihydro‐2‐azaphenalen‐2‐yloxyl (TMAO), was used in the free‐radical polymerization of styrene. The conversion of styrene during NMP was studied using FT‐Raman spectroscopy and the effectiveness of TMAO as a NMP control agent was assessed by GPC analysis. Fidelity of the TMAO‐alkoxyamine end‐group on the synthesized polymers was confirmed by GPC, UV‐Vis and fluorescence spectroscopic analyses. Comparison to the well known NMP control agent, TEMPO was made. TMAO showed control of molecular weight approaching that of TEMPO. Attempts to improve the properties of TMAO as an NMP control agent by synthesizing an analogue with bulkier substituents around the nitroxide did not generate the target molecule but demonstrated some of the interesting chemistry of the azaphenalene ring system.

A novel nitroxide-mediated polymerization (NMP) control agent; 1,1,3,3-tetramethyl-2,3-dihydro-2-azaphenalen-2-yloxyl (TMAO), was used in the free-radical polymerization of styrene. The conversion of styrene during NMP was studied using FT-Raman spectroscopy and the effectiveness of TMAO as a NMP control agent was assessed by GPC analysis. Fidelity of the TMAO-alkoxyamine end-group on the synthesized polymers was confirmed by GPC, UV-Vis and fluorescence spectroscopic analyses. Comparison to the well known NMP control agent, TEMPO was made. TMAO showed control of molecular weight approaching that of TEMPO. Attempts to improve the properties of TMAO as an NMP control agent by synthesizing an analogue with bulkier substituents around the nitroxide did not generate the target molecule but demonstrated some of the interesting chemistry of the azaphenalene ring system.

Exchange reactions between the isoindoline profluorescent nitroxide 1,1,3,3-tetramethyldibenzo[e,g]isoindolin-2-yloxyl (TMDBIO) and a TEMPO capped polystyrene were carried out. High conversions to the desired products were achieved using only stoichiometric ratios of nitroxide relative to polymer. The scope of this study was expanded by exploiting a di-nitroxide 9,10-bis(5-[1,1,3,3-tetramethylisoindolin-2-yloxy])anthracene (BTMIOA) as a connector between two polymer chains forming PS–nitroxide–PS systems.

The cover picture shows the minimal fluorescence emitted from a nitroxide-quenched diphenylanthracene fluorophore (left-hand side) and the contrasting strongly fluorescent result after the spin of the nitroxide radical has been removed by reduction or radical trapping (second from left). The same differential can be seen for the acetylene-extended system. The top right of the picture shows the same four flasks viewed in visible light. Details are discussed in the article by K. E. Fairfull-Smith and S. E. Bottle on p. 5391 ff. Photo courtesy of Dr. Aaron Micallef, AIBN, University of Queensland, Australia.