Antioxidant

Buckyballs as antioxidants

The medical field is one place that buckyballs appear to have a promising future. C Sixty, Inc., is one of the companies developing medical applications for buckyballs. They are focusing on the ability of buckyballs to act as antiox-idants, counteracting free radicals in the human body. A free radical is a molecule or atom that has an unpaired electron which makes it very reactive. An antioxidant is a molecule that can supply an electron and neutralize a free radical. The human body normally has a balance of free radicals and antioxidants a certain level of free radicals is actually necessary to make your immune system work. However, the level of antioxidants found naturally in your body decreases as you get older. The resulting high level of free radicals roaming around your system could be the cause of certain diseases. Buckyballs can act as antioxidants to neutralize free radicals. When a bucky-ball meets a free radical, the unpaired electron in the free radical pairs up with one...

Data on Ultrafine Particles

Several toxicology studies have shown that different nanoparticles are toxic when inhaled. For example, exposing human volunteers to nano-sized zinc oxide particles for 30 minutes resulted in bronchoalveolar inflammation.33 Other studies have shown that titanium dioxide nanoparticles are toxic in rats.34 Although the precise cause of toxicity is uncertain, researchers predict that the greater surface areas of the nanoparticles facilitate the release of transition metals or generation of free radicals.

Forbes Wolfe Nanotech Reports

Given the range of cosmetics using nanoparticulate metal oxides primarily for UV protection it is interesting to note a cosmetics product containing fullerene in the list. In this case the fullerene is claimed to have antioxidant properties. Carbon nanotubes have been used as a reinforcing component in a new baseball bat. Silver nanoparticles feature again, this time in socks where enhanced bonding of the 19 nm silver particles to the polyester fibres is claimed to provide enhanced and longer-lasting antimicrobial and antifungal performance. A novel chewing gum having chocolate flavour, which is apparently difficult to achieve, has been produced using nanoscale crystals'' of unknown chemistry to enhance the compatibility of the cocoa butter with the polymers that are used to give the gum elasticity. So-called self-cleaning windows and paint surfaces are also included in the top 10. These are based on photoactive titanium dioxide with the windows gaining a further benefit when it...

Plasma Induced Graft CoPolymerization

Plasma is the fourth state of material and is composed of electrons, ions, free radicals, atoms, and molecules. There are two subdivisions for plasma thermal equilibrium and nonthermal equilibrium plasma. For current use on polymers, the subdivision of nonthermal equilibrium is frequently used, which constitutes different plasma species having different temperatures. More precisely, the electrons usually have much higher temperature than the heavier particles (ions, atoms, molecules). In a plasma, important parameters include average electron temperature, ranging from 1 to 10 eV, electron density, varying from 109 to 1012 cm-3, and degree of ionization, lying between 10-6 to 0.3 27 . It is notable that, in plasma, compared to the high temperature of the electron, heavy particles have temperature around ambient condition (300 K or 0.025 eV) 28 . This heavy particle temperature is obviously suitable for treating many temperature-sensitive polymers, which will otherwise undergo...

Advantages and Disadvantageous

Grafting as a technique is simple, useful, and versatile. The key advantage of this technique is that the surface of the same polymer can be modified to have very distinctive properties through the choice of different monomers. Grafting can occur both at the surface as well as in the bulk. The depth of grafting is controlled by the interaction between the substrate polymer and the solvent. If penetration of the solvent is limited to a very small depth, surface grafting predominates. On the other hand, if the solution can diffuse uniformly into the polymer substrate, homogeneous grafting prevails. This method cannot totally eliminate homopoly-merization initiated by free radicals formed during irradiation of the monomer. However, a two-step method can be employed to minimize the formation of the homopolymer. The polymer is preirradiated in air to produce peroxide groups on the surface. Grafting is subsequently initiated thermally in contact with a monomer. Methods such as corona...

Emulsion Polymerization

Emulsion polymerization is one of the most rapid and most frequently used methods for nanoparticle preparation. Here, the monomer is added to a continuous phase, usually an aqueous phase at room temperature under constant stirring conditions. It is also possible to use an organic phase as the continuous phase. The polymerization can be initiated either by free radicals or by ion formation. The polymerization is initiated by the reaction of a monomer molecule with an initiator molecule. Triggers for the initiation of the reaction can be ultraviolet (UV) light, hydroxyl ions, or high-energy radiation. The polymer chain starts to grow when these initiated monomer ions or monomer radicals react with other monomer molecules. Additional monomer is solubilized in surfactant micelles or emulsified in larger droplets. After completion of polymerization, the reaction mixture is filtered, neutralized, and purified by centrifugation to remove any residual monomer. An example for an anionic...

Ultrasonic Irradiation

In recent years the formation of gold nanoparticles in an ultrasound field has been studied as an alternative to other methods 98, 107-109 . Caruso et al. 98 . summarizes the description of the ultrasonic irradiation phenomenon and the details of this method can be found in the references therein. The mechanisms of formation of gold nanoparticles have also been proposed before. 106, 107 In short, ultrasonic irradiation causes pyrolysis of water and other organic compounds present in an aqueous solution resulting in formation of free radicals at extremely high temperatures and pressures. These radicals reduce the gold (III) ions into gold

Disease Called Aging

Still, researchers have made progress toward understanding and slowing the aging process. They have identified some of its causes, such as uncontrolled cross-linking. They have devised partial treatments, such as antioxidants and free-radical inhibitors. They have proposed and studied other mechanisms of aging, such as clocks in the cell and changes in the body's

International Coordination

In January 2006, the first international symposium on nanotoxicology was held in Miami, Florida. The program included presentations and discussion on purified and non-purified nanomaterial toxicity, antioxidants, as well as tissue specific response, recognition, and clearance of nanoparticles.

Extensions New Chemistries Applications And Measurements

One relatively simple example is illustrated in Figure 9.13 where the so-called Briggs-Rauscher (BR) oscillations and waves37,38 are induced by Wet Stamping hydrogen peroxide (H2O2) onto a polyacrylamide (PAAm) gel containing a mixture of potassium iodate, malonic and sulfuric acids, manganese sulfate, and thyodene indicator. The BR system is sensitive to the antioxidants (e.g., vitamin C,39 polyphenol compounds,40,41 substituted diphenols42) whose delivery into the gel eliminates the micropatterned oscillators - significantly, the antioxidant concentration can be estimated by the number of eliminated oscillators. Figure 9.13 (a) Chemical oscillations and waves in a BR system patterned using WETS delivering H2O2 from 500 mm circular posts into a polyacrylamide (PAAm) gel.37 The rightmost image shows a freestanding PAAm gel with over 50 active oscillators. (b) Spatially distributed sensing of antioxidants. An antioxidant (2,6-dihydroxybenzoic acid) was delivered to the PAAm film from 1...

Nanotechnologys Complicated Risk Benefit Dichotomy

''Our recent work with fullerenes provides two core findings,'' says Emppu Salonen, a scientist at Helsinki University of Technology in Finland. ''We found that fullerenes, which are inherently insoluble in water, can be efficiently solubilized by gallic acid, a phenolic acid which is ubiquitous in plants and can be found for instance in tea, grapes, oak bark, and cosmetic products as an antioxidant. Furthermore, when exposed to gallic-acid-solubi-lized fullerenes, human tumor cells were shown to contract rapidly within tens of minutes and subsequently die.'' ''Fullerenes are excellent antioxidants and have already shown great promise in in vitro experiments. Gallic acid is abundant in substances like tea, red wines, or walnuts. What our work shows is that, when acting together, these a priori beneficial compounds induce a fast and dramatic death of tumor cells. What we do not know at present, though, is whether the same effect could also be observed with healthy cells.''

Potential Applications

The molecular nature of carbon nanotube fabrics allows various CNT physical properties, including electromagnetic, mechanical, chemical, and optical behaviors, to be exploited to create integrated electronic devices (including nonvolatile memory devices) chemical, biological, and radiation sensors passive low-resistance, low-capacitance conformal interconnects and electromagnetic field emission devices, scaffolds for cell growth, antioxidants, and near infrared imaging tags for biological samples and cells, to name a few. Table 13-1 summarizes a number of proposed applications that could use SWNT fabrics as an enabling component.-7

Carbon blackfilled polypropylene composites

Carbon additives are used in polymer composites as fillers, reinforcing agents and pigments. In addition, carbon black is used to enhance UV stability, electrical conductivity and weather resistance.12 PP geotextiles containing carbon black are applied for soil reinforcement, filtration and other construction purposes.11, 12 In addition, carbon black can be used for preparation of magnetostrictive materials which are defined as materials that undergo a change in shape due to the change in the magnetization state of the material.66 Carbon black, which has a polyaromatic structure containing various oxygen functional groups, is produced by partial combustion of liquid or gaseous hydrocarbons. Its antioxidant activity is due to the catalytic decomposition of peroxides and free radical scavenging, which is more effective at low temperature.11 However, the opposite effect of the carbon black with highest volatile content on thermal stability was observed.12 This phenomenon is attributed to...

Iron Chelation and Chelate Geometry Influence Reactivity

The knowledge that irreversible oxidative damage can be done by the ROS present in the physiological systems has prompted a significant amount of research to elucidate the nature of biological ligands as either anti- or pro-oxidant in character (Blokhina et al., 1991 Cheng and Breen, 2000). Although completely anthropogenic, EDTA can be used as an analogue to proteins and amino acids found in biological systems (Englemann et al., 2003). When used in biological studies, it has been found that EDTA may exert both anti- and pro-oxidant behaviors (Englemann et al., 2003). Previous research with FeII IIIEDTA has shown high ratios of EDTA to Fe (ratios of 2.5 1 and greater) to inhibit the Fenton reaction (Englemann et al., 2003). Antioxidant characteristics of the FeII IIIEDTA complex are seen when EDTA is in large excess, and this is attributed to steric effects around the metal center, thus presenting a kinetic barrier (Englemann et al., 2003 Noradoun and Cheng, 2005). It can be concluded...

Poly Alkyl Cyanoacrylate Nanocapsules

Palumbo et al.25 adopted a similar technique for the preparation of polyethyl-2-cyanoacrylate nanocapsules containing idebenone (an antioxidant). In this method, the acetonic solution of Miglyol 812, idebenone, and monomer was added to 100 mL of aqueous phase (pH 7) containing Tween 80. The presence of nonionic surfactant allowed the polymerization of the ethylcyanoacry-late at the oil-water interface, thus encapsulating Miglyol 812 droplets. The immediate polymerization triggered the formation of drug-loaded nanocapsules, with the suspensions concentrated under a vacuum to remove any acetone. Tween 80 reduced the hydrodynamic size of the emulsion droplets as a function of its concentration, resulting in smaller-sized nanocapsules. These nanocapsules exhibited a negative charge that was determined by zeta-potential measurements. The freeze-fracture electron microscopy revealed the presence of internal oil droplets surrounded by the polymeric shell of the nanocapsule.

Interactions of nanoparticles with isolated cells

In addition to their many non-biological applications, the potential biologically to use carbon nanotubes with a diameter as little as a few nanometres and a length of thousands of nanometres, and which can be filled with pharmaceutical and other desirable materials for delivery to bodily tissues, is regarded by many as a major technological development. However, it appears that these insoluble carbon nanotubes can also present major risks in biological applications. There is in fact a substantial body of experimental evidence to suggest that exposure to nanotubes may be harmful even for some cultured cells. Thus, the formation of free radicals, the accumulation of peroxidative products, antioxidant depletion and the loss of cell viability due to major ultrastructural and morphological changes in cultured human keratinocyte cells resulting from their interaction with unrefined single-walled carbon nanotubes (SWCNTs) indicate that these SWCNTs possess strong cytotoxicity, even though...

How Medicine can Learn from Materials Science

Can a major component of a catalytic converter or a fullerene derivative lead to an eventual treatment for Parkinson's disease or arthritis Research to date certainly hints at this possibility. In chemistry, radicals (often referred to as free radicals) are atomic or molecular species with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly reactive, so radicals are likely to take part in chemical reactions. Radicals play an important role in physiology but, because of their reactivity, they also can participate in unwanted side reactions resulting in cell damage. Free radicals damage components of the cell's membranes, proteins, or genetic material by oxidizing them the same chemical reaction that causes iron to rust. This is called oxidative stress. Many forms of cancer are thought to be the result of reactions between free radicals and DNA, resulting in mutations that can adversely affect the cell cycle and potentially lead to...

Fullerene Derivatives for Biological and Biomedical Applications

The biological and biomedical application potentials of fullerenes have received considerable attention 508 . These properties emerge from fullerenes efficiently scavenging free radicals. Additionally fullerenes generate singlet oxygen very efficiently in presence of UV and visible light 509 . In order for fullerenes to be used for these applications, they should be water-soluble. This is possible when hydrophilic groups are appended to the otherwise highly hydrophilic fullerenes.

Polymer Based Nuclear Imaging and Radiotherapy

RGD peptides labeled with therapeutically relevant isotopes such as b-particle emitters have been investigated as potential angiogenesis targeted radiotherapy (Table 9.5). The chelation conditions for 90Y and lutetium-177 (177Lu) labeled RGD have revealed that time, temperature, pH, presence of trace metal contaminants, and stoichiometric ratio of chelator to isotope all have significant effects on the rate of chelation and radiolabeling efficiency.175 A major challenge in development of therapeutic radiopharmaceuticals is radiolytic degradation of radiolabeled products because of production of free radicals in the presence of a large amount of high energy b-particles.176 A study on the stability of 90Y labeled, dimeric RGD peptide showed that presence

Results And Discussion

Fig. 2 shows XPS spectra of PTFE film before and after deposition of carbon layer by the plasma sputtering. For the PTFE substrate, the XPS spectrum consists of Fls peak (688.2 eV) and less intensive Cls peak (291.4 eV). In the XPS spectrum of the film obtained after 15 min deposition one can see intensive Cls peak (285.0 eV) as well as Ols (532.1 eV) and Nls (399.8 eV) peaks. The important point is that no significant Fls peak was observed in the XPS spectrum of carbon film obtained after 15 min carbon deposition. It means that pin-hole-free carbon layer with the thickness more then 30 A (depth of free electron path for 800 eV is formed on the PTFE surface already after 15 min of graphite sputtering. The atomic surface concentrations calculated from measured integral intensities of XPS peaks for as deposited carbon film are 72.2 at C, 10.5 at N and 14.0 at O. The appearance of relatively high concentration of oxygen on the surface of carbon layer may be explained by the surface...

Particle size and toxicity

In vitro studies on living cells have confirmed the increased ability of ultrafine particles to produce free radicals, which then cause cellular damage (Rahman et al, 2002 Uchino et al, 2002 Li et al, 2003). This damage can be manifested in different ways, including genotoxicity (Rahman et al, 2002) and altered rates of cell death, including apoptosis (Afaq et al, 1998 Kim et al, 1999 Rahman et al, 2002 Uchino et al, 2002).

Biodegradation of Carbon Nanotubes could Mitigate Potential Toxic Effects

''While it has been shown that CNTs can indeed act as a means for drug delivery, negative effects such as unusual and robust inflammatory response, oxidative stress and formation of free radicals, and the accumulation of per-oxidative products have also been found as a result of CNTs and their accumulated aggregates,'' Alexander Star points out. ''As a possible solution, we have provided compelling evidence of the biodegradation of CNTs by horseradish peroxidase and hydrogen peroxide over the course of several weeks. This marks a promising possibility for nanotubes to be degraded by horseradish peroxidase in environmentally relevant settings.''

Nanoparticles as the Drivers of Environment Particle Effects

In this paradigm surfaces, organics and metals can all contribute to inflammation via the production of free radicals. Diesel exhaust particles (DEPs) represent a good exemplar of combustion-derived NPs. Diesel exhaust particles cause inflammation in rat25,26 and human lungs27 following short-term, high-level exposure. Oxidative stress is demonstrable as an increased level of 8 OH dG, the oxidative adduct of hydroxyl radical, in the lungs of rats following exposure and in cells in culture treated with DEP.28,29 The component of DEP responsible for

Toxicology of Nanoparticles

While some particles of general respirable (i.e. not specifically nanoscale) size (e.g. TiO2) are found to be relatively harmless at doses to which humans are exposed, other particle types (e.g. silica and asbestos) have been shown to induce inflammation leading to diseases such as fibrosis and cancer - see, for example, Donaldson et al.25 and Donaldson and Tran.26 In toxicology studies, the ability of such particles to induce toxic effects is related to a number of physico-chemical properties such as size, shape, chemical composition, surface reactivity, surface charge, solubility biodurability.27 For insoluble particles or an insoluble core of a complex particle, only the surface interacts with the biological system.28 Therefore, the total surface area times its reactivity, in contact with the biological system, represents the dose . For a given mass of any particular kind of particle, particle size determines the specific surface area, and so we would expect that particle size is...

Ion Beam Deposition Technique

In the RF-PECVD deposition of carbon coating, as used by Bhushan et al. (e.g., 26.12 ), carbon coating is deposited by adsorption of most free radicals of hydrocarbon to the substrate and chemical bonding to other atoms on the surface. The hydrocarbon species are produced by the RF plasma decomposition of hydrocarbon precusors such as acetylene (C2H2), Fig. 26.4e 26.27,69,72-75 . Instead of requiring thermal energy in thermal CVD, the energetic electrons in the plasma (at pressures ranging from 1 to 5 x 102 Pa, typically less than 10 Pa) can activate almost any reaction among the gases in the glow discharge at relatively low substrate temperatures ranging from 100 to 600 C (typically less than 300 C). To deposit the coating on non-silicon substrates, an about 4-nm-thick amorphous silicon adhesion layer, used to improve adhesion, is first deposited under similar conditions from a gas mixture of 1 silane in argon 26.76 . In the process used by Bhushan and coworkers 26.12 , the plasma is...

Paradigms for Assessing NM Toxicity

Oxidative stress refers to a state in which cellular GSH is depleted while oxidized glutathione (GSSG) accumulates. Under normal coupling conditions, ROS are generated at low frequency, mostly in mitochondria, and are easily neutralized by antioxidant defense mechanisms such as the glutathione (GSH) glutathione disulfide (GSSG) redox couple. Ambient nanoparticles can elicit further ROS production in mitochondria, in addition to ROS generation by catalytic conversion pathways and NADPH oxidase activation 19, 21 . PM-induced ROS production is dependent on the particles themselves, as well as the redox cycling organic chemicals and transition metals that coat the particle surface 19, 21 . In addition to intrinsic redox cycling capabilities, the metabolic transformation of these chemicals and their ability to elicit intracellular calcium flux, disrupt electron flow in the mitochon-drial inner membrane, perturb the permeability transition pore, and deplete cellular GSH content could...

Buckyballs at work everywhere

I Additional buckyball-based antioxidant type drugs are being developed or tested. For example, anti-aging or anti-wrinkle creams are being developed by Mitsubishi, Taiwan University is testing a buckyball-based drug to fight arteriosclerosis, and C Sixty is working on both burn creams and an HIV drug.

Photoinduced Migration of Monomers or Oligomers

The high surface relief deformation of the hybrimer films induced by the exposure step may be explained by diffusion reactions of the monomers and or small molecular-weight oligomers in the films 148-150,152-154,156-160,173 . When a coated hybrimer film is exposed, the photoinitiator in the film absorbs light, decomposes into free radicals initiating the polymerization. If a selective exposure is performed, e.g., with a patterned photomask, the photo-polymerization of the matrix and photolocking of the photo-decomposed radicals take place only in the illuminated area, leading to the formation of concentration and density gradients in the film. This selective exposure results in a diffusion of the constituents from the non-illuminated region to the illuminated region of the films, and a surface deformation is produced. The same diffusion behavior was found and explored in the photopolymers 32, 37 . The photopolymers containing a photo-polymerizable monomer, a photoinitiator, and a...

Linear Polymer Chain Containing 250monomeric

The proclivity for C60 to form free radicals and react with various reagents, as already described throughout this chapter, indicates that the incorporation of C60 into a polymer structure should be possible. This incorporation might be accomplished in one of two general ways in-chain addition, as shown in Fig. 10.25(a), and side-chain addition, as shown in Fig. 10.25(b). These C60 polymers are sometimes referred to as pearl necklace (in-chain) and pendant (side-chain) C60 polymers. Below we give a few examples of C60 pendant and pearl necklace polymers, which form either as ordered copolymers or as block copolymers.

Radiation Induced Graft CoPolymerization

Absorption of high-energy radiation by polymers induces excitation and ionization and these excited and ionized species are the initial chemical reactants for graft polymerization as shown in the following table. The ejected electron must lose energy until it reaches thermal stability. The resulting species can further react to give free radicals, which can cause monomers to polymerize (6) and polymers to crosslink and degrade (7 and 8) and, in mixtures, monomers to graft to polymers (9). As can be seen, the radiation chemistry of polymers is a chemistry of neutral, cation, and anion radical, cations and anions, and excited species. The chemical nature and morphology of the material determine which of these reactions are predominant 49,50 . The primary reactive species involved in the radiation chemistry of macro-molecules is the free radical. Free radicals are species having an unpaired electron, which results from cleavage of a chemical bond 46 . The electronic excitation or removal...

Simultaneous Cross Linking Polymerization

Reaction Between Mba And Pnipam

Simultaneous cross-linking polymerization allows one to prepare gel network in a single step in which polymerization as well as cross-linking processes occur simultaneously 144-148 . In these polymerizations, apart from monomer, a cross-linking agent (functionality 3) is used to allow three-dimensional network formation. In such polymerization process, the free radicals formed in the initiation step of the reaction tend to react with monomer and cross-linker molecules to obtain polymeric chains along with some cross-linking points. Intermolecular cross-linking leads to the formation of branched and highly network structure that ultimately is responsible for macroscopic gel product. The intramolecular cross-linking process is responsible for the formation internally cross-linked polymeric chain networks. Figure 6.12 illustrates the difference between inter- and intra-cross-linking behaviors in the simultaneous cross-linking polymerization process. 6.3.1.3 Emulsion Polymerization....

Metal Oxides

Modified forms of titanium dioxide have also found markets. Oxonica has developed and is selling a manganese-doped titanium dioxide that exhibits significantly enhanced UVA absorption and minimises the generation of free radicals resulting from the absorption of UV light by the titanium dioxide.47 49 This product is already being used commercially in sunscreens and cosmetics and is being evaluated for applications in coatings and plastics.

Cytotoxicity

Limits cellular uptake, resulting in extracellular reduction.91 MTT, with a net positive charge, readily crosses cell membranes and is reduced intracellularly, primarily in the mitochondria. Because nanoparticles have been shown to interact with cell membranes and could potentially interfere with the reduction of the newer generation analog via trans-plasma membrane electron transport, the traditional MTT assay would appear to be a better choice to assess cellular viability in nanoparticle cytotoxicity experiments. Analytes that are antioxidants, or are substrate inhibitors of drug efflux pumps, have been shown to interfere with the MTT assay.92,93 Functionalized fullerenes, which have not identified as efflux pump inhibitors or substrates, but do possess potent antioxidant activity, have been observed in our laboratory to cause MTT assay interference, resulting in enhanced MTT reduction and overestimation of cell viability (unpublished data).

Oxidative Stress

The generation of free radicals by nanomaterials is well documented.97'98 In most cases, the studied material was of ambient or industrial origin (quartz, carbon black, metal fumes, and diesel exhaust particles). However, engineered nanomaterials, such as fullerenes and polystyrene nanoparticles, have been shown to generate oxidative stress as well.40,99,100 Lovric et al., for example, determined ROS to play an important role in cytotoxicity of quantum dots that have lost their protective coating.101 The unique surface chemistries, large surface area, and redox active or catalytic contaminants (e.g., metals, quinones) of nanoparticles can facilitate ROS generation.102 For example, fullerenes can perform electron transfer (phase-I pathway) or energy transfer (phase-II pathway) reactions with molecular oxygen following photoexcitation,44 resulting in the formation of the superoxide anion radical or singlet oxygen, respectively. The superoxide anion radical can then undergo further...

Reason for concern

A variety of nanomaterials has the capacity to cause tissue and cellular damage by causing oxidative stress (the same type of damage that people take antioxidant pills to protect against). Buckyballs caused oxidative damage to brain and liver cells in a study in largemouth bass other nanoparticles have also been shown to cause oxidative stress in skin cells and in the liver. Most research has used prototypical or 'plain' nanoparticles, such as uncoated bucky-balls and carbon nanotubes. The few studies that have looked at the effects of variations and coatings have shown that these changes modify the toxicity of the original particle, further complicating the picture and raising the question of how these coatings may degrade over time within the body or in the environment. Oxidative stress may also be part of the mechanism behind the damage to lung tissue that has been observed in several studies of carbon

Fullerenes

Buckminster fullerene or C60 is a compact, cage-like molecule comprising 60 carbon atoms. C60 can be viewed as a nanoparticle and has received some toxicological attention. The basic graphene structure of fullerene can be func-tionalised in various ways to change the physical properties of the fullerene, for instance making it more dispersible soluble.103 Carboxylated fullerenes are slightly less toxic than the native C60 and hydroxylated fullerenes are virtually non-toxic to human dermal fibroblasts.103 The toxicity of the native C60 appeared to be due to the ability to generate superoxide anions.103 Isakovic et al. showed a similar effect with the native C60 being 30 times more toxic on a mass basis than a soluble hydroxylated C60 in a range of human tumour cell lines. The authors concluded through the use of antioxidants, and by identifying different types of cell death with the two fullerenes, that unmodified C60 had strong pro-oxidant capacity responsible for the rapid necrotic...

The Debate Heats Up

ANTIOXIDANTS Chemicals that protect against oxidation, which causes rancidity in fats and damage to DNA. FREE RADICAL A molecule containing an unpaired electron, typically highly unstable and reactive. Free radicals can damage the molecular machinery of biological systems, leading to cross-linking and mutation.

Abbreviations

ARE, antioxidant response element ESR, electron spin resonance GPx, glutathione peroxidese GSH, glutathione GSSG, glutathione disulfide GST, glutathione S-transferase JNK, NH2-terminal Jun kinase HO-1, heme oxygenase 1 MAPK, mitogen-activated protein kinase NAC, N-acetylcysteine O2-, superoxide OH, hydroxyl radical PM, particle matter PT, permeability transition ROS, reactive oxygen

Toxicity Mechanisms

9.2.2.1 Production of Reactive Oxygen Species. One of the most important toxicity mechanisms is the production of reactive oxygen species (ROS). For example, electron capture of O2 can lead to the formation of the superoxide radical O2-, which then generates additional ROS. Normally, glutathione and other antioxidant enzymes maintain equilibrium in the body. An increasing ROS generation rate causes oxidative stress and triggers inflammatory responses. High levels of oxidative stress perturb the mitochondrial PT pore and disrupt electronic transfer, which can produce cellular apoptosis or necrosis 25 . Reactive oxygen species can damage cellular proteins, lipids, membranes, and DNA. 9.2.2.5 Carbon Nanostructures. Carbon nanostructures, such as fullerenes and nanotubes, deserve special attention because these materials receive the most popular press. Carbon nanostructures have many potential applications because they have a unique free radical chemistry and, due to their strong...

Reaction Mechanism

Disproportionate of these free radicals is likely to occur relatively rapidly at low pH (fci2a 9.7x 107 M-1s-1 (Bielski et al., 1985)) (slower at higher pH at pH 8, k4.i3b 6.1 x 104 M-1s-1), resulting in the formation of hydrogen peroxide at or near the ZVI surface (Equation (4.13))