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9/7/11

Fullerenes applications


Fullerene
Fullerenes find wide application in different fields of science since their discovery in 1985. Their size, hydrophobicity, three-dimensionality and electronic configurations make them an appealing subject in science, engineering and medicinal fields. Their unique physical, chemical and biological properties have yielded promising contributions to the industries and many industrial applications are now being commercialized.
Structure
Fullerenes are cage-structured carbon molecules such as C60, C70, C76, and C84 having a spherical shape with a wide range of sizes and molecular weights. For example the C60 fullerene also known as buckminsterfullerene or Buckyball is a good representative. Buckminsterfullerenes are hard crystals, red by transmission, black by reflection, yellow in film form and have approximately 0.7 nm in diameter. In the fullerene structure, all C sites are equivalent and the bond lengths are 0.14 nm for the double bond and 0.146 nm for the single bond.
Properties
By virtue of their high chemical activity and a broad versatility of chemical reactions their physical and chemical properties may be tuned by the addition of element and molecular species into the fullerene lattice (C59N), within the cage (N at center of C60), or coating the surface of fullerene with transition metals.
Fullerenes and fullerenic black are chemically reactive and can be added to polymer structures to create new copolymers with specific physical and mechanical properties. They can also be added to make composites.

Electrochemical and physical properties of the fullerene family especially C60 can be exploited in various medical fields.
Fullerene is able to fit inside the hydrophobic cavity of HIV proteases, inhibiting the access of substrates to the catalytic site of enzyme. At the same time, if exposed to light, fullerene can produce singlet oxygen in high quantum yields. This action, together with direct electron transfer from excited state of fullerene and DNA bases, can be used to cleave DNA.
Synthesis
Fullerenes, a new form of carbon, were discovered in 1985 in graphite vaporization under inert gas at low pressure. Fullerenes are produced using electric arc discharge or thermal CVD processes.
Originally, fullerenes were produced by the carbon arc method developed at the University of Arizona. Only small quantities of fullerenes can be produced by this method as it encounters problems due to the low yield, non-selective carbon cage formation, associated purification issues and the process is not scalable. In the arc discharge process, fullerenes cannot be produced if hydrogen atoms are present in the reaction gas. But, synthetic methods can produce a single isomer of a desired fullerene, free from impurities of other isomers or fullerenes of different sizes. This route is based on planar polycyclic aromatic hydrocarbon precursor molecules containing the carbon framework required for the formation of the target fullerene cage.
Applications
Fullerenes have many properties different from either diamond or graphite. There are many applications of practical importance of fullerene in a wide range of areas and application-oriented patents span a spectrum of potential commercial applications. They include areas such as IT devices, diagnostics, pharmaceuticals, environmental, and energy industries, Few examples include facial creams, moisturizers, lubrications, trace monitors, electronic circuits, electronic devices, sensors, superconductors, catalysts, optical, polymer composites, high-energy fuels, anticancer anti cancer drug delivery systems using photodynamic therapy, HIV drugs, MRI agents and cosmetics to slow down the aging of human skin.
Other interesting classes of fullerenic or curved-layer carbon, as opposed to graphitic or planar-layer carbon, that can also be found in fullerene-producing systems are nanostructures with tubular, spheroidal, or other shapes and consisting of onion like or nested closed shells and soot particles with considerable curved-layer content.
Medical
The medical applications of fullerenes include antiviral activity, antioxidant activity, powerful photo induced biological activities as a potential scaffold for photodynamic therapy and diagnostic applications. In addition, fullerenes have been used as a carrier for gene and drug delivery systems. Also they are used for serum protein profiling as MELDI material for biomarker discovery
Antioxidant
Fullerenes are powerful antioxidants, reacting readily at a high rate with free radicals. Fullerenes hold great promise in health and personal care applications to prevention of oxidative cell damage or death, as well as in non-physiological applications where oxidation and radical processes such as food spoilage, plastics deterioration, and metal corrosion are to be avoided. Major pharmaceutical companies are exploring the use of fullerenes in controlling the neurological damage of such diseases as Alzheimer's disease and Lou Gehrig's disease (ALS), which are a result of radical damage. Drugs for atherosclerosis, photodynamic therapy, and anti-viral agents are also being developed.
Fullerene derivatives hold great potential as inhibitors of HIV aspartic protease enzyme and in the development of novel anti HIV drugs. Fullerenes are known to behave like a "radical sponge," as they can sponge-up and neutralize 20 or more free radicals per fullerene molecule. They have shown performance 100 times more effective than current leading antioxidants such as Vitamin E.
The antioxidant property is based on the fact that fullerenes possess large amount of conjugated double bonds and low lying lowest unoccupied molecular orbital (LUMO) which can easily take up an electron, making an attack of radical species highly possible. In other words the fullerene can react with many super oxides without being consumed considered as the most efficient radical scavenger or radical sponges.
Further water soluble fullerenes namely fullerenols and malonic acid derivatives of C60 have attracted great attention in the field of neurosciences
Catalyst
As catalyst fullerenes have marked ability to accept and to transfer hydrogen atoms, hydrogenation and hydrodealkylations, they are highly effective in promoting the conversion of methane into higher hydrocarbons and inhibiting coking reactions.
Fullerenes are used in Water purification, bio-hazard protection, singlet oxygen catalysis of organics, in proton exchange membranes for fuel cells, in vehicles to provide enhanced durability, lower heat build-up, and better fuel economy with use of fullerene black/rubber compounds.
Polymer Electronics
Organic Field Effect Transistors (OFETS) and photo detectors performance has also been increased due to the n-type semi conducting properties of fullerenes based on C60, C70 along with C84. Fullerene OFETS fabricated with C84 show greater mobility and stability than C60 or C70. While more work is needed, the world of polymer electronics is opening up for both fullerenes and single-walled carbon nanotubes.




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