Fullerenes and Their Applications in Medicine
Fullerene is a molecular compound, which belongs to the class of allotropes of carbon and can have different forms such as tube, sphere, ellipsoid, and many other forms. Cylindrical fullerenes are called buckytubes and spherical ones are called buckyballs. After finding them in the outer space, the astronomers established the theory that fullerenes could provide seeds for life on the planet. The structure of fullerene is similar to the structure of graphite, which is linked with hexagonal rings and consists of grapheme sheets. Originally, this class of compounds has been limited by structures involving only five- and hexagonal faces. Besides carbon atoms, the composition of fullerene molecules includes atoms of other chemical elements. Nowadays, these two structures are under scientific study because of their unique chemistry features and ability to apply them in modern technological devices and processes. Their discovery is significantly important for the development of nanotechnology and electronics. Fullerenes are already used in superconducting materials, sensors, solar panels, logical elements. They are also used as antiwear additives for industrial lubricating oils, greases, and coatings, the polymeric materials in the manufacture of catalysts, rubber, pharmaceuticals. It is very important to notice that the discovery of fullerenes serves as a basis for the development of new applications in medicine. Proper and deep involvement of medical researchers into the study of fullerenes may give the ability for future medicine to treat different types of diseases that are now considered as incurable.
Richard Buckminster Fuller is an American system theorist, inventor, architect, and designer who popularized the geodesic dome, which is the spherical structure based on a network of circles on the surface of a sphere. Because of the resemblance to geodesic spheres and similarity between their shape and shape of fullerenes, fullerenes were named after its name. For the first time, fullerenes were synthesized in 1985. In 1992, they were found in the rocks of the Precambrian period (Browne, 1992). The discovery of fullerene had a strong influence on the entire scientific world. The Anglo-American group of scientists, namely Harold Kroto, Robert Curl, and Richard Smalley discovered a new molecule consisting of only atoms of carbon and received the Nobel Prize in chemistry in 1996. The singularity of this discovery was that nobody expected to make any discoveries in carbon as its numerous compounds have been already extensively studied. A new structure of carbon compounds was extremely unusual that strongly shook the chemical community. It is well-known that the carbon compound forms long carbon chains or flat cyclic structures, but a new molecule had a spherical structure. The discovery of fullerenes was so fundamental that affected almost every field of scientific knowledge and contributed to the further development of world science.
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Currently, the structure, properties, and possible scope of fullerenes appliance are intensively studied in laboratories of different countries. There are known fullerenes, which consist of 60, 70, 76, 78, 84, 90 carbon atoms that also have the form of a closed surface. Among them, there are molecules with more and less stable structure. The most studied member of the family of fullerenes is fullerene-60 (C60) in which carbon atoms form polyhedron. The structure of this polyhedron resembles a soccer ball. It is also the most stable molecule of the family of fullerenes. The reason for the stability of C60 is an exceptionally high degree of symmetry of truncated icosahedrons. The high degree of symmetry is an important property of this molecule. The ductility properties of fullerenes are similar to graphite. At a certain atmospheric pressure and room temperature they turn into a diamond. Fullerene is a semiconductor and stable on air. Currently, scientists are trying to study the ability of fullerenes to superconductivity and heat resistance. As a result, there were created on the basis of fullerenes not only compounds with superconductivity, but also the material, which exceeds the bulk modulus and hardness of the superior diamonds. Despite the fact that fullerenes are stable, they are not totally nonreactive and accept other electrons during different reactions. There was obtained the simplest fullerene with hydrogen C60H2. The molecule can be chlorinated, ammonated, methylated, and fluorinated (Burley, Keller, & Pyne, 1999). The researchers also conducted the introduction of metal particles in the fullerenes. The first production of such particles was based on the laser vaporization of the lanthanum salt mixtures and graphite.
From the time of fullerenes discovery, especially since the development of the methods of obtaining them in macroscopic, organic chemistry of fullerene has gained unprecedented popularity and become an independent branch of organic chemistry. Crystalline fullerenes and films are semiconductors and have photoconductivity under optical irradiation. C60 crystals doped with alkali metal atoms exhibit metallic conductivity and move to a superconducting state at temperatures of 19-33 K, depending on the type of alkali metal. Solutions of fullerenes have nonlinear optical properties and can therefore be used as a basis for the nonlinear optical shutters used to protect optical devices from intense optical radiation. Fullerenes are used as catalysts for synthesizing diamonds (Kronholm & Hummelen, 2007).
The chemical activity of fullerenes has interested the representatives of medicine in terms of their use. First of all, fullerenes are important for medicine because of their antiviral activity. “Fullerenes (C60) and their derivatives have potential antiviral activity, which has strong implications on the treatment of HIV-infection” (Bakry, Vallant, Najam-ul-Hag, Rainer, Szabo, Huck, & Bonn, 2007). Antioxidant activity and molecular structure of fullerenes are the basis for antiviral activity. It has been studied that a series of fullerene derivatives can decrease the activity of HIV virus. When fullerenes interact with virus, they are capable to change its conformation. As a result, they can affect its function. Some fullerene derivatives are able to interact directly with the DNA and inhibit the action of enzymes that cut the DNA at specific places.
One of the most remarkable properties of fullerenes for medicine is their ability to produce aqueous solutions. By integrating the most stable fullerene C60 in a water molecule, scientists have been able to create the aquatic environment very similar to the environment in healthy cells. Water with built fullerene neutralizes free radicals, which cause many diseases. Free radicals are molecules, which damage chromosomes and lead to cell aging, cancer, reduced immunity. Antioxidants are nutrients that bind free radicals and prevent their destructive action. In such a way, the water with fullerenes works as an antioxidant and can be used in medicine as a treatment for many diseases. In addition, fullerene solutions accelerate the process of neutralization of free radicals and they are much more efficient than conventional antioxidants.
The capabilities of these nanospheres are truly inexhaustible and are not only limited to fighting free radicals. Fullerenes are able to create entire sets of bioactive compounds. By filling the cavity of fullerene with healing substance, it is possible to deliver it to the desired position in the human body. “Through nanotechnology it is now possible to target therapeutic agents to specific body cells, tissues and organs more effectively and with less adverse consequences” (Nazem & Mansoori, 2008). These fullerenes may be used for the delivery of antibiotics, vitamins, and hormones to the diseased cells. Scientists are working hard on the creation of fullerene drugs to treat brain diseases (De Jong & Borm, 2008). There is also assumed further development of this technique for the treatment of multiple sclerosis and Alzheimer's disease (Nazem & Mansoori, 2008). The current experiments with fullerenes give hope for medical workers in future to deliver drugs through the skin without the use of injections.
Fullerenes also have multiple properties with the biological benefits. Biologists have conducted an unusual experiment on mice in order to check whether fullerene C60 has a toxic effect. During this experiment, they added fullerene C60 to the food, which was dissolved in olive oil. “In the current study researchers fed the molecule dissolved in olive oil to rats and compared outcomes to a control group of rats who got plain olive oil” (“Chronic buckyball ingestion doubles lifespan in rats”, 2012). It was concluded that rats, which were regularly receiving solution of C60, lived longer than those who were given olive oil or just kept a regular diet. There are many other directions in medicine how fullerenes can be applied. They could be used for the protection of a human body from radiation and allergy; for the protection of the brain from alcohol; for stimulation of the nerve growth; for stimulation of the skin regeneration processes; for stimulation of the hair growth. Fullerenes can also be used in medicine as medicines for cancer control.
In the 21st century, the fullerenes are objects for discovering further perspective directions in bio- and nanotechnology. At the time of their discovery, they were applied in medicine in different ways because of their physical and chemical properties. However, the studies of fullerenes and their properties are only at the initial stage. Until their complete use in the medical practice, it is necessary to study in detail their impact on living organisms, toxicity, and mechanisms of interaction with the cell and its separate compartments.