In 1985, three scientists produced a fullerene, named C60, in fewer quantities by vaporizing the graphite in the arc or the laser beam or with an electric current in a low-pressure argon or helium atmosphere. Since then, they have gained significant attention in different fields. 

The newly found molecule was named by these scientists after Richard Buckminster Fuller, in 1967, he made a dome of shape like the carbon cluster, whereas, in 1970, the possibility of fullerenes existence was predicted. Later, it’s observed that fullerenes occur in interstellar dust and also in Earth's geological formations, only in the ppm-range. Fullerenes, also known as buckyballs, are carbon's new allotrope and their appearance also resembles soccer balls. Fullerenes consist out of 20 hexagons and 12 pentagons with a carbon atom in each edge of this lattice structure. Fullerenes also exist in different stones, naturally. Earlier, on the cave walls, they were deposited as soot. In 1990, fullerenes were produced on a larger scale for the first time. In this article, the making of fullerene is explained properly, and the fact that fullerenes' unique structure joined with immense derivatization makes them a possible agent for many therapeutic applications, including free radical scavenger, anti-HIV- protease activity, antimicrobial action, photodynamic DNA cleavage, and their use as the diagnostic agents and in biomedicine.

Introduction

Fullerene is an allotrope of carbon with molecules that consist of carbon atoms joined by double and single bonds to make a partially closed or closed mesh, with fused rings of 5 to 7 atoms. Carbon's allotropes were limited to graphite, diamond, etc. but then, carbon's third form called fullerenes got discovered. An experiment was done in which laser irradiation vaporizes graphite's surface into plasma containing free ions and atoms. Due to the collision with helium atoms, those free atoms and ions were chilled down. Clusters containing numerous amount of carbon atoms were made because of the collision, ranging in size from 20 carbon molecules and larger. It's also discovered that Carbon 60 molecules concentration was increased by permitting the plasma to react longer, a mass spectrometer examines the clusters, and it was seen that clusters having 70 to 60 carbon atoms dominated, making up Carbon 60, 40-times more as compared to carbon's other structures. These were the most studied fullerenes. In the beginning, only less than 10-15 g was prepared, but in 1990, new preparative methods for high yielding of fullerenes were developed. Fullerenes got named after an architect, Richard Buckminster Fuller, who made a so-called geodesic dome structure of hexagonal and pentagonal cells in 1967, which is very similar to the fullerene molecules. Fullerenes exist in nature, particularly where high energy and carbon exist and close to volcano craters. They are even formed when gas burns in the household cooker, in regular lighter's flame or in places of ancient carbon rock accumulation. In 1999, C60 fullerenes were found in schungite.

Properties of Fullerenes

Fullerenes are not self-inflammable and mostly yellow in color. Under ignition source influence, fullerenes are flammable (dust explosion). Fullerenes are the only carbon modifications that are not soluble in water, but soluble in organic solvents. Hydrated C60 fullerene helps an organism in returning to its "normal condition" in the case of any negative changes, and it does that for the maintenance and restoration of those structures it has generated as a matrix in the process of life's origin. The C60 fullerenes are the smallest ones like the buckyball, C70 is the next larger fullerene having the shape of a rugby ball. Nowadays, most of Carbon 60 is synthesized in the laboratory by treating soot with organic solvents, to extract carbon 60. The soot is made between two carbon electrodes by using an electric arc. Extracted Carbon 60 can be separated and then purified using chromatography, along with other fullerenes. C60 molecules are incorporated into frames and shafts to achieve very thin-walled and lightweight, robust structures of carbon. These are highly used in medical fields and have various applications in biomedicine.

Topology

Schlegel diagrams are usually used for viewing closed-shell fullerenes 3D structure. A closed fullerene of the sphere-like shell should have some heptagon or pentagon cycles at-least. Open fullerenes, e.g. graphene and carbon nanotubes, consist entirely of rings of the hexagon. In theory, a long nanotube with joined ends forms a torus-like closed sheet that could also consist entirely of hexagons.

Bonding

Three neighbors were connected with each carbon atom, so it is usual to label those bonds as a mixture of single and double covalent bonds.

Encapsulation

Endohedral fullerenes are one of the fullerene derivatives having small molecules or ions incorporated inside the cage atoms.

Aromaticity

Scientists have increased the reactivity of the fullerene by assigning active groups to their surfaces. Super aromaticity is not exhibited by fullerenes. C60 diameter is 0.7nm, and, is just like a soccer ball, due to which, it is usually called a "soccer ball molecule". Comparing one such molecule's dimensions with the Earth, one finds, that the soccer ball-fullerene relation resembles the relation between the Earth and soccer ball. Fullerenes have a very low density of 1,68 g/cm³ in comparison with, graphite having a density of 2,1-2,3 g/cm³, or diamond having a density of 3,51 g/cm³, that is because of their hollow ball shape. C60 is the smallest stable fullerene because of the two pentagons that are side by side. C60 molecule's important property is high symmetry because there are 120 symmetrical operations, like rotation around the axis and reflection in a plane, which maps the molecule onto itself. Bond lengths are of 2 types in the fullerene: C5-C6 double bonds (hexagons) and C5-C5 single bonds (pentagons). Each C atom makes bond via sp2 hybridization with three other adjacent atoms.

A C60 molecule has a diameter of 7 Å. C60 molecules form a solid of weakly bound molecules together. Fullerites are fullerenes' crystalline state. It looks like a yellow powder, but after dissolving in toluene, it turns to pink. The molecule is quite stable, chemically. The temperature of over 1000°C is required to break the balls. In the absence of air, fullerenes can transform into graphite when heated up to 1500C. C70 looks more like a rugby ball and has 25 hexagons. When hexagons are removed or added from the structure of the soccer ball, the roundness begins to lose. Giant fullerenes appear in the shape of a pentagon. Smaller fullerenes appear as asteroids. Carbon 60 is the most stable one. A loss of stability comes with the loss of roundness. Other than C60 and C78, C70, C86, C76 C84, have been separated and discussed in detail. Carbon disulphide, toluene, and xylene are good solvents.

Applications of Fullerenes

Fullerenes are hollow, inert, and indefinitely modifiable. They are not absorbed in water-soluble form when given orally, but they get quickly distributed to various tissues of the body when given through IV. They are excreted by the kidney without any change. Fullerenes are widely used for many biomedical applications like photodynamic therapy, and gene and drug delivery, etc.

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Tumor Research

In cancer research, HeLa cells were used in recent experiments. This includes the production of new photosensitizers which get absorbed by cancer cells and still trigger the death of the cell. To prevent damage to the cell, the body shouldn't contain a new photosensitizer in it for long. When cancer cells absorb them, and they get exposed to light radiation, creating reactive oxygen that damages the lipids, proteins, and DNA that makes up the cancer cell. The cellular level damage leads to the cancer cell going through apoptosis, which causes a reduction in tumor size. When the light radiation treatment ends, free radicals will be reabsorbed by the fullerenes to prevent tissue damage. The treatment may penetrate deeper into the body and be absorbed effectively by cancer cells in the near future.

Diagnostic Applications

Endohedral metallofullerenes have metal ion fixed inside the cage of fullerene. Water solubilized forms are used as Magnetic Resonance Imaging (MRI) and X-ray contrast agents, and radiopharmaceuticals. One of these derivatives has been studied in detail as a radioactive tracer for diseased organ imaging and to kill the cancerous tumors. Inside the carbon shell, there is a stable radioactive metal that is very resistant to the body's metabolism. Metallo-fullerenes are not toxic, and they allow imaging of the circulatory system by staying in the body for at least an hour.

Anti-HIV Activity

Wudl et al. hypothesized that Carbon60 has the almost same radius as of the cylinder which explains HIV-Protease active site, a chance exists for a strong hydrophobic interaction between the active site surfaces and C60 derivatives. HIV-Protease inhibition in C60 presence was explained through experimental observations and molecular modelling studies. Inactivation of virus assays proved fullerene derivatives' activity against HIV-2 and HIV-1.

DNA Photo-Cleavage

C60 derivatives cytotoxicity was mediated by its DNA cleaving capability. So, other usages of fullerenes are related to its easy photoexcitation, that's why Photodynamic compounds, which are fullerene-based, are being established for cancer treatment.

Free Radical Scavenger

Fullerene compounds have a unique cage structure, combines in the core with numerous conjugated double bonds, interacts with the biomolecules, and have avid reactivity with free radicals. Fullerene derivatives protective effect is explained in numerous systems, containing reduced injury on the ischemia-reperfusion intestine, protecting different types of cells from going through apoptosis, reducing the free radical level in organ perfusion, and neuroprotective effect. Derivatives of fullerene have shown good results in pre-toxicity studies. Also, both water and lipid-soluble derivatives are possible, and this point has increased their importance as an antioxidant in health and personal care products, e.g., burn creams, nutritional supplements, and skin creams.

Antimicrobial Activity

Monomethoxy triethylene glycol (mTEG) substituted fuller-pyrrolidines shows inhibition of M. tuberculosis and Mycobacterium Avium. Carboxy-fullerenes inhibits E. coli-induced meningitis by lessening the damage which is caused by infiltrating neutrophils on the blood-brain barrier. Later, it was observed that carboxy-fullerenes could insert into Gram+ve cocci's cell wall, disrupt its cell wall structure, and cause the death of bacteria. The gram-ve organisms' cell wall has an outer membrane consisting of lipo-poly-saccharides, phospholipids, and lipoproteins. Fullerenes can't assess it. This advises that carboxy fullerenes could be taken against Gram +ve cocci as new antimicrobial agents

Osteoporosis

Fullerene derivatives in bones, i.e. poly fluoro-bi-phosphonated derivatives are being considered as a bimodal drug for osteoporosis

Conclusion

In this review, Fullerene and many of its derivatives have been stated along with their uses in different pharmaceutical applications. Fullerenes has a specific structure, and it helps in the treatment of some diseases. What makes Fullerene good for delivering the drug is the ability to, cross the blood-brain barrier, carry the load of multiple drugs, deliver to the targeted cells, not dissolving before reaching the targeted cells. Fullerenes are used to deliver anti-tumor drugs, drugs for cancer therapy, and drugs that need to enter the brain. They can inhibit HIV-1 and also Gram +ve bacteria. Fullerenes and their derivatives are widely used in the medical field.

Fullerene, namely C60, named after Architect Richard Buckminster Fuller, was produced by vaporizing graphite in the laser beam. Fullerenes are soluble in organic solvents and not in water. C60 fullerenes are the smallest ones like the buckyball; meanwhile, C70 has the structure of a rugby ball. Nowadays, most of Carbon 60 is manufactured in the laboratory. The remarkable carbon cage structure makes them a potential therapeutic agent for many potential therapeutic applications, in biomedicine and diagnostics.

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