Retrieved 29 August This confusion persists as today some nutritionists use the term complex carbohydrate to refer to any sort of digestible saccharide present in a whole food, where fiber, vitamins and minerals are also found as opposed to processed carbohydrates, which provide energy but few other nutrients. August Learn how and when to remove this template message. Monosaccharides with three carbon atoms are called trioses , those with four are called tetroses , five are called pentoses , six are hexoses , and so on. Carbohydrates are polyhydroxy aldehydes, ketones, alcohols, acids, their simple derivatives and their polymers having linkages of the acetal type. Trimetaspheres have the potential for use in diagnostics as safe imaging agents , therapeutics  and in organic solar cells. The C 60 derivatives can be delivered to the cells by using the functional groups L-phenylalanine , folic acid , and L-arginine among others.
C 60 and other fullerenes were later noticed occurring outside the laboratory for example, in normal candle - soot. By it was relatively easy to produce gram-sized samples of fullerene powder using the techniques of Donald Huffman , Wolfgang Krätschmer , Lowell D. Lamb , and Konstantinos Fostiropoulos. Fullerene purification remains a challenge to chemists and to a large extent determines fullerene prices.
So-called endohedral fullerenes have ions or small molecules incorporated inside the cage atoms. Fullerene is an unusual reactant in many organic reactions such as the Bingel reaction discovered in Carbon nanotubes were first discovered and synthesized in Minute quantities of the fullerenes, in the form of C 60 , C 70 , C 76 , C 82 and C 84 molecules, are produced in nature, hidden in soot and formed by lightning discharges in the atmosphere.
In , fullerenes C 60 have been discovered in a cloud of cosmic dust surrounding a distant star light years away. Using NASA's Spitzer infrared telescope the scientists spotted the molecules' unmistakable infrared signature. Sir Harry Kroto, who shared the Nobel Prize in Chemistry for the discovery of buckyballs commented: The discoverers of the Buckminsterfullerene C 60 allotrope of carbon named it after Richard Buckminster Fuller , a noted architectural modeler who popularized the geodesic dome.
Since buckminsterfullerenes have a similar shape to those of such domes, they thought the name appropriate. The suffix "-ene" indicates that each C atom is covalently bonded to three others instead of the maximum of four , a situation that classically would correspond to the existence of bonds involving two pairs of electrons " double bonds ".
Since the discovery of fullerenes in , structural variations on fullerenes have evolved well beyond the individual clusters themselves. Buckminsterfullerene is the smallest fullerene molecule containing pentagonal and hexagonal rings in which no two pentagons share an edge which can be destabilizing, as in pentalene. It is also most common in terms of natural occurrence, as it can often be found in soot. The structure of C 60 is a truncated icosahedron , which resembles an association football ball of the type made of twenty hexagons and twelve pentagons, with a carbon atom at the vertices of each polygon and a bond along each polygon edge.
The van der Waals diameter of a C 60 molecule is about 1. The C 60 molecule has two bond lengths. Its average bond length is 1. A type of buckyball which uses boron atoms, instead of the usual carbon, was predicted and described in The B 80 structure, with each atom forming 5 or 6 bonds, is predicted to be more stable than the C 60 buckyball.
However, this work has been subject to much criticism by quantum chemists   as it was concluded that the predicted I h symmetric structure was vibrationally unstable and the resulting cage undergoes a spontaneous symmetry break, yielding a puckered cage with rare T h symmetry symmetry of a volleyball. There is an additional atom in the center of each six-member ring, bonded to each atom surrounding it.
By employing a systematic global search algorithm, later it was found that the previously proposed B80 fullerene is not global minimum for 80 atom boron clusters and hence can not be found in nature. Another fairly common fullerene is C 70 ,  but fullerenes with 72, 76, 84 and even up to carbon atoms are commonly obtained. In mathematical terms, the structure of a fullerene is a trivalent convex polyhedron with pentagonal and hexagonal faces.
In graph theory , the term fullerene refers to any 3- regular , planar graph with all faces of size 5 or 6 including the external face. The smallest fullerene is the dodecahedral C There are no fullerenes with 22 vertices. For instance, there are non-isomorphic fullerenes C Note that only one form of C 60 , the buckminsterfullerene alias truncated icosahedron , has no pair of adjacent pentagons the smallest such fullerene.
To further illustrate the growth, there are ,, non-isomorphic fullerenes C , 15,, of which have no adjacent pentagons. Optimized structures of many fullerene isomers are published and listed on the web. Heterofullerenes have heteroatoms substituting carbons in cage or tube-shaped structures. They were discovered in  and greatly expand the overall fullerene class of compounds. Notable examples include boron, nitrogen azafullerene , oxygen, and phosphorus derivatives.
Trimetasphere carbon nanomaterials were discovered by researchers at Virginia Tech and licensed exclusively to Luna Innovations. This class of novel molecules comprises 80 carbon atoms C 80 forming a sphere which encloses a complex of three metal atoms and one nitrogen atom. These fullerenes encapsulate metals which puts them in the subset referred to as metallofullerenes. Trimetaspheres have the potential for use in diagnostics as safe imaging agents , therapeutics  and in organic solar cells.
Nanotubes are cylindrical fullerenes. These tubes of carbon are usually only a few nanometres wide, but they can range from less than a micrometer to several millimeters in length.
They often have closed ends, but can be open-ended as well. There are also cases in which the tube reduces in diameter before closing off. Their unique molecular structure results in extraordinary macroscopic properties, including high tensile strength , high electrical conductivity , high ductility , high heat conductivity , and relative chemical inactivity as it is cylindrical and "planar" — that is, it has no "exposed" atoms that can be easily displaced. One proposed use of carbon nanotubes is in paper batteries , developed in by researchers at Rensselaer Polytechnic Institute.
Fullerites are the solid-state manifestation of fullerenes and related compounds and materials. Such treatment converts fullerite into a nanocrystalline form of diamond which has been reported to exhibit remarkable mechanical properties. In the early s, the chemical and physical properties of fullerenes were a hot topic in the field of research and development.
Popular Science discussed possible uses of fullerenes graphene in armor. In the field of nanotechnology , heat resistance and superconductivity are some of the more heavily studied properties. A common method used to produce fullerenes is to send a large current between two nearby graphite electrodes in an inert atmosphere. The resulting carbon plasma arc between the electrodes cools into sooty residue from which many fullerenes can be isolated.
There are many calculations that have been done using ab-initio quantum methods applied to fullerenes. Results of such calculations can be compared with experimental results. Researchers have been able to increase the reactivity of fullerenes by attaching active groups to their surfaces. Buckminsterfullerene does not exhibit " superaromaticity ": A spherical fullerene of n carbon atoms has n pi-bonding electrons, free to delocalize.
These should try to delocalize over the whole molecule. This has been shown to be the case using quantum chemical modelling, which showed the existence of strong diamagnetic sphere currents in the cation.
As a result, C 60 in water tends to pick up two more electrons and become an anion. The n C 60 described below may be the result of C 60 trying to form a loose metallic bond.
Fullerenes are stable, but not totally unreactive. The sp 2 -hybridized carbon atoms, which are at their energy minimum in planar graphite , must be bent to form the closed sphere or tube, which produces angle strain.
The characteristic reaction of fullerenes is electrophilic addition at 6,6-double bonds, which reduces angle strain by changing sp 2 -hybridized carbons into sp 3 -hybridized ones. This decrease in bond angles allows for the bonds to bend less when closing the sphere or tube, and thus, the molecule becomes more stable. Other atoms can be trapped inside fullerenes to form inclusion compounds known as endohedral fullerenes. An unusual example is the egg-shaped fullerene Tb 3 N C 84 , which violates the isolated pentagon rule.
Fullerenes are sparingly soluble in many solvents. Common solvents for the fullerenes include aromatics, such as toluene , and others like carbon disulfide. Solutions of pure buckminsterfullerene have a deep purple color. Solutions of C 70 are a reddish brown. The higher fullerenes C 76 to C 84 have a variety of colors. C 76 has two optical forms, while other higher fullerenes have several structural isomers.
Fullerenes are the only known allotrope of carbon that can be dissolved in common solvents at room temperature. Some fullerene structures are not soluble because they have a small band gap between the ground and excited states. These include the small fullerenes C 28 ,  C 36 and C The C 72 structure is also in this class, but the endohedral version with a trapped lanthanide -group atom is soluble due to the interaction of the metal atom and the electronic states of the fullerene.
Researchers had originally been puzzled by C 72 being absent in fullerene plasma-generated soot extract, but found in endohedral samples. Small band gap fullerenes are highly reactive and bind to other fullerenes or to soot particles. Solvents that are able to dissolve buckminsterfullerene C 60 and C 70 are listed at left in order from highest solubility.
The solubility value given is the approximate saturated concentration. Solubility of C 60 in some solvents shows unusual behaviour due to existence of solvate phases analogues of crystallohydrates.
For example, solubility of C 60 in benzene solution shows maximum at about K. Out of solution, this structure decomposes into usual face-centered cubic fcc C 60 in few minutes' time. At temperatures above solubility maximum the solvate is not stable even when immersed in saturated solution and melts with formation of fcc C Crystallization at temperatures above the solubility maximum results in formation of pure fcc C Millimeter-sized crystals of C 60 and C 70 can be grown from solution both for solvates and for pure fullerenes.
In , researchers from the University of Vienna demonstrated that wave-particle duality applied to molecules such as fullerene. C 76 , C 78 , C 80 , and C 84 are inherently chiral because they are D 2 -symmetric, and have been successfully resolved. Research efforts are ongoing to develop specific sensors for their enantiomers. Two theories have been proposed to describe the molecular mechanisms that make fullerenes. In researchers discovered that asymmetrical fullerenes formed from larger structures settle into stable fullerenes.
The synthesized substance was a particular metallofullerene consisting of 84 carbon atoms with two additional carbon atoms and two yttrium atoms inside the cage. The process produced approximately micrograms. However, they found that the asymmetrical molecule could theoretically collapse to form nearly every known fullerene and metallofullerene. Minor perturbations involving the breaking of a few molecular bonds cause the cage to become highly symmetrical and stable.
This insight supports the theory that fullerenes can be formed from graphene when the appropriate molecular bonds are severed. Fullerene production processes comprise the following five subprocesses: The two synthesis methods used in practice are the arc method, and the combustion method. The latter, discovered at the Massachusetts Institute of Technology , is preferred for large scale industrial production.
Fullerenes have been extensively used for several biomedical applications including the design of high-performance MRI contrast agents, X-ray imaging contrast agents, photodynamic therapy and drug and gene delivery, summarized in several comprehensive reviews.
Polysaccharides serve for the storage of energy e. The 5-carbon monosaccharide ribose is an important component of coenzymes e. The related deoxyribose is a component of DNA. Saccharides and their derivatives include many other important biomolecules that play key roles in the immune system , fertilization , preventing pathogenesis , blood clotting , and development. Starch and sugars are the most important carbohydrates in human diet. They are found in a wide variety of natural and processed foods.
Starch is a polysaccharide. It is abundant in cereals wheat, maize, rice , potatoes, and processed food based on cereal flour , such as bread, pizza or pasta. Sugars appear in human diet mainly as table sugar sucrose, extracted from sugarcane or sugar beets , lactose abundant in milk , glucose and fructose, both of which occur naturally in honey , many fruits, and some vegetables.
Table sugar, milk, or honey are often added to drinks and many prepared foods such as jam, biscuits and cakes. Cellulose, a polysaccharide found in the cell walls of all plants, is one of the main components of insoluble dietary fiber. Although it is not digestible, insoluble dietary fiber helps to maintain a healthy digestive system  by easing defecation.
Other polysaccharides contained in dietary fiber include resistant starch and inulin , which feed some bacteria in the microbiota of the large intestine , and are metabolized by these bacteria to yield short-chain fatty acids.
In scientific literature, the term "carbohydrate" has many synonyms, like "sugar" in the broad sense , "saccharide", "ose",  "glucide",  "hydrate of carbon" or " polyhydroxy compounds with aldehyde or ketone ". Some of these terms, specially "carbohydrate" and "sugar", are also used with other meanings.
In food science and in many informal contexts, the term "carbohydrate" often means any food that is particularly rich in the complex carbohydrate starch such as cereals, bread and pasta or simple carbohydrates, such as sugar found in candy, jams , and desserts.
Often in lists of nutritional information , such as the USDA National Nutrient Database , the term "carbohydrate" or "carbohydrate by difference" is used for everything other than water, protein, fat, ash, and ethanol. It also includes dietary fiber which is a carbohydrate but which does not contribute much in the way of food energy kilocalories , even though it is often included in the calculation of total food energy just as though it were a sugar. In the strict sense, " sugar " is applied for sweet, soluble carbohydrates, many of which are used in food.
Formerly the name "carbohydrate" was used in chemistry for any compound with the formula C m H 2 O n. Following this definition, some chemists considered formaldehyde CH 2 O to be the simplest carbohydrate,  while others claimed that title for glycolaldehyde.
For example, while the above representative formulas would seem to capture the commonly known carbohydrates, ubiquitous and abundant carbohydrates often deviate from this. For example, carbohydrates often display chemical groups such as: Natural saccharides are generally built of simple carbohydrates called monosaccharides with general formula CH 2 O n where n is three or more.
Examples of monosaccharides are glucose , fructose , and glyceraldehydes. However, some biological substances commonly called "monosaccharides" do not conform to this formula e.
Monosaccharides can be linked together into what are called polysaccharides or oligosaccharides in a large variety of ways. Many carbohydrates contain one or more modified monosaccharide units that have had one or more groups replaced or removed. For example, deoxyribose , a component of DNA , is a modified version of ribose ; chitin is composed of repeating units of N-acetyl glucosamine , a nitrogen -containing form of glucose.
Carbohydrates are polyhydroxy aldehydes, ketones, alcohols, acids, their simple derivatives and their polymers having linkages of the acetal type. They may be classified according to their degree of polymerization, and may be divided initially into three principal groups, namely sugars, oligosaccharides and polysaccharides .
Monosaccharides are the simplest carbohydrates in that they cannot be hydrolyzed to smaller carbohydrates. They are aldehydes or ketones with two or more hydroxyl groups. Monosaccharides are important fuel molecules as well as building blocks for nucleic acids. Note the position of the hydroxyl group red or green on the anomeric carbon relative to the CH 2 OH group bound to carbon 5: Monosaccharides are classified according to three different characteristics: If the carbonyl group is an aldehyde , the monosaccharide is an aldose ; if the carbonyl group is a ketone , the monosaccharide is a ketose.
Monosaccharides with three carbon atoms are called trioses , those with four are called tetroses , five are called pentoses , six are hexoses , and so on. For example, glucose is an aldohexose a six-carbon aldehyde , ribose is an aldopentose a five-carbon aldehyde , and fructose is a ketohexose a six-carbon ketone.
Each carbon atom bearing a hydroxyl group -OH , with the exception of the first and last carbons, are asymmetric , making them stereo centers with two possible configurations each R or S. Because of this asymmetry, a number of isomers may exist for any given monosaccharide formula. In the case of glyceraldehydes , an aldotriose, there is one pair of possible stereoisomers, which are enantiomers and epimers.
The assignment of D or L is made according to the orientation of the asymmetric carbon furthest from the carbonyl group: The "D-" and "L-" prefixes should not be confused with "d-" or "l-", which indicate the direction that the sugar rotates plane polarized light. This usage of "d-" and "l-" is no longer followed in carbohydrate chemistry.
The aldehyde or ketone group of a straight-chain monosaccharide will react reversibly with a hydroxyl group on a different carbon atom to form a hemiacetal or hemiketal , forming a heterocyclic ring with an oxygen bridge between two carbon atoms. Rings with five and six atoms are called furanose and pyranose forms, respectively, and exist in equilibrium with the straight-chain form.
During the conversion from straight-chain form to the cyclic form, the carbon atom containing the carbonyl oxygen, called the anomeric carbon , becomes a stereogenic center with two possible configurations: The oxygen atom may take a position either above or below the plane of the ring. The resulting possible pair of stereoisomers is called anomers.
Monosaccharides are the major source of fuel for metabolism , being used both as an energy source glucose being the most important in nature and in biosynthesis.
When monosaccharides are not immediately needed by many cells they are often converted to more space-efficient forms, often polysaccharides. In many animals, including humans, this storage form is glycogen , especially in liver and muscle cells.
In plants, starch is used for the same purpose. The most abundant carbohydrate, cellulose , is a structural component of the cell wall of plants and many forms of algae. Ribose is a component of RNA. Deoxyribose is a component of DNA. Lyxose is a component of lyxoflavin found in the human heart. Galactose , a component of milk sugar lactose , is found in galactolipids in plant cell membranes and in glycoproteins in many tissues.
Mannose occurs in human metabolism, especially in the glycosylation of certain proteins. Fructose , or fruit sugar, is found in many plants and in humans, it is metabolized in the liver, absorbed directly into the intestines during digestion , and found in semen.
Trehalose , a major sugar of insects, is rapidly hydrolyzed into two glucose molecules to support continuous flight. Two joined monosaccharides are called a disaccharide and these are the simplest polysaccharides. Examples include sucrose and lactose. They are composed of two monosaccharide units bound together by a covalent bond known as a glycosidic linkage formed via a dehydration reaction , resulting in the loss of a hydrogen atom from one monosaccharide and a hydroxyl group from the other.
The formula of unmodified disaccharides is C 12 H 22 O Although there are numerous kinds of disaccharides, a handful of disaccharides are particularly notable. Sucrose , pictured to the right, is the most abundant disaccharide, and the main form in which carbohydrates are transported in plants.
It is composed of one D-glucose molecule and one D-fructose molecule. Lactose , a disaccharide composed of one D-galactose molecule and one D-glucose molecule, occurs naturally in mammalian milk. Disaccharides can be classified into two types: If the functional group is present in bonding with another sugar unit, it is called a reducing disaccharide or biose.
Carbohydrate consumed in food yields 3. Lower amounts of carbohydrate are usually associated with unrefined foods, including beans, tubers, rice, and unrefined fruit. Organisms typically cannot metabolize all types of carbohydrate to yield energy. Glucose is a nearly universal and accessible source of energy. Many organisms also have the ability to metabolize other monosaccharides and disaccharides but glucose is often metabolized first.
In Escherichia coli , for example, the lac operon will express enzymes for the digestion of lactose when it is present, but if both lactose and glucose are present the lac operon is repressed, resulting in the glucose being used first see: Polysaccharides are also common sources of energy.
Many organisms can easily break down starches into glucose; most organisms, however, cannot metabolize cellulose or other polysaccharides like chitin and arabinoxylans.
These carbohydrate types can be metabolized by some bacteria and protists. Ruminants and termites , for example, use microorganisms to process cellulose. Even though these complex carbohydrates are not very digestible, they represent an important dietary element for humans, called dietary fiber.
Fiber enhances digestion, among other benefits. Nutritionists often refer to carbohydrates as either simple or complex. However, the exact distinction between these groups can be ambiguous. The term complex carbohydrate was first used in the U. Senate Select Committee on Nutrition and Human Needs publication Dietary Goals for the United States where it was intended to distinguish sugars from other carbohydrates which were perceived to be nutritionally superior.