Cellulose is an
organic compoundwith the formula chem|(C|6|H|10|O|5|)|n, a polysaccharideconsisting of a linear chain of several hundred to over ten thousand β(1→4) linked D- glucoseunits.cite book
author=Crawford, R. L.
title=Lignin biodegradation and transformation
publisher=John Wiley and Sons
location = New York
id=ISBN 0-471-05743-6 ] [cite journal
title=Semimicro determination of cellulose in biological materials
year=1969 | volume=32 | pages=420 – 424
Cellulose is the structural component of the primary
cell wallof green plants, many forms of algaeand the oomycetes. Some species of bacteriasecrete it to form biofilms.Cellulose is the most common organic compound on Earth. About 33 percent of all plant matter is cellulose (the cellulose content of cottonis 90 percent and that of wood is 50 percent). [Cellulose. (2008). In " Encyclopædia Britannica". Retrieved January 11, 2008, from Encyclopædia Britannica Online.]
For industrial use, cellulose is mainly obtained from
wood pulpand cotton. It is mainly used to produce cardboardand paper; to a smaller extent it is converted into a wide variety of derivative products such as cellophaneand rayon.
Some animals, particularly
ruminants and termites, can digest cellulose with the help of symbiotic micro-organisms that live in their guts. Cellulose is not digestible by humans and is often referred to as ' dietary fiber' or 'roughage', acting as a hydrophilicbulking agent for feces.
Cellulose was discovered in 1838 by the French chemist
Anselme Payen, who isolated it from plant matter and determined its chemical formula.cite book
last = Young
first = Raymond
title = Cellulose structure modification and hydrolysis
publisher = Wiley
location = New York
year = 1986
isbn = 0471827614 ] Cellulose was used to produce the first successful thermoplastic polymer,
celluloid, by Hyatt Manufacturing Company in 1870. Hermann Staudingerdetermined the polymer structure of cellulose in 1920. The compound was first chemically synthesized (without the use of any biologically-derived enzymes) in 1992, by Kobayashi and Shoda.Cite journal
volume = 36
issue = 36
last = Klemm
first = Dieter
coauthors = Brigitte Heublein, Hans-Peter Fink, Andreas Bohn
title = Cellulose: Fascinating Biopolymer and Sustainable Raw Material
journal = ChemInform
date = 2005 | doi = 10.1002/chin.200536238 ]
Cellulose is the major constituent of paper and cardboard and of textiles made from
cotton, linen, and other plant fibers.
Cellulose can be converted into
cellophane, a thin transparent film, and into rayon, an important fiber that has been used for textiles since the beginning of the 20th century. Both cellophane and rayon are known as "regenerated cellulose fibers"; they are identical to cellulose in chemical structure and are usually made from viscose, a viscoussolution made from cellulose. A more recent and environmentally friendly method to produce rayon is the Lyocellprocess.
Cellulose is used in the laboratory as the stationary phase for thin layer chromatography. It is the raw material in the manufacture of
nitrocellulose(cellulose nitrate) which was historically used in smokeless gunpowder and as the base material for celluloidused for photographic and movie films until the mid 1930s. Cellulose insulationmade from recycled newsprint is becoming popular as an environmentally preferable material for building insulation.
Cellulose is used to make
hydrophilicand highly absorbent sponges, as well as water-soluble adhesivesand binders such as methyl celluloseand carboxymethyl cellulosewhich are used in wallpaperpaste. Microcrystalline cellulose(E460i) and powdered cellulose (E460ii) are used as inactive fillers in tablets and as thickeners and stabilizers in processed foods.
Cellulose source and energy crops
The major combustible component of non-food
energy crops is cellulose, with ligninsecond. Non-food energy crops are more efficient than edible energy crops (which have a large starchcomponent), but still compete with food crops for agricultural land and water resources. [Holt-Gimenez, Eric 2007. Biofuels: Myths of the Agrofuels Transition. "Backgrounder." Institute for Food and Development Policy, Oakland, CA. 13:2] Typical non-food energy crops include industrial hemp, switchgrass, " Miscanthus", "Salix" ( willow), and "Populus" ( poplar) species.
Some bacteria can convert cellulose into
ethanolwhich can then be used as a fuel; see cellulosic ethanol.
tructure and properties
Cellulose has no taste, is odourless, is
hydrophilic, is insoluble in waterand most organic solvents, is chiral and it is biodegradable.
Cellulose is derived from D-glucose units, which condense through β(1→4)-
glycosidic bonds. This linkage motif contrasts with that for α(1→4)-glycosidic bonds present in starch, glycogen, and other carbohydrates. Cellulose is a straight chain polymer: unlike starch, no coiling occurs, and the molecule adopts an extended and rather stiff rod-like conformation. The multiple hydroxyl groups on the glucose residues from one chain form hydrogen bonds with oxygen molecules on another chain, holding the chains firmly together side-by-side and forming "microfibrils" with high tensile strength. This strength is important in cell walls, where they are meshed into a carbohydrate "matrix", conferring rigidity to plant cells.
Compared to starch, cellulose is also much more crystalline. Whereas starch undergoes a crystalline to amorphous transition when heated beyond 60-70 °C in water (as in cooking), cellulose requires a temperature of 320 °C and pressure of 25 MPa to become amorphous in water."Cooking cellulose in hot and compressed water" Shigeru Deguchi, Kaoru Tsujii and Koki Horikoshi
Chem. Commun., 2006, 3293 - 3295, DOI|10.1039/b605812d]
Chemically, cellulose can be broken down into its glucose units by treating it with concentrated acids at high temperature.
Many properties of cellulose depend on its
degree of polymerizationor chain length, the number of glucose units that make up one polymer molecule. Cellulose from wood pulp has typical chain lengths between 300 and 1700 units; cotton and other plant fibers as well as bacterial celluloses have chain lengths ranging from 800 to 10,000 units. Molecules with very small chain length resulting from the break down of cellulose are known as cellodextrins; in contrast to long-chain cellulose, cellodextrins are typically soluble in water and organic solvents.
Plant-derived cellulose is usually contaminated with
hemicellulose, lignin, pectinand other substances, while microbial celluloseis quite pure, has a much higher water content, and consists of long chains.
Given a cellulose-containing material, the portion that does not dissolve in a 17.5% solution of
sodium hydroxideat 20 °C is "α cellulose", which is true cellulose. Acidification of the extract precipitates "β cellulose". The portion that dissolves in base but does not precipitate with acid is "γ cellulose".
Cellulose can be assayed using a method described by Updegraff in 1969, where the fiber is dissolved in acetic and
nitric acidto remove lignin, hemicellulose, and xylosans. The resulting cellulose is allowed to react with anthronein sulfuric acid. The resulting coloured compound is assayed spectrophotometrically at a wavelength of approximately 635 nm.
In addition, cellulose is represented by the difference between acid detergent fiber (ADF) and acid detergent lignin (ADL).
vascular plants cellulose is synthesized at the plasma membraneby rosette terminal complexes (RTC's). The RTC's are hexameric protein structures, approximately 25 nm in diameter, that contain the cellulose synthaseenzymes that synthesise the individual cellulose chains. [Kimura, Laosinchai, Itoh, Cui, Linder, Brown, "Plant Cell", 1999, 11, "'2075-2085] Each RTC floats in the cell's plasma membrane and "spins" a microfibril into the cell wall.
The RTC's contain at least three different cellulose synthases, encoded by "CesA" genes, in an unknown
stoichiometry. [Taylor, Howells, Huttly, Vickers, Turner, "PNAS", 2003, 100, 1450-1455] Separate sets of "CesA" genes are involved in primary and secondary cell wallbiosynthesis. Cellulose synthase utilizes UDP-D-glucose precursors to generate microcrystalline cellulose. Cellulose synthesis requires chain initiation and elongation, and the two processes are separate. "CesA" glucosyltransferaseinitiates cellulose polymerization using a steroidprimer, sitosterol-beta- glucoside, and UDP-glucose. [Peng, Kawagoe, Hogan, Delmer, "Sitosterol-beta-glucoside as primer for cellulose synthesis in plants", "Science", 2002, 295, 147-150. PMID 11778054] A cellulasemay function to cleave the primer from the mature chain.
Cellulolysis is the process of breaking down cellulose into smaller polysaccharides called
cellodextrinsor completely into glucose units; this is a hydrolysisreaction. Because cellulose molecules bind strongly to each other, cellulolysis is relatively difficult compared to the break down of other polysaccharides. [David G. Barkalow, Roy L. Whistler, "Cellulose", in AccessScience@McGraw-Hill, DOI 10.1036/1097-8542.118200. Retrieved 11 January 2008.]
Mammals do not have the ability to break down cellulose directly. Some
ruminants like cows and sheep contain certain symbiotic anaerobicbacteria (like " Cellulomonas") in the flora of the gut wall, and these bacteria produce enzymes to break down cellulose; the break down products are then used by the mammal. Similarly, lower termites contain in their hindguts certain flagellate protozoawhich produce such enzymes; higher termites contain bacteria for the job. Fungi, which in nature are responsible for recycling of nutrients, are also able to break down cellulose.
The enzymes utilized to the
glycosidic linkagein cellulose are glycoside hydrolases including endo-acting cellulases and exo-acting glucosidases. Such enzymes are usually secreted as part of multienzyme complexes that may include dockerins and cellulose binding modules; these complexes are in some cases referred to as cellulosomes.
Hemicelluloseis a polysaccharide related to cellulose that comprises ca. 20% of the biomass of most plants. In contrast to cellulose, hemicellulose is derived from several sugars in addition to glucose, including especially xylosebut also mannose, galactose, rhamnose, and arabinose. Hemicellulose consists of shorter chains - around 200 sugar units as opposed to 7,000 - 15,000 glucose molecules in the average cellulose polymer. Furthermore, hemicellulose is branched, whereas cellulose is unbranched.
hydroxylgroups of cellulose can be partially or fully reacted with various reagents to afford derivatives with useful properties. Cellulose esters and cellulose ethers are the most important commercial materials. In principle, though not always in current industrial practice, cellulosic polymers are renewable resources.
Among the esters are
cellulose acetateand cellulose triacetate, which are film- and fiber-forming materials that find a variety of uses. The inorganic ester nitrocellulosewas initially used as an explosive and was an early film forming material.
Ether derivatives include
Ethylcellulose, a water-insoluble commercial thermoplastic used in coatings, inks, binders, and controlled-release drug tablets;
Hydroxypropyl methyl cellulose, E464, used as a viscosity modifier, gelling agent, foaming agent and binding agent;
* Hydroxyethyl methyl cellulose, used in production of cellulose films.
Cellulosic ethanol commercialization
* [http://www.lsbu.ac.uk/water/hycel.html LSBU cellulose page]
* [http://msa.ars.usda.gov/la/srrc/fb/ca.html Clear description of a cellulose assay method] at the Cotton Fiber Biosciences unit of the USDA.
* [http://www.technologyreview.com/read_article.aspx?ch=infotech&sc=&id=17127&pg=1 Cellulose films could provide flapping wings and cheap artificial muscles for robots] - TechnologyReview.com
* [http://www1.eere.energy.gov/biomass/cellulase_enzyme.html Using cellulase enzymes in the bioethanol process] .
* [http://www.wzw.tum.de/mbiotec/cellmo.htm A list of cellulolytic bacteria] .
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