Cellulose

A Glucosedimer represented in chair conformation ( cellobiose unit )

White odorless powder

Fixed

~ 1.5 g/cm3

Insoluble in water

Cellulose (often cellulose) is the major constituent of plant cell walls ( mass fraction of approximately 50% ) and thus the common organic compound, and also the most abundant polysaccharide ( multiple sugar). Is unbranched, and is comprised of several hundred to tens of thousands of β -D-glucose molecules ( β -1 ,4- glycosidic bond ) or cellobiose units. The cellulose molecules self-assemble into higher structures that have a high tensile strength fibers in plants often static functions. Cellulose is important as a raw material for paper making, but also in the chemical industry and other fields.

  • 5.1 raw material
  • 5.2 food 5.2.1 Animals
  • 5.2.2 cellulase record from animals ( termites)
  • 5.2.3 bacteria, fungi and flagellates

History

Cellulose was discovered in 1838 by the French chemist Anselme Payen, who isolated it from plants and their specific chemical formula. Cellulose was used in the year 1870 by Hyatt Manufacturing Company is the first to Plastomer, celluloid to produce. Hermann Staudinger determined in 1920 the structure of cellulose. 1992 cellulose was chemically synthesized for the first time by Kobayashi and Shoda ( without the help of bio -based enzymes).

Chemistry

Cellulose is a polymer (polysaccharide, multiple sugar ') from the monomer cellobiose, a disaccharide (, double sugar '). The monomers are linked by β -1 ,4 -glycosidic bonds. Cellobiose itself consists of two molecules of monosaccharide (, simple sugar ') glucose. Here also there is a β -1 ,4- glycosidic bond, so that often the glucose is defined as a monomer of the cellulose.

The linking of the monomers is carried out by a condensation reaction in which two hydroxyl groups (-OH), a water molecule (H2O) and the remaining oxygen atom form the ring-shaped base structure ( pyran ) connects the two monomers. In addition to this strong, covalent bond, the less strong hydrogen bonds are formed intramolecularly in addition. Often there is a cellulose molecule of several thousand glucose units.

Properties

Cellulose is insoluble in water and in most organic solvents. Solvents such as dimethylacetamide / lithium chloride or dimethyl sulfoxide / tetrabutylammonium fluoride and Ammoniak/Cu2 ( Schweizer's reagent ) are able, however, to solve cellulose. It may be cleaved by strong acids. With concentrated acids at elevated temperature, the cellulose can be broken down into glucose by the glycosidic bonds are cleaved.

The chemical company BASF has developed an injection method, is purely physically dissolved in the cellulose in an ionic liquid. This solution can be used for chemical synthesis, which were previously not possible.

Metabolism

Biosynthesis

In most plants, cellulose has a fundamental importance as a structural substance. And woody fibers nichtverholzenden plants consist of a plurality of fibrils, which in turn consist of a number of, mutually parallel cellulose molecules. Cellulose microfibrils are synthesized in the plasma membrane of a cell in the so-called rosette complexes. These contain the enzyme cellulose synthase which is β -D-glucans prepared ( D-glucose polymers having β - bonding), thereby linking the first carbon atom of D-glucose molecule, with the fourth carbon atom of another D-glucose molecule. The production of the glucan chain requires two essential steps. First splitting the disaccharide sucrose synthase ( disaccharide ) sucrose in its monomers, glucose and fructose, in order to provide as glucose. The glucose is now linked by the cellulose synthase with uridine diphosphate (UDP) UDP -glucose. In a further step, the bound glucose is transferred to the non-reducing sugar of the growing glucan chain. Then the glucan or the enzyme moves further, so that another step of the synthesis can take place.

Cellulose is formed in the plasma membrane and cross-linked with each other to fibrous structures. Subsequently, the spatial arrangement of cellulose fibrils by microtubules occurs.

Reduction

Since plants produced even install cellulose in their cell walls, they require endogenous cellulases for the conversion of cell walls, for example, in growth processes. In the plant cellulase is a very old gene.

Use

Mainly consisting of cellulose plant material is used by humans at least since the Paleolithic as fuel for cooking and heating. Cellulose is next to an important raw material for materials production, but also as a natural or of added components of food and feed is important. Since cellulose also occurs in almost all types of plant biomass, it is also important in many other areas, such as in wood ( lignocellulose ) as a building material, etc.

Commodity

Cellulose is an important raw material for making paper. As a starting raw material, the lignin and cellulose- rich wood used. From this pulp is prepared, which is used for paper less high quality. By removing the lignin pulp can be used, which is mainly composed of cellulose and can be used for higher quality papers.

In the clothing industry, mainly composed of cellulosic plant fibers are used for various materials. Examples are cotton and bast fibers of flax ( flax), which are processed into linen.

Another regenerated cellulose is cellophane ( cellulose ), which is a common packaging material in the form of films. Synthetic cellulose fibers ( "Cell wool" ) can be produced. For this purpose, an alkaline solution of cellulose xanthogenierter ( " viscose " solution ) is processed into fibers, the so-called regenerated fiber (eg viscose).

A wide variety of cellulose derivatives are widely used, such as methyl cellulose, cellulose acetate and cellulose nitrate in the construction, textile and chemical industries. Derived from cellulose nitrate celluloid, the first thermoplastic.

Since cellulose is available in large quantities in nature, it will try to make this renewable resource, for example, as a biofuel cellulosic ethanol available. Currently, intensive research in order to develop plant biomass, especially as wood and straw, for it.

Cellulose can also serve as a natural insulation material. These assorted newspaper is crushed in a mechanical process first. The cellulose insulation material obtained can be seamlessly injected and used for heat insulation and sound insulation. The injection method is applied in Canada and the United States since about 1940. Advantage of this insulation material is the most environmentally friendly production, or the continued use of assorted newspaper.

In the laboratory, it may be used in the separation of mixtures of materials as filling material for the column chromatography.

Food

Animals

Almost all animals - except for a few mollusks, such as some snails, such as the snail and less termite species - including most herbivores can cellulose as opposed to strength not degrade through its own metabolic activities, although both molecules are made up of glucose molecules. These animals have only the enzymes α -1, 4 - or α -1 ,6 -glycosidic bonds capable of cleaving ( for example, starch) ( amylases ), but not β -1 ,4- glucosidic bonds of the cellulose. Therefore, these animals (eg, cows) open up the high energy content of this carbohydrate only with the aid of endosymbiotic prokaryotes that live in their intestines. Cellulose -eating animals then feed on the ever- renewable Symbiontenmasse in their digestive system.

Ruminants digest a large proportion of cellulose and other polysaccharides in the rumen using anaerobic prokaryotes that convert the cellulose into fatty acids. The same is true for horses and water fowl, but in which the processing takes place in the colon.

Man, too, has no digestive enzymes for the degradation of cellulose. With the help of anaerobic bacteria in the first part of the colon, the cecum and the ascending colon, a portion of the cellulose is broken down into short-chain fatty acids from the diet. About the colonic mucosa, they are absorbed and utilized by the metabolism. Cellulose is thus adjacent to hemicellulose, pectin and lignin, an important vegetable dietary fiber in the human diet.

Some terrestrial crustaceans as the Isopoda can degrade cellulose with the support endosymbiotischer bacteria. The same is true for insects such as silverfish, almost all termites, cockroaches or leaf-cutter ants. In 200 termite species investigated more than 450 different endosymbionts were identified. Endosymbionts fossilized termites have been detected from the Cretaceous directly ( in Burmese amber ).

Cellulase record from animals ( termites)

The view that animals generally lack cellulases, however, contradict reports of cellulase evidence of termites. In some species of termites ( Reticulitermes and Coptotermes formosanus speratus ), the cancer Cherax destructor, the nematode Bursaphelenchus xylophilus and the clams Corbicula japonica and Lyrodus pedicellatus cellulase genes were detected.

Bacteria, fungi and flagellates

Many bacteria, fungi, flagellates and can decompose only the cellulose to cellobiose Glucosedimer about their cellulases. Few protozoa and fungi such as Aspergillus, Penicillium and Fusarium species in addition have the required β -1 ,4- glucosidase or cellobiases, which split the cellobiose into glucose. Some wood rotting fungi such as Ceriporiopsis subvermispora can cellobiose using the Cellobiosedehydrogenase ( CDH), an extracellular Hämoflavoenzym, reduce oxidation. Here, instead of glucose produced gluconic acid.

The degradation of cellulose by other hydrolytic enzymes is supported by carbohydrate -binding regions ( CBMs ) of the enzymes.

Food additive

Also in the food and pharmaceutical industries is cellulose or cellulose derivatives are used, for example, as a thickening agent, carrier, filler, release agent, coating agent and foaming agent. As a food additive cellulose carries the designations E 460 to E 466:

The proof is carried out by means of an iodine - zinc chloride solution ( blue color ).

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