CELLULOSE

From Big Medical Encyclopedia

CELLULOSE (a synonym cellulose) — polysaccharide, linear stralght chains to-rogo are constructed generally of constitutional repeating units of An - hydro - In - glucose, connected among themselves 1,4-| by 3-glucosidic bonds:

C., contained in food, is one of the main ballast



substances, or the food fibers playing extremely important role in normal food and digestion (see Carbohydrates, in food). These fibers are not digested in went. - kish. a path, but promote its normal functioning, and also can occlude on themselves nek-ry toxins, interfering with their absorption in intestines. Microcrystallic C. it is widely used in pharmaceutical industry as a filler at production of medicines. Not replaced C., and also C., the containing ionogenic groups (e.g., DEAE-tsellyulo-za), are widely used in biol. and medical researches for division and purification of biologically active agents. C. and its derivatives apply during the receiving synthetic fibers, and also in the chemical industry.

C. — the main component of plants, the contained hl. obr. in walls -


ka of plant cells. It occurs also in nek-ry bacteria and at a number of the lowest animals. Maintenance of C. in fibers of cotton seeds reaches 95 — 98%, in bast fibers of flax, jute, Rami — 60 — 85%; tree species contain up to 50% of cellulose in terms of nonvolatile solid.

Polymerization degree vegetable C. fluctuates over a wide range — from 1400 to 14 000 that there corresponds the pier. to the weight (weight) 250 000 to 2 200 000. Pier. weight of bacterial C. makes from 600 000 to 1 000 000. Along with Angidro-B-glucose of a macromolecule C. may contain the remains of other monosaccharides of hexoses (see), pentoses (see), and also at fatal acids (see).

Long straight chains of macromolecules C. easily enter intermolecular interactions with formation of elementary fibrilla. Molecules C., being a part of elementary fibrilla, longwise are extended; in the diameter they are densely packed into the high-arranged crystal structure stabilized by hydrogen bindings. In total 36 chains of cellulose participate in formation of elementary fibrilla. Next molecules C. glucosidic bonds of the next molecules C are oriented antiparallelno, i.e. have an opposite direction. Between couples of antiparal-lelny chains of C. strong hydrogen bindings are formed. Elementary fibrilla aggregates among themselves with formation of microfibrils. At the same time along with the arranged crystal sites in microfibrils there are amorphous (less arranged) sites which are characterized by more friable packaging of chains of cellulose. Reactivity of amorphous sites of microfibrils of C. much higher than reactivity of crystal sites C. Microfibrils of C. make a mechanical basis of cell walls of plants. The fastening of microfibrils with each other in cell walls is carried out by hemicelluloses, pectic substances and a lignin.

Wet C. it is elastic, dry — is in a so-called vitreous state. Temperature of melting of C. higher than temperature of its decomposition; glass transition temperature of cellulose apprx. 220 °. Cellulose is not dissolved neither in water, nor in organic solvents. It is a rastvorima only in water solutions of complex connections of hydroxides of nek-ry polyvalent metals with ammonia or amines, napr, in ammoniac solution of copper oxide, and also in the concentrated solution of zinc chloride. Rast-


cooking of cellulose in 80 — 95% phosphoric to - those and in the concentrated chamois to - those is followed by partial destruction of polymer.

The glucosidic bonds connecting the remains of glucose in polymer chains of C., are rather easily hydrolyzed under the influence of mineral to - t. Products of partial acid hydrolysis of C. call hydrocellulose. Careful acid hydrolysis of native microfibrils of C. leads to a rupture of glucosidic bonds almost only in amorphous sites of polymer. This circumstance is used for receiving microcrystallic by C. Full acid hydrolysis of C. leads to formation of glucose (see) — a key product for receiving alcohol (see) an industrial way.

Oxidation of C. and its reaction with the concentrated solutions of alkalis is applied to production of viscose. Etherification and Au-alkiliro-vaniye of C. lead to education difficult and ethers C., the synthetic fibers used in production. Reaction of nitration of C. is the cornerstone of methods of production of nitrovarnishes, and also smokeless powder (guncotton).

For receiving C. from wood the sulphitic method consisting in processing of tsellyulozosoderzhashchy raw materials mix of calcium bisulphite (or sodium) and sulphurous to - you is most often applied at the increased temperature and pressure. Such procedure leads to extraction from wood of the accompanying C. lignin, hemicellulose, pectic substances, etc. Processing of wood raw materials caustic soda (a soda method) is also used for industrial production of C.

Biosynthesis of C. it is carried out by means of a tsellyulozosintaza, the enzyme catalyzing transfer of glucose from a guanidindifosfatglyu-goat (Gdfglyukoza) and (or) from at a ridindifosfatglyukoza (U D Fglyu-koza) to a molecule of polymer acceptor. Zymolysis of C. it is catalyzed by a complex it is whole-lyulaz, the C consisting from endo-and ekzo-tsellyulaz and r-glucosidases and leading to consecutive hydrolysis. to tsellooligosakharid of various polymerization degree, cellobiose, and eventually to glucose.

Bibliography: Bochkova. T., Afa

having pressed V. A. and 3 and and to about in G. E. Carbohydrates, M., 1980; R about about in and N 3. A. Himiya of cellulose, M., 1972; Stepanenko

B. N. Chemistry and biochemistry of carbohydrates (polysaccharides), M., 1978; Cellulose and its derivatives, under the editorship of N. Bayklz and L. Segal, lane with English, t. 1 — 2, M.,

1974. D. M. Belenky.

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