From Big Medical Encyclopedia

CARBON (Carboneum, C) — chemical element of the main subgroup

of the IV group of a periodic system of D. I. Mendeleyev; the major biogenic element making a basis of organic compounds to-rye participate in creation of live organisms and maintenance of their life activity.

From atoms U. the skeleton of molecules of proteins (see), carbohydrates (with - m), nucleic acids (see), lipids (see), vitamins (see), hormones (see), various mediators (see), etc. consists. Emergence of life (see Life) on Earth is considered as complex process of evolution of carbonaceous connections. Sources At. on Earth served methane (see) and HCN hydrogen cyanide (see. Cyanhydric acid) primary atmosphere. With emergence of life the only source At. for formation of organic matter of the biosphere carbon dioxide gas of the biosphere is. Depending on the chemical form of carbon used by living cells the last divide into autotrophic (autotrophs) and heterotrophic (heterotrophs). Autotrophic cells as the only source At. can use C02, forming of it all carbon-containing components of a cell; all photosynthesizing cells concern to them (cai. Photosynthesis) and nek-ry bacteria (see). Heterotrophic cells are not capable to acquire C02 and shall receive At. in the form of rather complex recovered organic compounds; cells of the highest animals and the majority of microorganisms belong to such cells. Green plants carry out photosynthesis — education from atmospheric C02 organic. substances thanks to a radiant energy of the Sun (annually by means of photosynthesis on Earth assimilates apprx. 100 billion t of C02).

The microorganisms acquiring C02 by so-called chemosynthesis use for formation of organic compounds (see) energy of oxidation of inorganic matters. The organic compounds and oxygen (see) formed by autotrophic organisms serve for maintenance of life activity of heterotrophs (see. Food chains). In the course of life activity of live organisms, generally due to tissue respiration (see biological oxidation), organic compounds are exposed to an oxidative breakdown and C02 is released to the environment. Transformation of a part of organic compounds into C02, returned to the atmosphere, is carried out also during the rotting (see), fermentation (see), burning, etc. The remained organic matter turns into sapropel, a humus, peat, to-rye give rise to other so-called kaustobioli-tics — coals, oil, gases. Thus circulation is carried out At. in the nature. In active circulation At. only its small part participates. Annual education At. in the form of organic weight makes 1,5-1011 t. Annual balance At. for the atmosphere the hl is defined. obr. quantity At., used on formation of mass of plants, and C02 coming to the atmosphere at decomposition of organic matter of the soil; a significant amount of C02 is allocated also at volcanic activity. Increase in maintenance of C02 in the atmosphere causes temperature increase of air (so-called greenhouse effect). At temperature increase the mass of plants increases, reducing concentration of C02 in the atmosphere; there is also an acceleration of decomposition of organic matter to C02. The economic activity of the person leading to allocation of C02 in fuel combustion process and operation of power plants, and also deforestation cause an imbalance of flows At. from the atmosphere to plants and from the soil in the atmosphere, to-ry, in turn, leads to changes of concentration of C02 in the atmosphere and air temperature.

At. has two stable isotopes with mass numbers 12 (98,89%) and 13 (1,11%), and also six radioisotopes with mass numbers 9, 10, 11, 14, 15, 16. Five of these isotopes ultra-short-lived with the half-lives which are estimated seconds and minutes, one of them — short-lived isotope 1HS (half-life of 20,38 min.) found application in biol. researches and in radio isotope diagnosis (see). Connections, marked 14C (half-life of 5730 years), widely use in biochemistry, phytophysiology and animals, pharmacology, microbiology and other fields of biology and medicine. With their help, in particular, the mechanism of important stages of photosynthesis is found out; marked 14C connections successfully apply in studying of a structure of molecules of proteins and nucleinic to - t, the mechanism of synthesis and exchange nucleinic to - t, proteins, fats, carbohydrates and nek-ry other biologically active agents in a live organism.

14C it is constantly formed in the atmosphere of Earth of nitrogen under the influence of neutrons of space radiation and contains in it in concentration apprx. 2 - 1010% on weight, participating in the general circulation of U. Obrazuyushchiysya in the atmosphere 14C it is acquired by vegetable and animal organisms, and after their death contents in them 14C decreases under the law of radioactive decay. On atom the method of radio-carbon dating, i.e. any age determination of substances and objects of a biogenic origin, and also geological formations of the carbonate nature which found broad application is based.

Artificially 14C receive by long radiation by neutrons in nuclear reactors of nitrogen-containing targets. The domestic industry numerous connections, marked 14C are issued.

The PS short-lived isotope is usually received on a cyclotron bombing of the targets containing boron, protons or deuterons allocate from flowing gas targets in the form of 11 CO or X1C02 and applied in medicine (see Radiofarmatsevti-chesky drugs).

14C breaks up with emission (3 particles with the maximum energy of ER - = = 0,155 Mei (100%), accompanying 7 radiations have no. “With breaks up with emission of positrons with the maximum energy of E3+ = 0,9608 Mei (99,7%) and partially (0,24%) — by electron capture. At the same time annihilation radiation with Et = 0,51 Mei (apprx. 200%), on Krom usually is formed and define this radionuclide.

On radio toxicity 14C carry to group G (in a workplace without the permission of service of the State sanitary inspection the open drugs containing 14C, activity to 100 mkkyura or 3,7 MBK can be used).

In the nature At. meets in a free look and in the form of connections with other elements. Crystal modifications are known At.: cubic — diamond and hexagonal — graphite and lonsdaleite (see Polymorphism in chemistry). Graphite represents gray-black opaque soft weight. At. in the form of coke, soot, wood charcoal possesses the random amorphous structure, the cut is the cornerstone of a structure structure of fine-crystalline graphite. Diamond — exclusively firm (hardness is equal 10 on Mohs scale) crystal substance. Lonsdaleite is found as a part of meteorites and received artificially. Karbin — artificially received form U., represents fine-crystalline powder of black color, in structure to-rogo a chain of atoms U. are laid in parallel each other. Diamond and graphite widely apply in the equipment, the industry, and also in medicine and medical - biol. researches. «Amorphous» At. use as fuel and as a reducer in metallurgy, in medicine and medical - biol. researches — as effective adsorbent.

On prevalence on Earth At. takes the 13th place, and in the Sun — the 4th place (after hydrogen, helium and oxygen). At. it is found also in space. Content At. in crust makes 2,3 * 10 "2% but weight. In the biosphere concentration At. much higher. In living material U. contains apprx. 18%, in wood — 50%, black coal — 80%, oil — 85%, anthracite — 96%. In the atmosphere At. there is a hl. obr. in the form of C02 (0,03% on volume). In crust the most widespread inorganic compounds U. carbonates (see), carbonates and bicarbonates are. Many minerals are carbonates of metals. Carbonates and bicarbonates of alkali metals (see) and alkaline earth metals (see), and also a large amount of carbon dioxide is dissolved in waters of the terrestrial hydrosphere. In crust there are extensive stocks organic At. as a part of black and brown coals, peat, oil shales, oil, asphalt, combustible gases. In nonvolatile solid of plants At. 45%, and contain in an organism of animals — apprx. 60% (according to other data, contents At. in live organisms in terms of nonvolatile solid makes 34,5 — 40% at water plants and animals, 45,4 — 46,5% at geophytes and animals, 54% at bacteria).

In connections U. shows valencies — 4, +2, - (-4. In usual conditions At. it is chemically inert, and at high temperatures it is capable to connect to many elements, showing strong recovery properties. Connections U are known. with halogens — halogenides, including perchloromethane (see), the mixed fluoride-chloride of carbon — CF2C12 freon and oksigalo-genida, napr, chloroxide of COC12 carbon — phosgene (see. Suffocating toxic agents). With sulfur (see) carbon forms carbon sulfur (see), with nitrogen (see) — cyan (CN)2. Connection U. with nitrogen and hydrogen (see) — hydrocianic to - that and cyanic connections (see. Cyanhydric acid) treat the strongest poisons (see). At direct interaction with metals U. forms the carbides which are widely used in the industry (e.g., Sas2 calcium carbide). Connection U. with silicon — the carborundum of SiC on hardness concedes only to diamond. With oxygen U. forms the SO toxic carbon oxide (see Carbon monoxide), C02 carbon dioxide (see Anhydride of carbonic acid) and nedooksid C302 carbon. At dissolution of C02 in water it turns out coal to - that, playing a large role in maintenance of acid-base balance (see) in a human body and animals. Connections U are of special interest. with hydrogen — hydrocarbons (see). The majority

of sky connections known to an organicha can be considered derivatives of hydrocarbons, in to-rykh one or several hydrogen atoms are replaced with atoms or groups of atoms of other elements. Emergence of huge number of connections U., studied by organic chemistry (see), it is caused by unique ability of atoms U. to form the strong chains and cycles based on stable carbon-to-carbon linkages. At. forms also double and acetylene bonds. Thus there are frameworks of infinite number of organic molecules: linear,


branched, cyclic. Owing to easy formation of bonds At. with oxygen, hydrogen, nitrogen and sulfur organic molecules can join considerable number of various functional groups. The coupled electrons form around each atom U. a tetrahedral configuration therefore different types of organic molecules have three-dimensional structure. One of the reasons of a variety of organic compounds is their isomerism (see). Any of the known chemical elements, except At., cannot be a basis for stable molecules with so various configurations, the sizes and functional groups.

In medicine elementary At. under the name Carbo activatus, or Carbolenum, apply at dyspepsia (see), a meteorism (see), food and other poisonings (see) as medicine. Connections elementary At., napr, its dioxide, use in anesthesiology, dermatology and other fields of medicine.

Bibliography: Calvin M. Chemical evolution, M., 1971; Levi A. and Xing in both F. Struktur's c and function of a cell, the lane with English, page 119, M., 1971; L e-in and V. I N. Receiving radioisotopes, M., 1972; Nenitsesku K. The general chemistry, the lane from Romanians., page 460, M., 1968; X e in e sh and. Radiotracers, their use in biochemistry, normal physiology and pathological human physiology and animals, the lane with English, M., 1950; Table of isotopes, ed.

by C. M. Lederer a. V. S. Shiley, N. Y. a. o., 1978. H. V. Gulyaeva; V. V. Bochkaryov (I am glad.).