Many of the non-protein nitrogen-containing substances are intermediate or end products of the protein metabolism of plant and animal organisms. . Non-protein nitrogen-containing substances are involved in the formation of a specific taste and aroma of products. Some of them stimulate the activity of the digestive glands.

Amino acids are the main structural components of protein molecules and appear in free form in foods mainly in the process of protein breakdown. Free amino acids are found in plant and animal tissues in small quantities. When food is stored, their number increases.

Acid amides are derivatives fatty acids with the general formula RCH 2 CONH 2. They are common in plant and animal products as a natural constituent. These include asparagine, glutamine, urea, etc.

Ammonia compounds are found in foodstuffs in small quantities in the form of ammonia and its derivatives, in particular amines. A significant content of ammonia and amines indicates putrefactive decomposition of proteins. food products. Ammonia derivatives include methylamines CH 3 NH 2, dimethylamines (CH 3) 2 NH, and trimethylamines (CH 3) 3 N which have a specific odor. When the proteins of meat and fish rot, amines that are poisonous to humans are formed - cadaverine, putrescine, histamine .

Nitrates, i.e. salts of nitric acid, as a natural food compound, are found in small quantities, but in some products the amount of nitrates is significant. At present, the maximum permissible concentrations (MPC) of nitrates in various types vegetables and fruits.

In the human body, under the influence of intestinal microflora, nitrates are reduced to nitrites, which are absorbed into the blood and block the centers of respiration. The maximum allowable dose of nitrates for a person should not exceed 5 mg per 1 kg of body weight.

nitrites, in particular, NaNO 2 is added to meat as a preservative in the production of sausages, smoked meats, corned beef, to preserve the pink-red color of finished products. Nitrites are more toxic than nitrates; in the human stomach, nitrosamines are formed from them - the strongest of the currently known chemical carcinogens. The maximum allowable daily dose for them is 0.4 mg per 1 kg of human body weight. The sanitary legislation establishes the maximum allowable norm for the content of nitrites in meat products.

alkaloids - a group of physiologically active nitrogen-containing compounds that have basic properties and have a heterocyclic structure. Many of them in large doses are potent poisons.

Alkaloids include nicotine C 10 H 14 N 2, caffeine C 8 H 10 N 4 O 2 and theobromine C 7 H 8 N 4 O 2. The lethal dose of nicotine for humans is 0.01-0.04 g. A sharp burning taste is given to products by alkaloids - piperine C 17 H 19 O 3 N and piperovatin C 16 H 21 O 2 N (in hot pepper), etc.

Purine nitrogenous bases - adenine C 5 H 5 N 5, guanine C 5 H 5 N 5 O, xanthine, C 5 H 5 N 4 O 2, hypoxanthine C 5 H 4 N 4 O - occur during the hydrolysis of nucleic acids, are found in the muscles of animals and fish, tea, yeast, brain tissue. These are biologically active substances.

Nitro compounds. Nitro compounds are called organic substances, the molecules of which contain a nitro group - NO 2 at the carbon atom.

They can be considered as derivatives of hydrocarbons obtained by replacing a hydrogen atom with a nitro group. According to the number of nitro groups, they distinguish mono-, di- and polynitro compounds.

Names of nitro compounds produced from the names of the original hydrocarbons with the addition of the prefix nitro-:

The general formula of these compounds is R—NO 2 .

The introduction of a nitro group into organic matter is called nitration. It can be carried out in different ways. Nitration of aromatic compounds is easily carried out under the action of a mixture of concentrated nitric and sulfuric acids (the first is a nitrating agent, the second is a water-removing agent):

Trinitrotoluene is well known as an explosive. Explodes only on detonation. Burns with a smoky flame without explosion.

Nitration of saturated hydrocarbons is carried out by the action of dilute hydrocarbons nitric acid with heat and high pressure (reaction of M.I. Konovalov):

Nitro compounds are often also prepared by reacting alkyl halides with silver nitrite:

When reducing nitro compounds, amines are formed.

Nitrogen-containing heterocyclic compounds. Heterocyclic compounds are organic compounds containing rings (cycles) in their molecules, in the formation of which, in addition to the carbon atom, atoms of other elements also take part.

Atoms of other elements that make up the heterocycle are called heteroatoms. The most common heterocycles are nitrogen, oxygen, and sulfur heteroatoms, although there may be heterocyclic compounds with a wide variety of elements having a valence of at least two.

Heterocyclic compounds can have 3, 4, 5, 6 or more atoms in the cycle. However highest value have five- and six-membered heterocycles. These cycles, as in the series of carbocyclic compounds, are formed most easily and are distinguished by the greatest strength. A heterocycle may contain one, two or more heteroatoms.

In many heterocyclic compounds, the electronic structure of bonds in the ring is the same as in aromatic compounds. Therefore, typical heterocyclic compounds are conventionally denoted not only by formulas containing alternating double and single bonds, but also by formulas in which the conjugation of p-electrons is indicated by a circle inscribed in the formula.

For heterocycles, empirical names are usually used.

Five-membered heterocycles

Six-membered heterocycles

Of great importance are heterocycles fused with a benzene ring or with another heterocycle, such as purine:

Six-membered heterocycles. Pyridine C 5 H 5 N - the simplest six-membered aromatic heterocycle with one nitrogen atom. It can be considered as an analogue of benzene, in which one CH group is replaced by a nitrogen atom:

Pyridine is a colorless liquid, slightly lighter than water, with a characteristic unpleasant odor; miscible with water in any ratio. Pyridine and its homologues are isolated from coal tar. Under laboratory conditions, pyridine can be synthesized from hydrocyanic acid and acetylene:

Chemical properties pyridine are determined by the presence of an aromatic system containing six p-electrons and a nitrogen atom with an unshared electron pair.

1. Basic properties. Pyridine is a weaker base than aliphatic amines. Its aqueous solution turns litmus blue:

When pyridine reacts with strong acids, pyridinium salts are formed:

2. aromatic properties. Like benzene, pyridine reacts electrophilic substitution, however, its activity in these reactions is lower than that of benzene due to the high electronegativity of the nitrogen atom. Pyridine nitrates at 300 ° With low output:

The nitrogen atom in electrophilic substitution reactions behaves as a substituent of the 2nd kind, so electrophilic substitution occurs in meta- position.

Unlike benzene pyridine can react nucleophilic substitution, since the nitrogen atom draws electron density from the aromatic system and ortho-para- positions relative to the nitrogen atom are depleted in electrons. So, pyridine can react with sodium amide, forming a mixture ortho- and pair- aminopyridines (Chichibabin reaction):

At pyridine hydrogenation the aromatic system breaks down and forms piperidine, which is a cyclic secondary amine and is a much stronger base than pyridine:

Pyrimidine C 4 H 4 N 2 - six-membered heterocycle with two nitrogen atoms. It can be considered as an analogue of benzene, in which two CH groups are replaced by nitrogen atoms:

Due to the presence of two electronegative nitrogen atoms in the ring, pyrimidine is even less active in electrophilic substitution reactions than pyridine. Its basic properties are also less pronounced than those of pyridine.

The main meaning of pyrimidine is that it is the ancestor of the class of pyrimidine bases.

Pyrimidine bases are derivatives of pyrimidine, the residues of which are part of nucleic acids: uracil, thymine, cytosine.

Each of these bases can exist in two forms. In the free state, bases exist in the aromatic form, and they are included in the composition of nucleic acids in the NH form.

Compounds with a five-membered cycle. Pyrrole C 4 H 4 NH - five-membered heterocycle with one nitrogen atom.

The aromatic system contains six p-electrons (one each from four carbon atoms and a pair of electrons from the nitrogen atom). Unlike pyridine, the electron pair of the nitrogen atom in pyrrole is part of the aromatic system, therefore pyrrole is practically devoid of basic properties.

Pyrrole is a colorless liquid with an odor similar to that of chloroform. Pyrrole is slightly soluble in water (< 6%), но растворим в органических растворителях. На воздухе быстро окисляется и темнеет.

Pyrrole receive condensation of acetylene with ammonia:

or ammonolysis of five-membered rings with other heteroatoms (Yuriev's reaction):

Strong mineral acids can pull the electron pair of the nitrogen atom from the aromatic system, while the aromaticity is broken and the pyrrole is converted into an unstable compound, which immediately polymerizes. The instability of pyrrole in an acidic environment is called acidophobia.

Pyrrole exhibits the properties of a very weak acid. It reacts with potassium to form pyrrole-potassium:

Pyrrole, as an aromatic compound, is prone to electrophilic substitution reactions that occur predominantly at the a-carbon atom (adjacent to the nitrogen atom).

When pyrrole is hydrogenated, pyrrolidine is formed - a cyclic secondary amine, which exhibits the main properties:

Purine - heterocycle, including two articulated cycles: pyridine and imidazole:

The aromatic system of purine includes ten p-electrons (eight electrons of double bonds and two electrons of the pyrrole nitrogen atom). Purine is an amphoteric compound. The weak basic properties of purine are associated with the nitrogen atoms of the six-membered ring, and the weak acidic properties are associated with the NH group of the five-membered ring.

The main significance of purine is that it is the ancestor of the class of purine bases.

Purine bases are derivatives of purine, the remains of which are part of nucleic acids: adenine, guanine.

Nucleic acids. Nucleic acids are natural macromolecular compounds (polynucleotides) that play a huge role in the storage and transmission of hereditary information in living organisms. The molecular weight of nucleic acids can vary from hundreds of thousands to tens of billions. They were discovered and isolated from cell nuclei as early as the 19th century, but they biological role was discovered only in the second half of the 20th century.

The structure of nucleic acids can be established by analyzing the products of their hydrolysis. With complete hydrolysis of nucleic acids, a mixture of pyrimidine and purine bases, a monosaccharide (b-ribose or b-deoxyribose) and phosphoric acid are formed. This means that nucleic acids are built from fragments of these substances.

With partial hydrolysis of nucleic acids, a mixture is formed nucleotides the molecules of which are built from residues of phosphoric acid, a monosaccharide (ribose or deoxyribose) and a nitrogenous base (purine or pyrimidine). The phosphoric acid residue is attached to the 3rd or 5th carbon atom of the monosaccharide, and the base residue is attached to the first carbon atom of the monosaccharide. General nucleotide formulas:

where X=OH for ribonucleotides, built on the basis of ribose, and X \u003d\u003d H for deoxyribonucleotides, based on deoxyribose. Depending on the type of nitrogenous base, purine and pyrimidine nucleotides are distinguished.

Nucleotide is the main structural unit of nucleic acids, their monomeric link. Nucleic acids that are made up of ribonucleotides are called ribonucleic acids(RNA). Nucleic acids made up of deoxyribonucleotides are called deoxyribonucleic acids (DNA). The composition of the molecules RNA nucleotides containing bases adenine, guanine, cytosine and uracil. The composition of the molecules DNA contains nucleotides containing adenine, guanine, cytosine and thymine. One-letter abbreviations are used to designate bases: adenine - A, guanine - G, thymine - T, cytosine - C, uracil - U.

The properties of DNA and RNA are determined by the sequence of bases in the polynucleotide chain and the spatial structure of the chain. The base sequence contains genetic information, and the monosaccharide and phosphoric acid residues play a structural role (carriers, bases).

With partial hydrolysis of nucleotides, a phosphoric acid residue is cleaved off and nucleosides, molecules of which consist of a residue of a purine or pyrimidine base associated with a monosaccharide residue - ribose or deoxyribose. Structural formulas of the main purine and pyrimidine nucleosides:

Purine nucleosides:

Pyrimidine nucleosides:

In DNA and RNA molecules, individual nucleotides are linked into a single polymer chain due to the formation of ester bonds between phosphoric acid residues and hydroxyl groups at the 3rd and 5th carbon atoms of the monosaccharide:

Spatial structure polynucleotide chains of DNA and RNA was determined by X-ray diffraction analysis. One of the greatest discoveries in biochemistry of the 20th century. turned out to be a model of the double-stranded structure of DNA, which was proposed in 1953 by J. Watson and F. Crick. According to this model, the DNA molecule is a double helix and consists of two polynucleotide chains twisted in opposite directions around a common axis. The purine and pyrimidine bases are located inside the helix, while the phosphate and deoxyribose residues are outside. The two helices are held together by hydrogen bonds between base pairs. The most important property of DNA is selectivity in the formation of bonds. (complementarity). The sizes of the bases and the double helix are chosen in nature in such a way that thymine (T) forms hydrogen bonds only with adenine (A), and cytosine (C) only with guanine (G).

Thus, two strands in a DNA molecule are complementary to each other. The sequence of nucleotides in one of the helices uniquely determines the sequence of nucleotides in the other helix.

In each pair of bases linked by hydrogen bonds, one of the bases is purine and the other is pyrimidine. It follows that the total number of purine base residues in a DNA molecule is equal to the number of pyrimidine base residues.

The length of DNA polynucleotide chains is practically unlimited. The number of base pairs in a double helix can vary from a few thousand in the simplest viruses to hundreds of millions in humans.

Unlike DNA, RNA molecules consist of a single polynucleotide chain. The number of nucleotides in the chain ranges from 75 to several thousand, and the molecular weight of RNA can vary from 2500 to several million. The RNA polynucleotide chain does not have a strictly defined structure.

The biological role of nucleic acids. DNA is the main molecule in a living organism. It stores the genetic information that it passes on from one generation to the next. In DNA molecules, the composition of all the proteins of the body is recorded in an encoded form. Each amino acid that is part of proteins has its own code in DNA, i.e., a certain sequence of nitrogenous bases.

DNA contains all genetic information, but is not directly involved in the synthesis of proteins. The role of an intermediary between DNA and the site of protein synthesis is performed by RNA. The process of protein synthesis based on genetic information can be schematically divided into two main stages: reading information (transcription) and protein synthesis (broadcast).

Cells contain three types of RNA that perform different functions.

1. Information, or matrix. RNA(it is denoted by mRNA) reads and transfers genetic information from the DNA contained in the chromosomes to the ribosomes, where a protein is synthesized with a strictly defined sequence of amino acids.

2. Transfer RNA(tRNA) carries amino acids to ribosomes, where they are connected by a peptide bond in a specific sequence that mRNA sets.

3. Ribosomal RNA (rRNA) directly involved in the synthesis of proteins in ribosomes. Ribosomes are complex supramolecular structures that consist of four rRNAs and several dozen proteins.. In fact, ribosomes are factories for the production of proteins.

All types of RNA are synthesized on the DNA double helix.

The base sequence in mRNA is the genetic code that controls the sequence of amino acids in proteins. It was deciphered in 1961-1966. A remarkable feature of the genetic code is that it is universal for all living organisms. The same bases in different RNAs (whether human or virus RNA) correspond to the same amino acids. Each amino acid has its own sequence of three bases called codon. Some amino acids are coded for by more than one codon. So, leucine, serine and arginine correspond to six codons, five amino acids - four codons, isoleucine - three codons, nine amino acids - two codons, and methionine and tryptophan - one each. Three codons are signals to stop the synthesis of the polypeptide chain and are called terminator codons.

Amines. Amines are organic compounds that can be considered as derivatives of ammonia, in which hydrogen atoms (one or more) are replaced by hydrocarbon radicals.

Depending on the nature of the radical, amines can be aliphatic (limiting and unsaturated), alicyclic, aromatic, heterocyclic. They are subdivided into primary, secondary, tertiary depending on how many hydrogen atoms are replaced by a radical.

Quaternary ammonium salts of the +Cl- type are organic analogues of inorganic ammonium salts.

Names of primary amines usually produced from the names of the corresponding hydrocarbons, adding to them the prefix amino or ending -amine . Names of secondary and tertiary amines most often they form according to the principles of rational nomenclature, listing the radicals present in the compound:

primary R-NH 2:CH 3 -NH 2 - methylamine; C 6 H 5 -NH 2 - phenylamine;

secondary R-NH-R ": (CH 2) NH - dimethylamine; C 6 H 5 -NH-CH 3 - methylphenylamine;

tertiary R-N(R")-R": (CH 3) 3 H - trimethylamine; (C 6 H 5) 3 N - triphenylamine.

Receipt. one. Heating alkyl halides with ammonia under pressure leads to the sequential alkylation of ammonia, with the formation of a mixture of salts of primary, secondary and tertiary amines, which are dehydrohalogenated by the action of bases:

2. Aromatic amines obtained by reduction of nitro compounds:

Zinc or iron in an acidic environment or aluminum in an alkaline environment can be used for reduction.

3. Lower amines obtained by passing a mixture of alcohol and ammonia over the surface of the catalyst:

physical properties. The simplest aliphatic amines under normal conditions are gases or liquids with a low boiling point and a pungent odor. All amines are polar compounds, which leads to the formation of hydrogen bonds in liquid amines, and therefore, their boiling points exceed the boiling points of the corresponding alkanes. The first representatives of a number of amines dissolve in water, as the carbon skeleton grows, their solubility in water decreases. Amines are also soluble in organic solvents.

Chemical properties. 1. Basic properties. Being derivatives of ammonia, all amines have basic properties, with aliphatic amines being stronger bases than ammonia, and aromatic ones being weaker. This is due to the fact that the radicals CH 3 -, C 2 H 5 — and others show positive inductive (+I) effect and increase the electron density on the nitrogen atom:

which leads to the enhancement of the basic properties. On the contrary, the phenyl radical C 6 H 5 - exhibits negative mesomeric (-M) effect and reduces the electron density on the nitrogen atom:

The alkaline reaction of amine solutions is explained by the formation of hydroxyl ions during the interaction of amines with water:

Amines in pure form or in solutions interact with acids, forming salts:

Amine salts are usually odorless solids, readily soluble in water. While amines are highly soluble in organic solvents, amine salts are insoluble in them. Under the action of alkalis on amine salts, free amines are released:

2. Combustion. Amines burn in oxygen to form nitrogen, carbon dioxide and water:

3. Reactions with nitrous acid. a) Primary aliphatic amines under the action of nitrous acid converted to alcohols

b) Primary aromatic amines under the action of HNO 2 converted to diazonium salts:

c) Secondary amines (aliphatic and aromatic) give nitroso compounds - substances with a characteristic odor:

The most important representatives of amines. The simplest aliphatic amines are methylamine, dimethylamine, diethylamine — are used in the synthesis of medicinal substances and other products of organic synthesis. Hexamethylenediamine NH 2 -(CH 2) 2 -NH 6 is one of the starting materials for obtaining the important polymeric material of nylon.

Aniline C 6 H 5 NH 2 is the most important of the aromatic amines. It is a colorless oily liquid, slightly soluble in water. For qualitative detection of aniline use its reaction with bromine water, as a result of which a white precipitate of 2,4,6-tribromoaniline precipitates:

Aniline is used to make dyes, medicines, plastics, etc.

Amino acids. Amino acids are organic bifunctional compounds, which include a carboxyl group -COOH and an amino group -NH 2 . Depending on the relative position of both functional groups, a -, b -, g -amino acids, etc. are distinguished:

The Greek letter at the carbon atom denotes its distance from the carboxyl group. Usually only a -amino acids, since other amino acids do not occur in nature.

The composition of proteins includes 20 basic amino acids (see table).

The most important a-amino acids of the general formula

Name	-R
Glycine	—N
Alanine	—CH 3
Cysteine	-CH 2 -SH
Serene	-CH 2 -OH
Phenylalanine	-CH 2 -C 6 H 5
Tyrosine
Glutamic acid	-CH 2 -CH 2 -COOH
Lysine	-(CH 2) 4 -NH 2

All natural amino acids can be divided into the following main groups:

1) aliphatic limiting amino acids(glycine, alanine);

2) sulfur-containing amino acids(cysteine);

3) amino acids with an aliphatic hydroxyl group(serine);

4) aromatic amino acids(phenylalanine, tyrosine);

5) amino acids with an acid radical(glutamic acid);

6) amino acids with a basic radical(lysine).

Isomerism. In all a-amino acids, except for glycine, the a-carbon atom is bonded to four different substituents, so all these amino acids can exist as two isomers that are mirror images of each other.

Receipt. one. Hydrolysis of proteins usually produces complex mixtures of amino acids. However, a number of methods have been developed that make it possible to obtain individual pure amino acids from complex mixtures.

2. Substitution of a halogen for an amino group in the corresponding halo acids. This method of obtaining amino acids is completely analogous to the production of amines from halogen derivatives of alkanes and ammonia:

physical properties. Amino acids are solid crystalline substances, highly soluble in water and slightly soluble in organic solvents. Many amino acids have a sweet taste. They melt at high temperatures and usually decompose as they do so. They cannot go into a vapor state.

Chemical properties. Amino acids are organic amphoteric compounds. They contain two functional groups of the opposite nature in the molecule: an amino group with basic properties and a carboxyl group with acidic properties. Amino acids react with both acids and bases:

When amino acids are dissolved in water, the carboxyl group splits off a hydrogen ion, which can join the amino group. This creates internal salt, whose molecule is a bipolar ion:

Acid-base transformations of amino acids in various environments can be represented by the following scheme:

Aqueous solutions of amino acids have a neutral, alkaline or acidic environment, depending on the number of functional groups. So, glutamic acid forms an acidic solution (two groups -COOH, one -NH 2), lysine - alkaline (one group -COOH, two -NH 2).

Amino acids can react with alcohols in the presence of hydrogen chloride gas to form an ester:

The most important property of amino acids is their ability to condense to form peptides.

Peptides. Peptides. are the condensation products of two or more amino acid molecules. Two amino acid molecules can react with each other with the elimination of a water molecule and the formation of a product in which the fragments are linked peptide bond—CO—NH—.

The resulting compound is called a dipeptide. A dipeptide molecule, like amino acids, contains an amino group and a carboxyl group and can react with one more amino acid molecule:

The reaction product is called a tripeptide. The process of building up the peptide chain can, in principle, continue indefinitely (polycondensation) and lead to substances with a very high molecular weight (proteins).

The main property of peptides is the ability to hydrolyze. During hydrolysis, complete or partial cleavage of the peptide chain occurs and shorter peptides with a lower molecular weight or a-amino acids that make up the chain are formed. Analysis of the products of complete hydrolysis makes it possible to determine the amino acid composition of the peptide. Complete hydrolysis occurs with prolonged heating of the peptide with concentrated hydrochloric acid.

Hydrolysis of peptides can occur in an acidic or alkaline environment, as well as under the action of enzymes. In acidic and alkaline environments, salts of amino acids are formed:

Enzymatic hydrolysis is important in that it proceeds selectively, t . e. allows you to cleave strictly defined sections of the peptide chain.

Qualitative reactions to amino acids. one) All amino acids are oxidized ninhydrin with the formation of products, colored in blue-violet color. This reaction can be used for the quantitative determination of amino acids by the spectrophotometric method. 2) When aromatic amino acids are heated with concentrated nitric acid, the benzene ring is nitrated and yellow-colored compounds are formed. This reaction is called xantoprotein(from Greek. xanthos - yellow).

Squirrels. Proteins are naturally occurring polypeptides with high molecular weights. (from 10,000 to tens of millions). They are part of all living organisms and perform a variety of biological functions.

Structure. There are four levels in the structure of the polypeptide chain. The primary structure of a protein is the specific sequence of amino acids in the polypeptide chain. The peptide chain has a linear structure only in a small number of proteins. In most proteins, the peptide chain is folded in space in a certain way.

The secondary structure is the conformation of the polypeptide chain, i.e., the way the chain is twisted in space due to hydrogen bonds between the NH and CO groups. The main way of laying the chain is a spiral.

The tertiary structure of a protein is a three-dimensional configuration of a twisted helix in space. The tertiary structure is formed by disulfide bridges -S-S- between cysteine ​​residues located in different places of the polypeptide chain. Also involved in the formation of the tertiary structure are ionic interactions oppositely charged groups NH 3 + and COO- and hydrophobic interactions, i.e., the desire of a protein molecule to curl up so that hydrophobic hydrocarbon residues are inside the structure.

Tertiary structure - highest form spatial organization of proteins. However, some proteins (such as hemoglobin) have Quaternary structure, which is formed due to the interaction between different polypeptide chains.

Physical properties proteins are very diverse and determined by their structure. According to their physical properties, proteins are divided into two classes: globular proteins dissolve in water or form colloidal solutions, fibrillar proteins insoluble in water.

Chemical properties. one . The destruction of the secondary and tertiary structure of a protein while maintaining the primary structure is called denaturation. . It occurs when heated, changing the acidity of the medium, the action of radiation. An example of denaturation is the curdling of egg whites when eggs are boiled. Denaturation is either reversible or irreversible. Irreversible denaturation can be caused by the formation of insoluble substances when heavy metal salts, such as lead or mercury, act on proteins.

2. Hydrolysis of proteins is the irreversible destruction of the primary structure in an acidic or alkaline solution with the formation of amino acids. Analyzing the products of hydrolysis, it is possible to establish the quantitative composition of proteins.

3. For proteins, there are several quality responses. All compounds containing a peptide bond give a violet color when exposed to copper (II) salts in an alkaline solution. This reaction is called biuret. Proteins containing aromatic amino acid residues (phenylalanine, tyrosine) give a yellow color when exposed to concentrated nitric acid. (xantoprotein reaction).

The biological significance of proteins:

1. Everything chemical reactions in the body proceed in the presence of catalysts - enzymes. All known enzymes are protein molecules. Proteins are very powerful and selective catalysts. They speed up reactions millions of times, and each reaction has its own single enzyme.

2. Some proteins perform transport functions and carry molecules or ions to sites of synthesis or accumulation. For example, protein in the blood hemoglobin transports oxygen to tissues, and protein myoglobin stores oxygen in the muscles.

3. Proteins are the building blocks of cells. Of these, supporting, muscle, integumentary tissues are built.

4. Proteins play an important role in immune system organism. There are specific proteins (antibodies), which are able to recognize and bind foreign objects - viruses, bacteria, foreign cells.

5. Receptor proteins receive and transmit signals from neighboring cells or from environment. For example, the action of light on the retina is perceived by the photoreceptor rhodopsin. Receptors activated by low molecular weight substances such as acetylcholine transmit nerve impulses at the junctions of nerve cells.

From the above list of protein functions, it is clear that proteins are vital to any organism and, therefore, are the most important component of food. In the process of digestion, proteins are hydrolyzed to amino acids, which serve as the raw material for the synthesis of proteins necessary for this organism. There are amino acids that the body is not able to synthesize itself and acquires them only with food. These amino acids are called irreplaceable.

Amines called derivatives of ammonia NH 3, in the molecule of which one or more hydrogen atoms are replaced by hydrocarbon residues.

Amines can also be considered as derivatives of hydrocarbons formed by replacing hydrogen atoms in hydrocarbons with groups

 NH 2 (primary amine);  NHR(secondary amine);  NR" R" (tertiary amine).

Depending on the number of hydrogen atoms at the nitrogen atom, substituted by radicals, amines are called primary, secondary or tertiary.

The group - NH 2, which is part of the primary amines, is called amino group. Group >NH in secondary amines is called imino group.

Amine nomenclature

Usually amines are called by those radicals that are included in their molecule, with the addition of the word amine.

CH 3 NH 2 - methylamine; (CH 3) 2 NH - dimethylamine; (CH 3) 3 N - trimethylamine.

Aromatic amines have specific nomenclature.

C 6 H 5 NH 2 – phenylamine or aniline.

Physical properties of amines

The first representatives of amines - methylamine, dimethylamine, trimethylamine - are gaseous substances at ordinary temperature. The remaining lower amines are liquids. Higher amines are solids.

The first representatives, like ammonia, dissolve in water in large quantities; higher amines are insoluble in water.

The lower representatives have a strong smell. Methylamine CH 3 NH 2 is found in some plants and smells like ammonia; Trimethylamine in a concentrated state has an odor similar to that of ammonia, but in the low concentrations that are commonly encountered, it has a very unpleasant smell of rotten fish.

Trimethylamine (CH 3) 3 N is contained in fairly large quantities in herring brine, as well as in a number of plants, for example, in the flowers of one species of hawthorn.

Diamines- This is a group of compounds that can be considered as hydrocarbons, in the molecules of which two hydrogen atoms are replaced by amino groups (NH 2).

Putrescine was first found in pus. It is tetramethylenediamine:

H 2 C - CH 2 - CH 2 - CH 2

  tetramethylenediamine

Cadaverine, a homologue of putrescine, has been found in decaying corpses (cadaver - corpse), it is pentamethylenediamine:

H 2 C - CH 2 - CH 2 - CH 2 - CH 2

  pentamethylenediamine

Putrescine and cadaverine are formed from amino acids during the decay of protein substances. Both substances are strong bases.

Organic bases formed during the decay of corpses (including putrescine and cadaverine) are united by the common name ptomains. Ptomains are poisonous.

The next representative of diamines - hexamethylenediamine - is used to obtain a valuable synthetic fiber - nylon.

H 2 C - CH 2 - CH 2 - CH 2 - CH 2 - CH 2

  hexamethylenediamine

Methods for obtaining amines

1. The action of ammonia on alkyl halides (halohydrocarbons) - the Hoffmann reaction.

Initial reaction:

CH 3 I + NH 3 \u003d I

I + NH 3 CH 3 NH 2 + NH 4 I

methylamine

CH 3 NH 2 + CH 3 I [(CH 3) 2 NH 2] I

dimethylammonium iodide

[(CH 3) 2 NH 2] I + NH 3  (CH 3) 2 NH + NH 4 I

dimethylamine

(CH 3) 2 NH + CH 3 I  [(CH 3) 3 NH] I

trimethylammonium iodide

[(CH 3) 3 NH] I + NH 3  (CH 3) 3 N + NH 4 I

trimethylamine

(CH 3) 3 N + CH 3 I  [(CH 3) 4 N] I

tetramethylammonium iodide -

tetra-ammonium salt

The starting methylamine can also be obtained as follows:

I + NaOH \u003d CH 3 NH 2 + NaI + H 2 O

methylamine

As a result of these reactions, a mixture of substituted ammonium salts is obtained (it is impossible to stop the reaction at the first stages).

Such a reaction makes it possible to obtain the so-called invert soaps, soaps that are used in an acidic environment.

(CH 3) 3 N+ C 16 H 33 Cl [(CH 3) 3 NC 16 H 33] Cl

trimethylcetylammonium chloride

The washing effect here is not an anion, as in conventional soaps, but a cation. The peculiarity of this soap is that they are used in an acidic environment.

Such soaps do not dry the skin, which, as you know, has an acidic environment with

A substituent exhibiting antimicrobial activity can be introduced into the structure of an invert soap. In this case, bactericidal soaps used in surgical practice are synthesized.

2. Recovery of nitro compounds (nickel catalyst)

CH 3 NO 2 + 3H 2 \u003d CH 3 NH 2 + 2H 2 O

3. Under natural conditions, aliphatic amines are formed as a result of putrefactive bacterial processes of decomposition of nitrogenous substances - primarily during the decomposition of amino acids formed from proteins. Such processes occur in the intestines of humans and animals.

Chemical properties of amines

1. Interaction with acids

Amine + acid = salt

The reaction is similar to the reaction of the formation of ammonium salts:

NH 3 + HCl \u003d NH 4 Cl

ammonia ammonium chloride

CH 3 NH 2 + HCl \u003d Cl

methylamine methylammonium chloride

2. Reaction with nitrous acid

This reaction makes it possible to distinguish between primary, secondary and tertiary aliphatic, as well as aromatic amines, because they relate differently to the action of nitrous acid.

Nitrous acid is used at the time of isolation by the reaction of dilute hydrochloric acid with sodium nitrite, carried out in the cold:

NaNO 2 (tv) + HCl (aq) NaCl (aq) + HON \u003d O (aq)

Amino acids, combining with each other, form proteins - the most important nitrogen-containing organic substances, without which life is unthinkable. They are part of the cells of living organisms. Proteins are not only building material organisms, but also regulate all biochemical processes. We know the huge role of biocatalysts - enzymes. They are based on proteins.

Protein characterization

Without enzymes, reactions cease, and therefore life itself ceases. Proteins are the main participants in the processes of growth, development, reproduction of organisms, inheritance of traits. Metabolism, respiratory processes, the work of glands, muscles occur with the participation of proteins.

The amino groups and carboxyl groups that make up the amino acids are opposite to each other in properties. Therefore, amino acid molecules interact with each other. In this case, the amino group of one molecule reacts with the carboxyl group of another:

NH2-CH2-CO-OH + H-NH-CH2-COOH => NH2-CH2-CO-NH-CH2-COOH + H2O

Protein molecules have a high molecular weight in excess of 5,000. Some proteins have a molecular weight in excess of 1,000,000 and are composed of many thousands of amino acid residues. So, the hormone insulin consists of 51 residues of various amino acids, and the blue respiratory pigment protein of the snail contains about 100 thousand amino acid residues.

Plant organisms synthesize all the necessary amino acids. In organisms of animals and humans, only some of them can be synthesized. They are called replaceable. Nine amino acids enter the body only with food. They are called indispensable. Lack of at least one of the amino acids leads to serious diseases. For example, a lack of lysine in food causes circulatory disorders, leads to a decrease in hemoglobin, muscle wasting, and a decrease in bone strength.

Protein composition

The sequence of connecting amino acid residues in protein molecules is called the primary structure of proteins. It is the basis of protein structure.

The molecules contain oxygen atoms that have unshared electron pairs, and hydrogen atoms associated with electronegative nitrogen atoms.

Hydrogen bonds form between separate sections of the protein molecule. As a result of all interactions, the molecule twists into a spiral. The spatial arrangement of the peptide chain is called the secondary structure of the protein.

Hydrogen and covalent bonds in proteins can be broken. Then protein denaturation occurs - the destruction of the secondary structure. This occurs during heating, mechanical action, changes in the acidity of the blood, and other factors.

Helical protein molecules have a specific shape. If these helices are elongated, then fibrillar proteins are formed. Muscles, cartilage, ligaments, animal hair, human hair are built from such proteins. But most proteins have a spherical shape of molecules - these are globular proteins. Proteins that form the basis of enzymes, hormones, blood proteins, milk and many others have this form. Individual protein particles (fibers or globules) are combined into more complex structures.

Knowledge of the composition and structure of proteins helps to decipher the essence of a number of human genetic diseases, and therefore, to search for effective ways their treatment. Chemical knowledge is used in medicine to fight diseases, as well as to prevent them, and facilitate the existence of man on Earth.

Characteristic chemical properties of nitrogen-containing organic compounds: amines and amino acids

Amines

Amines are organic derivatives of ammonia, in the molecule of which one, two or all three hydrogen atoms are replaced by a carbon residue.

Accordingly, three types of amines are commonly distinguished:

Amines in which the amino group is bonded directly to the aromatic ring are called aromatic amines.

The simplest representative of these compounds is aminobenzene, or aniline:

Basic hallmark The electronic structure of amines is the presence of a lone electron pair at the nitrogen atom, which is part of the functional group. This leads to the fact that amines exhibit the properties of bases.

There are ions that are the product of formal substitution for a hydrocarbon radical of all hydrogen atoms in the ammonium ion:

These ions are part of salts similar to ammonium salts. They're called quaternary ammonium salts.

Isomerism and nomenclature

Amines are characterized by structural isomerism:

— isomerism of the carbon skeleton:

— functional group position isomerism:

Primary, secondary, and tertiary amines are isomeric to each other ( interclass isomerism):

$(CH_3-CH_2-CH_2-NH_2)↙(\text"primary amine (propylamine)")$

$(CH_3-CH_2-NH-CH_3)↙(\text"secondary amine (methylethylamine)")$

As can be seen from the above examples, in order to name an amine, list the substituents associated with the nitrogen atom (in order of precedence), and add the suffix -amine.

Physical and chemical properties of amines

physical properties.

The simplest amines (methyl amine, dimethylamine, trimethylamine) are gaseous substances. The remaining lower amines are liquids that dissolve well in water. They have a characteristic smell reminiscent of the smell of ammonia.

Primary and secondary amines are capable of forming hydrogen bonds. This leads to a marked increase in their boiling points compared to compounds having the same molecular weight but not capable of forming hydrogen bonds.

Aniline is an oily liquid, sparingly soluble in water, boiling at a temperature of $184°C$.

Chemical properties.

The chemical properties of amines are determined mainly by the presence of an unshared electron pair at the nitrogen atom.

1. Amines as bases. The nitrogen atom of the amino group, like the nitrogen atom in the ammonia molecule, due to the lone pair of electrons can form covalent bond according to the donor-acceptor mechanism, acting as a donor. In this regard, amines, like ammonia, are capable of adding a hydrogen cation, i.e. serve as a base:

$NH_3+H^(+)→(NH_4^(+))↙(\text"ammonium ion")$

$CH_3CH_2—NH_2+H^(+)→CH_3—(CH_2—NH_3^(+))↙(\text"ethylammonium ion")$

It is known that the reaction of ammonia with water leads to the formation of hydroxide ions:

$NH_3+H_2O⇄NH_3 H_2O⇄NH_4^(+)+OH^(-)$.

A solution of an amine in water has an alkaline reaction:

$CH_3CH_2-NH_2+H_2O⇄CH_3-CH_2-NH_3^(+)+OH^(-)$.

Ammonia reacts with acids to form ammonium salts. Amines are also able to react with acids:

$2NH_3+H_2SO_4→((NH_4)_2SO_4)↙(\text"ammonium sulfate")$,

$CH_3—CH_2—NH_2+H_2SO_4→((CH_3—CH_2—NH_3)_2SO_4)↙(\text"ethylammonium sulfate")$.

The main properties of aliphatic amines are more pronounced than those of ammonia. Increasing the electron density turns nitrogen into a stronger electron pair donor, which increases its basic properties:

2. Amines are burning in air with the formation of carbon dioxide, water and nitrogen:

$4CH_3NH_2+9O_2→4CO_2+10H_2O+2N_2$

Amino acids

Amino acids are heterofunctional compounds that necessarily contain two functional groups: an amino group $—NH_2$ and a carboxyl group $—COOH$ associated with a hydrocarbon radical.

The general formula of the simplest amino acids can be written as follows:

Since amino acids contain two different functional groups that influence each other, the characteristic reactions differ from those of carboxylic acids and amines.

Properties of amino acids

The amino group $—NH_2$ determines the basic properties of amino acids, because is capable of attaching a hydrogen cation to itself by the donor-acceptor mechanism due to the presence of a free electron pair at the nitrogen atom.

The $—COOH$ group (carboxyl group) determines the acidic properties of these compounds. Therefore, amino acids are amphoteric organic compounds.

They react with alkalis like acids:

With strong acids - like amine bases:

In addition, the amino group in an amino acid interacts with its carboxyl group, forming an internal salt:

Since the amino acids in aqueous solutions behave like typical amphoteric compounds, then in living organisms they play the role of buffer substances that maintain a certain concentration of hydrogen ions.

Amino acids are colorless crystalline substances that melt with decomposition at temperatures above $200°C$. They are soluble in water and insoluble in ether. Depending on the $R—$ radical, they can be sweet, bitter, or tasteless.

Amino acids are divided into natural (found in living organisms) and synthetic. Among natural amino acids (about $150$), proteinogenic amino acids (about $20$) are distinguished, which are part of proteins. They are L-shaped. Approximately half of these amino acids are indispensable, because they are not synthesized in the human body. Essential acids are valine, leucine, isoleucine, phenylalanine, lysine, threonine, cysteine, methionine, histidine, tryptophan. These substances enter the human body with food. If their amount in food is insufficient, the normal development and functioning of the human body is disrupted. In certain diseases, the body is not able to synthesize some other amino acids. So, with phenylketonuria, tyrosine is not synthesized.

The most important property of amino acids is the ability to enter into molecular condensation with the release of water and the formation of an amide group $—NH—CO—$, for example:

$(nNH_2—(CH_2)_5—COOH)↙(\text"aminocaproic acid")→((…—NH—(CH_2)_5—COO—…)_n)↙(\text"kapron")+(n+ 1)H_2O$.

The macromolecular compounds obtained as a result of such a reaction contain a large number of amide fragments and, therefore, are called polyamides.

To obtain synthetic fibers suitable amino acids with the location of the amino and carboxyl groups at the ends of the molecules.

Polyamides of $α$-amino acids are called peptides. Based on the number of amino acid residues dipeptides, peptides, polypeptides. In such compounds, the $—NH—CO—$ groups are called peptide groups.

Some amino acids that make up proteins.

Squirrels

Proteins, or protein substances, are high-molecular (molecular weight varies from $5-10 thousand to $1 million or more) natural polymers, the molecules of which are built from amino acid residues connected by an amide (peptide) bond.

Proteins are also called proteins (from the Greek. protos- first, important). The number of amino acid residues in a protein molecule varies greatly and sometimes reaches several thousand. Each protein has its own inherent sequence of amino acid residues.

Proteins perform a variety of biological functions: catalytic (enzymes), regulatory (hormones), structural (collagen, fibroin), motor (myosin), transport (hemoglobin, myoglobin), protective (immunoglobulins, interferon), spare (casein, albumin, gliadin) and others.

Proteins are the basis of biomembranes, the most important part of the cell and cellular components. They play a key role in the life of the cell, forming, as it were, the material basis of its chemical activity.

The unique property of protein self-organization structure, i.e. his ability spontaneously create a specific spatial structure peculiar only to a given protein. Essentially, all the activities of the body (development, movement, performance of various functions, and much more) are associated with protein substances. It is impossible to imagine life without proteins.

Proteins are the most important component of human and animal food, a supplier of essential amino acids.

The structure of proteins

All proteins are formed by twenty different $α$-amino acids, the general formula of which can be represented as

where the radical R can have a wide variety of structures.

Proteins are polymer chains consisting of tens of thousands, millions or more $α$-amino acid residues linked by peptide bonds. The sequence of amino acid residues in a protein molecule is called its primary structure.

Protein bodies are characterized by huge molecular weights (up to a billion) and almost macrosized molecules. Such a long molecule cannot be strictly linear, so its sections bend and fold, which leads to the formation of hydrogen bonds involving nitrogen and oxygen atoms. A regular helical structure is formed, which is called the secondary structure.

In a protein molecule, ionic interactions can occur between the carboxyl and amino groups of various amino acid residues and the formation of disulfide bridges. These interactions lead to tertiary structure.

Proteins with $M_r > 50,000$ usually consist of several polypeptide chains, each of which already has primary, secondary, and tertiary structures. Such proteins are said to have a quaternary structure.

Protein properties

Proteins are amphoteric electrolytes. At a certain $pH$ value of the medium (it is called the isoelectric point), the number of positive and negative charges in the protein molecule is the same.

This is one of the main properties of protein. Proteins at this point are electrically neutral, and their solubility in water is the lowest. The ability of proteins to reduce solubility when their molecules become electrically neutral is used for isolation from solutions, for example, in the technology of obtaining protein products.

Hydration. The process of hydration means the binding of water by proteins, while they exhibit hydrophilic properties: they swell, their mass and volume increase. The swelling of individual proteins depends on their structure. The hydrophilic amide ($—CO—NH—$, peptide bond), amine ($—NH_2$) and carboxyl ($—COOH$) groups present in the composition and located on the surface of the protein macromolecule attract water molecules to themselves, strictly orienting them to surface of the molecule. The hydration (water) shell surrounding the protein globules prevents aggregation and sedimentation and, consequently, contributes to the stability of protein solutions. At the isoelectric point, proteins have the least ability to bind water, the hydration shell around the protein molecules is destroyed, so they combine to form large aggregates. Aggregation of protein molecules also occurs when they are dehydrated with some organic solvents, such as ethyl alcohol. This leads to the precipitation of proteins. When the $pH$ of the medium changes, the protein macromolecule becomes charged, and its hydration capacity changes.

With limited swelling, concentrated protein solutions form complex systems called jelly. The jellies are not fluid, elastic, have plasticity, a certain mechanical strength, and are able to maintain their shape.

Different hydrophilicity of gluten proteins is one of the features that characterize the quality of wheat grain and the flour obtained from it (the so-called strong and weak wheat). The hydrophilicity of grain and flour proteins plays an important role in the storage and processing of grain, in baking. The dough, which is obtained in the baking industry, is a protein swollen in water, a concentrated jelly containing starch grains.

Protein denaturation. During denaturation under the influence external factors(temperature, mechanical impact, the action of chemical agents and a number of other factors) there is a change in the secondary, tertiary and quaternary structures of the protein macromolecule, i.e. its native spatial structure. The primary structure and, consequently, the chemical composition of the protein do not change. are changing physical properties: reduced solubility, ability to hydrate, loss of biological activity. The shape of the protein macromolecule changes, aggregation occurs. At the same time, the activity of some chemical groups increases, the effect of proteolytic enzymes on proteins is facilitated, and, consequently, it is more easily hydrolyzed.

In food technology, thermal denaturation of proteins is of particular practical importance, the degree of which depends on temperature, duration of heating and humidity. This must be remembered when developing modes of heat treatment of food raw materials, semi-finished products, and sometimes finished products. The processes of thermal denaturation play a special role in blanching vegetable raw materials, drying grain, baking bread, and obtaining pasta. Protein denaturation can also be caused by mechanical action (pressure, rubbing, shaking, ultrasound). Finally, the action of chemical reagents (acids, alkalis, alcohol, acetone) leads to the denaturation of proteins. All these techniques are widely used in food and biotechnology.

Foaming. The process of foaming is understood as the ability of proteins to form highly concentrated liquid-gas systems, called foams. The stability of the foam, in which the protein is a blowing agent, depends not only on its nature and concentration, but also on temperature. Proteins as foaming agents are widely used in the confectionery industry (marshmallow, marshmallow, soufflé). The structure of the foam has bread, and this affects its taste.

Protein molecules under the influence of a number of factors can be destroyed or interact with other substances to form new products. For the food industry, two important processes can be distinguished: 1) protein hydrolysis under the action of enzymes; 2) interaction of amino groups of proteins or amino acids with carbonyl groups of reducing sugars. Under the influence of protease enzymes that catalyze the hydrolytic cleavage of proteins, the latter break down into more simple products(poly- and dipeptides) and eventually into amino acids. The rate of protein hydrolysis depends on its composition, molecular structure, enzyme activity, and conditions.

Protein hydrolysis. The hydrolysis reaction with the formation of amino acids in general terms can be written as follows:

Combustion. Proteins burn with the formation of nitrogen, carbon dioxide and water, as well as some other substances. Burning is accompanied by the characteristic smell of burnt feathers.

color reactions. The following reactions are used:

— xantoprotein, in which the interaction of aromatic and heteroatomic cycles in the protein molecule with concentrated nitric acid occurs, accompanied by the appearance of a yellow color;

— biuret, at which weakly alkaline solutions of proteins interact with a solution of copper sulfate (II) with the formation of complex compounds between $Cu^(2+)$ ions and polypeptides. The reaction is accompanied by the appearance of a violet-blue color.