Special properties of amino acids. Amino acids
Amino acids belong to heterofunctional compounds, i.e. substances exhibiting the properties of two classes of compounds. In inorganic chemistry, such compounds are called amphoteric.
PHYSICAL PROPERTIES OF AMINO ACIDS
In terms of physical properties, amino acids differ sharply from the corresponding acids and bases. All of them are crystalline substances, dissolve better in water than in organic solvents, and have fairly high melting points; many of them have a sweet taste. These properties clearly indicate the salt-like nature of these compounds.
CHEMICAL PROPERTIES OF AMINO ACIDS
The peculiarities of the physical and chemical properties of amino acids are determined by their structure - the presence at the same time of two functional groups with opposite properties: acidic and basic. $\alpha$-amino acids are amphoteric electrolytes. Having at least two dissociating and oppositely charged groups, amino acids in solutions with a neutral pH value are almost always found in the form of bipolar ions, or zwitterions, in which opposite charges are spatially separated, for example $H_3^+N-CH_2-CH_2-COO^-$.
It is the amphotericity of amino acids that determines their most characteristic properties.
1. Acid properties amino acids appear by carboxyl group in their ability to interact, for example, with alkalis:
or enter into an esterification reaction with alcohols to form esters:
2. Basic properties amino acids appear by amino group in their ability to interact with acids, forming complex ions according to the donor-acceptor mechanism:
3. Amphotericity of amino acids is also manifested in their ability to form a bipolar ion in solution as a result of dissociation - an internal salt, and most importantly, due to amphotericity, amino acids can enter into polycondensation reactions with each other. forming polypeptides and proteins:
QUALITATIVE (COLOR) REACTIONS TO AMINO ACIDS AND PROTEINS
Qualitative color reactions can be divided into two types: universal And specific. Universal reactions include those that give color in the presence of any proteins.
Specific reactions prove the presence of a particular amino acid. All qualitative reactions can be observed using the example of an egg white solution, which is a multicomponent mixture of amino acids:
UNIVERSAL COLOR REACTIONS
1 . Biuret reaction - a universal reaction to all proteins and peptides, since it is a reaction to peptide bond. Represents the interaction of an alkaline solution biuret($(H_2NC(O))_2NH$ with a solution of copper sulfate in the presence of sodium hydroxide (Fehling's reagent) .
Many substances containing at least two amide groups in the molecule, amides and imides of amino acids and some other compounds enter into a reaction similar to biuret. The reaction products in this case are violet or blue in color.
Under the conditions of the biuret reaction, proteins give a violet color, which is used for their qualitative and quantitative analysis. The biuret reaction is caused by the presence of peptide bonds in proteins, which in an alkaline environment form colored salt-like copper complexes with copper (II) sulfate.
2. Ninhydrin reaction - color reaction to α-amino acids, which is carried out by heating the latter in an excess of alkaline solution ninhydrin(1,2,3-indantrione hydrate).
The compound formed as a result of the reaction (diketohydrinimine - the leftmost reaction product in the figure) has a violet-blue color. This is used for the colorimetric quantitative determination of $\alpha$-amino acids, including in automatic amino acid analyzers.
SPECIFIC COLOR REACTIONS
1. Schultz-Raspailly reaction(carried out similarly Adamkiewicz reaction, only with the addition of glyoxylic acid) - is a specific reaction to an amino acid tryptophan- interaction of an egg white solution with a 10% sucrose solution and an equal volume of concentrated $H_2SO_4$. At the interface of two liquids, a red-violet ring(when heated in a water bath, the reaction goes faster - the main thing is not to mix the liquids).
2 . Milo's reaction- used for detection tyrosine, which contains phenolic hydroxyl. When Milon's reagent is added to a protein solution (a solution of $HgNO_3$ and $Hg(NO_3)_2$ in dilute nitric acid $HNO_3$ containing an admixture of nitrous acid $HNO_2$), a precipitate is formed, first colored pink and then purple-red color. Heating to $50^\circ C$ speeds up this reaction.
3. Ksantoprotein reaction - is a specific reaction and is used to detect $\alpha$-amino acids containing in the radical aromatic cycle, For example phenylalanine. To carry this out, concentrated nitric acid $HNO_3$ is added to the protein solution until the formation of a precipitate stops, which turns yellow when heated. Coloring occurs as a result of nitration of the aromatic rings of protein amino acid residues (tyrosine and tryptophan). When an excess of alkali is added to a cooled liquid, an orange color appears due to the formation of nitronic acid salts.
4. Foll reaction to sulfur-containing amino acids (cysteine, methionine)- interaction of an egg white solution with a 30% NaOH solution and a 5% lead acetate solution - $Pb(CH_3COO)_2$. When heated for a long time, the liquid turns brown and a black precipitate of lead sulfide precipitates.
Chemical behavior of amino acids is determined by two functional groups -NH 2 and -COOH. Amino acids are characterized by reactions at the amino group, carboxyl group and at the radical part, and depending on the reagent, the interaction of substances can occur through one or more reaction centers.
Amphoteric nature of amino acids. Having both an acidic and a basic group in the molecule, amino acids in aqueous solutions behave like typical amphoteric compounds. In acidic solutions they exhibit basic properties, reacting as bases, in alkaline solutions - as acids, respectively forming two groups of salts:
Due to its amphotericity in a living organism, amino acids play the role of buffer substances that maintain a certain concentration of hydrogen ions. Buffer solutions obtained by the interaction of amino acids with strong bases are widely used in bioorganic and chemical practice. Salts of amino acids with mineral acids are more soluble in water than free amino acids. Salts with organic acids are sparingly soluble in water and are used to identify and separate amino acids.
Reactions caused by the amino group. With the participation of the amino group, amino acids form ammonium salts with acids, are acylated, alkylated , react with nitrous acid and aldehydes according to the following scheme:
Alkylation is carried out with the participation of R-Ha1 or Ar-Hal:
In the acylation reaction, acid chlorides or acid anhydrides are used (acetyl chloride, acetic anhydride, benzyloxycarbonyl chloride):
Acylation and alkylation reactions are used to protect the NH 2 group of amino acids during the synthesis of peptides.
Reactions caused by a carboxyl group. With the participation of the carboxyl group, amino acids form salts, esters, amides, and acid chlorides in accordance with the scheme presented below:
If at the a-carbon atom in the hydrocarbon radical there is an electron-withdrawing substituent (-NO 2, -CC1 3, -COOH, -COR, etc.) that polarizes the C®COOH bond, then carboxylic acids easily undergo decarboxylation reactions. Decarboxylation of a-amino acids containing a + NH 3 group as a substituent leads to the formation of biogenic amines. In a living organism, this process occurs under the action of the enzyme decarboxylase and vitamin pyridoxal phosphate.
In laboratory conditions, the reaction is carried out by heating an a-amino acid in the presence of CO 2 absorbers, for example, Ba(OH) 2.
Decarboxylation of b-phenyl-a-alanine, lysine, serine and histidine produces phenamine, 1,5-diaminopentane (cadaverine), 2-aminoethanol-1 (colamine) and tryptamine, respectively.
Reactions of amino acids involving a side group. When the amino acid tyrosine is nitrated with nitric acid, a dinitro derivative compound is formed, colored orange (xanthoprotein test):
Redox transitions take place in the cysteine-cystine system:
2HS CH 2 CH(NH 2)COOH ¾¾¾® HOOCCH(NH 2)CH 2 S-S CH2CH(NH2)COOH
HOOCCH(NH 2)CH 2 S-S CH 2 CH(NH 2)COOH ¾¾¾® 2 NS CH2CH(NH2)COOH
In some reactions, amino acids react on both functional groups simultaneously.
Formation of complexes with metals. Almost all a-amino acids form complexes with divalent metal ions. The most stable are complex internal copper salts (chelate compounds), formed as a result of interaction with copper (II) hydroxide and colored blue:
Action of nitrous acid on aliphatic amino acids leads to the formation of hydroxy acids, on aromatic amino acids - diazo compounds.
Formation of hydroxy acids:
Diazotization reaction:
(diazo compound)
1. with the release of molecular nitrogen N2:
2. without the release of molecular nitrogen N2:
The chromophore group of azobenzene -N=N in azo compounds causes yellow, yellow, orange or other colors of substances when absorbed in the visible region of light (400-800 nm). Auxochrome group
COOH changes and enhances the color due to π, π - conjugation with the π - electronic system of the main group of the chromophore.
Relation of amino acids to heat. When heated, amino acids decompose to form different products depending on their type. When heated a-amino acids As a result of intermolecular dehydration, cyclic amides are formed - diketopiperazines:
valine (Val) diisopropyl derivative
diketopiperazine
When heated b-amino acids Ammonia is split off from them to form α, β-unsaturated acids with a conjugated system of double bonds:
β-aminovaleric acid penten-2-oic acid
(3-aminopentanoic acid)
Heating g- and d-amino acids accompanied by intramolecular dehydration and the formation of internal cyclic amides - lactams:
γ-aminoisovaleric acid γ-aminoisovaleric lactam
(4-amino-3-methylbutanoic acid) acids
Based on the nature of hydrocarbon substituents, amines are divided into
General structural features of amines
Just like in the ammonia molecule, in the molecule of any amine the nitrogen atom has a lone electron pair directed to one of the vertices of the distorted tetrahedron:
For this reason, amines, like ammonia, have significantly expressed basic properties.
Thus, amines, similar to ammonia, react reversibly with water, forming weak bases:
The bond between the hydrogen cation and the nitrogen atom in the amine molecule is realized using a donor-acceptor mechanism due to the lone electron pair of the nitrogen atom. Saturated amines are stronger bases compared to ammonia, because in such amines, hydrocarbon substituents have a positive inductive (+I) effect. In this regard, the electron density on the nitrogen atom increases, which facilitates its interaction with the H + cation.
Aromatic amines, if the amino group is directly connected to the aromatic ring, exhibit weaker basic properties compared to ammonia. This is due to the fact that the lone electron pair of the nitrogen atom is shifted towards the aromatic π-system of the benzene ring, as a result of which the electron density on the nitrogen atom decreases. In turn, this leads to a decrease in basic properties, in particular the ability to interact with water. For example, aniline reacts only with strong acids, but practically does not react with water.
Chemical properties of saturated amines
As already mentioned, amines react reversibly with water:
Aqueous solutions of amines have an alkaline reaction due to the dissociation of the resulting bases:
Saturated amines react with water better than ammonia due to their stronger basic properties.
The basic properties of saturated amines increase in the series.
Secondary saturated amines are stronger bases than primary saturated amines, which in turn are stronger bases than ammonia. As for the basic properties of tertiary amines, if we are talking about reactions in aqueous solutions, then the basic properties of tertiary amines are expressed much worse than those of secondary amines, and even slightly worse than those of primary ones. This is due to steric hindrances, which significantly affect the rate of amine protonation. In other words, three substituents “block” the nitrogen atom and interfere with its interaction with H + cations.
Interaction with acids
Both free saturated amines and their aqueous solutions react with acids. In this case, salts are formed:
Since the basic properties of saturated amines are more pronounced than those of ammonia, such amines react even with weak acids, such as carbonic acid:
Amine salts are solids that are highly soluble in water and poorly soluble in non-polar organic solvents. The interaction of amine salts with alkalis leads to the release of free amines, similar to the displacement of ammonia when alkalis act on ammonium salts:
2. Primary saturated amines react with nitrous acid to form the corresponding alcohols, nitrogen N2 and water. For example:
A characteristic feature of this reaction is the formation of nitrogen gas, and therefore it is qualitative for primary amines and is used to distinguish them from secondary and tertiary ones. It should be noted that most often this reaction is carried out by mixing the amine not with a solution of nitrous acid itself, but with a solution of a salt of nitrous acid (nitrite) and then adding a strong mineral acid to this mixture. When nitrites interact with strong mineral acids, nitrous acid is formed, which then reacts with the amine:
Under similar conditions, secondary amines give oily liquids, so-called N-nitrosamines, but this reaction does not occur in real USE tests in chemistry. Tertiary amines do not react with nitrous acid.
Complete combustion of any amines leads to the formation of carbon dioxide, water and nitrogen:
Interaction with haloalkanes
It is noteworthy that exactly the same salt is obtained by the action of hydrogen chloride on a more substituted amine. In our case, when hydrogen chloride reacts with dimethylamine:
Preparation of amines:
1) Alkylation of ammonia with haloalkanes:
In case of ammonia deficiency, its salt is obtained instead of amine:
2) Reduction by metals (to hydrogen in the activity series) in an acidic environment:
followed by treatment of the solution with alkali to release the free amine:
3) The reaction of ammonia with alcohols when passing their mixture through heated aluminum oxide. Depending on the alcohol/amine proportions, primary, secondary or tertiary amines are formed:
Chemical properties of aniline
Aniline - the trivial name for aminobenzene, having the formula:
As can be seen from the illustration, in the aniline molecule the amino group is directly connected to the aromatic ring. Such amines, as already mentioned, have much less pronounced basic properties than ammonia. Thus, in particular, aniline practically does not react with water and weak acids such as carbonic acid.
Reaction of aniline with acids
Aniline reacts with strong and medium strength inorganic acids. In this case, phenylammonium salts are formed:
Reaction of aniline with halogens
As was already said at the very beginning of this chapter, the amino group in aromatic amines is drawn into the aromatic ring, which in turn reduces the electron density on the nitrogen atom, and as a result increases it in the aromatic ring. An increase in electron density in the aromatic ring leads to the fact that electrophilic substitution reactions, in particular reactions with halogens, proceed much more easily, especially in the ortho and para positions relative to the amino group. Thus, aniline easily reacts with bromine water, forming a white precipitate of 2,4,6-tribromoaniline:
This reaction is qualitative for aniline and often allows it to be identified among other organic compounds.
Reaction of aniline with nitrous acid
Aniline reacts with nitrous acid, but due to the specificity and complexity of this reaction, it does not appear in the real Unified State Exam in chemistry.
Aniline alkylation reactions
Using sequential alkylation of aniline at the nitrogen atom with halogenated hydrocarbons, secondary and tertiary amines can be obtained:
Obtaining aniline
1. Reduction of nitrobenzene by metals in the presence of strong non-oxidizing acids:
C 6 H 5 -NO 2 + 3Fe + 7HCl = +Cl- + 3FeCl 2 + 2H 2 O
Cl - + NaOH = C 6 H 5 -NH 2 + NaCl + H 2 O
Any metals located before hydrogen in the activity series can be used as metals.
Reaction of chlorobenzene with ammonia:
C 6 H 5 −Cl + 2NH 3 → C 6 H 5 NH 2 + NH 4 Cl
Chemical properties of amino acids
Amino acids are compounds whose molecules contain two types of functional groups - amino (-NH 2) and carboxy- (-COOH) groups.
In other words, amino acids can be considered as derivatives of carboxylic acids, in the molecules of which one or more hydrogen atoms are replaced by amino groups.
Thus, the general formula of amino acids can be written as (NH 2) x R(COOH) y, where x and y are most often equal to one or two.
Since amino acid molecules contain both an amino group and a carboxyl group, they exhibit chemical properties similar to both amines and carboxylic acids.
Acidic properties of amino acids
Formation of salts with alkalis and alkali metal carbonates
Esterification of amino acids
Amino acids can react with esterification with alcohols:
NH 2 CH 2 COOH + CH 3 OH → NH 2 CH 2 COOCH 3 + H 2 O
Basic properties of amino acids
1. Formation of salts when interacting with acids
NH 2 CH 2 COOH + HCl → + Cl —
2. Interaction with nitrous acid
NH 2 -CH 2 -COOH + HNO 2 → HO-CH 2 -COOH + N 2 + H 2 O
Note: interaction with nitrous acid proceeds in the same way as with primary amines
3. Alkylation
NH 2 CH 2 COOH + CH 3 I → + I —
4. Interaction of amino acids with each other
Amino acids can react with each other to form peptides - compounds containing in their molecules the peptide bond –C(O)-NH-
At the same time, it should be noted that in the case of a reaction between two different amino acids, without observing some specific synthesis conditions, the formation of different dipeptides occurs simultaneously. So, for example, instead of the reaction of glycine with alanine above, leading to glycylananine, the reaction leading to alanylglycine can occur:
In addition, the glycine molecule does not necessarily react with the alanine molecule. Peptization reactions also occur between glycine molecules:
And alanine:
In addition, since the molecules of the resulting peptides, like the original amino acid molecules, contain amino groups and carboxyl groups, the peptides themselves can react with amino acids and other peptides due to the formation of new peptide bonds.
Individual amino acids are used to produce synthetic polypeptides or so-called polyamide fibers. Thus, in particular, using the polycondensation of 6-aminohexane (ε-aminocaproic) acid, nylon is synthesized in industry:
The resulting nylon resin is used to produce textile fibers and plastics.
Formation of internal salts of amino acids in aqueous solution
In aqueous solutions, amino acids exist predominantly in the form of internal salts - bipolar ions (zwitterions):
Obtaining amino acids
1) Reaction of chlorinated carboxylic acids with ammonia:
Cl-CH 2 -COOH + 2NH 3 = NH 2 -CH 2 -COOH + NH 4 Cl
2) Breakdown (hydrolysis) of proteins under the action of solutions of strong mineral acids and alkalis.
Among nitrogen-containing organic substances there are compounds with dual functions. Particularly important of them are amino acids.
About 300 different amino acids are found in the cells and tissues of living organisms, but only 20 ( α-amino acids ) of them serve as units (monomers) from which peptides and proteins of all organisms are built (therefore they are called protein amino acids). The sequence of location of these amino acids in proteins is encoded in the nucleotide sequence of the corresponding genes. The remaining amino acids are found both in the form of free molecules and in bound form. Many of the amino acids are found only in certain organisms, and there are others that are found only in one of the great variety of described organisms. Most microorganisms and plants synthesize the amino acids they need; Animals and humans are not capable of producing the so-called essential amino acids obtained from food. Amino acids are involved in the metabolism of proteins and carbohydrates, in the formation of compounds important for organisms (for example, purine and pyrimidine bases, which are an integral part of nucleic acids), they are part of hormones, vitamins, alkaloids, pigments, toxins, antibiotics, etc.; Some amino acids serve as intermediaries in the transmission of nerve impulses.
Amino acids- organic amphoteric compounds, which include carboxyl groups - COOH and amino groups -NH 2 .
Amino acids can be considered as carboxylic acids, in the molecules of which the hydrogen atom in the radical is replaced by an amino group.
CLASSIFICATION
Amino acids are classified according to their structural characteristics.1. Depending on the relative position of the amino and carboxyl groups, amino acids are divided into α-, β-, γ-, δ-, ε- etc.
2. Depending on the number of functional groups, acidic, neutral and basic groups are distinguished.
3. Based on the nature of the hydrocarbon radical, they distinguish aliphatic(fat), aromatic, sulfur-containing And heterocyclic amino acids. The above amino acids belong to the fatty series.
An example of an aromatic amino acid is para-aminobenzoic acid:
An example of a heterocyclic amino acid is tryptophan, an essential α-amino acid.
NOMENCLATURE
According to systematic nomenclature, the names of amino acids are formed from the names of the corresponding acids by adding the prefix amino and indicating the location of the amino group in relation to the carboxyl group. Numbering of the carbon chain from the carbon atom of the carboxyl group.
For example:
Another method of constructing the names of amino acids is also often used, according to which the prefix is added to the trivial name of the carboxylic acid amino indicating the position of the amino group by a letter of the Greek alphabet.
Example:
For α-amino acidsR-CH(NH2)COOH
Which play an extremely important role in the life processes of animals and plants, trivial names are used.
Table.
Amino acid |
Abbreviated designation |
Structure of the radical (R) |
Glycine |
Gly |
H- |
Alanin |
Ala (Ala) |
CH 3 - |
Valin |
Val |
(CH 3) 2 CH - |
Leucine |
Leu (Lei) |
(CH 3) 2 CH – CH 2 - |
Serin |
Ser |
OH-CH2- |
Tyrosine |
Tyr (Shooting Range) |
HO – C 6 H 4 – CH 2 - |
Aspartic acid |
Asp |
HOOC – CH 2 - |
Glutamic acid |
Glu |
HOOC – CH 2 – CH 2 - |
Cysteine |
Cys (Cis) |
HS – CH 2 - |
Asparagine |
Asn (Asn) |
O = C – CH 2 – │ NH 2 |
Lysine |
Lys (Liz) |
NH 2 – CH 2 - CH 2 – CH 2 - |
Phenylalanine |
Phen |
C 6 H 5 – CH 2 - |
If an amino acid molecule contains two amino groups, then the prefix is used in its namediamino-, three NH 2 groups – triamino- etc.
Example:
The presence of two or three carboxyl groups is reflected in the name by the suffix –diovy or -triic acid:
ISOMERIA
1. Isomerism of the carbon skeleton
2. Isomerism of the position of functional groups
3. Optical isomerism
α-amino acids, except glycine NH 2 -CH 2 -COOH.
PHYSICAL PROPERTIES
Amino acids are crystalline substances with high (above 250°C) melting points, which differ little among individual amino acids and are therefore uncharacteristic. Melting is accompanied by decomposition of the substance. Amino acids are highly soluble in water and insoluble in organic solvents, which makes them similar to inorganic compounds. Many amino acids have a sweet taste.
RECEIVING
3. Microbiological synthesis. Microorganisms are known that during their life processes produce α - amino acids of proteins.
CHEMICAL PROPERTIES
Amino acids are amphoteric organic compounds; they are characterized by acid-base properties.
I . General properties
1. Intramolecular neutralization → a bipolar zwitterion is formed:
Aqueous solutions are electrically conductive. These properties are explained by the fact that amino acid molecules exist in the form of internal salts, which are formed by the transfer of a proton from the carboxyl to the amino group:
zwitterion
Aqueous solutions of amino acids have a neutral, acidic or alkaline environment depending on the number of functional groups.
APPLICATION
1) amino acids are widely distributed in nature;
2) amino acid molecules are the building blocks from which all plant and animal proteins are built; amino acids necessary for building body proteins are obtained by humans and animals as part of food proteins;
3) amino acids are prescribed for severe exhaustion, after severe operations;
4) they are used to feed the sick;
5) amino acids are necessary as a therapeutic agent for certain diseases (for example, glutamic acid is used for nervous diseases, histidine for stomach ulcers);
6) some amino acids are used in agriculture to feed animals, which has a positive effect on their growth;
7) have technical significance: aminocaproic and aminoenanthic acids form synthetic fibers - capron and enanth.
ABOUT THE ROLE OF AMINO ACIDS
Occurrence in nature and biological role of amino acids
Finding in nature and the biological role of amino acids
1.Amino acids exhibit amphoteric properties and acids and amines, as well as specific properties due to the joint presence of these groups. In aqueous solutions, AMK exist in the form of internal salts (bipolar ions). Aqueous solutions of monoaminomonocarboxylic acids are neutral to litmus, because their molecules contain an equal number of -NH 2 - and -COOH groups. These groups interact with each other to form internal salts:
Such a molecule has opposite charges in two places: positive NH 3 + and negative on the carboxyl –COO -. In this regard, the internal salt of AMK is called a bipolar ion or Zwitter ion (Zwitter - hybrid).
A bipolar ion in an acidic environment behaves like a cation, since the dissociation of the carboxyl group is suppressed; in an alkaline environment - as an anion. There are pH values specific for each amino acid, in which the number of anionic forms in solution is equal to the number of cationic forms. The pH value at which the total charge of the AMK molecule is 0 is called the isoelectric point of AMK (pI AA).
Aqueous solutions of monoaminodicarboxylic acids have an acidic reaction:
HOOC-CH 2 -CH-COOH « - OOC-CH 2 -CH–COO - + H +
The isoelectric point of monoaminodicarboxylic acids is in an acidic environment and such AMAs are called acidic.
Diaminomonocarboxylic acids have basic properties in aqueous solutions (the participation of water in the dissociation process must be shown):
NH 2 -(CH 2) 4 -CH-COOH + H 2 O « NH 3 + -(CH 2) 4 -CH–COO - + OH -
The isoelectric point of diaminomonocarboxylic acids is at pH>7 and such AMAs are called basic.
Being bipolar ions, amino acids exhibit amphoteric properties: they are able to form salts with both acids and bases:
Interaction with hydrochloric acid HCl leads to the formation of salt:
R-CH-COOH + HCl ® R-CH-COOH
NH 2 NH 3 + Cl -
Interaction with a base leads to the formation of a salt:
R-CH(NH 2)-COOH + NaOH ® R-CH(NH 2)-COONa + H 2 O
2. Formation of complexes with metals– chelate complex. The structure of the copper salt of glycol (glycine) can be represented by the following formula:
Almost all of the copper available in the human body (100 mg) is bound to proteins (amino acids) in the form of these stable claw-shaped compounds.
3. Similar to other acids amino acids form esters, halogen anhydrides, amides.
4. Decarboxylation reactions occur in the body with the participation of special decarboxylase enzymes: the resulting amines (tryptamine, histamine, serotinine) are called biogenic amines and are regulators of a number of physiological functions of the human body.
5. Interaction with formaldehyde(aldehydes)
R-CH-COOH + H 2 C=O ® R-CH-COOH
Formaldehyde binds the NH 2 group, the -COOH group remains free and can be titrated with alkali. Therefore, this reaction is used for the quantitative determination of amino acids (Sørensen method).
6. Interaction with nitrous acid leads to the formation of hydroxy acids and the release of nitrogen. Based on the volume of released nitrogen N2, its quantitative content in the object under study is determined. This reaction is used for the quantitative determination of amino acids (Van-Slyke method):
R-CH-COOH + HNO 2 ® R-CH-COOH + N 2 + H 2 O
This is one of the ways to deaminate AMK outside the body
7. Acylation of amino acids. The amino group of AMK can be acylated with acid chlorides and anhydrides already at room temperature.
The product of the recorded reaction is acetyl-α-aminopropionic acid.
Acyl derivatives of AMK are widely used in studying their sequence in proteins and in the synthesis of peptides (protection of the amino group).
8.Specific properties reactions associated with the presence and mutual influence of amino and carboxyl groups - the formation of peptides. The general property of a-AMK is polycondensation process, leading to the formation of peptides. As a result of this reaction, amide bonds are formed at the site of interaction between the carboxyl group of one AMK and the amino group of another AMK. In other words, peptides are amides formed as a result of the interaction of amino groups and carboxyls of amino acids. The amide bond in such compounds is called a peptide bond (explain the structure of the peptide group and peptide bond: three-center p, p-conjugated system)
Depending on the number of amino acid residues in the molecule, di-, tri-, tetrapeptides, etc. are distinguished. up to polypeptides (up to 100 AMK residues). Oligopeptides contain from 2 to 10 AMK residues, proteins contain more than 100 AMK residues. In general, a polypeptide chain can be represented by the diagram:
H 2 N-CH-CO-NH-CH-CO-NH-CH-CO-... -NH-CH-COOH
Where R 1, R 2, ... R n are amino acid radicals.
Concept of proteins.
The most important biopolymers of amino acids are proteins - proteins. There are about 5 million in the human body. various proteins that make up the skin, muscles, blood and other tissues. Proteins (proteins) get their name from the Greek word “protos” - first, most important. Proteins perform a number of important functions in the body: 1. Construction function; 2. Transport function; 3. Protective function; 4. Catalytic function; 5. Hormonal function; 6. Nutritional function.
All natural proteins are formed from amino acid monomers. When proteins are hydrolyzed, a mixture of AMK is formed. There are 20 of these AMKs.
4. Illustrative material: presentation
5. Literature:
Main literature:
1. Bioorganic chemistry: textbook. Tyukavkina N.A., Baukov Yu.I. 2014
- Seitembetov T.S. Chemistry: textbook - Almaty: EVERO LLP, 2010. - 284 p.
- Bolysbekova S. M. Chemistry of biogenic elements: textbook - Semey, 2012. - 219 p. : silt
- Verentsova L.G. Inorganic, physical and colloidal chemistry: textbook - Almaty: Evero, 2009. - 214 p. : ill.
- Physical and colloidal chemistry / Edited by A.P. Belyaev. - M.: GEOTAR MEDIA, 2008
- Verentseva L.G. Inorganic, physical and colloidal chemistry, (verification tests) 2009
Additional literature:
- Ravich-Scherbo M.I., Novikov V.V. Physical and colloidal chemistry. M. 2003.
2. Slesarev V.I. Chemistry. Fundamentals of living chemistry. St. Petersburg: Khimizdat, 2001
3. Ershov Yu.A. General chemistry. Biophysical chemistry. Chemistry of biogenic elements. M.: VSh, 2003.
4. Asanbaeva R.D., Ilyasova M.I. Theoretical foundations of the structure and reactivity of biologically important organic compounds. Almaty, 2003.
- Guide to laboratory classes in bioorganic chemistry, ed. ON THE. Tyukavkina. M., Bustard, 2003.
- Glinka N.L. General chemistry. M., 2003.
- Ponomarev V.D. Analytical chemistry part 1, 2 2003
6. Test questions (feedback):
1. What determines the structure of the polypeptide chain as a whole?
2. What does protein denaturation lead to?
3. What is the isoelectric point called?
4. What amino acids are called essential?
5. How are proteins formed in our body?
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