A group of substances with which amino acids are able to react. Chemical properties of amino acids

Amino acids, proteins and peptides are examples of the compounds described below. Many biologically active molecules include several chemically distinct functional groups that can interact with each other and with each other's functional groups.

Amino acids.

Amino acids- organic bifunctional compounds, which include a carboxyl group - UNSD, and the amino group - NH 2 .

share α and β - amino acids:

Mostly found in nature α - acids. Proteins are composed of 19 amino acids and one imino acid ( C 5 H 9NO 2 ):

The simplest amino acid- glycine. The remaining amino acids can be divided into the following main groups:

1) glycine homologues - alanine, valine, leucine, isoleucine.

Getting amino acids.

Chemical properties of amino acids.

Amino acids- these are amphoteric compounds, tk. contain in their composition 2 opposite functional groups - an amino group and a hydroxyl group. Therefore, they react with both acids and alkalis:

Acid-base conversion can be represented as:

Properties of amino acids can be divided into two groups: chemical and physical.

Chemical properties of amino acids

Depending on the compounds, amino acids can exhibit different properties.

Amino acid interaction:

Amino acids as amphoteric compounds form salts with both acids and alkalis.

As carboxylic acids, amino acids form functional derivatives: salts, esters, amides.

Interaction and properties of amino acids with grounds:
Salts are formed:

NH 2 -CH 2 -COOH + NaOH NH 2 -CH 2 -COONa + H2O

Sodium salt + 2-aminoacetic acid Sodium salt of aminoacetic acid (glycine) + water

Interaction with alcohols:

Amino acids can react with alcohols in the presence of hydrogen chloride gas, becoming ester. Esters of amino acids do not have a bipolar structure and are volatile compounds.

NH 2 -CH 2 -COOH + CH 3 OH NH 2 -CH 2 -COOCH 3 + H 2 O.

Methyl ester / 2-aminoacetic acid /

Interaction ammonia:

Amides are formed:

NH 2 -CH (R) -COOH + H-NH 2 \u003d NH 2 -CH (R) -CONH 2 + H 2 O

The interaction of amino acids with strong acids:

Getting Salts:

HOOC-CH 2 -NH 2 + HCl → Cl (or HOOC-CH 2 -NH 2 *HCl)

These are the basic chemical properties of amino acids.

Physical properties of amino acids

We list the physical properties of amino acids:

• Colorless
• Have a crystalline form
• Most amino acids taste sweet, but depending on the radical (R) may be bitter or tasteless
• Highly soluble in water, but poorly soluble in many organic solvents
• Amino acids have the property of optical activity
• Melt with decomposition at temperatures above 200°C
• non-volatile
• Aqueous solutions of amino acids in acidic and alkaline media conduct electricity

Among nitrogen-containing organic substances, there are compounds with a dual function. Particularly important of these 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 links (monomers) from which the peptides and proteins of all organisms are built (therefore they are called protein amino acids). The sequence 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 those that are found in only one of the great many described organisms. Most microorganisms and plants synthesize the amino acids they need; animals and humans are not capable of forming 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), 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 structural features.

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 are distinguished.

3. By 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 the 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. The numbering of the carbon chain from the carbon atom of the carboxyl group.

For example:

Another way 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 the 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	The structure of the radical (R)
Glycine	Gly (Gly)	H-
Alanine	Ala (Ala)	CH3-
Valine	Val (Val)	(CH 3) 2 CH -
Leucine	Leu (Leu)	(CH 3) 2 CH - CH 2 -
Serene	Ser (Ser)	OH-CH2-
Tyrosine	Tyr (Tyr)	HO - C 6 H 4 - CH 2 -
Aspartic acid	Asp (Asp)	HOOC–CH2-
Glutamic acid	Glu (Glu)	HOOC-CH2-CH2-
Cysteine	Cys (Cys)	HS-CH2-
Asparagine	Asn (Asn)	O \u003d C - CH 2 - │ NH2
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 its name uses the prefixdiamino, three groups of NH 2 - triamino- etc.

Example:

The presence of two or three carboxyl groups is reflected in the name by the suffix – diovaya or -triic acid:

isomerism

1. Isomerism of the carbon skeleton

2. Isomerism of the position of functional groups

3. Optical isomerism

α-amino acids, except for glycine NH 2-CH 2 -COOH.

PHYSICAL PROPERTIES

Amino acids are crystalline substances with high (above 250°C) melting points, which differ little in individual amino acids and are therefore uncharacteristic. Melting is accompanied by the decomposition of matter. Amino acids are highly soluble in water and insoluble in organic solvents, which is how they are similar to inorganic compounds. Many amino acids have a sweet taste.

RECEIVING

3. Microbiological synthesis. Known microorganisms that in the process of life 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 due to 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 of which all plant and animal proteins are built; amino acids necessary for the construction of body proteins, humans and animals receive as part of food proteins;

3) amino acids are prescribed for severe exhaustion, after heavy operations;

4) they are used to feed the sick;

5) amino acids are necessary as a remedy for certain diseases (for example, glutamic acid is used for nervous diseases, histidine for stomach ulcers);

6) some amino acids are used in agriculture for feeding animals, which positively affects their growth;

7) are of technical importance: aminocaproic and aminoenanthic acids form synthetic fibers - nylon and enanth.

ON THE ROLE OF AMINO ACIDS

Finding in nature and the biological role of amino acids

Finding in nature and the biological role of 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, since it is able to attach a hydrogen cation to itself according to 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 bases - amines:

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

The ionization of amino acid molecules depends on the acidic or alkaline nature of the medium:

Since amino acids in aqueous solutions behave like typical amphoteric compounds, 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:

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

These include, in addition to the synthetic fiber of capron mentioned above, for example, enanth, which is formed during the polycondensation of aminoenanthic acid. Synthetic fibers are suitable for amino acids with amino and carboxyl groups at the ends of the molecules.

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

Isomerism and amino acid nomenclature

The isomerism of amino acids is determined by the different structure of the carbon chain and the position of the amino group, for example:

The names of amino acids are also widespread, in which the position of the amino group is indicated by the letters of the Greek alphabet: α, β, y, etc. So, 2-aminobutanoic acid can also be called α-amino acid:

Methods for obtaining amino acids

Amino acids are called organic compounds containing functional groups in the molecule: amino and carboxyl.

Nomenclature of amino acids. According to the systematic nomenclature, the names of amino acids are formed from the names of the corresponding carboxylic acids and the addition of the word "amino". The position of the amino group is indicated by numbers. The countdown is from the carbon of the carboxyl group.

Isomerism of amino acids. Their structural isomerism is determined by the position of the amino group and the structure of the carbon radical. Depending on the position of the NH 2 group, -, - and -amino acids are distinguished.

Protein molecules are built from α-amino acids.

They are also characterized by isomerism of the functional group (interclass isomers of amino acids can be esters of amino acids or amides of hydroxy acids). For example, for 2-aminopropanoic acid CH 3 – CH(NH) 2 – COOH the following isomers are possible

Physical properties of α-amino acids

Amino acids are colorless crystalline substances, non-volatile (low saturated vapor pressure), melting with decomposition at high temperatures. Most of them are highly soluble in water and poorly in organic solvents.

Aqueous solutions of monobasic amino acids are neutral. -Amino acids can be considered as internal salts (bipolar ions): + NH 3  CH 2  COO - . They act as cations in an acidic environment and as anions in an alkaline environment. Amino acids are amphoteric compounds that exhibit both acidic and basic properties.

Methods for obtaining -amino acids

1. Action of ammonia on salts of chlorinated acids.

Cl  CH 2  COOH 4 + NH 3
NH2  CH2COOH

2. Action of ammonia and hydrocyanic acid on aldehydes.

3. By hydrolysis of proteins, 25 different amino acids are obtained. Separating them is not an easy task.

Methods for obtaining -amino acids

1. Addition of ammonia to unsaturated carboxylic acids.

CH 2 = CH  COOH + 2NH 3  NH 2  CH 2  CH 2  COOH 4 .

2. Synthesis based on dibasic malonic acid.

Chemical properties of amino acids

1. Reactions on the carboxyl group.

1.1. Formation of esters under the action of alcohols.

2. Reactions on the amino group.

2.1. Interaction with mineral acids.

NH2  CH 2 COOH + HCl  H 3 N +  CH 2  COOH + Cl

2.2. Interaction with nitrous acid.

NH2  CH 2 COOH + HNO 2  HO  CH 2  COOH + N 2 + H 2 O

3. Transformation of amino acids when heated.

3.1.-amino acids form cyclic amides.

3.2.-amino acids split off the amino group and the hydrogen atom of the -carbon atom.

Individual representatives

Glycine NH 2 CH 2 COOH (glycocol). One of the most common amino acids that make up proteins. Under normal conditions - colorless crystals with T pl = 232-236С. It is highly soluble in water, insoluble in absolute alcohol and ether. Hydrogen index of the aqueous solution6.8; рК a = 1.510 - 10; pK in \u003d 1.710 - 12.

-alanine - aminopropionic acid

Widely distributed in nature. It is found in free form in blood plasma and as part of most proteins. Tm = 295-296С, soluble in water, poorly soluble in ethanol, insoluble in ether. pK a (COOH) = 2.34; pK a (NH ) = 9,69.

-alanine NH 2 CH 2 CH 2 COOH - small crystals with Тmelt = 200С, highly soluble in water, poorly in ethanol, insoluble in ether and acetone. pK a (COOH) = 3.60; pK a (NH ) = 10.19; absent in proteins.

Complexons. This term is used to name a number of -amino acids containing two or three carboxyl groups. The most simple:

H The most common complexone is ethylenediaminetetraacetic acid.

Its disodium salt, Trilon B, is extremely widely used in analytical chemistry.

The bond between the residues of -amino acids is called a peptide bond, and the resulting compounds themselves are called peptides.

Two residues of -amino acids form a dipeptide, three - a tripeptide. Many residues form polypeptides. Polypeptides, like amino acids, are amphoteric, each with its own isoelectric point. Proteins are polypeptides.