Physio Chemical Properties of Amino acids? (Guide)

Amino acids are basically building blocks of proteins. This chapter includes the Physio chemical properties of Amino acids. Before going to the physical and chemical properties of amino acids, we should brush back the amino acids basic points.

What is an Amino acid? Amino acids are biological organic molecules containing both an amino group(s) and a carboxyl group (s).

physiochemical properties of amino acids
Physiochemical properties of Amino acids

An amino acid is an organic molecule with an amino group (-NH2) and a carboxyl group (-COOH). The most frequent and of greatest interest are those amino acids forming part of proteins.

Two amino acids are combined in a condensation reaction between the amino group and the carboxyl group of another amino acid, releasing one molecule of water and forming an amide bond is called a peptide bond.

These two amino acids form a dipeptide. If you join a third amino acid is formed one tripeptide and so on, to form a polypeptide. This reaction occurs naturally within cells, in ribosomes.

All components of the protein amino acids are L-alpha-amino acids. This means that the amino group is attached to the carbon adjacent to the carboxyl group ( alpha carbon ) or, in other words, both the carboxyl and the amino attached to the same carbon; also this one unite alpha carbon-hydrogen and a chain (usually called side chain or radical R ) of variable structure, which determines the identity and properties of each of the different amino acids.

Hundreds of radicals so hundreds of different amino acids are known, but only 22 (the latter two were discovered in 1986 – selenocysteine ​​- and 2002 – pyrrolysine -) 2 are part of proteins and have codons at specific genetic code.

The human body is made up of 20 percent protein. Proteins play in almost all biological processes a key role. Amino acids are the basis of proteins.

Since much of our cells, muscles, and tissues are composed of amino acids, they are part of many important functions in our body: the amino acids give the cell not only its structure but are also responsible for transporting and storing all kinds of vital nutrients. Amino acids influence the functions of organs, glands, tendons or arteries.

They are essential in wound healing and tissue repair, especially muscles, bones, skin, and hair, as well as eliminating the negative impacts associated with metabolic disorders of all types.

This topic included the complete list of the Physio chemical properties of amino acids.

Physical and Chemical Properties of Amino acids

Let us discuss Physical and chemical properties of amino acids. Here are the Physical properties of Amino acids

1. Solubility

Most of the amino acids are usually soluble in water and insoluble in organic solvents.

2. Melting Point

Amino acids are generally melted at a higher temperature of ten above 2000C.

3. Taste

Amino acids may be sweet (Gly, Ala & Val), tasteless (Leu) or Bitter (Arg & Ile).

4. Optical Properties

All amino acids possess optical isomers due to the presence of asymmetric α-carbon atoms.

5. Zwitter ion and Isoelectric point

The name zwitter is derived from the German word which means “hybrid”.  Zwitter ion (or) dipolar ion is a hybrid molecule containing positive & negatively ionic groups.

Basically the proton shifts from carboxyl group to the amino group of the self molecule at normal pH cellular levels.

6. Titration Curve of Glycine

Glycine is optically inactive, simplest amino acid because it has no asymmetric carbon atom. Acid-Base titration involves the gradual addition (or) removal of protons.

It has three different stages when the Glycine undergoes acid-base titration.

Chemical Properties of Amino acids

Here are the Chemical reactions of amino acids due to carboxyl and amino groups

I) Due to the Carboxyl group

a) Decarboxylation

The amino acids will undergo alpha decarboxylation to form the corresponding “amines”. Thus important amines are produced from amino acids.

  • Histidine   → Histamine + CO2
  • Tyrosine    →Tyramine + CO2
  • Tryptophan   →Tryptamine + CO2
  • Lysine     →Cadaverine + CO2
  • Glutamic acid     → Gamma Amino Butyric Acid (GABA) + CO2

b) Reaction with Alkalies (Salt formation)

The carboxyl group of amino acids can release an H+ ion with the formation of Carboxylate (COO) ions. These may be neutralized by cations like Na+ and Ca+2 to form Salts. Thus amino acids react with alkalies to form “Salts”.

reaction with alkali: What are the Physio Chemical Properties of Amino acids?

c) Reaction with Alcohols (Esterification)

When the amino acids are reacted with an alcohol to form, “Ester”. The esters are volatile in contrast to the form of amino acids.

Reaction with alcohols : What are the Physio Chemical Properties of Amino acids?

d) Reaction with Amines

Amino acid reacts with Amines to form “Amides”.

Reaction with Amines: What are the Physio Chemical Properties of Amino acids?

II) Due to Amino group

a) Reaction with Mineral acids (Salt formation)

When the amino acids are treated with mineral acids (like HCl), it forms “Acid Salts”.

b) Reaction with Formaldehyde

When the amino acid reacts with two molecules of Formaldehyde it forms “N-dimethylol derivative” (Hydroxy-methyl derivative). This reaction is done in two steps. These derivatives are insoluble in water and resistant to attack by microorganisms.

Reaction with formaldehyde: What are the Physio Chemical Properties of Amino acids?

c) Reaction with Benzaldehyde

When the amino acid reacts with Benzaldehyde, it gives “Schiff’s base”.

Reaction with Benzaldehyde: What are the Physio Chemical Properties of Amino acids?

d) Reaction with Nitrous acid (Van Slyke reaction)

When the amino acids react with Nitrous acid (HNO2) to liberate N2 gas and to produce the corresponding “α-hydroxyl acid”. The imino acids Proline and Hydroxyproline do not respond to this reaction.

Reaction with Nitrous acid : What are the Physio Chemical Properties of Amino acids?

e) Reaction with Sanger’s reagent

“1-fluoro-2,4-dinitrobenzene” is called Sanger’s reagent (FDNB). In a mildly alkaline solution, the sanger’s reagent reacts with α-amino acid to produce Yellow-colored derivative, DNB-amino acid.

Reaction with Sanger’s reagent: What are the Physio Chemical Properties of Amino acids?

f) Reaction with DANSYl Chloride

DANSYl chloride means “Dimethyl Amino Naptha Sulphonyl Chloride”. When the amino acid reacts with DANSYl chloride reagent, it gives a “Flourescent DANSYl derivative”.

Reaction with DANSYLChloride: What are the Physio Chemical Properties of Amino acids?

g) Reaction with acylating agents (Acylation)

When the amino acids react with “Acid chloride” and acid anhydride (Phthalic anhydride) in an alkaline medium it gives “pthaloyl amino acid”.

Reaction with acylating agents: What are the Physio Chemical Properties of Amino acids?

c) Due to amino & carboxyl group

Ninhydrin reaction


Ninhydrin (=indane 1,2,3-trione hydrate) is a powerful oxidizing agent and causes oxidative decarboxylation of α-amino acids producing CO2, NH3 and an aldehyde with one less carbon atom than the parent amino acid.

Ninhydrin reaction step 1


The reduced ninhydrin then reacts with the liberated NH3 and a mole of ninhydrin, forming Blue-colored Rhumann’s complex.

Ninhydrin reaction step 2

This reaction is a very sensitive reaction and it is used for amino acid and imino acid identification.

When Amino acids (or) Imino acid reacts with the Ninhydrin molecule it gives Color. When it gives Purple color (Rhumann’s Complex) –the Unknown sample is Amino acids (Which have primary amine –NH2) or it gives Yellow color – the Unknown sample is Imino acid (-NH-).

Reaction with Edmann’s degradation

Erdmann’s reagent is “phenylisothiocyanate”. When amino acids react with Edmann’s reagent it gives “phenyl thiohydantoic acid” finally it turns into cyclized form “Phenyl thiohydantoin” (Edmann’s derivative).

Reaction with Edmanns degradation

The above physical and chemical properties of amino acids are giving positive results after complete the reaction.

Reference readings: Prediction of Physical-Chemical Properties

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