Oxidation number and Peptide Bond

The gaining or losing of electrons from an atom can be tracked by using a number called oxidation number. This can be either positive, negative or zero. If an atom loses an electron from its outermost shell, the corresponding oxidation number will be positive and if an atom gains electrons the sign will change to a negative number. If atom neither loses nor gain electron then it becomes zero.

How to assign the oxidation number?

Step 1: Determine whether it is in its pure elemental form

Oxidation number can be identified easily by finding the atom whether combined with other elements or not. Then it can be said that the number will be zero. For example, Ag, Cl2 etc.

Step 2: An ion can have the oxidation number as same as its charge 

An ion can be represented by marking a sign on the superscript after the atom. It indicates that the atom either gained or lost an electron from its shell.  For example, if we are taking potassium ion. It loses one electron and forms K+. This shows a positive charge(+1) on potassium which indicates the oxidation number is +1.

Step 3: The metals in group 1 and group 2 will have an oxidation state of +1 and +2 respectively.

An example from group 1 and group 2 can be taken to illustrate this step. Lithium has +1 oxidation state as it belongs to group 1 and magnesium has +2 oxidation number as it belongs to the group 2.

Step 4: The first element in the periodic table has +1 and -1 oxidation state.

If we take an example of hydrochloric acid HCl, hydrogen will have a +1 oxidation state as it is bonded with non-metal chlorine. In the case of sodium hydride, hydrogen will have an oxidation state of -1 which is bonded with sodium metal.

Step 5: Multiple oxidation states is adopted by oxygen. -1, -2 and +2.

Oxygen can have an oxidation state of -2 in general. Whereas in its peroxide form it adopts -1 oxidation number.

Step 6: For a neutral compound, the oxidation number will be zero.

The oxidation state of hydrogen fluoride will be zero. 

Calculation of Oxidation state of H2 in H2O

Hydrogen in water is not in the form of hydride. Here 2 molecule of hydrogen combines with oxygen to form a water molecule. It is a neutral molecule. 

(-2 x 1) + (+1 x 2) = +1

Calculation of Oxidation number of Cl in KCl

For a neutral molecule, the oxidation state comes zero. Here KCl is a neutral molecule. Thus the oxidation number will be zero.

The oxidation state of KCl = Oxidation state of potassium + oxidation state of chlorine

The oxidation state of K = +1

+1 + (x) = 0

Therefore x = -1

Oxidation state of Cl in KCl is -1.

Peptide bond

An amino acid has two groups attached. One is the carboxyl group and the other one is an amino group. These amino group of amino acid when combining with a carboxyl group of another amino acid results in the peptide bond. 

There are different peptide bond according to the number of amino acid molecules composing a chain. They are dipeptide( Contain 2 amino acid units), tripeptide (Contain 3 amino acid units), Tetrapeptide (Contain 4 amino acid units) and so on. 

Formation of Peptide bond

The two amino acids bond together to form a peptide bond as shown in the picture. This is a dehydration process because one molecule of water is released during the reaction.

Characteristics of a peptide bond

  • It is rigid and planar
  • It exists in trans configuration and has a partial double bond character
  • The 4 atoms of the peptide bonds lie in the single plane
  • The carboxyl group and amino group are involved in hydrogen bond formation.

Summary

  • The oxidation number is used to track the number of electrons present in an atom or molecule according to the losing or gaining of electrons.
  • For neutral compound, the oxidation state will be zero
  • A peptide bond is nothing but an amino group of amino acid combines with a carboxyl group of another amino acid.
  • It is a covalent bond found within the protein molecule.
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