Is Peptide Bond A Hydrogen Bond: Why, How, Detailed Facts

In this article we are going to analyze is peptide bond a hydrogen bond or not.

A peptide bond cannot be a Hydrogen bond because a peptide bond formation takes place when two amino acids combine together and form a bond. Based on the number of amino acids coming together or combining peptide bond can be classified as dipeptide bond (combination of 2 amino acids and so on ).

A peptide bond has Trans Configuration:

The reason it has trans configuration and not a cis configuration because if it is in cis configuration there will be a steric hindrance or steric interference due to the presence of side chains at the r groups. If all the r groups are present on the same side then there will be a steric hindrance, that is why a peptide bond has a trans configuration and it is uncharged but it is polar, though it is uncharged it has a polarity and this polarity is due to resonance or the delocalization of the electrons.

For detailed analysis of peptide bond formation refer Peptide Bond formation: How, Why, Where, Exhaustive Facts around it.

Why there is a need for us to study hydrogen bond or what is its significance in chemistry, we are going to have a closer approach towards this. We can predict the solubility and boiling point with the help of the concept of hydrogen bonding. So compounds that can form better hydrogen bonding tend to be more soluble in water and have higher boiling point.

Hydrogen bond (has bond energy around 8-42 KJ/mole), is smaller than ionic or covalent bond (having a bond energy greater than 200 KJ/mole) but stronger than Vander Waal force (that has bond energy less than 8KJ/mole).

Consider a covalent bond between A—H having a bond energy of 200 KJ/mole (consider A to be an electronegative atom whose electronegativity is greater or equal to 3. It could be Fluorine, Oxygen and Nitrogen but a special exception in case of organic chemistry it could be Carbon and Chlorine). Atom A being an electronegative atom will attract the electron pair of the covalent bond towards itself. So a (electronegative atom) will develop partial negative charge and H (hydrogen) will develop partial positive charge.

Then consider an atom B having an electron pair (hydrogen has a partial positive charge) , so what B will do is come and bond with the hydrogen of A—H ( which are bonded covalently). So the bond formation between B and H is called hydrogen bonding or hydrogen bonding. B should be an electronegative atom, must have small size and should have a lone pair (Fluorine, Oxygen, Nitrogen and in case of organic chemistry it will be Chlorine).

And the bond energy of the formed hydrogen bond is somewhere between 8-42 KJ/mole (and the bond energy of covalent bond A—H is 200 KJ/mole). So we say covalent bond (A—H ) is a strong bond as compared to hydrogen bond and will have a shorter bond length. H—B being comparatively weaker will have longer bond length.

Most of the time hydrogen bond is weaker then covalent bond wherein bond energy of covalent bond is more then the bond energy of hydrogen bond. But only in one special case bond energy of covalent bond is equal to the bond energy of hydrogen bond i.e. HF2-. The bond energy of both covalent bond and hydrogen bond in HF2- is 200 kJ/mole. But bond energy of covalent bond can never be less than the bond energy of hydrogen bond.

In hydrogen bonding the covalently bonded atom should be electronegative enough. In the above case Fluorine is the most electronegative atom hence will form stronger hydrogen bonding and will have more bond energy or bond strength (F, O, N). We can say bond energy, hydrogen bond strength are directly proportional to the electronegativity of the covalently bonded atom in the hydrogen bonding.

In the above example how can we identify which one will have or form stronger hydrogen bonding? The concept followed here is hydrogen bond strength is inversely proportional to the electronegativity of the atom bonded to hydrogen in the hydrogen bonding process. We know oxygen is more electronegative then Nitrogen, so that means if hydrogen bond strength is inversely proportional to the atom bonded to hydrogen atom (should have less electronegativity), so Nitrogen has less electronegativity and the answer which is appropriate is O–H—N.

Intermolecular Hydrogen bonding:

In this type of Hydrogen bonding the bond will be formed between two different molecules (can be of same nature but there should be two molecules).

For example consider the H2O molecule.

HF molecule

NH3 (ammonia) molecule

The above hydrogen bonding is with homo-molecules meaning with same kind of molecule.

R—O—H (alcohol) and H—O—H (water)

Here hydrogen bonding is within hetero-molecules as two different molecules are involved.

Let’s study the molecule of H3BO3 (Boric acid)

It exists as a dimer ( H₃BO₃) ,the reason is due to the intermolecular hydrogen bonding between the molecule.

(Chelation-It is the formation of ring)

Intramolecular Hydrogen bonding

In this type of hydrogen bonding the bond will be formed within the same molecule or single molecule.

Consider O-nitrophenol

This is an example of Intramolecular Hydrogen bonding.

Some properties of hydrogen bonding:

Referring to the solubility concept, when alcohol (basically the lower ones) can be soluble in water due to the presence of hydrogen bonding between alcohol (R—O—H) and water (H—O—H) molecule.

Taking into account the volatility of compounds having hydrogen bonding, they have quite high boiling point and hence they are not very less volatile.

When compounds have hydrogen bonding what happens is they occur in association with molecules, so the flow is quite difficult hence they possess quite high surface tension and viscosity.

Peptide bond v/s hydrogen bond

This two types of bond are quite different in nature.

In the section followed we are going to analyze peptide bond and hydrogen bond based on formation of bond, strength and where they are usually found.

Factors	Peptide bond	Hydrogen bond
Formation of bond	A peptide bond is formed when two amino acids combine together and form a bond.	A hydrogen bond is formed when hydrogen atom covalently bonded with another atom also forms a bond with one more electronegative atom (F, O ad N).
StrengthA peptide bond is much more stronger and cannot be easily broken.	A hydrogen bond is much more weaker.
Found in	Peptide bond can be found between amino acids and also in fish, meat , wheat etc.	Hydrogen bond is found in many molecules such as water, ammonia, etc.

Why do proteins have hydrogen bonds?

Hydrogen bond is found in most of the proteins.

Hydrogen Bonds are very important to proteins as they provide stability and rigidity to the proteins. In secondary structure of proteins hydrogen bond is present between the amino acid.

We can see that the hydrogen bond is formed between the hydrogen atom of amino group of one amino acid and with the electronegative atom (oxygen) of the amino group of the one more amino acid. The twisting of linear chain (of the amino acid) to form alpha helical (referred basically as form ) is the result of the phenomenon of hydrogen bonding. So we can say in proteins hydrogen bonding has mostly has got a structural role to play.

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Sania Jakati

This is Sania Jakati from Goa. I am an aspiring chemist pursuing my post graduation in organic chemistry. I believe education is the key element that moulds you into a great human being both mentally and physically. I’m glad to be a member of scintillating branch of chemistry and will try my best to contribute whatever I can from my side and Lambdageeks is the best platform where I can share as well as gain knowledge at the same time.

Types of Hydrogen bonding

Peptide bond v/s hydrogen bond

Why do proteins have hydrogen bonds?

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