The presentation is all about the types of non covalent interactions in a biological system

1. Stabilizing interactions (Vander Waals, electrostatic,
hydrogen bonding, hydrophobic interaction)
Dr. P. Samuel
Assistant Professor,
Department of Biotechnology,
Ayya Nadar Janaki Ammal College (Autonomous), Sivakasi

2. What is “interaction” means in chemistry?
• Interaction refers to the attraction between
molecules constituting the biological system.

3. Molecules in the biological system

4. Stabilizing “interaction” (or) Non-covalent interaction
A non-covalent interaction does not
involve the sharing of electrons.
More dispersed variations of electromagnetic
interaction between molecules or within
molecules.
Chemical energy released during the
formation of non-covalent interaction in on the
order of 1–5 kcal/mol.
A mole can be defined as the “base unit of
amount of substance in the international system
of units” [6.02214076×1023]

5. What are the importance of non covalent
interaction?
• Typically needed for maintaining the three-
dimensional structure of large molecules,
such as nucleic acids and proteins.
• These non covalent interactions are also
important in many biological processes in
which the molecules bind specifically but
transiently to one another.
• This type of interaction greatly influences
field like drug design

6. Types of non covalent interaction
• Vander Waals force
• Electrostatic interaction
• hydrogen bonding,
• hydrophobic interaction

7. relative weakness of Van der Waals forces to
other intermolecular attractions

8. Van der Waals Forces
Dutch scientist Johannes Diderik van der Waals
(1873)
Van der Waals forces' can be defined as the attraction
of intermolecular forces between molecules.
 Van der Waals force depends on the distance
between atoms and molecules.
There are two kinds of Van der Waals forces:
weak London Dispersion Forces and stronger dipole-
dipole forces.

9. Fluctuation of electrons

11. Van der Waals Forces
When the distance between the atoms is greater
than 0.6 nanometres, the forces are extremely
weak and cannot be observed.
When the distance between the atoms ranges from
0.6 to 0.4 nanometres, the forces are attractive.
If the interatomic distance is smaller than 0.4
nanometres, the forces are repulsive in nature.

12. Van der Waals Forces
 Van der Waals interactions: A
weak force of attraction between
electrically neutral molecules that
collide with or pass very close to
each other.
 The van der Waals force is caused
by temporary attractions between
electron-rich regions of one
molecule and electron-poor
regions of another. https://periodictable.me/what-are-the-
understanding-of-electron/

13. London dispersion force
• Dispersion forces are also considered a type of van der Waals
force and are the weakest of all intermolecular forces.
• They are often called London forces after Fritz London (1900-
1954), who first proposed their existence in 1930.
• London dispersion forces are the intermolecular forces that
occur between atoms and between nonpolar molecules as a
result of the motion of electrons.

14. • The electron cloud of a helium atom contains two electrons,
which can normally be expected to be equally distributed
spatially around the nucleus.
• However, at any given moment the electron distribution
may be uneven, resulting in an instantaneous dipole.
• This weak and temporary dipole subsequently influences
neighboring helium atoms through electrostatic attraction
and repulsion. It induces a dipole on nearby helium atoms.

15. Hydrogen bonding
• Hydrogen bonds provide many of the critical, life-
sustaining properties of water and also stabilize the
structures of proteins and DNA, the building block of
cells.
• When polar covalent bonds containing hydrogen form,
the hydrogen in that bond has a slightly positive charge
because hydrogen’s one electron is pulled more
strongly toward the other element and away from the
hydrogen.

16. Hydrogen bonding
• Because the hydrogen is slightly positive, it will
be attracted to neighbouring negative charges.
• When this happens, an interaction occurs between
the δ+ of the hydrogen from one molecule and
the δ– charge on the more electronegative atoms
of another molecule, usually oxygen or nitrogen,
or within the same molecule.

17. Hydrogen bonding
• This interaction is called a hydrogen bond.
• This type of bond is common and occurs regularly
between water molecules.
• Individual hydrogen bonds are weak and easily broken;
however, they occur in very large numbers in water and
in organic polymers, creating a major force in
combination.
• Hydrogen bonds are also responsible for zipping
together the DNA double helix.

18. Applications of hydrogen bonding
• Hydrogen bonds occur in inorganic
molecules, such as water, and
organic molecules, such as DNA
and proteins.
• The two complementary strands of
DNA are held together by hydrogen
bonds between complementary
nucleotides (A&T, C&G).
• Hydrogen bonding in water
contributes to its unique properties,
including its high boiling point (100
°C) and surface tension.

19. Applications of hydrogen bonding
In biology, intramolecular
hydrogen bonding is partly
responsible for the
secondary, tertiary, and
quaternary structures of
proteins and nucleic acids.
The hydrogen bonds help the
proteins and nucleic acids
form and maintain specific
shapes.

20. Electrostatic interaction
An electrostatic
interaction depends
on the electric
charges on atoms.
The energy of an
electrostatic
interaction is given
by Coulomb’s law.

21. Electrostatic interaction
 Electrostatic forces originate from the electric charges
and dipoles of atoms and groups of atoms.
 They function inside macromolecules to maintain and to
stabilize the molecular structure and to regulate the
biological functions of catalysis and electron transfer.
 Electrostatic forces between molecules, facilitate
specific molecular recognition and molecular assembly.
 The specific electrostatic field is determined by
contributions from several factors, which originate from
the intrinsic heterogeneity of biological macromolecules
and from aqueous solvents.

22. Question for you!!!!
• A cell membrane is a thin layer enveloping a cell. The
thickness of the membrane is much less than the size
of the cell. In a static situation the membrane has a
charge distribution of −2.5 × 10−6 C/m2 on its inner
surface and +2.5 × 10−6 C/m2 on its outer surface. Draw
a diagram of the cell and the surrounding cell
membrane. Include on this diagram the charge
distribution and the corresponding electric field. Is
there any electric field inside the cell? Is there any
electric field outside the cell?

23. Hydrophobic interaction
• Hydrophobic interactions describe the relations between water
and hydrophobes (low water-soluble molecules).
• Hydrophobes are nonpolar molecules and usually have a long chain
of carbons that do not interact with water molecules.
• The mixing of fat and water is a good example of this particular
interaction.
• The common misconception is that water and fat doesn’t mix
because the Van der Waals forces that are acting upon both water
and fat molecules are too weak. However, this is not the case.
• The behavior of a fat droplet in water has more to do with the
enthalpy and entropy of the reaction than its intermolecular forces.

24. Causes of Hydrophobic Interactions
• American chemist Walter
Kauzmann discovered that
nonpolar substances like fat
molecules tend to clump up
together rather than
distributing itself in a water
medium, because this allow
the fat molecules to have
minimal contact with water.

25. Strength of Hydrophobic Interactions
• Temperature: As temperature increases, the strength of
hydrophobic interactions increases also. However, at an extreme
temperature, hydrophobic interactions will denature.
• Number of carbons on the hydrophobes: Molecules with the
greatest number of carbons will have the strongest hydrophobic
interactions.
• The shape of the hydrophobes: Aliphatic organic molecules have
stronger interactions than aromatic compounds. Branches on a
carbon chain will reduce the hydrophobic effect of that molecule
and linear carbon chain can produce the largest hydrophobic
interaction.

26. Biological Importance of Hydrophobic
Interactions