Stabilizing interactions

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” [ 6.02214076×10 23 ]

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

10. 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.

11. 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/

12. 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.

13. 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.

14. 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.

15. 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.

16. 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.

17. 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.

18. 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.

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

20. 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.

21. 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/m 2  on its inner surface and +2.5 × 10 −6  C/m 2  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?

22. 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.

23. 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.

24. 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.

25. Biological Importance of Hydrophobic Interactions