Non Covalent Interaction of Water Molecule

Q1: Explain non covalent interaction of water molecule?
Ans: The non-covalent interaction are different from the covalent interaction because they do not share electron with another. Due to the formation of non-covalent interaction energy released. Intermolecular forces are non-covalent interactions that occur between different molecules, rather than between different atoms of the same molecules.

a)      Hydrogen bonds between water molecules: When hydrogen atom attaches to a highly electronegative atoms such as oxygen or nitrogen the resulting covalent bond is polar. Hydrogen atom acquire a slight positive charge. Such hydrogen atom can then participate in a hydrogen bonding.  Hydrogen bond is weak interaction to a negatively charged atom in another molecule. Water molecules forms four neighboring water molecules. The most common hydrogen bonds are those between water molecules, but other hydrogen bonds also play a critical role in the structure of proteins and DNA.

b)     Hydrogen bonds between solute molecules: hydrogen bonds are also found between an electronegative atoms (O₂, N) and a hydrogen atom covalently bonded to another atom in same or another molecule. Hydrogen bonds are strongest when hydrogen atom and the two atoms that share this bond are in straight line. Thus hydrogen bonds are highly directional and capable of holding two hydrogen bonded molecules or group in a specific geometric arrangement. Note that in biological systems, the electronegative atom (hydrogen acceptor) is usually oxygen or nitrogen. The distance between to hydrogen bonded atoms are varies from 0.26 to 0.31 nm.

c)      Interaction between water and charged solute: Water is a polar solvent. Compounds that dissolve readily in water are hydrophilic.

d)     Interaction between water and non-polar gases: Biologically important gases CO₂, O₂ and N₂ are non-polar. Non polar nature of these gases and decrease in entropy when they enter into a solution make them very poorly soluble in water. Some organism have water soluble carrier protein which are involve in transportation of these gases.

e)      Interaction between water and non-polar compounds: Nonpolar compounds such as Benzene and Hexane are hydrophobic and they interfere with boding among water molecules. Amphipathic compounds have region that are polar and nonpolar. The forces that hold nonpolar regions of the molecules together are called hydrophobic interaction.

f)       Van der Waals Interactions: Van der Waals interactions are weak, non-specific, interatomic interaction. These occur when any two uncharged atoms are 3 to 4 Aº apart. Basic of Van der Waal interaction is that distribution of charge around an atom changes with time.

Role of non-covalent interaction: Macro molecules such as proteins, DAN, RAN involves many sites of different non-covalent interaction have large effect on these macro molecules. Non covalent interaction are important in protein folding. These interaction are important in binding of an antigen to specific antibody. These interaction are involved in catalytic power of enzyme. Non covalent interaction are important in biding of a hormone to its receptor. These are important binding of neurotransmitter to its cellular receptor.