Interaction of Amino Acids

         A few basic interactions are responsible for holding proteinstogether. The properties of water are intimately involved in these interactions.The dielectric constant is a fundamental and obscure property of matter that puts a number on how hard it is to separate charged particles or groups when they’re in this material. In water, charge is easy to separate .This dipolar nature of water makes it easy for it to dissolve ionic material.  There are two kinds of Interactions. They are

1.HYDROPHILIC INTERACTION:-

• The properties of water dominate the way we think about the interactions of biological molecules. That’s why many texts start with a lengthy, but boring, discussion of water structure, and that’s why you probably do need to read it. 
• Basically, water is a polar molecule. The H—O bond is polarized the H end is more positive than the O end. This polarity is reinforced by the other H—O bond. Because of the polarity difference, water is both a hydrogen-bond donor and a hydrogen-bond acceptor.

Water does two important things:

1. It squeezes out oily stuff because the oily stuff interferes with the interaction of water with itself 
2.  It interacts favorably with anything that can enter into it hydrogen-bonding network.

2.HYDROPHOBIC INTERACTION:-

• As hydrophobic surfaces contact each other, the ordered water molecules that occupied the surfaces are liberated to go about their normal business. The increased entropy  of the water is favorable and drives  the association of the hydrophobic surfaces.

•  Putting a hydrophobic group into water is difficult to do. Normally, water forms an extensive hydrogen-bonding network with itself. The water molecules are constantly on the move, breaking and making new hydrogen bonds with neighboring water molecules. Water has two hydrogen bond donors  and two hydrogen bond acceptors , so a given water molecule can make hydrogen bonds with neighboring water molecules in a large number of different ways and in a large number of different directions.

• When a hydrophobic molecule is dissolved in water, the water molecules next to the hydrophobic molecule can interact with other water molecules only in a direction away from the hydrophobic molecule.  In this case, organization means restricting the number of ways that the water molecules can be arranged in space. The increased organization of water that occurs around a hydrophobic molecule represents an unfavorable decrease in the entropy of water.